Ultrasound in Medical Diagnosis
Content
Ultrasound in Medical Diagnosis
The wave properties of ultrasound
Ultrasound relies on high frequency sounds to image the body and diagnose patients. Ultrasounds are therefore longitudinal waves which cause particles to oscillate back and forth and produce a series of compressions and rarefactions. Using the following formula, it is possible to calculate the velocity, frequency or wavelength of a wave if the other two values are known: v = fλ Where:
• • •
he velocity !v" is the speed of the wave. #t is measured in m s$%. he frequency !f" is the number of times a particle oscillates per second. #t is measured in &'. he wavelength !λ" is the distance between two compressions or rarefactions. #t is measured in m.
he amplitude is the distance a particle moves back or forth.
(ompressions are areas of the wave where particles are close together and there is high pressure. )arefactions are areas of the wave where particles are far apart and there is low pressure.
The frequencies used in ultrasound diagnosis
Ultrasound uses high frequency sounds that are higher than the human ear can hear. ie. *+ +++ &'. Ultrasound can,t detect ob-ects that are smaller than its wavelength and therefore higher frequencies of ultrasound produce better resolution. .n the other hand, higher frequencies of ultrasound have short wavelengths and are absorbed easily and therefore are not as penetrating. /or this reason high frequencies are used for scanning areas of the body close to the surface and low frequencies are used for areas that are deeper down in the body. hese frequencies generally range between %$0+ 1&'.
How ultrasound is produced and detected
Ultrasound is produced and detected using an ultrasound transducer. Ultrasound transducers are capable of sending an ultrasound and then the same transducer can detect the sound and convert it to an electrical signal to be diagnosed. o produce an ultrasound, a pie'oelectric crystal has an alternating current applied across it. he pie'oelectric crystal grows and shrinks depending on the voltage run through it. )unning an alternating current through it causes it to vibrate at a high speed and to produce an ultrasound. his conversion of electrical energy to mechanical energy is known as the pie'oelectric effect. he sound then bounces back off the ob-ect under investigation. he sound hits the pie'oelectric
crystal and then has the reverse effect $ causing the mechanical energy produced from the sound vibrating the crystal to be converted into electrical energy. 2y measuring the time between when the sound was sent and received, the amplitude of the sound and the pitch of the sound, a computer can produce images, calculate depths and calculate speeds.
The nature of A-scans, B-scans, sector scans and phase scans
A-scans
3$scans can be used in order to measure distances. 3 transducer emits an ultrasonic pulse and the time taken for the pulse to bounce off an ob-ect and come back is graphed in order to determine how far away the ob-ect is. 3$scans only give one$dimensional information and therefore are not useful for imaging.
B-Scans
2$scans can be used to take an image of a cross$section through the body. he transducer is swept across the area and the time taken for pulses to return is used to determine distances, which are plotted as a series of dots on the image. 2$4cans will give two$dimensional information about the cross$section.
Sector scans
4ector scans can be used to take a sector shaped image of the body. he transducer is swept back and forth across the area, producing a series of 2$scans that build up an image. 4ector scans are much harder to produce than phase scans and are much less common. &owever, they are useful for taking images when there is only a small amount of space.
Phase scans
5hase scans have hundreds of transducers in the same probe in order to take a high resolution real$time scan. he angle of the wavefront can be altered by firing the transducers one after another, when this happens they are out of phase. 2y changing the angle of the wavefront, a three$dimensional image can be built up over a large area.
!a"ples of i"ages attained using ultrasound technolog#
his image is of some tissue and demonstrates how ultrasound can image blood flow using the 6oppler effect.
his is an image obtained of the heart,s left ventricle.
$egions of the lectro"agnetic Spectru"
The following table gives approximate wavelengths, frequencies, and energies for selected regions of the electromagnetic spectrum.
Spectrum of Electromagnetic Radiation
Region Wavelen gth ( ngstro ms! > 109 Wavelength (centimeter s! "requenc# ($%! Energ# (e&!
Radio
> 10
< 3 x 109
< 10-5 10-5 0.01
Microwave
109 - 106
10 - 0.01
3 x 109 - 3 x 1012
Infrared
106 - 7000 0.01 - 7 x 10-5
3 x 1012 - 4.3 x 1014 4.3 x 1014 - 7.5 x 1014 7.5 x 1014 - 3 x 1017 3 x 1017 - 3 x 1019
0.01 - 2
Visi !e
7000 4000
7 x 10-5 - 4 x 10-5
2-3
"!#ravio!e#
4000 - 10
4 x 10-5 - 10-7
3 - 103
$-Ra%s
10 - 0.1
10-7 - 10-9
103 - 105
&a''a Ra%s
< 0.1
< 10-9
> 3 x 1019
> 105
(!ec#ro'a)ne#ic waves co'e in a ver% wide ran)e of wave!en)#*s+ #*ere are radio, 'icrowave, infrared -*ea#., visi !e !i)*#, /!#ravio!e#, $-ra%, and )a''a-ra% waves. 0!! are /sed in 'edicine in one wa% or ano#*er. 1or ins#ance, radio-fre2/enc% waves are /sed in 'a)ne#ic resonance i'a)in) -MRI.. Microwave radia#ion is /sed in cer#ain 3inds of *ea# #rea#'en#, w*ere #*e *ea# is )enera#ed in #*e #ar)e# #iss/e -as in a 'icrowave oven.. Infrared is /sed in 'an% 3inds of *ea#in) a44!ica#ions5 i#6s a!so /sed in s/r)ica! !asers. Visi !e !i)*# is /sed for 'a3in) exa'ina#ions5 i# is a!so /sed, in !asers, for so'e 3inds of s/rface #rea#'en#s. "!#ravio!e# !i)*# is )er'icida!, for one #*in)5 i# is a!so /sed #o #rea# neona#a! *%4er i!ir/ ine'ia -#ransi#or% new orn6s 7a/ndice.. $ ra%s are /sed 'ain!% for i'a)in) in#erna! #iss/es, ones 'os# no#a !%. 8ones can e i'a)ed % direc# 4*o#o)ra4*%5 ones and o#*er #iss/es can e i'a)ed in a 9: -or, 90:. scan. $ ra%s are a!so #*e 3ind of radia#ion /sed in cancer #rea#'en#. &a''a radia#ion is /sed in so'e 3inds of i'a)in) #oo, 4ar#ic/!ar!% ;(: scans. radio waves for 'o i!e 4*ones < infra red for 4/!se oxi'e#r%, 'eas/rin) !ood f!ow and #*er'a! i'a)in) < visi !e !i)*# for endosco4%, a scannin) !aser o4#*a!'osco4e, 4*o#od%na'ic #*era4% and in #rea#in) 7a/ndice < $-ra%s in i'a)in), 9:-scans and radio#*era4%
Isotopes used in Medicine
Many radioisotopes are made in nuclear reactors, some in cyclotrons. Generally neutron-rich ones and those resulting from nuclear fission need to be made in reactors, neutron-depleted ones are made in cyclotrons. There are about 40 activation product radioisotopes and five fission product ones made in reactors.
The notation %e&% stands for electron-volts, a co""on unit of energ# "easure in ato"ic ph#sics' A graphical representation of the electro"agnetic spectru" is shown in the figure (elow'
The electromagneticspectrum
AM $adio Band
he 3mplitude 1odulated !31" radio carrier frequencies are in the frequency range 070$%8+0 k&'. he frequencies 7+$070 k&' are used for maritime communication and navigation and for aircraft navigation. (arrier frequencies of 09+ to %8++ k&' are assigned at %+ k&' intervals.
/requencies: 0++$%0++ k&' Wavelengths: 8++ $ *++ m :uantum energies: * $ 8 ; %+$< e=
Short )ave
he frequencies from the top end of the 31 band to the bottom of the =&/ television band are generally called the >short wave> range, a historical term. hey are part of the general range referred to as >radio frequencies> or )/. he range from %8+0 k&' to 09 1&' has multiple communication uses. %,8+0 k&' $ 7+ 3mateur radio, government radio, international shortwave broadcast, fi;ed and 1&' mobile communications. ?overnment and non$government, fi;ed and mobile. #ncludes police, fire, 7+$0+ 1&' forestry, highway, and railroad services. 0+$09 1&' 3mateur he )/ frequency range around 9+$0+ 1&' is important as the proton resonance frequency range used in nuclear magnetic resonance !@1)" and magnetic resonance imaging !1)#". /requencies: %.8+0 $ 09 1&' Wavelengths: %AB $ 0.00 m :uantum energies: .88 ; %+$A $ .** ; %+$8 e=
T& and *M $adio Band
he carrier frequencies for =&/ television (hannels *$9 cover the frequency range 09 to B* 1&'. here is a band from B*$B8 1&' which is reserved for government and non$government services, including a standard aeronautical beacon at B0 1&'. =&/ = channels 0 and 8 are between B8 and AA 1&'. he /1 radio band is from AA to %+A 1&' between =&/ television (hannels 8 and B.3bove the /1 is a range %+A$%** 1&' for aeronautical navigation including locali'ers, radio ranging and airport control. /rom %** to %B9 1&' is another general service band for both government and non$government signals. #t includes fi;ed and mobile units and amateur broadcast. (hannels B through %7 span the frequency range %B9$*%8 1&'. *%8$9B+ 1&' includes a number of fi;ed and mobile communication modes, including some aeronautical navigation and citi'ens radio. 9B+$A<+ 1&' includes U&/ television channels %9 to A7. /requencies A<+$7+++ 1&' include a variety of aeronautical and amateur uses, studio$ transmitter relays, etc. here are radar bands %,7++$%,8++ 1&'. he /1 stations are assigned center frequencies at *++ k&' separation starting at AA.% 1&', for a ma;imum of %++ stations. hese /1 stations have a B0 k&' ma;imum deviation from the
center frequency, which leaves *0 k&' upper and lower >gaurd bands> to minimi'e interaction with the ad-acent frequency band. elevision channels have 0 1&' separation. he frequency range for mobile cellular telephones is listed as A*9.+9+ $ A9A.<B+ 1&'. /requencies: 09$%8++ 1&' Wavelengths: 0.00 m $ +.%AB m :uantum energies: +.** ; %+$8 $ +.88 ; %+$0 e=
+-Band for Satellite ,o""unication
he range 7<+$%00+ 1&' in the ultrahigh radio frequency range is designated as the C$2and and is used for a variety of satellite communication purposes. /or e;ample, the ?lobal 5ositioning 4ystem uses two carrier frequencies in this band for broadcasting navigation data.
Microwaves, $adar
While there are some radar bands from %,7++ to %,8++ 1&', most microwave applications fall in the range 7,+++ to 7+,+++ 1&' !7$7+ ?&'". (urrent microwave ovens operate at a nominal frequency of *90+ 1&', a band assigned by the /((. here are also some amateur and radio navigation uses of the 7$7+ ?&' range. #n interactions with matter, microwave radiation primarily acts to produce molecular rotation and torsion, and microwave absorption manifests itself by heat. 1olecular structure information can be obtained from the analysis of molecular rotational spectra, the most precise way to determine bond lengths and angles of molecules. 1icrowave radiation is also used in electron spin resonance spectroscopy. /or microwave ovens and some radar applications, the microwaves are produced by magnetrons. .f great astrophysical significance is the 7D background radiation in the universe, which is in the microwave region. #t has recently been mapped with great precision by the W135 probe. /requencies: %.8$7+ ?&' Wavelengths: %AB $ %+ mm :uantum energies: +.88 ; %+$0 $ +.%* ; %+$7 e=
Milli"eter )aves, Tele"etr#
he range 7+$7++ ?&' is used for a variety of e;perimental, government and amateur purposes in communication.
/requencies: 7+$7++ ?&' Wavelengths: %+ $ % mm :uantum energies: +.%* ; %+$7 $ +.%* ; %+$* e=
-nfrared
he term >infrared> refers to a broad range of frequencies, beginning at the top end of those frequencies used for communication and e;tending up the the low frequency !red" end of the visible spectrum. he wavelength range is from about % millimeter down to B0+ nm. he range ad-acent to the visible spectrum is called the >near infrared> and the longer wavelength part is called >far infrared>. #n interactions with matter, infrared primarily acts to set molecules into vibration. #nfrared spectrometers are widely used to study the vibrational spectra of molecules. #nfrared does not penetrate the atmosphere well, but astronomy in the infrared is carried out with the 4pit'er 4pace elescope. /requencies: .++7 $ 9 ; %+%9 &' Wavelengths: % mm $ B0+ nm :uantum energies: +.++%* $ %.80 e=
lectro"agnetic spectru"
&isi(le +ight
he narrow visible part of the electromagnetic spectrum corresponds to the wavelengths near the ma;imum of the 4un,s radiation curve. #n interactions with matter, visible light primarily acts to elevate electrons to higher energy levels. White light may be separated into its spectral colors by dispersion in a prism.
/requencies: 9 $ B.0 ; %+%9 &' Wavelengths: B0+ $ 9++ nm :uantum energies: %.80 $ 7.% e=
Ultraviolet
he region -ust below the visible in wavelength is called the near ultraviolet. #t is absorbed very strongly by most solid substances, and even absorbed appreciably by air. he shorter wavelengths reach the ioni'ation energy for many molecules, so the far ultraviolet has some of the dangers attendent to other ioni'ing radiation. he tissue effects of ultraviolet include sunburn, but can have some therapeutic effects as well. he sun is a strong source of ultraviolet radiation, but atmospheric absorption eliminates most of the shorter wavelengths. he eyes are quite susceptible to damage from ultraviolet radiation. Welders must wear protective eye shields because of the uv content of welding arcs can inflame the eyes. 4now$blindness is another e;ample of uv inflamationE the snow reflects uv while most other substances absorb it strongly. /requencies: B.0 ; %+%9 $ 7 ; %+%8 &' Wavelengths: 9++ nm $ %+ nm :uantum energies: 7.% $ %*9 e=
.-$a#s
F$ray was the name given to the highly penetrating rays which emanated when high energy electrons struck a metal target. Within a short time of their discovery, they were being used in medical facilities to image broken bones. We now know that they are high frequency
electromagnetic rays which are produced when the electrons are suddenly decelerated $ these rays are called bremsstrahlung radiation, or >braking radiation>. F$rays are also produced when electrons make transitions between lower atomic energy levels in heavy elements. F$rays produced in this way have have definite energies -ust like other line spectra from atomic electrons. hey are called characteristic ;$rays since they have energies determined by the atomic energy levels. #n interactions with matter, ;$rays are ioni'ing radiation and produce physiological effects which are not observed with any e;posure of non$ioni'ing radiation, such as the risk of mutations or cancer in tissue. 3stronomical observations in the F$ray region of the spectrum are obtained with the (handra F$ ray .bservatory. /requencies: 7 ; %+%8 &' upward F$rays are part of the
lectro"agnetic spectru" :uantum energies: %*9 e= $G upward
Wavelengths: %+ nm $ G downward
/a""a-$a#s
he term gamma ray is used to denote electromagnetic radiation from the nucleus as a part of a radioactive process. he energy of nuclear radiation is e;tremely high because such radiation is born in the intense conflict between the nuclear strong force and the electromagnetic force, the two strongest basic forces. he gamma ray photon may in fact be identical to an ;$ray, since both are electromagnetic raysE the terms ;$ray and gamma rays are statements about origin rather than implying different kinds of radiation. #n interactions with matter, gamma rays are ioni'ing radiation and produce physiological effects which are not observed with any e;posure of non$ioni'ing radiation, such as the risk of mutations or cancer in tissue. /requencies: typically G%+*+ &' Wavelengths: typically H %+$%* m :uantum energies: typically G% 1e=
$adiation and the Hu"an Bod#
Microwave -nteractions
he quantum energy of microwave photons is in the range +.++++% to +.++% e= which is in the range of energies separating the quantum states of molecular rotation and torsion. he interaction of microwaves with matter other than metallic conductors will be to rotate molecules and produce heat as result of that molecular motion. (onductors will strongly absorb microwaves and
any lower frequencies because they will cause electric currents which will heat the material. 1ost matter, including the human body, is largely transparent to microwaves. &igh intensity microwaves, as in a microwave oven where they pass back and forth through the food millions of times, will heat the material by producing molecular rotations and torsions. 4ince the quantum energies are a million times lower than those of ;$rays, they cannot produce ioni'ation and the characteristic types of radiation damage associated with ioni'ing radiation.
-nfrared -nteractions
he quantum energy of infrared photons is in the range +.++% to %.B e= which is in the range of energies separating the quantum states of molecular vibrations. #nfrared is absorbed more strongly than microwaves, but less strongly than visible light. he result of infrared absorption is heating of the tissue since it increases molecular vibrational activity. #nfrared radiation does penetrate the skin further than visible light and can thus be used for photographic imaging of subcutaneous blood vessels.
&isi(le +ight -nteractions
he primary mechanism for the absorption of visible light photons is the elevation of electrons to higher energy levels. here are many available states, so visible light is absorbed strongly. With a strong light source, red light can be transmitted through the hand or a fold of skin, showing that the red end of the spectrum is not absorbed as strongly as the violet end.
While e;posure to visible light causes heating, it does not cause ioni'ation with its risks. Iou may be heated by the sun through a car windshield, but you will not be sunburned $ that is an effect of the higher frequency uv part of sunlight which is blocked by the glass of the windshield.
Ultraviolet -nteractions
he near ultraviolet is absorbed very strongly in the surface layer of the skin by electron transitions. 3s you go to higher energies, the ioni'ation energies for many molecules are reached and the more dangerous photoioni'ation processes take place. 4unburn is primarily an effect of uv, and ioni'ation produces the risk of skin cancer. he o'one layer in the upper atmosphere is important for human health because it absorbs most of the harmful ultraviolet radiation from the sun before it reaches the surface. he higher frequencies in the ultraviolet are ioni'ing radiation and can produce harmful physiological effects ranging from sunburn to skin cancer. &ealth concerns for U= e;posure are mostly for the range *<+$77+ nm in wavelength, the range called U=2. 3ccording to 4cotto, et al, the most effective biological wavelength for producing skin burns is *<B nm. heir research indicates that the biological effects increase logarithmically within the U=2 range, with 77+ nm being only +.%J as effective as *<B nm for biological effects. 4o it is clearly important to control e;posure to U=2.
4ince the quantum energies of ;$ray photons are much too high to be absorbed in electron transitions between states for most atoms, they can interact with an electron only by knocking it completely out of the atom. hat is, all ;$rays are classified as ioni'ing radiation. his can occur by giving all of the energy to an electron !photoioni'ation" or by giving part of the energy to the electron and the remainder to a lower energy photon !(ompton scattering". 3t sufficiently high energies, the ;$ray photon can create an electron positron pair
The 'se (f Electromagnetic Waves )n *edicine
Reactor Radioisotopes
(half-life indicated) ismuth-!"# (4$ min)% &sed for targeted alpha therapy (T'T), especially cancers, as it has a high energy ((.4 Me)). *hromium-+" (!( d)% &sed to label red blood cells and ,uantify gastro-intestinal protein loss. *obalt-$0 (+.!- yr)% .ormerly used for e/ternal beam radiotherapy, no0 used more for sterilising 1ysprosium-"$+ (! h)% &sed as an aggregated hydro/ide for synovectomy treatment of arthritis. 2rbium-"$3 (3.4 d)% &se for relieving arthritis pain in synovial 4oints. 5olmium-"$$ (!$ h)% eing developed for diagnosis and treatment of liver tumours. 6odine-"!+ ($0 d)% &sed in cancer brachytherapy (prostate and brain), also diagnostically to evaluate the filtration rate of 7idneys and to diagnose deep vein thrombosis in the leg. 6t is also 0idely used in radioimmuno-assays to sho0 the presence of hormones in tiny ,uantities. 6odine-"#" (( d)8% 9idely used in treating thyroid cancer and in imaging the thyroid: also in diagnosis of abnormal liver function, renal (7idney) blood flo0 and urinary tract obstruction. ' strong gamma emitter, but used for beta therapy.
6ridium-"3! (-4 d)% ;upplied in 0ire form for use as an internal radiotherapy source for cancer treatment (used then removed). eta emitter.
6ron-+3 (4$ d)% &sed in studies of iron metabolism in the spleen. <ead-!"! ("0.$ h)% &sed in T'T for cancers, 0ith decay products i-!"!, =o-!"!, Tl-!0(. <utetium-"-- ($.- d)% <u-"-- is increasingly important as it emits 4ust enough gamma for imaging 0hile the beta radiation does the therapy on small (eg endocrine) tumours. 6ts half-life is long enough to allo0 sophisticated preparation for use. 6t is usually produced by neutron activation of natural or enriched lutetium-"-$ targets. Molybdenum-33 ($$ h)8% &sed as the >parent> in a generator to produce technetium-33m. =alladium-"0# ("- d)% &sed to ma7e brachytherapy permanent implant seeds for early stage prostate cancer. =hosphorus-#! ("4 d)% &sed in the treatment of polycythemia vera (e/cess red blood cells). eta emitter. =otassium-4! ("! h)% &sed for the determination of e/changeable potassium in coronary blood flo0. ?henium-"($ (#.( d)% &sed for pain relief in bone cancer. eta emitter 0ith 0ea7 gamma for imaging. ?henium-"(( ("- h)% &sed to beta irradiate coronary arteries from an angioplasty balloon. ;amarium-"+# (4- h)% ;m-"+# is very effective in relieving the pain of secondary cancers lodged in the bone, sold as @uadramet. 'lso very effective for prostate and breast cancer. eta emitter. ;elenium--+ ("!0 d)% &sed in the form of seleno-methionine to study the production of digestive enAymes. ;odium-!4 ("+ h)% .or studies of electrolytes 0ithin the body. ;trontium-(3 (+0 d)8% )ery effective in reducing the pain of prostate and bone cancer. eta emitter. Technetium-33m ($ h)% &sed in to image the s7eleton and heart muscle in particular, but also for brain, thyroid, lungs (perfusion and ventilation), liver, spleen, 7idney (structure and filtration rate), gall bladder, bone marro0, salivary and lacrimal glands, heart blood pool, infection and numerous specialised medical studies. =roduced from Mo-33 in a generator. Benon-"## (+ d)8% &sed for pulmonary (lung) ventilation studies. Ctterbium-"$3 (#! d)% &sed for cerebrospinal fluid studies in the brain.
Ctterbium-"-- (".3 h)% =rogenitor of <u-"--. Cttrium-30 ($4 h)8% &sed for cancer brachytherapy and as silicate colloid for the relieving the pain of arthritis in larger synovial 4oints. =ure beta emitter and of gro0ing significance in therapy. ?adioisotopes of caesium, gold and ruthenium are also used in brachytherapy.
8 fission product
Cyclotron Radioisotopes
*arbon-"", Ditrogen-"#, E/ygen-"+, .luorine-"(% These are positron emitters used in =2T for studying brain physiology and pathology, in particular for localising epileptic focus, and in dementia, psychiatry and neuropharmacology studies. They also have a significant role in cardiology. .-"( in .1G (fluorodeo/yglucose) has become very important in detection of cancers and the monitoring of progress in their treatment, using =2T. *obalt-+- (!-! d)% &sed as a mar7er to estimate organ siAe and for in-vitro diagnostic 7its. *opper-$4 ("# h)% &sed to study genetic diseases affecting copper metabolism, such as 9ilson>s and Men7e>s diseases, and for =2T imaging of tumours, and therapy. *opper-$- (!.$ d)% eta emitter, used in therapy. .luorine-"( as .<T (fluorothymidine), .-miso (fluoromisonidaAole), "(.-choline% tracer. Gallium-$- (-( h)% &sed for tumour imaging and localisation of inflammatory lesions (infections). Gallium-$( ($( min)% =ositron emitter used in =2T and =2T-*T units. 1erived from germanium-$( in a generator. Germanium-$( (!-" d)% &sed as the >parent> in a generator to produce Ga-$(. 6ndium-""" (!.( d)% &sed for specialist diagnostic studies, eg brain studies, infection and colon transit studies. 6odine-"!# ("# h)% 6ncreasingly used for diagnosis of thyroid function, it is a gamma emitter 0ithout the beta radiation of 6-"#". 6odine-"!4% tracer. Frypton-("m ("# sec) from ?ubidium-(" (4.$ h)% Fr-("m gas can yield functional images of pulmonary ventilation, e.g. in asthmatic patients, and for the early diagnosis of lung diseases and function.
?ubidium-(! (".!$ min)% *onvenient =2T agent in myocardial perfusion imaging. ;trontium-(! (!+ d)% &sed as the >parent> in a generator to produce ?b-(!. Thallium-!0" (-# h)% &sed for diagnosis of coronary artery disease other heart conditions such as heart muscle death and for location of lo0-grade lymphomas.
What are radioisotopes?
Many of the chemical elements have a number of isotopes. The isotopes of an element have the same number of protons in their atoms (atomic number) but different masses due to different numbers of neutrons. 6n an atom in the neutral state, the number of e/ternal electrons also e,uals the atomic number. These electrons determine the chemistry of the atom. The atomic mass is the sum of the protons and neutrons. There are (! stable elements and about !-+ stable isotopes of these elements.
Electromagnetic Radiation
'lthough the electromagnetic spectrum is made up of many different 0aves 0ith different properties, they are all electromagnetic radiations. 2lectromagnetic radiations can be considered as a stream of photons. Photons are particles of zero mass and charge which travel in a wave like pattern at the speed of light Each photon has a certain !uantity or pattern of energy Thus a beam of electromagnetic radiation delivers energy in photons and the difference bet0een the various electromagnetic radiations is the amount of energy 0ithin the photons they possess. 2lectromagnetic radiations 0ith high fre,uencies such as gamma rays and B-rays have photons of high energies 0hereas electromagnetic radiations 0ith lo0 fre,uencies such as radio 0aves have photons of lo0 energies. The energy delivered by each electromagnetic radiation beam increases 0ith the fre,uency of the electromagnetic 0ave.
Intensity of an Electromagnetic Radiation "eam
The intensity of a beam of electromagnetic radiation is the energy it delivers per second. The energy of the beam of electromagnetic radiation is delivered by the photons. Therefore the intensity depends on t0o things:
". The number of photons that are arriving per second !. The amount of energy carried by each photon
# $he amount of energy carried "y each photon
5igh fre,uency radiations have high energy photons. Therefore, if a gamma ray source 0as emitting the same photons per second as an infrared source the intensity from the gamma rays 0ould be higher as the photons from this source carry a greater amount of energy than infrared source. 6nfrared have a smaller fre,uency than gamma rays and so the photons have a smaller amount of energy.
%amma Rays
Properties &escription Gamma rays have the smallest 0avelength and their photons have the most energy of all the 0aves in the electromagnetic spectrum. They are generated by the decay of radioactive atoms and nuclear e/plosions. The high energy of gamma ray photons means they can pass through most things. Gamma rays are a form of ionising radiation, 0hich means that 0hen they pass through matter they pass on their energy to electrons in the atoms they hit. This ma7es them dangerous as they can ionise atoms in the body thereby damaging and 7illing cells. 6f the 1D' in a cell is damaged by gamma radiation it can mutate and cause cancer. 'ses The ionising nature of gamma rays has been used by medicine to its advantage. y carefully directing and controlling a beam of gamma radiation onto cancer cells they can be destroyed and their development controlled. Gamma rays are used to sterilise food and hospital e,uipment. Gamma rays 7ill bacteria and mould in food prolonging its shelf life.
Wavelength ()*(# meters +re!uency ()#) ,ertz Energy ()- Electron .olts
/0Rays
Properties &escription 'ses
Wavelength ()*() meters +re!uency ()(1 ,ertz Energy ()2 Electron .olts
B-rays are produced from the collision of high speed electrons 0ith metals. 9ith a high fre,uency and small 0avelength the high energy photons associated 0ith B-rays enables them to penetrate most materials. B-rays are also ionising radiations 0hich ma7es them dangerous as they can cause biological changes in living cells.
B-rays are mainly used in the field of medicine. They are used to produce images of bones and teeth vital for diagnosis and treatment. y placing a photographic film underneath the area of interest and directing a beam of /-rays an image is produced on the film. =arts of the body 0here the /-rays pass through easily are sho0n up as dar7 areas on the film. 9here the /-rays find it difficult to penetrate such as bones or teeth sho0n up as lighter areas on the film. <i7e gamma rays the ionising potential of /-rays can also be used in the treatment of cancer. B-rays are also used in airports to chec7 baggage and in industry as a ,uality control tool for e.g. to chec7 pac7aged food do not contain metal or stones
'ltraviolet Rays
Properties &escription <raviolet radiation is produced by hot ob4ects such as the sun or by the high temperature spar7s produced during electric 0elding. <raviolet rays have less energetic photons compared to gamma rays and /rays and a lo0er penetration po0er. Their effect on humans is therefore limited to the s7in. 2/posure to ultraviolet rays can cause a suntan (pigmentation of the s7in) and sunburn. 't high levels of e/posure s7in cancer can result and damage to the retina. This 0hy sunscreen and 'ses <raviolet is used in detecting forged ban7 notes G forged notes glo0 differently in ultraviolet light. ;ecurity pens for mar7ing goods contain a special in7 0hich only sho0s up under ultraviolet light. <raviolet has positive effects on the human body as it stimulates the production of vitamin 1. 6t is used in the field of medicine for phototherapy in the treatment of some s7in disorders. <raviolet radiations 7ill microbes and are used in the sterilisation of surgical
Wavelength ()*1 meters +re!uency ()(3 ,ertz Energy ()# Electron .olts
glasses 0ith ultraviolet protection are important. .ortunately most of the ultraviolet radiation in sunlight is absorbed by the o/ygen in the oAone layer of the 2arthHs atmosphere.
e,uipment. .luorescent lamps ma7e use of ultraviolet radiations. 9hen an electric current passes through a mercury vapour ultraviolet rays are produce. These rays collide 0ith fluorescent po0der on the inside of the tube ma7ing them fluoresce and converting the energy to visible light. .luorescent lamps are more efficient than ordinary filament lamps.
.isi"le 4ight
Properties &escription This is the small part of the electromagnetic spectrum that is detectable by the human eye. 'll ob4ects 0ith enough heat to glo0 emit light 0aves. The sun is the main source of light. <ight bulbs 0or7 on the heating effect caused by electrical resistance in a filament lamp to cause it to glo0 and emit light. Wavelength ()*- meters +re!uency - 2 5 ()(6 ,ertz Energy ()( Electron .olts 9hite light is made up of a mi/ture of colours. This spectrum of colours ma7ing up 0hite light can be vie0ed 0hen light is dispersed such as in a rainbo0. The colours, in order are red, orange, yello0, green, blue, indigo and violet. 'ses 5uman sight ma7es use of the 0avelengths from visible light, thus 0e need light in order to see. <ight plays a critical role in communication systems. <ighthouses use light to communicate the potential haAards along a stretch of coastline. Morse code bet0een ships during radio silence can be achieved using a flash light. Transmitting light through air has setbac7s in that the transmitter and receiver must be in vie0 of each other. 'lso light 0aves are absorbed by rain, fog and other bad 0eather conditions. These setbac7s 0ere resolved 0ith the advent of optical fibres. Eptical fibres are made from very pure glass and allo0 light 0aves carrying information to travel through them using the principle of total internal reflection. The information the light 0aves carry is digital and is in the form of "Hs
and 0Hs. 's the light 0ave carries a digital signal, it is of high ,uality and does not get 0ea7er over long distances. <ight 0aves are therefore used to carry vast amount of information at high speeds through optical fibre systems ma7ing the e/tremely important in the field of communications.
Infrared
Properties &escription 'll ob4ects above the temperature of absolute Aero (!-#I*) emit infra-red radiation. 6n other 0ords all 0arm ob4ects give off infra-red rays. 6nfra-red radiations cannot be seen by the human eye but their effects can be sense by the s7in as 0armth. Wavelength ()*2 meters +re!uency 6 5 ()(6 ,ertz Energy ()*( Electron .olts 'ses Thermal imaging cameras ma7e use of infra-red radiations emitted from ob4ects to form an image. These are used by firemen to detect people 0here visibility is severely reduced by smo7e. =olice also use thermal imaging cameras to trac7 criminal during the night. Thermal imaging cameras are also used to produce thermographs of ob4ects so the heat loss from them can be studied. .or e/ample a thermograph of a house can give information about 0here the main areas of heat loss are therefore ensuring the correct areas are insulated. 6nfrared 0aves are also used as a source for carrier signals in fibre optics. urglar alarms use sensors 0hich detect the infra-red rays given off by intruders.
Microwaves
Properties &escription 'ses
Micro0aves are categorised as radio 0aves. They have the shortest 0avelengths of all the radio 0aves.
Wavelength ()*7 meters +re!uency ()() ,ertz Energy ()*6 Electron .olts
The property of micro0aves to cause molecules to vibrate is put to use to coo7 food in micro0ave ovens. 6n a micro0ave oven the micro0aves are produced by a device called a Magnetron. Micro0aves are non ionising These produce micro0aves of a radiations. Their fre,uencies longer 0avelength are a lot lo0er than those of gamma rays and /-rays and the (appro/imately "0 to !0 cm). The micro0aves are absorbed energy of their photons is by the 0ater and the fat considerably lesser. They molecules in the food heating therefore do not have the damaging properties of ionising them up from inside thereby coo7ing the food. Micro0aves radiations. 5o0ever, in are not absorbed by dry sufficient intensity they can materials such as glass and cause molecules in matter to ceramics. The food is placed on vibrate 0hich in turn cause friction and produces heat. This a turntable to ensure the even distribution of the micro0aves to heating effect of micro0aves allo0 the food to be coo7ed does present a ris7 to living evenly. The metal casing of the tissue. micro0ave oven ensures all the micro0aves are reflected bac7 into the oven and the door has a 0ire mesh over the 0indo0 0hich serves the same purpose. Micro0aves can penetrate clouds, light rain, sno0, haAe and smo7e. This ma7es them good for transmitting information from one place to another. Micro0aves can be focussed into highly directional beams using parabolic dish antennas. These beams can be directed li7e a searchlight to a receiving aerial based on the 2arth or to a satellite orbiting the 2arth. Micro0aves are the principle carriers of telegraphic data transmission (mobile phones) and also carry television transmissions.
Radio waves
Properties &escription 'ses
?adio 0aves are produced over a large range of fre,uencies thus li7e light have their o0n spectrum. This radio spectrum is divided into radio fre,uency bands. The high fre,uency short 0avelength band as discussed earlier ma7e up *7 2 the micro0ave category of Wavelength () to () meters the electromagnetic () 6 spectrum these are 7no0n +re!uency () to () ,ertz as <ra 5igh .re,uencies Energy ()*2 Electron .olts (&5.). The other fre,uency bands are )ery 5igh Radio 8pectrum .re,uencies ()5.), 5igh .re,uencies (5.), Medium ;uper 5igh .re,uencies(;5.) # - #0G5A .re,uencies (M.) <o0 <ra 5igh .re,uencies (&5.) 0.# - #G5A )ery 5igh .re,uencies ()5.) #0 - #00M5A .re,uencies (<.) and )ery 5igh .re,uencies (5.) # - #0M5A <o0 .re,uencies ()<.).
Medium .re,uencies (M.) 0.# - #M5A <o0 .re,uencies (&.) #0 - #0075A )ery <o0 .re,uencies ()<.) # - #075J G5A K Giga 5ertA K "03 5ertA M5A K Mega 5ertA K "0$ 5ertA 75A K Filo 5ertA K "0# 5ertA
?adio 0aves are used in communication. ?adio 0aves are not strongly absorbed by the atmosphere and can therefore travel long distances. ?adio 0aves ma7e use of the ionosphere a region of the atmosphere about "007m above the 2arthHs surface and appro/imately #007m thic7. 6n the ionosphere the atmosphere is partially ionised by the action of ultraviolet radiations from the sunlight. ?adio 0aves are bent and reflected bac7 to0ards the 2arth by the ionosphere. This bouncing off the ionosphere and the 2arthHs surface may occur repeatedly allo0ing radio 0aves to travel long distances around the 2arth.
The wave properties of ultrasound
Ultrasound relies on high frequency sounds to image the body and diagnose patients. Ultrasounds are therefore longitudinal waves which cause particles to oscillate back and forth and produce a series of compressions and rarefactions. Using the following formula, it is possible to calculate the velocity, frequency or wavelength of a wave if the other two values are known: v = fλ Where:
• • •
he velocity !v" is the speed of the wave. #t is measured in m s$%. he frequency !f" is the number of times a particle oscillates per second. #t is measured in &'. he wavelength !λ" is the distance between two compressions or rarefactions. #t is measured in m.
he amplitude is the distance a particle moves back or forth.
(ompressions are areas of the wave where particles are close together and there is high pressure. )arefactions are areas of the wave where particles are far apart and there is low pressure.
The frequencies used in ultrasound diagnosis
Ultrasound uses high frequency sounds that are higher than the human ear can hear. ie. *+ +++ &'. Ultrasound can,t detect ob-ects that are smaller than its wavelength and therefore higher frequencies of ultrasound produce better resolution. .n the other hand, higher frequencies of ultrasound have short wavelengths and are absorbed easily and therefore are not as penetrating. /or this reason high frequencies are used for scanning areas of the body close to the surface and low frequencies are used for areas that are deeper down in the body. hese frequencies generally range between %$0+ 1&'.
How ultrasound is produced and detected
Ultrasound is produced and detected using an ultrasound transducer. Ultrasound transducers are capable of sending an ultrasound and then the same transducer can detect the sound and convert it to an electrical signal to be diagnosed. o produce an ultrasound, a pie'oelectric crystal has an alternating current applied across it. he pie'oelectric crystal grows and shrinks depending on the voltage run through it. )unning an alternating current through it causes it to vibrate at a high speed and to produce an ultrasound. his conversion of electrical energy to mechanical energy is known as the pie'oelectric effect. he sound then bounces back off the ob-ect under investigation. he sound hits the pie'oelectric
crystal and then has the reverse effect $ causing the mechanical energy produced from the sound vibrating the crystal to be converted into electrical energy. 2y measuring the time between when the sound was sent and received, the amplitude of the sound and the pitch of the sound, a computer can produce images, calculate depths and calculate speeds.
The nature of A-scans, B-scans, sector scans and phase scans
A-scans
3$scans can be used in order to measure distances. 3 transducer emits an ultrasonic pulse and the time taken for the pulse to bounce off an ob-ect and come back is graphed in order to determine how far away the ob-ect is. 3$scans only give one$dimensional information and therefore are not useful for imaging.
B-Scans
2$scans can be used to take an image of a cross$section through the body. he transducer is swept across the area and the time taken for pulses to return is used to determine distances, which are plotted as a series of dots on the image. 2$4cans will give two$dimensional information about the cross$section.
Sector scans
4ector scans can be used to take a sector shaped image of the body. he transducer is swept back and forth across the area, producing a series of 2$scans that build up an image. 4ector scans are much harder to produce than phase scans and are much less common. &owever, they are useful for taking images when there is only a small amount of space.
Phase scans
5hase scans have hundreds of transducers in the same probe in order to take a high resolution real$time scan. he angle of the wavefront can be altered by firing the transducers one after another, when this happens they are out of phase. 2y changing the angle of the wavefront, a three$dimensional image can be built up over a large area.
!a"ples of i"ages attained using ultrasound technolog#
his image is of some tissue and demonstrates how ultrasound can image blood flow using the 6oppler effect.
his is an image obtained of the heart,s left ventricle.
$egions of the lectro"agnetic Spectru"
The following table gives approximate wavelengths, frequencies, and energies for selected regions of the electromagnetic spectrum.
Spectrum of Electromagnetic Radiation
Region Wavelen gth ( ngstro ms! > 109 Wavelength (centimeter s! "requenc# ($%! Energ# (e&!
Radio
> 10
< 3 x 109
< 10-5 10-5 0.01
Microwave
109 - 106
10 - 0.01
3 x 109 - 3 x 1012
Infrared
106 - 7000 0.01 - 7 x 10-5
3 x 1012 - 4.3 x 1014 4.3 x 1014 - 7.5 x 1014 7.5 x 1014 - 3 x 1017 3 x 1017 - 3 x 1019
0.01 - 2
Visi !e
7000 4000
7 x 10-5 - 4 x 10-5
2-3
"!#ravio!e#
4000 - 10
4 x 10-5 - 10-7
3 - 103
$-Ra%s
10 - 0.1
10-7 - 10-9
103 - 105
&a''a Ra%s
< 0.1
< 10-9
> 3 x 1019
> 105
(!ec#ro'a)ne#ic waves co'e in a ver% wide ran)e of wave!en)#*s+ #*ere are radio, 'icrowave, infrared -*ea#., visi !e !i)*#, /!#ravio!e#, $-ra%, and )a''a-ra% waves. 0!! are /sed in 'edicine in one wa% or ano#*er. 1or ins#ance, radio-fre2/enc% waves are /sed in 'a)ne#ic resonance i'a)in) -MRI.. Microwave radia#ion is /sed in cer#ain 3inds of *ea# #rea#'en#, w*ere #*e *ea# is )enera#ed in #*e #ar)e# #iss/e -as in a 'icrowave oven.. Infrared is /sed in 'an% 3inds of *ea#in) a44!ica#ions5 i#6s a!so /sed in s/r)ica! !asers. Visi !e !i)*# is /sed for 'a3in) exa'ina#ions5 i# is a!so /sed, in !asers, for so'e 3inds of s/rface #rea#'en#s. "!#ravio!e# !i)*# is )er'icida!, for one #*in)5 i# is a!so /sed #o #rea# neona#a! *%4er i!ir/ ine'ia -#ransi#or% new orn6s 7a/ndice.. $ ra%s are /sed 'ain!% for i'a)in) in#erna! #iss/es, ones 'os# no#a !%. 8ones can e i'a)ed % direc# 4*o#o)ra4*%5 ones and o#*er #iss/es can e i'a)ed in a 9: -or, 90:. scan. $ ra%s are a!so #*e 3ind of radia#ion /sed in cancer #rea#'en#. &a''a radia#ion is /sed in so'e 3inds of i'a)in) #oo, 4ar#ic/!ar!% ;(: scans. radio waves for 'o i!e 4*ones < infra red for 4/!se oxi'e#r%, 'eas/rin) !ood f!ow and #*er'a! i'a)in) < visi !e !i)*# for endosco4%, a scannin) !aser o4#*a!'osco4e, 4*o#od%na'ic #*era4% and in #rea#in) 7a/ndice < $-ra%s in i'a)in), 9:-scans and radio#*era4%
Isotopes used in Medicine
Many radioisotopes are made in nuclear reactors, some in cyclotrons. Generally neutron-rich ones and those resulting from nuclear fission need to be made in reactors, neutron-depleted ones are made in cyclotrons. There are about 40 activation product radioisotopes and five fission product ones made in reactors.
The notation %e&% stands for electron-volts, a co""on unit of energ# "easure in ato"ic ph#sics' A graphical representation of the electro"agnetic spectru" is shown in the figure (elow'
The electromagneticspectrum
AM $adio Band
he 3mplitude 1odulated !31" radio carrier frequencies are in the frequency range 070$%8+0 k&'. he frequencies 7+$070 k&' are used for maritime communication and navigation and for aircraft navigation. (arrier frequencies of 09+ to %8++ k&' are assigned at %+ k&' intervals.
/requencies: 0++$%0++ k&' Wavelengths: 8++ $ *++ m :uantum energies: * $ 8 ; %+$< e=
Short )ave
he frequencies from the top end of the 31 band to the bottom of the =&/ television band are generally called the >short wave> range, a historical term. hey are part of the general range referred to as >radio frequencies> or )/. he range from %8+0 k&' to 09 1&' has multiple communication uses. %,8+0 k&' $ 7+ 3mateur radio, government radio, international shortwave broadcast, fi;ed and 1&' mobile communications. ?overnment and non$government, fi;ed and mobile. #ncludes police, fire, 7+$0+ 1&' forestry, highway, and railroad services. 0+$09 1&' 3mateur he )/ frequency range around 9+$0+ 1&' is important as the proton resonance frequency range used in nuclear magnetic resonance !@1)" and magnetic resonance imaging !1)#". /requencies: %.8+0 $ 09 1&' Wavelengths: %AB $ 0.00 m :uantum energies: .88 ; %+$A $ .** ; %+$8 e=
T& and *M $adio Band
he carrier frequencies for =&/ television (hannels *$9 cover the frequency range 09 to B* 1&'. here is a band from B*$B8 1&' which is reserved for government and non$government services, including a standard aeronautical beacon at B0 1&'. =&/ = channels 0 and 8 are between B8 and AA 1&'. he /1 radio band is from AA to %+A 1&' between =&/ television (hannels 8 and B.3bove the /1 is a range %+A$%** 1&' for aeronautical navigation including locali'ers, radio ranging and airport control. /rom %** to %B9 1&' is another general service band for both government and non$government signals. #t includes fi;ed and mobile units and amateur broadcast. (hannels B through %7 span the frequency range %B9$*%8 1&'. *%8$9B+ 1&' includes a number of fi;ed and mobile communication modes, including some aeronautical navigation and citi'ens radio. 9B+$A<+ 1&' includes U&/ television channels %9 to A7. /requencies A<+$7+++ 1&' include a variety of aeronautical and amateur uses, studio$ transmitter relays, etc. here are radar bands %,7++$%,8++ 1&'. he /1 stations are assigned center frequencies at *++ k&' separation starting at AA.% 1&', for a ma;imum of %++ stations. hese /1 stations have a B0 k&' ma;imum deviation from the
center frequency, which leaves *0 k&' upper and lower >gaurd bands> to minimi'e interaction with the ad-acent frequency band. elevision channels have 0 1&' separation. he frequency range for mobile cellular telephones is listed as A*9.+9+ $ A9A.<B+ 1&'. /requencies: 09$%8++ 1&' Wavelengths: 0.00 m $ +.%AB m :uantum energies: +.** ; %+$8 $ +.88 ; %+$0 e=
+-Band for Satellite ,o""unication
he range 7<+$%00+ 1&' in the ultrahigh radio frequency range is designated as the C$2and and is used for a variety of satellite communication purposes. /or e;ample, the ?lobal 5ositioning 4ystem uses two carrier frequencies in this band for broadcasting navigation data.
Microwaves, $adar
While there are some radar bands from %,7++ to %,8++ 1&', most microwave applications fall in the range 7,+++ to 7+,+++ 1&' !7$7+ ?&'". (urrent microwave ovens operate at a nominal frequency of *90+ 1&', a band assigned by the /((. here are also some amateur and radio navigation uses of the 7$7+ ?&' range. #n interactions with matter, microwave radiation primarily acts to produce molecular rotation and torsion, and microwave absorption manifests itself by heat. 1olecular structure information can be obtained from the analysis of molecular rotational spectra, the most precise way to determine bond lengths and angles of molecules. 1icrowave radiation is also used in electron spin resonance spectroscopy. /or microwave ovens and some radar applications, the microwaves are produced by magnetrons. .f great astrophysical significance is the 7D background radiation in the universe, which is in the microwave region. #t has recently been mapped with great precision by the W135 probe. /requencies: %.8$7+ ?&' Wavelengths: %AB $ %+ mm :uantum energies: +.88 ; %+$0 $ +.%* ; %+$7 e=
Milli"eter )aves, Tele"etr#
he range 7+$7++ ?&' is used for a variety of e;perimental, government and amateur purposes in communication.
/requencies: 7+$7++ ?&' Wavelengths: %+ $ % mm :uantum energies: +.%* ; %+$7 $ +.%* ; %+$* e=
-nfrared
he term >infrared> refers to a broad range of frequencies, beginning at the top end of those frequencies used for communication and e;tending up the the low frequency !red" end of the visible spectrum. he wavelength range is from about % millimeter down to B0+ nm. he range ad-acent to the visible spectrum is called the >near infrared> and the longer wavelength part is called >far infrared>. #n interactions with matter, infrared primarily acts to set molecules into vibration. #nfrared spectrometers are widely used to study the vibrational spectra of molecules. #nfrared does not penetrate the atmosphere well, but astronomy in the infrared is carried out with the 4pit'er 4pace elescope. /requencies: .++7 $ 9 ; %+%9 &' Wavelengths: % mm $ B0+ nm :uantum energies: +.++%* $ %.80 e=
lectro"agnetic spectru"
&isi(le +ight
he narrow visible part of the electromagnetic spectrum corresponds to the wavelengths near the ma;imum of the 4un,s radiation curve. #n interactions with matter, visible light primarily acts to elevate electrons to higher energy levels. White light may be separated into its spectral colors by dispersion in a prism.
/requencies: 9 $ B.0 ; %+%9 &' Wavelengths: B0+ $ 9++ nm :uantum energies: %.80 $ 7.% e=
Ultraviolet
he region -ust below the visible in wavelength is called the near ultraviolet. #t is absorbed very strongly by most solid substances, and even absorbed appreciably by air. he shorter wavelengths reach the ioni'ation energy for many molecules, so the far ultraviolet has some of the dangers attendent to other ioni'ing radiation. he tissue effects of ultraviolet include sunburn, but can have some therapeutic effects as well. he sun is a strong source of ultraviolet radiation, but atmospheric absorption eliminates most of the shorter wavelengths. he eyes are quite susceptible to damage from ultraviolet radiation. Welders must wear protective eye shields because of the uv content of welding arcs can inflame the eyes. 4now$blindness is another e;ample of uv inflamationE the snow reflects uv while most other substances absorb it strongly. /requencies: B.0 ; %+%9 $ 7 ; %+%8 &' Wavelengths: 9++ nm $ %+ nm :uantum energies: 7.% $ %*9 e=
.-$a#s
F$ray was the name given to the highly penetrating rays which emanated when high energy electrons struck a metal target. Within a short time of their discovery, they were being used in medical facilities to image broken bones. We now know that they are high frequency
electromagnetic rays which are produced when the electrons are suddenly decelerated $ these rays are called bremsstrahlung radiation, or >braking radiation>. F$rays are also produced when electrons make transitions between lower atomic energy levels in heavy elements. F$rays produced in this way have have definite energies -ust like other line spectra from atomic electrons. hey are called characteristic ;$rays since they have energies determined by the atomic energy levels. #n interactions with matter, ;$rays are ioni'ing radiation and produce physiological effects which are not observed with any e;posure of non$ioni'ing radiation, such as the risk of mutations or cancer in tissue. 3stronomical observations in the F$ray region of the spectrum are obtained with the (handra F$ ray .bservatory. /requencies: 7 ; %+%8 &' upward F$rays are part of the
lectro"agnetic spectru" :uantum energies: %*9 e= $G upward
Wavelengths: %+ nm $ G downward
/a""a-$a#s
he term gamma ray is used to denote electromagnetic radiation from the nucleus as a part of a radioactive process. he energy of nuclear radiation is e;tremely high because such radiation is born in the intense conflict between the nuclear strong force and the electromagnetic force, the two strongest basic forces. he gamma ray photon may in fact be identical to an ;$ray, since both are electromagnetic raysE the terms ;$ray and gamma rays are statements about origin rather than implying different kinds of radiation. #n interactions with matter, gamma rays are ioni'ing radiation and produce physiological effects which are not observed with any e;posure of non$ioni'ing radiation, such as the risk of mutations or cancer in tissue. /requencies: typically G%+*+ &' Wavelengths: typically H %+$%* m :uantum energies: typically G% 1e=
$adiation and the Hu"an Bod#
Microwave -nteractions
he quantum energy of microwave photons is in the range +.++++% to +.++% e= which is in the range of energies separating the quantum states of molecular rotation and torsion. he interaction of microwaves with matter other than metallic conductors will be to rotate molecules and produce heat as result of that molecular motion. (onductors will strongly absorb microwaves and
any lower frequencies because they will cause electric currents which will heat the material. 1ost matter, including the human body, is largely transparent to microwaves. &igh intensity microwaves, as in a microwave oven where they pass back and forth through the food millions of times, will heat the material by producing molecular rotations and torsions. 4ince the quantum energies are a million times lower than those of ;$rays, they cannot produce ioni'ation and the characteristic types of radiation damage associated with ioni'ing radiation.
-nfrared -nteractions
he quantum energy of infrared photons is in the range +.++% to %.B e= which is in the range of energies separating the quantum states of molecular vibrations. #nfrared is absorbed more strongly than microwaves, but less strongly than visible light. he result of infrared absorption is heating of the tissue since it increases molecular vibrational activity. #nfrared radiation does penetrate the skin further than visible light and can thus be used for photographic imaging of subcutaneous blood vessels.
&isi(le +ight -nteractions
he primary mechanism for the absorption of visible light photons is the elevation of electrons to higher energy levels. here are many available states, so visible light is absorbed strongly. With a strong light source, red light can be transmitted through the hand or a fold of skin, showing that the red end of the spectrum is not absorbed as strongly as the violet end.
While e;posure to visible light causes heating, it does not cause ioni'ation with its risks. Iou may be heated by the sun through a car windshield, but you will not be sunburned $ that is an effect of the higher frequency uv part of sunlight which is blocked by the glass of the windshield.
Ultraviolet -nteractions
he near ultraviolet is absorbed very strongly in the surface layer of the skin by electron transitions. 3s you go to higher energies, the ioni'ation energies for many molecules are reached and the more dangerous photoioni'ation processes take place. 4unburn is primarily an effect of uv, and ioni'ation produces the risk of skin cancer. he o'one layer in the upper atmosphere is important for human health because it absorbs most of the harmful ultraviolet radiation from the sun before it reaches the surface. he higher frequencies in the ultraviolet are ioni'ing radiation and can produce harmful physiological effects ranging from sunburn to skin cancer. &ealth concerns for U= e;posure are mostly for the range *<+$77+ nm in wavelength, the range called U=2. 3ccording to 4cotto, et al, the most effective biological wavelength for producing skin burns is *<B nm. heir research indicates that the biological effects increase logarithmically within the U=2 range, with 77+ nm being only +.%J as effective as *<B nm for biological effects. 4o it is clearly important to control e;posure to U=2.
4ince the quantum energies of ;$ray photons are much too high to be absorbed in electron transitions between states for most atoms, they can interact with an electron only by knocking it completely out of the atom. hat is, all ;$rays are classified as ioni'ing radiation. his can occur by giving all of the energy to an electron !photoioni'ation" or by giving part of the energy to the electron and the remainder to a lower energy photon !(ompton scattering". 3t sufficiently high energies, the ;$ray photon can create an electron positron pair
The 'se (f Electromagnetic Waves )n *edicine
Reactor Radioisotopes
(half-life indicated) ismuth-!"# (4$ min)% &sed for targeted alpha therapy (T'T), especially cancers, as it has a high energy ((.4 Me)). *hromium-+" (!( d)% &sed to label red blood cells and ,uantify gastro-intestinal protein loss. *obalt-$0 (+.!- yr)% .ormerly used for e/ternal beam radiotherapy, no0 used more for sterilising 1ysprosium-"$+ (! h)% &sed as an aggregated hydro/ide for synovectomy treatment of arthritis. 2rbium-"$3 (3.4 d)% &se for relieving arthritis pain in synovial 4oints. 5olmium-"$$ (!$ h)% eing developed for diagnosis and treatment of liver tumours. 6odine-"!+ ($0 d)% &sed in cancer brachytherapy (prostate and brain), also diagnostically to evaluate the filtration rate of 7idneys and to diagnose deep vein thrombosis in the leg. 6t is also 0idely used in radioimmuno-assays to sho0 the presence of hormones in tiny ,uantities. 6odine-"#" (( d)8% 9idely used in treating thyroid cancer and in imaging the thyroid: also in diagnosis of abnormal liver function, renal (7idney) blood flo0 and urinary tract obstruction. ' strong gamma emitter, but used for beta therapy.
6ridium-"3! (-4 d)% ;upplied in 0ire form for use as an internal radiotherapy source for cancer treatment (used then removed). eta emitter.
6ron-+3 (4$ d)% &sed in studies of iron metabolism in the spleen. <ead-!"! ("0.$ h)% &sed in T'T for cancers, 0ith decay products i-!"!, =o-!"!, Tl-!0(. <utetium-"-- ($.- d)% <u-"-- is increasingly important as it emits 4ust enough gamma for imaging 0hile the beta radiation does the therapy on small (eg endocrine) tumours. 6ts half-life is long enough to allo0 sophisticated preparation for use. 6t is usually produced by neutron activation of natural or enriched lutetium-"-$ targets. Molybdenum-33 ($$ h)8% &sed as the >parent> in a generator to produce technetium-33m. =alladium-"0# ("- d)% &sed to ma7e brachytherapy permanent implant seeds for early stage prostate cancer. =hosphorus-#! ("4 d)% &sed in the treatment of polycythemia vera (e/cess red blood cells). eta emitter. =otassium-4! ("! h)% &sed for the determination of e/changeable potassium in coronary blood flo0. ?henium-"($ (#.( d)% &sed for pain relief in bone cancer. eta emitter 0ith 0ea7 gamma for imaging. ?henium-"(( ("- h)% &sed to beta irradiate coronary arteries from an angioplasty balloon. ;amarium-"+# (4- h)% ;m-"+# is very effective in relieving the pain of secondary cancers lodged in the bone, sold as @uadramet. 'lso very effective for prostate and breast cancer. eta emitter. ;elenium--+ ("!0 d)% &sed in the form of seleno-methionine to study the production of digestive enAymes. ;odium-!4 ("+ h)% .or studies of electrolytes 0ithin the body. ;trontium-(3 (+0 d)8% )ery effective in reducing the pain of prostate and bone cancer. eta emitter. Technetium-33m ($ h)% &sed in to image the s7eleton and heart muscle in particular, but also for brain, thyroid, lungs (perfusion and ventilation), liver, spleen, 7idney (structure and filtration rate), gall bladder, bone marro0, salivary and lacrimal glands, heart blood pool, infection and numerous specialised medical studies. =roduced from Mo-33 in a generator. Benon-"## (+ d)8% &sed for pulmonary (lung) ventilation studies. Ctterbium-"$3 (#! d)% &sed for cerebrospinal fluid studies in the brain.
Ctterbium-"-- (".3 h)% =rogenitor of <u-"--. Cttrium-30 ($4 h)8% &sed for cancer brachytherapy and as silicate colloid for the relieving the pain of arthritis in larger synovial 4oints. =ure beta emitter and of gro0ing significance in therapy. ?adioisotopes of caesium, gold and ruthenium are also used in brachytherapy.
8 fission product
Cyclotron Radioisotopes
*arbon-"", Ditrogen-"#, E/ygen-"+, .luorine-"(% These are positron emitters used in =2T for studying brain physiology and pathology, in particular for localising epileptic focus, and in dementia, psychiatry and neuropharmacology studies. They also have a significant role in cardiology. .-"( in .1G (fluorodeo/yglucose) has become very important in detection of cancers and the monitoring of progress in their treatment, using =2T. *obalt-+- (!-! d)% &sed as a mar7er to estimate organ siAe and for in-vitro diagnostic 7its. *opper-$4 ("# h)% &sed to study genetic diseases affecting copper metabolism, such as 9ilson>s and Men7e>s diseases, and for =2T imaging of tumours, and therapy. *opper-$- (!.$ d)% eta emitter, used in therapy. .luorine-"( as .<T (fluorothymidine), .-miso (fluoromisonidaAole), "(.-choline% tracer. Gallium-$- (-( h)% &sed for tumour imaging and localisation of inflammatory lesions (infections). Gallium-$( ($( min)% =ositron emitter used in =2T and =2T-*T units. 1erived from germanium-$( in a generator. Germanium-$( (!-" d)% &sed as the >parent> in a generator to produce Ga-$(. 6ndium-""" (!.( d)% &sed for specialist diagnostic studies, eg brain studies, infection and colon transit studies. 6odine-"!# ("# h)% 6ncreasingly used for diagnosis of thyroid function, it is a gamma emitter 0ithout the beta radiation of 6-"#". 6odine-"!4% tracer. Frypton-("m ("# sec) from ?ubidium-(" (4.$ h)% Fr-("m gas can yield functional images of pulmonary ventilation, e.g. in asthmatic patients, and for the early diagnosis of lung diseases and function.
?ubidium-(! (".!$ min)% *onvenient =2T agent in myocardial perfusion imaging. ;trontium-(! (!+ d)% &sed as the >parent> in a generator to produce ?b-(!. Thallium-!0" (-# h)% &sed for diagnosis of coronary artery disease other heart conditions such as heart muscle death and for location of lo0-grade lymphomas.
What are radioisotopes?
Many of the chemical elements have a number of isotopes. The isotopes of an element have the same number of protons in their atoms (atomic number) but different masses due to different numbers of neutrons. 6n an atom in the neutral state, the number of e/ternal electrons also e,uals the atomic number. These electrons determine the chemistry of the atom. The atomic mass is the sum of the protons and neutrons. There are (! stable elements and about !-+ stable isotopes of these elements.
Electromagnetic Radiation
'lthough the electromagnetic spectrum is made up of many different 0aves 0ith different properties, they are all electromagnetic radiations. 2lectromagnetic radiations can be considered as a stream of photons. Photons are particles of zero mass and charge which travel in a wave like pattern at the speed of light Each photon has a certain !uantity or pattern of energy Thus a beam of electromagnetic radiation delivers energy in photons and the difference bet0een the various electromagnetic radiations is the amount of energy 0ithin the photons they possess. 2lectromagnetic radiations 0ith high fre,uencies such as gamma rays and B-rays have photons of high energies 0hereas electromagnetic radiations 0ith lo0 fre,uencies such as radio 0aves have photons of lo0 energies. The energy delivered by each electromagnetic radiation beam increases 0ith the fre,uency of the electromagnetic 0ave.
Intensity of an Electromagnetic Radiation "eam
The intensity of a beam of electromagnetic radiation is the energy it delivers per second. The energy of the beam of electromagnetic radiation is delivered by the photons. Therefore the intensity depends on t0o things:
". The number of photons that are arriving per second !. The amount of energy carried by each photon
# $he amount of energy carried "y each photon
5igh fre,uency radiations have high energy photons. Therefore, if a gamma ray source 0as emitting the same photons per second as an infrared source the intensity from the gamma rays 0ould be higher as the photons from this source carry a greater amount of energy than infrared source. 6nfrared have a smaller fre,uency than gamma rays and so the photons have a smaller amount of energy.
%amma Rays
Properties &escription Gamma rays have the smallest 0avelength and their photons have the most energy of all the 0aves in the electromagnetic spectrum. They are generated by the decay of radioactive atoms and nuclear e/plosions. The high energy of gamma ray photons means they can pass through most things. Gamma rays are a form of ionising radiation, 0hich means that 0hen they pass through matter they pass on their energy to electrons in the atoms they hit. This ma7es them dangerous as they can ionise atoms in the body thereby damaging and 7illing cells. 6f the 1D' in a cell is damaged by gamma radiation it can mutate and cause cancer. 'ses The ionising nature of gamma rays has been used by medicine to its advantage. y carefully directing and controlling a beam of gamma radiation onto cancer cells they can be destroyed and their development controlled. Gamma rays are used to sterilise food and hospital e,uipment. Gamma rays 7ill bacteria and mould in food prolonging its shelf life.
Wavelength ()*(# meters +re!uency ()#) ,ertz Energy ()- Electron .olts
/0Rays
Properties &escription 'ses
Wavelength ()*() meters +re!uency ()(1 ,ertz Energy ()2 Electron .olts
B-rays are produced from the collision of high speed electrons 0ith metals. 9ith a high fre,uency and small 0avelength the high energy photons associated 0ith B-rays enables them to penetrate most materials. B-rays are also ionising radiations 0hich ma7es them dangerous as they can cause biological changes in living cells.
B-rays are mainly used in the field of medicine. They are used to produce images of bones and teeth vital for diagnosis and treatment. y placing a photographic film underneath the area of interest and directing a beam of /-rays an image is produced on the film. =arts of the body 0here the /-rays pass through easily are sho0n up as dar7 areas on the film. 9here the /-rays find it difficult to penetrate such as bones or teeth sho0n up as lighter areas on the film. <i7e gamma rays the ionising potential of /-rays can also be used in the treatment of cancer. B-rays are also used in airports to chec7 baggage and in industry as a ,uality control tool for e.g. to chec7 pac7aged food do not contain metal or stones
'ltraviolet Rays
Properties &escription <raviolet radiation is produced by hot ob4ects such as the sun or by the high temperature spar7s produced during electric 0elding. <raviolet rays have less energetic photons compared to gamma rays and /rays and a lo0er penetration po0er. Their effect on humans is therefore limited to the s7in. 2/posure to ultraviolet rays can cause a suntan (pigmentation of the s7in) and sunburn. 't high levels of e/posure s7in cancer can result and damage to the retina. This 0hy sunscreen and 'ses <raviolet is used in detecting forged ban7 notes G forged notes glo0 differently in ultraviolet light. ;ecurity pens for mar7ing goods contain a special in7 0hich only sho0s up under ultraviolet light. <raviolet has positive effects on the human body as it stimulates the production of vitamin 1. 6t is used in the field of medicine for phototherapy in the treatment of some s7in disorders. <raviolet radiations 7ill microbes and are used in the sterilisation of surgical
Wavelength ()*1 meters +re!uency ()(3 ,ertz Energy ()# Electron .olts
glasses 0ith ultraviolet protection are important. .ortunately most of the ultraviolet radiation in sunlight is absorbed by the o/ygen in the oAone layer of the 2arthHs atmosphere.
e,uipment. .luorescent lamps ma7e use of ultraviolet radiations. 9hen an electric current passes through a mercury vapour ultraviolet rays are produce. These rays collide 0ith fluorescent po0der on the inside of the tube ma7ing them fluoresce and converting the energy to visible light. .luorescent lamps are more efficient than ordinary filament lamps.
.isi"le 4ight
Properties &escription This is the small part of the electromagnetic spectrum that is detectable by the human eye. 'll ob4ects 0ith enough heat to glo0 emit light 0aves. The sun is the main source of light. <ight bulbs 0or7 on the heating effect caused by electrical resistance in a filament lamp to cause it to glo0 and emit light. Wavelength ()*- meters +re!uency - 2 5 ()(6 ,ertz Energy ()( Electron .olts 9hite light is made up of a mi/ture of colours. This spectrum of colours ma7ing up 0hite light can be vie0ed 0hen light is dispersed such as in a rainbo0. The colours, in order are red, orange, yello0, green, blue, indigo and violet. 'ses 5uman sight ma7es use of the 0avelengths from visible light, thus 0e need light in order to see. <ight plays a critical role in communication systems. <ighthouses use light to communicate the potential haAards along a stretch of coastline. Morse code bet0een ships during radio silence can be achieved using a flash light. Transmitting light through air has setbac7s in that the transmitter and receiver must be in vie0 of each other. 'lso light 0aves are absorbed by rain, fog and other bad 0eather conditions. These setbac7s 0ere resolved 0ith the advent of optical fibres. Eptical fibres are made from very pure glass and allo0 light 0aves carrying information to travel through them using the principle of total internal reflection. The information the light 0aves carry is digital and is in the form of "Hs
and 0Hs. 's the light 0ave carries a digital signal, it is of high ,uality and does not get 0ea7er over long distances. <ight 0aves are therefore used to carry vast amount of information at high speeds through optical fibre systems ma7ing the e/tremely important in the field of communications.
Infrared
Properties &escription 'll ob4ects above the temperature of absolute Aero (!-#I*) emit infra-red radiation. 6n other 0ords all 0arm ob4ects give off infra-red rays. 6nfra-red radiations cannot be seen by the human eye but their effects can be sense by the s7in as 0armth. Wavelength ()*2 meters +re!uency 6 5 ()(6 ,ertz Energy ()*( Electron .olts 'ses Thermal imaging cameras ma7e use of infra-red radiations emitted from ob4ects to form an image. These are used by firemen to detect people 0here visibility is severely reduced by smo7e. =olice also use thermal imaging cameras to trac7 criminal during the night. Thermal imaging cameras are also used to produce thermographs of ob4ects so the heat loss from them can be studied. .or e/ample a thermograph of a house can give information about 0here the main areas of heat loss are therefore ensuring the correct areas are insulated. 6nfrared 0aves are also used as a source for carrier signals in fibre optics. urglar alarms use sensors 0hich detect the infra-red rays given off by intruders.
Microwaves
Properties &escription 'ses
Micro0aves are categorised as radio 0aves. They have the shortest 0avelengths of all the radio 0aves.
Wavelength ()*7 meters +re!uency ()() ,ertz Energy ()*6 Electron .olts
The property of micro0aves to cause molecules to vibrate is put to use to coo7 food in micro0ave ovens. 6n a micro0ave oven the micro0aves are produced by a device called a Magnetron. Micro0aves are non ionising These produce micro0aves of a radiations. Their fre,uencies longer 0avelength are a lot lo0er than those of gamma rays and /-rays and the (appro/imately "0 to !0 cm). The micro0aves are absorbed energy of their photons is by the 0ater and the fat considerably lesser. They molecules in the food heating therefore do not have the damaging properties of ionising them up from inside thereby coo7ing the food. Micro0aves radiations. 5o0ever, in are not absorbed by dry sufficient intensity they can materials such as glass and cause molecules in matter to ceramics. The food is placed on vibrate 0hich in turn cause friction and produces heat. This a turntable to ensure the even distribution of the micro0aves to heating effect of micro0aves allo0 the food to be coo7ed does present a ris7 to living evenly. The metal casing of the tissue. micro0ave oven ensures all the micro0aves are reflected bac7 into the oven and the door has a 0ire mesh over the 0indo0 0hich serves the same purpose. Micro0aves can penetrate clouds, light rain, sno0, haAe and smo7e. This ma7es them good for transmitting information from one place to another. Micro0aves can be focussed into highly directional beams using parabolic dish antennas. These beams can be directed li7e a searchlight to a receiving aerial based on the 2arth or to a satellite orbiting the 2arth. Micro0aves are the principle carriers of telegraphic data transmission (mobile phones) and also carry television transmissions.
Radio waves
Properties &escription 'ses
?adio 0aves are produced over a large range of fre,uencies thus li7e light have their o0n spectrum. This radio spectrum is divided into radio fre,uency bands. The high fre,uency short 0avelength band as discussed earlier ma7e up *7 2 the micro0ave category of Wavelength () to () meters the electromagnetic () 6 spectrum these are 7no0n +re!uency () to () ,ertz as <ra 5igh .re,uencies Energy ()*2 Electron .olts (&5.). The other fre,uency bands are )ery 5igh Radio 8pectrum .re,uencies ()5.), 5igh .re,uencies (5.), Medium ;uper 5igh .re,uencies(;5.) # - #0G5A .re,uencies (M.) <o0 <ra 5igh .re,uencies (&5.) 0.# - #G5A )ery 5igh .re,uencies ()5.) #0 - #00M5A .re,uencies (<.) and )ery 5igh .re,uencies (5.) # - #0M5A <o0 .re,uencies ()<.).
Medium .re,uencies (M.) 0.# - #M5A <o0 .re,uencies (&.) #0 - #0075A )ery <o0 .re,uencies ()<.) # - #075J G5A K Giga 5ertA K "03 5ertA M5A K Mega 5ertA K "0$ 5ertA 75A K Filo 5ertA K "0# 5ertA
?adio 0aves are used in communication. ?adio 0aves are not strongly absorbed by the atmosphere and can therefore travel long distances. ?adio 0aves ma7e use of the ionosphere a region of the atmosphere about "007m above the 2arthHs surface and appro/imately #007m thic7. 6n the ionosphere the atmosphere is partially ionised by the action of ultraviolet radiations from the sunlight. ?adio 0aves are bent and reflected bac7 to0ards the 2arth by the ionosphere. This bouncing off the ionosphere and the 2arthHs surface may occur repeatedly allo0ing radio 0aves to travel long distances around the 2arth.
