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Table: basic information about and classifications of arsenic.      

Name: Arsenic Symbol: As Atomic number: 33 Atomic weight: 74.92160 (2) Standard state: solid at 298 K CAS Registry ID: 7440-38-2

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Group in periodic table: 15 Group name: Pnictogen Period in periodic table: 4 Block in periodic table: p-block Colour: metallic grey Classification: Semi-metallic

Arsenic: physical properties
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Melting point: 1090 [or 817 °C (1503 °F)] (under pressure) K Boiling point: 887 [or 614 °C (1137 °F)] (sublimes) K Density of solid: 5727 kg m-3

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Arsenic: orbital properties
      Arsenic Arsen Arsenico Arsenik

Ground state electron configuration: [Ar].3d10.4s2.4p3 Shell structure: Term symbol: 4S3/2 Pauling electronegativity: 2.18 (Pauling units) First ionisation energy: 947.0 kJ mol-1 Second ionisation energy: 1798 kJ mol-1
Arsenic Arseen Arsénico Arsênic

Biological and physiological significance
The toxicity of arsenic and its compounds varies widely, ranging from the exceedingly poisonous arsine and its organic derivatives (see arsenic poisoning) to elemental arsenic itself, which is relatively inert. Arsenical compounds in general are skin irritants, which easily cause dermatitis. Protection against inhalation of arseniccontaining dusts is recommended, but most poisoning appears to come from ingestion. The maximum tolerable concentration of arsenic in dusts during an eight-hour day is 0.5 milligrams per cubic metre. For arsine, exposure of similar duration requires that the concentration be less than 0.05 parts per million in the air. In addition to the many uses of arsenic compounds as herbicides and pesticides, they have in several instances been employed as pharmacological agents. The first successful antisyphilitic agent, for example, was an arsenic compound, “Salvarsan,” or “606,” or 3,3′-diamino-4,4′-dihydroxyarsenobenzene dihydrochloride. atomic number 33 atomic weight 74.9216 melting point (gray form) 814 °C (1,497 °F) at 36 atmospheres pressure

density (gray form) 5.73 g/cm3 at 14 °C (57 °F) (yellow form) 2.03 g/cm3 at 18 °C (64 °F) oxidation states-3, +3, +5 electron config. 1s22s22p63s23p63d104s24p3 Previous
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Principles of the method

In the process of NAA the neutrons interact with the stable isotopes of the target element converting them to radioactive ones. The so-called compound nucleus emits gamma rays promptly with extremely short half lives in the order of ms and these can be measured during irradiation through a technique called prompt gamma activation analysis (PGAA). In most cases, the radioactive isotopes decay and emit beta particles accompanied by gamma quanta of characteristic energies, and the radiation can be used both to identify and accurately quantify the elements of the sample. Subsequent to irradiation, the samples can be measured instrumentally by a high resolution semiconductor detector, or for better sensitivity, chemical separations can also be applied to reduce interferences. The qualitative characteristics are: the energy of the emitted gamma quanta (E) and the half life of the nuclide (T½). The quantitative characteristic is: the I intensity, which is the number of gamma quanta of energy E measured per unit time. 1. step of the analysis: sample preparation means in most cases only pulverising, homogenising, mass determination, packing, as well as the selection of the best analytical process and the preparation of the standards, if any. 2. step of the analysis: for irradiation one can choose from the various types of neutron sources according to need and availability. 3. step of the analysis: after the irradiation the analysts face the dilemma whether or not a chemical separation should be carried out for better sensitivity. If it is needed, the measurement shall be made after the separation. If there is no chemical treatment, the measurement is performed after a suitable cooling time (tc). 4. step of the analysis: measurement, evaluation and calculation involve taking the gamma spectra and the calculating trace element concentrations of the sample. The most widely used gamma spectrometers consist of germanium based semiconductor detectors connected to a computer used as a multichannel analyser for spectra evaluation and calculation.

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