Isotopos

ARSENIC
ATOMIC NUMBER: 33
GROUP: 15 or V A
ATOMIC MASS: 74.9216
PERIOD: 4

76As

75.922394(2)

1.0942(7)d

2-

660.26MeV

Elemental arsenic occurs in twosolid modifications: yellow, and gray or metallic, with specific gravities of 1.97, and 5.73, respectively. Gray arsenic, the ordinary stable form, hasa m.p. of 817°C (28 atm) and sublimes at 614°C. Several other allotropic forms of arsenic are reported in the literature. It is believed that AlbertusMagnus obtained the element in 1250 A.D. In 1649 Schroeder published two methods of preparing the element. It is found native, in the sulfides realgarand orpiment, as arsenides and sulfarsenides of heavy metals, as the oxide, and as arsenates. Mispickel, arsenopyrite, (FeSAs) is the most commonmineral, from which on heating the arsenic sublimes leaving ferrous sulfide. The element is a steel gray, very brittle, crystalline, semimetallic solid;it tarnishes in air, and when heated is rapidly oxidized to arsenous oxide (As2O3) with the odor of garlic. Arsenic and its compounds are poisonous.

COBALT

60 CO

27

3359.9338171(7)

5.2713(8)

 yβ−, γ60Ni5+

Naturally occurring cobalt (Co) is composed of 1 stable isotope, 59Co. 28 radioisotopes have been characterized with the most stable being 60Co with a half-life of 5.2714 years, 57Co with a half-life of 271.8 days, 56Co with a half-life of 77.27 days, and 58Co with a half-life of 70.86 days. All of the remaining radioactive isotopes have half-lives that are less than 18 hours and the majority of these have half-lives that are less than 1 second. 

Radio

• Science and industry use radioisotopes in a variety of ways to improve productivity and, in some cases, to gain information that cannot be obtained in any other way.
• Sealed radioactive sources are used in industrial radiography, gauging applications and mineral analysis.
• Short-lived radioactive material is used in flow tracing and mixing measurements.
• Various radioactive decay series are used to measure the ages of materials incorporating them.
• Gamma sterilisation is used for medical supplies, some bulk commodities and, increasingly, for food preservation.

Nuclear techniques are increasingly used in science, industry and environmental management. The continuous analysis and rapid response of nuclear techniques, many involving radioisotopes, mean that reliable flow and analytic data can be constantly available. This results in reduced costs with increased product quality.