29 May 2011

Radioisotopes and their applications

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 numbers of neutrons. There are 82 stable elements and about 275 stable isotopes of these elements.

What are radioisotopes?

When a combination of neutrons and protons, which does not already exist in nature, is produced artificially, the atom will be unstable and is called a radioactive isotope or radioisotope. There are also a number of unstable natural isotopes arising from the decay of primordial uranium and thorium. Overall there are some 1800 radioisotopes. At present there are up to 200 radioisotopes used on a regular basis, and most must be produced artificially.

Radioisotopes can be manufactured in several ways. The most common is by neutron activation in a nuclear reactor. Some radioisotopes are manufactured in a cyclotron. 

Naturally-occurring radioisotopes:

Carbon-14: Used to measure the age of water (up to 50,000 years)

Chlorine-36: Used to measure sources of chloride and the age of water (up to 2 million years)

Lead-210: Used to date layers of sand and soil up to 80 years

Tritium (H-3): Used to measure 'young' groundwater (up to 30 years)

Artificially-produced radioisotopes:

Americium-241:


Used in backscatter gauges, smoke detectors, fill height detectors and in measuring ash content of coal.

Caesium-137:


Used for radiotracer technique for identification of sources of soil erosion and deposition, in density and fill height level switches.

Chromium 57: Used to label sand to study coastal erosion.




Cobalt-60:
Used for gamma sterilisation, industrial radiography, density and fill height switches.


Gold-198: Used to label sand to study coastal erosion. 


Hydrogen-3 (Tritiated Water): Used as a tracer to study sewage and liquid wastes


Iridium-192 : Used in gamma radiography to locate flaws in metal components.


Krypton-85: Used for industrial gauging.


Manganese-54:

Used to predict the behaviour of heavy metal components in effluents from mining waste water.


Nickel-63 :


Used in light sensors in cameras and plasma display, also electronic discharge prevention and in electron capture detectors for thickness gauges.


Selenium-75: Used in gamma radiography and non-destructive testing.


Strontium-90: Used for industrial gauging.


Thallium-204: Used for industrial gauging.


Ytterbium-169: Used in gamma radiography and non-destructive testing.


Zinc-65: Used to predict the behaviour of heavy metal components in effluents from mining waste water.