Characteristics of Caesium-134 and Caesium-137

Radiological Characteristics

Caesium-134 has a radioactive half life of 2.06 years.  It decays by beta emission, yielding one beta particle per transformation with a mean energy of 0.157 MeV.  It also emits an average of 2.23 gamma rays per transformation with a mean energy of 0.698 MeV.


Caesium-137 has a radioactive half life of 30.2 years.  It decays by beta emission, yielding one beta particle per transformation with a mean energy of 0.188 MeV.  Its other emissions are negligible.  In 0.944 of transformations, barium 137m (radioactive half life 2.552 minutes) is produced.  This decays by gamma emission in 0.898 of transformations, emitting a gamma ray of energy 0.662 MeV.


Behaviour of Caesium in Soils and Plants1)2)3)

Caesium is a close chemical analogue of potassium and can substitute for it within the structure of clay minerals.  Thus, it binds strongly to clays, tending to be both immobile and relatively poorly available to plants in clay rich soils.  Conversely, it tends to be more mobile and available in soils that contain little clay and that are potassium deficient.



Demonstration projects


Depth distribution of radioactivity density in soil of schoolsand Playgrounds

Behaviour of Caesium in Domestic Animals and Humans1)2)3)

Caesium is well absorbed from the gastrointestinal tract of mammals and birds, with the fractional absorption typically being in the range 0.6 to 1.0.  The element is then relatively uniformly distributed throughout all organs and tissues of the body, though it is concentrated to a limited degree in muscle, following the distribution of stable potassium.  The biological half life of retention in the body differs between species and generally increases with increasing body mass both within and between species. Effective half-life of Cesium-137 in humans is approximately 110 days (ICRP Pub.78).


Fractional Systemic Retention of Caesium as a Function of Body Mass (applicable to mice, rats, guinea pigs, hens, dogs, monkeys and humans)




1) Coughtrey, P J and Thorne, M C, Radionuclide Distribution and Transport in Terrestrial and Aquatic Ecosystems, Volume 1, A A Balkema, Rotterdam, 1983

2) IAEA-TECDOC-1616, 2009

3) IAEA Technical Reports Series No. 472, 2010