text: An example of a medium lived is Cs, which has a half-life of 30 years. Caesium is released in bomb fallout and from the nuclear fuel cycle.  A paper has been written on the radioactivity in oysters found in the Irish Sea, these were found by gamma spectroscopy to contain Ce, Ce, Ru, Ru, Cs, Zr and Nb.  In addition, a zinc activation product (Zn) was found, this is thought to be due to the corrosion of magnox fuel cladding in cooling ponds. The concentration of all these isotopes in the Irish Sea attributable to nuclear facilities such as Sellafield has significantly decreased in recent decades.
  An important part of the Chernobyl release was the caesium-137, this isotope is responsible for much of the long term (at least one year after the fire) external exposure which has occurred at the site.  The caesium isotopes in the fallout have had an effect on farming. [http://www.uiar.org.ua/Eng/index.htm]
  A large amount of caesium was released during the Goiânia accident where a radioactive source (made for medical use) was stolen and then smashed open during an attempt to convert it into scrap metal.  The accident could have been stopped at several stages; first, the last legal owners of the source failed to make arrangements for the source to be stored in a safe and secure place; and second, the scrap metal workers who took it did not recognise the markings which indicated that it was a radioactive object.
  Soudek et al. reported in 2006 details of the uptake of Sr and Cs into sunflowers grown under hydroponic conditions.  The caesium was found in the leaf veins, in the stem and in the apical leaves.  It was found that 12% of the caesium entered the plant, and 20% of the strontium.  This paper also reports details of the effect of potassium, ammonium and calcium ions on the uptake of the radioisotopes.
  Caesium binds tightly to clay minerals such as illite and montmorillonite; hence it remains in the upper layers of soil where it can be accessed by plants with shallow roots (such as grass).  Hence grass and mushrooms can carry a considerable amount of Cs which can be transferred to humans through the food chain.  One of the best countermeasures in dairy farming against Cs is to mix up the soil by deeply ploughing the soil.  This has the effect of putting the Cs out of reach of the shallow roots of the grass, hence the level of radioactivity in the grass will be lowered.  Also, after a nuclear war or serious accident, the removal of top few cm of soil and its burial in a shallow trench will reduce the long term gamma dose to humans due to Cs as the gamma photons will be attenuated by their passage through the soil.  The more remote the trench is from humans and the deeper the trench is the better the degree of protection which will be afforded to the human population.
  In livestock farming, an important countermeasure against Cs is to feed to animals a little prussian blue. This iron potassium cyanide compound acts as an ion-exchanger.  The cyanide is so tightly bonded to the iron that it is safe for a human to eat several grams of prussian blue per day.  The prussian blue reduces the biological half-life (not to be confused with the nuclear half-life) of the caesium).  The physical or nuclear half-life of Cs is about 30 years, which is a constant and can not be changed; however, the biological half-life will change according to the nature and habits of the organism for which it is expressed. Caesium in humans normally has a biological half-life of between one and four months.  An added advantage of the prussian blue is that the caesium which is stripped from the animal in the droppings is in a form which is not available to plants.  Hence, it prevents the caesium from being recycled.  The form of prussian blue required for the treatment of humans or animals is a special grade.  Attempts to use the pigment grade used in paints have not been successful.