scheme 449.sch Louis J. Sheehan, Esquire

loosely bound to Louis J. Sheehan, Esquire and can be de-adsorbed with a weakly acidic salt solution containing HCl and NaCl. Small aliquots of the short lived Ba-137m isotope can then be extracted from the resin by this eluting solution. The cesium atoms have a half-life of 30 years and is always decaying and building up an equilibrium amount of Ba-137m. Ba-137m has a half-life of only 2.55 minutes (153 seconds) and quickly decays down to its stable ground state by the emission of a 0.662 MeV gamma ray.
137 55Cs

30.0 y 93.5% β-
E    =514 keV max
137mBa
6.5% β E    =1.176 MeV
max
γ
661.6 keV
137Ba
Figure 2. Decay scheme for cesium-137.
The Ba-137m is said to be selectively “milked” from the generator that is sometimes referred to as a “cow.” As the Ba-137m daughter product is washed out of the generator, the Cs-137 parent product is left behind to regenerate additional Ba-137m atoms. Regeneration of the Ba-137m occurs as the Cs-137 continues to decay and equilibrium is re-established in less than an hour. Since Ba-137m has a short half-life, it only takes approximately 30 minutes after a sample is acquired for the residual activity to have decayed to less than one thousandth of its initial activity, thus making it safe for disposal. However, regardless of how safe this isotopic generator system is to work with, care should be taken to avoid spills and contact with your skin. Should a spill occur or contact with the skin be made, wipe off the excess liquid and wash thoroughly with soap and water.

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