[Physics] How to detect Iodine 131

radiation

$I_{131}\rightarrow \beta \text{ 333.8 KeV(7.27%)}\rightarrow \gamma\text{ 636.989 KeV(7.17%)}$

$I_{131}\rightarrow\beta\text{ 606.3KeV(89.9%)}\rightarrow\gamma\text{ 364.489KeV(81.7%)}$

(you can also check the them here: [Click Here])(http://upload.wikimedia.org/wikipedia/commons/c/c0/Iodine-131-decay-scheme-simplified.svg)

we can see there has 2 line of iodine 131 decay, there release different mean amount of energy.

  1. Normally,which radiation should we choose to measure the decay intensity? $\gamma$ or $\beta$?（such as when we measure the iodine from the air)

2.which decay line we should choose to detect?and why?
enter image description here

Best Answer

There are actually quite a few more decay paths for $^{131}$I. In a practical situation, however, you don't select a particular decay to detect because your detector (unless you are using a single channel analyzer) will detect all of the radiation within it's range. In practice, you collect a gamma spectrum* from your sample and then analyze that spectrum to pick out what elements are there and in what ratios.

There are several programs (e.g. Genie 2000, GammaVision, PeakEasy) that will "automatically" analyze gamma spectra. Even with these programs, however, it is suprisingly easy to screw up the analysis. A well trained operator is by far the most significant factor in the quality of the analysis. I personally saw fresh data comming in from the Fukushima disaster and even in that situation many of the claims made about what was and wasn't present were questionable at best.

*select isotope 131 from I in the link for an example

Related Question