Sunday, May 22, 2011

More info on ingested Cesium, internal doses, and the efficacy of whole body counters in determining absorbed dose

Cs-137 and Co-60

Here's what the NRRPT (referencing the  International Commission on Radiological Protection (ICRP)) has to say:

"From the case examined above, it can be seen that even though the intake estimate rises using the new dosimetry models, the organ dose has fallen by approximately 50% and the whole body dose is lower by 63%, from 51 mSv to 19 mSv.

This reduction in assessed doses is as expected. The new Respiratory Tract Model is now based on greatly improved understanding of the processes that occur in the airways, and the tissues that make up this organ. The new model also takes account of differences in radiosensitivity of respiratory tract tissues. In vivo and autopsy measurements, following accidental intakes, show that there is a degree of very long term retention in the lungs. The long term component of the ICRP 66 model is 7000 days compared with 500 days for the ICRP 30 model, so that a percentage of material in the lungs is released much more slowly using the new model.

Apportionment factors have now been assigned to each region of the respiratory tract. These factors relating to risks of cancer incidence weight certain tissues more than others according to their radiosensitivity. This means that certain areas of the respiratory tract can receive much higher doses but with a very low risk of cancer. For these reasons a higher intake does not necessarily lead to higher doses received by the lungs as a whole."

The value with the information above is in the dose estimates, where it was additionally stated that 810 Bq = 4860 dpmRegarding whole body counts:

"Co-60 and Cs-137 are two nuclides that make up a large portion of most radioactive profiles. These isotopes also put out gamma radiation that is easily seen by the whole body counter.  We need to scale in hard to detects for a couple of reasons.

The “hard to detects” (alpha, beta, low activity gamma) cannot be seen by the whole body counter because it can’t penetrate outside the body or it’s just too low activity that it’s washed out by background, other nuclides, or noise.

The “hard-to-detects” are the major dose contributor. A small fraction of alpha emitters may give 50% of the exposure."

See the info, prepared by Chesapeake nuclear services here


  1. Interesting commentary under the last slide of that powerpoint you linked to... Doesn't that sound a little like downplaying to do?

  2. one concern i have is how 'they' calibrate the detectors, and who exactly 'they' are. For ex., energies from 400kv on down can be excluded from the measurement if they so desire, and that will bring the cpm down as well. I hope no hanky panky, seems up and up so far with stuff in Japan.

    Re: that ICRP downward dose revision, i see what you mean.

  3. would you kindly check out this thread?

    how credible is this from your expert opinion?