Query on :JAERI Lung phantom measurement using Whole Body Counter

[LAM HOI CHING <lamhc@HKUSUA.HKU.HK>]

Dear Radsafers,

  Is it possible to perform the JAERI Lung phantom measurement when the

isotopes within the phantom consisting of  Pu238(55.3keV branch yield

0.04%) and Am241(59.5keV branching yield 40%) and Th232(125keV branching

yield 0.05%) using a Canberra whole body counter ACCUSCAN 2280 which

included 2 NaI detectors and 2 Ge detectors in the system.



  I would be glad to know for someone who have that measuring experience of

that JAERI phantom using a whole body counter.



   I'm concerned of the following aspects:

1.  Ge detector though has higher energy resolution but has lower

efficiency which may not be favorable in counting

2. Nai detector though has higher sensitivity but the energy region below

100keV has very high background count thus shoot up the MDA value in that

region.

3. Original calibration of the whole body counter has used a mixed gamma

source which has calibrated energy range from 88keV(Cd109) to 1836keV(Y88)

so that an isotope with energy less than 88keV will have no energy

calibration by interpolation method but rather extrapolation alone which

will cause drastic discrepancy in estimating efficiency in this way.

4. Is it possible to include a low energy standard isotope of

Am241(59.5keV) incorporating with the mixed gamma source in the whole body

counting system. I guess that it may not be feasible or else that the

manufacturer Canberra should have already included that.

5. In the calibration of the ACCUSCAN counter, RMII phantom has been used

to simulate different organ locations of Lung, Whole Body, GI and Thyroid.

I have no idea whether the Lung of RMII behaves the same as Lung of JAERI,

by what extent in percentage?





Thank you for answers and response of this issue.



John Lam, Physicist

Pamela Eastern Hospital

Hong Kong







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