Dear Liji
A few things regarding your question.
The fact that there is a wall surrounding the source and that (maybe even an higher effect) the source is collimated easily explain the fact that the 1/R^2 law is not reproduce by looking at the dose rate in your different detectors.
Concerning the calculation of the ambient dose equivalent rate you have to keep in mind that when using USRTRACK, every time a particle (photon in your case) enter your detector the fluence (estimated by a track-length estimator) is folded by a conversion coefficient corresponding to the exposure of a phantom in a radiation field of the concerned particle for the corresponding energy. Basically you have a score independently from the interaction of the particle in your detector or not as it is based on the fluence. This concept which is now a built-in function in FLUKA use to require a user supplied routine to perform the online weighting of the fluence quantity... You can find more looking at the following document and in your case at Fig. 12.
http://info-fluka-discussion.web.cern.ch/info-fluka-discussion/download/deq2.pdf
If you edit the tab.lis files (fluence and DOSE-EQ for the same detector), you can derive the value of the coefficient in the different energy bins and convince yourself (comparing the ratio of different bins) that it is an energy dependent quantity as indicated in Figure 12 in the 400 - 700 keV range corresponding at your Cs-137 source.
With USRBIN and EM-ENRGY as you are scoring, you are getting the deposited energy in air (resulting by particle interaction). You cannot directly derive the ambient dose equivalent dose rate and compare to the previous quantity as it is a different concept (which energy conversion factor to use in that case ?). You could score USRBIN (per region) and DOSE-EQ however to compare the energy dependent scoring and region based one (integrated over energy....)
Hoping this help
Joachim
-----Original Message-----
From: owner-fluka-discuss_at_mi.infn.it [mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of ldaniel_at_barc.gov.in
Sent: 08 August 2016 11:31
To: Fluka Discuss <fluka-discuss_at_fluka.org>
Subject: [fluka-discuss]: discrepancy in usrtrack and usrbin results
Dear Fluka experts,
I am a beginner in Fluka studying the gamma interactions using collimated exposure device of Cesium-137 source of activity 2 Ci. I made geometry of a room of dimensions 1.5m x 1.5m x 1.7m with a wall made of carbon steel of thickness 20 cm. I used scoring card Usrtrack and Auxscore and Usrbin regionwise in the same input. But I got two different answers using both the scoring cards. Using usrbin, I got energy deposited and i multiplied the answer with correction factor to get the answer in exposure rate. I got the expected answer using Usrtrack and Auxscore by multiplying correction factor in exposure rate.
I am facing a problem with the Usrbin score card as the answer was much higher than expected and also it did not follow inverse square law.
Distance from source Using Usertrack & auxscore Using Userbin
30.5 cm 6.72 R/h 8.18 R/h
61 cm 1.85 R/h 2.25 R/h
91.5 cm 0.793 R/h 1.07 R/h
I am attaching the input file.
Please tell me where I am doing the mistake.
Thanks in advance,
Liji
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Received on Mon Aug 08 2016 - 18:12:33 CEST