Understanding EMF-CUT and residual dose rate

From: Mina Nozar <nozarm_at_triumf.ca>
Date: Fri, 09 Mar 2012 17:49:44 -0800

Hello everyone,

I have just finished simulating a few of our ISAC targets that have already been used and assayed after they have been
taken off-line. The targets themselves range from Ta, SiCGr (Silicon Carbide & Graphite compound), and Nb with
different heat shield assemblies. It took me a while to add all the components to the geometry where for the main
components I used design drawing information and for minor components (Stainless Steel screws for instance) I just used
the volume information for modelling the bodies in fluka.

Beam: 480 MeV protons
Beam intensities range between 40 and 80 uA (depending on the target). One target per FLUKA setup of course.

As usual, I used RADDECAY and IRRPROF cards for scoring residual nuclei and defining Irradiation time and beam
intensity. I have six regions of interest where I score gamma dose rates for a few ramp-up and cool-down times, using
times defined in DCYTIMES. I score DOSE-EQ using USRTRACK with DCYSCORE and AMB74 conversion factors in AUXSCORE cards.
   for regions of interest to look at gamma dose rates at a cylindrical detector (10 cm thick * 1 m radius) 1 m away from
the center of the beam.

At the end, I plot dose rates summed up over all energies and plot them as a function of time (attached figure).

Since we have assay results for few targets, I compare FLUKA results with assay results and see that FLUKA is off by a
factor of 2, giving lower dose rates than the measured.

Initially thought this might be due to the transport cut for e+,e-, and gamma set in the EMF-CUT card. I use the
NEW-DEFA with EMF-CUT of 20 keV for e+,e-, and gammas.

Here are my questions.

1) What are the thresholds set for e+,e-, and gammas if one does not specify a transport energy cut-off through the
EMF-CUT card? Is it 10 MeV as set in PART-THR?

2) If I don't specify a region for transport cut-off energy (i.e. leaving "Reg" and "to Reg" blank, is the cut still

3) I set 10 for "decay cut" and 99999 for "prompt cut" in RADDECAY card.
Does this mean 1 * the transport energy cut defined in the EMF-CUT? i.e. 1*20 keV for e+,e-,and g decay radiation?
I set the "prompt cut" to 999999 to kill the electromagnetic cascade in the prompt part.

4) In the USRTRACK estimator card, I use 0.0001 and 0.1 GeV as the min and max bins respectively, with 60 bins but when
I look at the lis files, I see a bunch of zeros printed, then there are values starting from energy bin
3.1622799E-04 (min) 3.4145513E-04 (max). I don't know why this is.

Thank you in advance for your help. I can provide other plots and output info.

Best wishes,

Received on Sun Mar 11 2012 - 13:28:42 CET

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