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Steve Nathan
Jul 18, 2018, 3:22:26 PM7/18/18
to SCALE Users Group
An external technical review group was trying to reproduce the photon spectra that we generated using ORIGEN-ARP. Both of us were using SCALE6.1. Our version of ORIGEN-ARP
(and ORIGEN-S) uses ORIGEN revision 6.1.2 with ENDF/B-VII.1 decay data that was
compiled August 30, 2012. The review team used ORIGEN revision 6.1.1. I don't know what library date. The spectra differed by a factor of 3.6 with very larg difference in the 200 Kev to~2 MeV range.
Anyone have some thoughts on why.
L Gross
Jul 19, 2018, 1:56:27 PM7/19/18
to SCALE Users Group
Yes! I believe I have the answer to your problem. I was running into a similar abundance of low energy gammas that weren't of decay energy.
SCALE has a default in it that is not really a good default if you are not working with UO2. There is a defualt to turn Bremstrahlung effects in a UO2 medium ON. This is the setting, even if you don't tell it to, so if your problem does not involve UO2, then you will most likely want to turn it off. Bremstrahlung physics can be turned on for water also, but besides water and UO2, there is no other data library (which means you should probably switch it to none).
This is detailed in the SCALE-6.2 manual (not sure about 6.1 manual) on page 5-58 (pdf page 731/2747 if you have the full manual pdf). Search for keyword brem_medium if you want more details. I am not sure how to turn this setting off in ORIGEN-ARP, but if you run an input file, the line "brem_medium=NONE" should do inside a gamma block.
Good Luck!
Lewis
SCALE has a default in it that is not really a good default if you are not working with UO2. There is a defualt to turn Bremstrahlung effects in a UO2 medium ON. This is the setting, even if you don't tell it to, so if your problem does not involve UO2, then you will most likely want to turn it off. Bremstrahlung physics can be turned on for water also, but besides water and UO2, there is no other data library (which means you should probably switch it to none).
This is detailed in the SCALE-6.2 manual (not sure about 6.1 manual) on page 5-58 (pdf page 731/2747 if you have the full manual pdf). Search for keyword brem_medium if you want more details. I am not sure how to turn this setting off in ORIGEN-ARP, but if you run an input file, the line "brem_medium=NONE" should do inside a gamma block.
Good Luck!
Lewis
Steve Nathan
Jul 19, 2018, 3:58:06 PM7/19/18
to SCALE Users Group
The impact of Bremsstrahlung on low energy photon production explains the difference between ~0.01 and 0.08 MeV as shown on the attached graph. It does not explain the difference at higher energies. The attached graph also includes cases with and without Bremsstrahlung run in SCALE6.2.3.
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