Photon detector

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engdan
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Photon detector

Hello everyone,

I would like to calculate dose (in units of Gy/s) in Serpent that will be equivalent to MCNP.

In MCNP, I define the tally as follows:
f4:p 2
fm4 1 1 -5 -6

(I changed the constant, i.e., the first entry on the fm4 card to 1 since I guess that there is no possibility to multiply the tally in some constant in Serpent).

In Serpent I set the det card as follows:
det 4 p dc 2 dr -25 m1 dr -26 m1

I get two different results. Why is that?

Thank you very much!

Ville Valtavirta
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Re: Photon detector

Hi,

the dr card for Serpent detectors specifies a response function for the detector. If you define multiple response functions, you will get multiple results, one for each response. I would imagine you would want to use one of the responses for the photon dose rate found here: http://serpent.vtt.fi/mediawiki/index.p ... eactions_2

-Ville

engdan
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Re: Photon detector

Dear Ville,

The macroscopic total heating cross-section obtained from Serpent (dr -26) is some orders of magnitude smaller than the one obtained from MCNP. The same is for the energy deposition detector (dr -12). Why is that? What are the units of the energy deposition detector?

Another question regarding source definition: is it possible to define source energy in discrete values?

Thank you very much!

Jaakko Leppänen
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Re: Photon detector

One difference between MCNP and Serpent is that MCNP divides the tally results by volume and Serpent doesn't. Could this explain the difference in the order of magnitude?

You should also check that the results are consistently normalized (use set srcrate 1 to normalize to unit source rate).

You can define a discrete energy spectrum using the sb option of the src card
- Jaakko

engdan
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Re: Photon detector

Dear Jaakko,

I set the tallies volume in MCNP to 1, so it should not be the problem.
Here is the tallis setting and the results:

MCNP:
f14:p 3
sd14 1
fm14 1 1 -5

Serpent: det 14 p dc 3 dr -25 m1

Results:
MCNP: 5.23955E-02 0.0023
Serpent: 5.19428E-02 0.0050

MCNP:
f24:p 3
sd24 1
fm24 1 1 -6

Serpent: det 24 p dc 3 dr -26 m1

Results:
MCNP: 5.67940E-04 0.0024
Serpent: 1.53047E-16 0.0051

The problem is with the dr -26.

I can't define a discrete energy spectrum with the sb option since it is required in the first entry (N) to give the number of bins. Therefore, I can only use the sb option for a histogram. Hence, I just defined different src for each energy and gave the relative source weight with the sw option.

I would also like to ask, please, how can I calculate energy deposition for photons (the dr -12 give the same problem as dr -26).
Also, I would like to ask if there is an equivalent detector to tally *f8 of MCNP.

Thank you very much!

Jaakko Leppänen
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Re: Photon detector

The several orders of magnitude difference probably comes from MeV vs. J, but that doesn't explain it alone. Are the MCNP tallies divided by mass? If so, that could explain the remaining factor of 6 or so difference.

The most recent version of Serpent has the discrete energy line option for the for the source spectrum.
- Jaakko

engdan
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Re: Photon detector

Dear Jaakko,

I understand that that the units of dr -12 and dr -26 is J.

Unfortunately, I didn't succeed to define a discrete energy spectrum with the sb option. The definition of the sb does not allow that ([ sb N INTT E1 WGT1 E2 WGT2 ... ]). It is still giving an error such as: "Probability of first energy point must be zero." Also, the first entry (N) limits the sb just for the histogram energy spectrum. I am using Version 2.1.31. Please let me know how to use the sb option for the discrete energy spectrum.

Thank you very much!

Jaakko Leppänen
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Re: Photon detector

The zero bin is included for compatibility with MCNP. For line spectrum you just need to add one more line at the beginning with zero probability.

This is what I get for a simple test input with different values of INTT:

Code: Select all

surf 1 sph 0 0 0 1

cell 1 0 air -1
cell 2 0 outside 1

mat air -1E-9
1001.03c 1

src 1 sp 0 0 0
sb 5 0
1 0
2 2
3 1
4 3
5 1

set nps 10000000
set srcrate 1

ene 1 2 1000 0 10
det 1 ds 1 1 de 1
Attachments
intt2.png (15.12 KiB) Viewed 223 times
intt1.png (14.31 KiB) Viewed 223 times
intt0.png (12.4 KiB) Viewed 223 times
- Jaakko

engdan
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