Determining number of n,gamma reactions

Determining number of n,gamma reactions

Hello everyone,

I'm using Serpent for my bachelor thesis and part of this is determining the amount of n,gamma reactions in a certain material. To do this I have used a detector with the response number 102. According to the old manual the output of a detector should contain 13 values, the 13th being the amount of reactions (if I understood correctly), but the version of Serpent I'm using (Version 2.1.25) only gives 12 values. I understand what the first 10 values are, but I can't find anywhere what the last 2 values are, that is to say, I know they are the mean value and relative statistical error, but I don't know mean value and relative error of what. Can anybody help me with this? I have included the detector output and my input below, but without all the energy bins for the source, as there are over 300. Thanks in advance.

DETtarget = [ 1 1 1 1 1 1 1 1 1 1 2.88526E+01 0.00038 ];

Input:

% --- spheres with different radii centered at x=0 y=0 z=0:

surf 1 sph 0.000 0.000 0.000 2.300 % molybdeen

surf 2 sph 0.000 0.000 0.000 27.300 % Moderator

surf 3 sph 0.000 0.000 0.000 37.300 % target

surf 4 sph 0.000 0.000 0.000 57.300 % reflector

surf 5 sph 0.000 0.000 0.000 80.000 %

% --- materials in the spheres:

mat molybdenum -5.14 rgb 255 0 0 % molybdenum with 50% density with red color in plot
42099.09c -1

mat graphite -2.267 rgb 0 255 0 % graphite moderator or reflector
6012.03c -1

mat holmium -8.79 rgb 0 128 127 % holmium target
67165.03c -1

% --- cells located in the spheres

cell 1 0 molybdenum -1

cell 2 0 graphite 1 -2

cell 3 0 holmium 2 -3

cell 4 0 graphite 3 -4

cell 5 0 void 4 -5

cell 6 0 outside 5

set acelib "/home/jblokker/SERPENT_calculations/sss_jeff311u.xsdata"

% --- detectors

det target dc 3 dm holmium dr 102 holmium % --- n,gamma reactions in holmium target

det flux ds 5 1

% --- Geometry plotter

plot 1 1000 1000

% --- Neutron source

set nps 1000000 [200]

src NeutronSource sp 0 0 0 sb 301
jblokker

Posts: 7
Joined: Tue Jun 06, 2017 3:40 pm

Re: Determining number of n,gamma reactions

The last two values are the mean and the relative statistical error. The detector entries in detector "target" are:

- dc 3 : integrate flux over cell 3
- dm holmium : integrate flux over material holmium (redundant because the spatial domain was already set by the dc entry)
- dr 102 holmium : multiply flux estimators by the microscopic cross section of holmium (Ho-165)

So the result that you get is the integral microscopic capture rate of Ho-165.
- Jaakko

Jaakko Leppänen

Posts: 1927
Joined: Thu Mar 18, 2010 10:43 pm
Location: Espoo, Finland

Re: Determining number of n,gamma reactions

Thank you for answering my question, but I have another question. I'm trying to determine the neutron flux through a certain surface and I'm using the surface current detector. I expected the output to be the total amount of neutrons that crossed the surface, but the value I got is way to small for that. Could you please tell me what the output of this detector is?
jblokker

Posts: 7
Joined: Tue Jun 06, 2017 3:40 pm

Re: Determining number of n,gamma reactions

How did you set the DIR parameter in the surface current detector card? The total current (DIR = 0), for example, is very close to zero if the flux is nearly isotropic.
- Jaakko

Jaakko Leppänen

Posts: 1927
Joined: Thu Mar 18, 2010 10:43 pm
Location: Espoo, Finland

Re: Determining number of n,gamma reactions

I set the DIR parameter to outward, like this:

det flux ds 1 1

Surface 1 is a sphere with an external neutron source in the center.
jblokker

Posts: 7
Joined: Tue Jun 06, 2017 3:40 pm

Re: Determining number of n,gamma reactions

Have you set the normalization?
- Jaakko

Jaakko Leppänen

Posts: 1927
Joined: Thu Mar 18, 2010 10:43 pm
Location: Espoo, Finland

Re: Determining number of n,gamma reactions

No, I have not.
jblokker

Posts: 7
Joined: Tue Jun 06, 2017 3:40 pm

Re: Determining number of n,gamma reactions

OK, then your results are normalized to unit source rate. See Sec. 5.8 in Serpent manual for different normalization options.
- Jaakko

Jaakko Leppänen

Posts: 1927
Joined: Thu Mar 18, 2010 10:43 pm
Location: Espoo, Finland

Re: Determining number of n,gamma reactions

Okay, thank you, I'll see if I can solve it using a different normalization.
jblokker

Posts: 7
Joined: Tue Jun 06, 2017 3:40 pm