USD website vs SOURCES4 radiogenic neutron calculations

1. Overview

This note is providing a comparison study between the USD website and SOURCES4 calculations for the radiogenic neutron from (alpha,n) reaction.

Step 1: TENDL vs EMPIRE cross sections comparison
TENDL 2011 and 2012 have been considered as the USD website inputs. TENDL is a nuclear data library (validated) which provides the output of the TALYS nuclear model code system.
EMPIRE cross section are the input libraries of SOURCES4
Step 2: USD website vs SOURCES4 calculations: compare the radiogenic neutron spectra coming from both codes.

2. Cross section comparison


---Tendl 2011------Tendl 2012------SOURCES4 inputs---
Figure 1 Figure 2
Overall View Zoom-in at the Empire Energy Range

C13, O17: SourceS4 inputs match tendl 2011 at low energy and then match tendl 2012 at high energy

Many isotopes rise at low energy and then drop at high energy, which is oppisite with tendl 2011/2012

Ti48: a peak observed at ~3.5MeV

3. Radiogenic neutron spectra comparison.

In this section, Fig1. and Fig2 show the spectra from USD website and SOURCES4 calculations for some materials in Tab2.: polyethylene, copper, stainless steel, titanium and borosilicate glass.
Composition of materials taken into account are detailed in Tab1.

Tab.1 Material definition
ELEMENT Z Name Atom fraction (%)
Copper
rho=8.94 g/cc 		29 Cu 100
Titanium
rho=4.506 g/cc 		81 Ti 100
Polyethylene CH2
rho=0.935 g/cc 		1 H 0.667
6 C 0.333
Steel (from G4)
rho=8 g/cc 		24 Cr 0.008
26 Fe 0.74
28 Ni 0.18
Borosilicate glass
(from Miniclean)
rho=2.23 g/cc 		3 Li 0.0027
5 B 0.104
8 O 0.624
11 Na 0.035
13 Al 0.035
14 Si 0.194
56 Ba 0.0058
Tab 2. Material and neutron yield (n/s/cm3)
ELEMENT Chain SOURCES4 n/s/cm3 USD n/s/cm3
COPPER U 2.90 E-12 3.46 E-12
Th 9.49 E-12 1.11 E-11
Total 1.24 E-11 1.45 E-11
POLYETHYLENE U 1.33 E-11 9.56 E-12
Th 5.28 E-12 2.87 E-12
Total 1.86 E-11 1.25 E-11
STEEL U 3.19 E-11 4.28 E-11
Th 4.05 E-11 4.71 E-11
Total 7.42 E-11 9.00 E-11
TITANIUM U 1.65 E-10 1.98 E-10
Th 9.96 E-11 1.24 E-10
Total 2.64 E-10 3.22 E-10
BOROSILICATE glass U 3.63 E-10 2.45 E-10
Th 1.27 E-10 6.98 E-11
Total 4.90 E-10 3.15 E-10



Figure 1 Figure 2
SOURCES4 (alpha,n) contributions USD website (alpha,n) contributions

4. Sanity checks: simulation

In order to check how the discrepancies from USD website and SOURCES4 calculations can affect experimental simulations, we have performed some quick simulation study, considering copper and borosilicate glass.

a. Copper Check

A standard shielding scheme - 2 layers of polyethilene and one of Lead in between - and the six copper layers of the vessel have been taken into account. Only the closer Cu cans of the experimental set-up (mixing chamber) has been contaminated with SOURCES4 and USD neutron spectra indipendently - bulk contamination, 1million neutrons from Uranium decay chain and 1 million from Th decay chain. Neutron rates in detectors from (alpha,n) reactions and spontaneous fission has been quoted from both studies.

SOURCES4

Events simulated: 2000000
Nuclear recoils in WIMP window: 289848
Single scatter NRs in WIMP window: 99907

USD

Events simulated: 2000000
Nuclear recoils in WIMP window: 292467
Single scatter NRs in WIMP window: 104293


Analyzing Hang's output files with my code I found: Events simulated: 2000000
Nuclear recoils in WIMP window: 298035
Single scatter NRs in WIMP window: 99496


For consistency, by comparing results from the same analysis: Single NRs -> 99496:99907 -> USD is underestimated singles by 0.5% Total NRs-> 298035:289848 -> USD is overestimated total by 3%

b. Borosilicate Glass Check

--- Kimberly TO UPDATE

5.Titanium oddity

Looking at Fig1. in section 3, Titanium is showing an high resonance at low energy ~1.5MeV. This is due to the cross section trend shown in Figures in section2. SoURCES4 cross section has a 3.5MeV peak that TENDL is not showing. By hand correcting the cross section value at 3.5MeV in SOURCES4 cross section libraries, the resonance in neutron sepctrum go away.

6.To do





Last updated February, 18 2013 - Silvia