Measurement of 40Ar(n,p) reaction
and neutron capture on 40Ar and 136Xe
Megha Bhike and Werner Tornow
Duke University and
Triangle Universities Nuclear Laboratory
AARM meeting, March 4 2013
TUNL and Duke Univ.
Motivation for the 40Ar(n,p), 40Ar(n,) and
136Xe(n,) Reaction Cross Section
Measurements
Standard  decay
0 decay
If detected, 0 decay would
indicate
• The neutrino is its own antiparticle
(Majorana Particle)
•Lepton number violation, contrary to
present formulation of standard model
•An absolute scale of neutrino mass (from
half-life) and nuclear matrix element
AARM meeting, March 4 2013
TUNL and Duke Univ.
Motivation for the 40Ar(n,p), 40Ar(n,) and
136Xe(n,) Reaction Cross Section
Measurements
Argon is a favorite detection and shielding
medium in:
 0 decay search-GERDA
 dark-matter search-DEAP
 Future Long Baseline Neutrino Experiment
AARM meeting, March 4 2013
TUNL and Duke Univ.
Motivation for the 40Ar(n,p), 40Ar(n,) and
136Xe(n,) Reaction Cross Section
Measurements
136Xe
 Enriched Xenon Observatory
(0 )
AARM meeting, March 4 2013
 KamLAND-Zen
(0 )
TUNL and Duke Univ.
Motivation for the 40Ar(n,p), 40Ar(n,) and
136Xe(n,) Reaction Cross Section
Measurements
Challenges in 0 Detection
 Long 0 decay half-life leads to low statistics in decay
spectrum
 Muon-induced spallation neutrons can produce background
signals indistinguishable from the signals of interest.
 Need to measure neutron induced cross sections on 40Ar and
136Xe upto En = 20 MeV
 136Xe(n, )137Xe,  decay, T1/2 = 3.82 mins,
Energy resolution of EXO = 1.67 %
2478.8 keV, 2463.3 keV,  -ray from 137Cs
Energy resolution of KamLAND = 4.2 %
2422.7keV, 2463.3 keV, 2474.8 keV and 2490.4 keV
AARM meeting, March 4 2013
TUNL and Duke Univ.
Status of the (n,) Measurements on 40Ar
 (n,) data for 40Ar between 0.1 -1
MeV
 Old measurements in low energy
region
Wright Air Devel. Centre Reports,
No.59, p.107 (1959) USA
 No data above 1 MeV
 Different evaluations
Goal: To measure 40Ar(n,)41Ar cross section from 0.7 to 14.8MeV
within 5-10 %
AARM meeting, March 4 2013
TUNL and Duke Univ.
Status of the (n,) Measurements on 136Xe
 few measurements in thermal
region
 No data in the entire energy range
from 0.7 to 14.8 MeV
 Different evaluation
Goal: To measure 136Xe(n,)137Xe cross section from 0.7 to 14.8 MeV
within 10-15 %
AARM meeting, March 4 2013
TUNL and Duke Univ.
Activation Measurements at TUNL
DENIS
Neutron production
 T(p,n), D(d,n) and T(d,n)
neutron sources
 Ip/d = 1 -2 mA
 En = 0.7 – 14.8 MeV
 Pulsed at 2.5 MHz
Activation parameters
Neutron TOF area
 n = (1-5)x107 n/(cm2 sec)
 High-purity Argon
(natural)/Xenon (enriched) gas
in high pressure stainless steel/
titanium sphere
 2 monitor foils (In & Au)
 n-flux monitoring: BC -501A
neutron monitor detector (00)
AARM meeting, March 4 2013
TUNL and Duke Univ.
Activation Measurements at TUNL
DENIS
Experimental Setup
High Res. Gamma Spec.
 4x60% HPGe detectors
 Genie 2006 spec. system
 Identical counting conditions
C. Bhatia et al.,
PRC 86, 041602(R) 2012
AARM meeting, March 4 2013
TUNL and Duke Univ.
41Ar
-Ray Signature
 Measured 7000-8000 -events after 2
hrs irradiation and 14 hrs counting time
 Measured 10 energies in Nov 2012 –
Feb 2013 runs
AARM meeting, March 4 2013
TUNL and Duke Univ.
137Xe
-Ray Signature
137Xe
99.6(11)%
5/2+; 455.5, T1/2 < 0.1 ns
31.2(5)%
137Cs
7/2+; 30.07
years
 Measured 300-550 -events after 15
mins irradiation and 25 mins counting time
 Measured 11 energies in Nov 2012 – Feb
2013 runs
AARM meeting, March 4 2013
TUNL and Duke Univ.
Monitor Reactions
Measurement of the neutron fluence using a set of witness foils mounted before &
after the 136Xe/40Ar targets
197Au(n,)
T1/2 = 2.69 d, E = 411.8 keV
115In(n,n)
T1/2 = 4.49 h, E =336.2 keV
197Au(n,2n)
T1/2 = 6.17 d, E = 355.7 keV
AARM meeting, March 4 2013
TUNL and Duke Univ.
Correction for parasitic neutrons
AARM meeting, March 4 2013
TUNL and Duke Univ.
Experimental Results: 40Ar(n,)41Ar
 Cross sections are of few mb
level
TALYS – 2012 agrees well with
TUNL data
 Good agreement with data
set of Bostrom et al.
AARM meeting, March 4 2013
TUNL and Duke Univ.
Experimental Results: 40Ar(n,p) 40Cl
 Fair agreement with the
ENDF-VII.1 evaluation up to
about 12.5 MeV and with
G4NDL3.13 above
 Good agreement with
measurement by Gray et al.,
1965.
C. Bhatia et al., PRC 86, 041602(R) 2012
AARM meeting, March 4 2013
TUNL and Duke Univ.
Experimental Results: 136Xe(n,)137Xe
 Cross sections are of mb level
 TUNL data do not agree with
both ENDF/B-VII.1 and TALYS2012 evaluations
AARM meeting, March 4 2013
TUNL and Duke Univ.
Future plans: 76Ge(n,)77Ge
 no measurement from 0.7 to
14.8 MeV
 Different evaluations
  transition at 2037.78 keV
 Ge target of 86% 76Ge and
14% 74Ge
 test run at 2 MeV last week
taken from nndc
AARM meeting, March 4 2013
TUNL and Duke Univ.
Summary
 Complete cross section measurements of the 40Ar(n,p)40Cl reaction
 Capture cross sections on 40Ar and 136Xe measured at 10 energies from
0.7 to 14.8 MeV. Plan to carry out measurements between 8 – 14 MeV
 These measurements are important for estimating potential background
events in the neutrinoless double-beta decay experiments, neutrino
detectors in general and dark matter experiments
AARM meeting, March 4 2013
TUNL and Duke Univ.