International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Neutron scattering systems for calibration of dark matter
search and low-energy neutrino detectors
A.Bondar, A.Buzulutskov, A.Burdakov, E.Grishnjaev, A.Dolgov, A.Makarov, S.Polosatkin,
A.Sokolov, S.Taskaev, L.Shekhtman
Novosibirsk State University
Budker Institute of Nuclear Physics SB RAS
Novosibirsk State Technical University
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Outline:
A problem of calibration of WIMP detectors
Neutron scattering systems for liquid noble gas detector calibration
- based on DD generator
- based on p7Li generator
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
WIMPs (weakly interacting massive particles) are a one possible
candidate for Dark Matter
Theoretical models predict a mass of WIMPs in the range 10-1000 GeV/c2
WIMPs expected to interact with matter by elastic scattering with
production on recoil nucleus with energies ~1-100 keV, the recoil spectrum
depend on mass of the WIMP and detector velocity in the Galaxy frame
Recoils spectrum measurements are required for estimation of WIMP
mass and interpretation of experimental data
R.W.Schnee, arXiv: 1101.5205v1
 Erec 
R
~ exp  

Erec
E
r
0 

r
4M  M A
M

 MA
E0  M  v02 2
2
- most probable WIMP incident energy
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Recoil spectrum measurements require calibration that is establishing of
energy scale of detector response
Such calibration can be done by measuring of detector response from
particles produced recoil nucleus with know energy
A response to electrons and recoil nucleus is different for ionization and
scintillation detectors
This difference often specified by quenching factor Leff:
Ee [keVee] = Leff × Er [keVnr]
Electrons (gammas)
e+A* eA+hn
e+A
e+A++e
Nucleus
R+A* R+A+hn
R+A R+A++e
R+A’
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Data of ionization and scintillation quenching factors below 10 keV for
liquid noble gases are insufficient and controversial
Scintillation quenching factors
Ar
D.Gastler et al. // Phys. Rev. C. 2012. V. 85. 065811
Xe
A.Manzur et al. // Phys. Rev. C. 2010. V. 81. 025808.
Ne
Lippincott W.H. et al. // Phys. Rev. C. 2012. V. 86. 015807
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
CrAD detector of dark matter
The project of two-phase avalanche cryogenic detector suitable for DM
search have proposed in Budker INP
The prototype of the detector is constructed in the Laboratory of
Cosmology and Elementary Particle Physics of NSU
The prototype will be applied for measurements of quenching factors in
the noble gases for recoil energy range 1-100 keV
Volume: 50 l
Working gases: Ar, Xe, Ne, He
Sensitivity: up to single electron (~100 eV)
Spatial resolution: ~1 mm
Measurements: both scintillation (bottom
PTMs) and ionization (side PMTs)
A.Buzulutskov et al. // this conf.
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
DM detector calibration scheme
Primary recoil nucleus required for detector calibration can be produced by
neutrons
Recoils is produced by elastic scattering on neutrons
A source of neutrons with constant energy and low divergence is required
Scintillation detector
of scattered neutrons
Neutron
source
Liquid
argon
q
Scattering event
Erec 
2mn M
 mn  M 
2

E0 1  cos θ sc

International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Neutron sources
•Isotopes (252Cf)
•Nuclear reactor
Wide spectrum of neutrons
•DD neutron generator (2.45 MeV)
•p7Li neutron generator
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
DD neutron generator
Utilizes nuclear fusion reaction D(D,n)3He (En=2.45 MeV)
Industrial neutron generators with neutron yield 106 n/s is produced for
geophysical applications
Neutron spot size ~1 mm
Target
Ion source
Heated cathode
Hydrogen
generator
Ion beam
Suppressor
Extractor
DD neutron generator
(produced by Budker INP)
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
DD neutrons scattering
Elastic scattering:
n+Arn+Arrec
Inelastic scattering:
n+Arn+Ar*n+Arrec+g(1.46 MeV)
Energy of Ar recoils
10
Cross-section, barn
Recoil energy, keV
250
200
150
100
50
0
0
30
60
90
120
150
Scattering angle, deg.
180
10
10
Cross-section of
scattering
0
-1
-2
0
30
60
90
120
150
Scattering angle, deg.
180
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
DD scattering system
Neutron generator:
n/s
Scintillators: slilbene
Water shield: 40 cm
Baseline: 80 cm
Count rate of scattering events ~0.1 min-1
0.8
Count rate, 10-10 keV-1
106
Pulse height spectrum
(90 scattering)
0.6
0.4
0.2
0
60
80
100
120
Recoil energy, keV
Neutron
generator
Water-filled
tank
Scintillation
detectors of
scattered
neutrons
Active region of
WIMP detector
140
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Background suppression
Neutron background (random coincidence):
- Neutron collimation
Cosmic ray background:
- Pulse shape discrimination (scintillation detector)
Neutron
generator
Water-filled
tank
Scintillation
detectors of
scattered
neutrons
Active region of
WIMP detector
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Pulse shape discrimination
Fast
Slow
Scintillation pulses from gammas and neutrons
in stilbene have different shape and can be
effectively distinguished
g
-50
0
n
50
100
150
Время, нс
Time, ns
4
4
6
x 10
6
x 10
w/ neutrons
5
5
4
4
Fast
Fast
w/o neutrons
3
3
2
2
1
1
0
0
2000
4000
6000
Slow
8000
10000
0
2.45 MeV
0
2000
4000
6000
Slow
8000
10000
200
250
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Calibration in low-energy range
Calibration below 10 keV is a challenge:
-Increase of “geometric” errors for low-angle scattering:
E rec
sin q

q
E rec
1  cos q
-Failure to shield scintillation detector from neutron source
Neutron
generator
Water-filled
tank
Scintillation
detectors of
scattered
neutrons
Active region of
WIMP detector
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Calibration in low-energy range
Calibration below 10 keV is a challenge:
-Increase of “geometric” errors for low-angle scattering:
E rec
sin q

q
E rec
1  cos q
-Failure to shield scintillation detector from neutron source
Neutron
generator
Water-filled
tank
Scintillation
detectors of
scattered
neutrons
Active region of
WIMP detector
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Calibration by inelastic scattering
Recoils energy for inelastic scattering
to small angle tend co constant value
-8.3 keV
Erec
~ q 2
Erec
Energy of Ar recoils
Escape of “geometric” error allow to increase
solid angle of scintillation detector without loss
of accuracy
Recoil energy, keV
30
25
20
15
10
5
0
0
10
30
40
Scattering angle, deg.
100 times gain in count rate is estimated
Pulse height spectrum for
small-angle scattering
3
10
event rate
Recoils with energy 1.2 keV can be produced
with 14 MeV DT neutrons
20
1
2
2
10
1
10
0
2
4
6
recoil energy, keV
8
10
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Calibration in low-energy range
Calibration below 10 keV is a challenge:
-Increase of “geometric” errors for low-angle scattering:
E rec
sin q

q
E rec
1  cos q
-Failure to shield scintillation detector from neutron
source
Neutron
generator
Water-filled
tank
Scintillation
detectors of
scattered
neutrons
Active region of
WIMP detector
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Generator of tagged neutrons
Neutron generating reaction:
D+Dn(2.45 MeV)+3He(0.8 MeV)
Recorded by build-in detector
Tagged neutron generator should provide effective trigger for suppression
of random coincidence
The generator of tagged neutrons in under development in Budker INP
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
p7Li neutron generator
Generator of epithermal neutrons in the reaction 11B(p,n)11Be have been
developed in Budker INP for medical applications (neutron cancer therapy)
Tandem accelerator
H- ion
source
HV power supply
Proton beam:
1.9 MeV, 3 mA
Neutron yield 1011 n/s
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
p7Li neutron generator
Generator of epithermal neutrons in the reaction 7Li(p,n)7Be have been
developed in Budker INP for medical applications (neutron cancer therapy)
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
p7Li neutron generator
7Li(p,n)7Be:
Neutron energy, keV
reaction threshold 1.822 MeV
Neutron energy is determined by beam energy and neutron escape direction
Operation point
En=77 keV
Neutron escape direction, degrees
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
p7Li neutron generator
Operation point for Ar detector calibration:
q=110, Ep=2.077 MeV, En=77 keV
40Ar
Scattering cross-section, barn
have a peak of scattering cross-section on 77 keV
Sulphur filter can be applied for additional monochromatization
The system produces Ar recoils in the range 0 - 7.5 keV
Neutron energy, keV
International conference: Dark matter, dark energy and their detection, 22-26 July 2013
Conclusion
Neutron scattering systems for calibration on liquid cryogenic
detectors are under development in the Laboratory of Cosmology
and and Elementary Particle Physics of NSU
The systems will allow to measure ionization and scintillation yield
for liquid noble gases in the range of recoil energies 0.5-200 keV