Measurement of ambient neutrons in an underground laboratory at - - PowerPoint PPT Presentation
Measurement of ambient neutrons in an underground laboratory at Kamioka Observatory Keita Mizukoshi Kobe University TAUP2019 at Toyama International Conference Center 9 Sep. 2019 Introduction Neutron is the one of the most serious
Keita Mizukoshi Kobe Univ.
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Keita Mizukoshi Kobe Univ.
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3He proportional counter
DAQ PC
3He + n → 3H + p + 0.76 MeV
3He - 10 atm
SUS
380mm φ52mm
~5 k barn at thermal
Keita Mizukoshi Kobe Univ.
Polyethylene
3He
Boron sheet
510mm
t5mm
3He
Efficiency estimated by Geant4
9 −
10
8 −
10
7 −
10
6 −
10
5 −
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4 −
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3 −
10
2 −
10
1 −
10 1 10
2
10 Generated neutron energy (MeV) 20 40 60 80 100 120 140 160 )
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Counts/(neutron/cm
Setup A Setup B Setup B w/o B-sheet
Thermal neutron ~0.025eV
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If 3H or p escapes, continuum region will be made in a low energy (Wall effect).
dominated by electric noise for ambient neutron measurement.
and down to 0.5 MeV, then the number
clear spectrum observed using 252Cf.
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Setup
A B
Count rate (×10-3cps)
1.295 ± 0.034 0.446 ± 0.018
Live time (day)
14.03 19.27
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Measured energy (MeV) 200 400 600 800 1000 1200 Counts/bins 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Measured energy (MeV) 20 40 60 80 100 Counts/bins
Spectrum of Source (252Cf) Measured spectrum in setup B
3He + n → 3H + p + 0.76 MeV
Count rate in each setup
Electric noise peak Wall effect
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ambient neutron flux, the spectral shape was
detector thus estimated by simulation.
made from (α,n) reaction of U/Th series decay.
they had much different abundance of chemical compositions.
neutrons.
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1 2 3 4 5 6 7 Neutron energy (MeV) 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2
6 −
10 × Number of nentrons /chain decay/0.1 MeV
, n) α JR-1 ( , n) α JA-3 ( , n) α Sample 1 ( Sample 1 + 3% of hydrogen , n) α Sample 2 ( , n) α Sample 3 ( U fission)
238
Sample 1 ( Sample 1 (Th series)
Bin width 0.1 MeV
Generated neutron in vary rocks
(wt. %) sample1 sample2 sample3
O 40.5 37.9 35.6 Ca 28.0 24.3 29.7 Si 16.6 15.6 12.0 Fe 7.6 16.6 13.5 Al 5.2 0.3 0.1 Mn 0.8 3.5 2.9
Main components in each samples
JR-1 and JA-3 are geometrical reference database
Much difference!
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components in details.
rock and chemical composition including Hydrogen will much affect thermalization of fast neutrons.
unknown.
(%of h. e.) in simulation as a thermalization parameter.
result (the ratio between setups A and B) in each rock component.
experimental data) in each sample are almost same.
Simulation. 7
1 2 3 4 5 6 7 % of h. e. 0.5 1 1.5 2 2.5 3 3.5 4
B
/R
A
Ratio of count rates R
Experimental ratio Error band Sample 1 Sample 2 Sample 3 JR-1 JA-3 9 −
10
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10
2
10 Neutron energy (MeV)
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10
2
10 /s
2
Counts /MeV /cm
Sample 1 with 3% of h.e. JR-1 with 1% of h.e. JA-3 with 1% of h.e. 1/E
The most likely spectrum
Experimental ratio v.s. parameter
Thermalization parameter
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the result simply because there are many difference in these measurement (e.g., detector, assumption
definition of flux) 8
9 −
10
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10
2
10 Neutron energy (MeV)
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10
2
10 /s
2
Counts /MeV /cm
The most likely spectrum 2% of hydrogen 4% of hydrogen 1/E
Flux (×10-6 cm-2 s-1) Thermal Non-thermal
Kamioka (This result, Mizukoshi) 7.9 ± 0.23 +0.7
15.6 ± 0.5 +1.2
Kamioka (Minamino 2004) 8.26 ± 0.58 11.5 ± 1.2 Gran Sasso (A. Lindi 1988)※ 13.3 ± 1.5 10.2 ± 1.1 LSM (K. Eitel 2012)※ 14.3 ± 1.3 4.2 ± 2.8
The most likely spectrum Neutron fluxes in previous researches
※They used the different definition of flux. We adjusted the same definition of us.
Thermal neutron ~0.025eV
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spectral shape was assumed (e.g., Boltzmann distribution and 1/E).
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9 −
10
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10
2
10 Neutron energy (MeV)
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10
2
10 /s
2
Counts /MeV /cm
The most likely spectrum 2% of hydrogen 4% of hydrogen 1/E
The most likely spectrum
Excess
high energy neutrons is small, it continues to be a high energy neutron.
cross section increases. it continues to lose energy.
remain at several MeV.
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+1.9
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placed in underground to reduce BGs ~ Cosmic muon
← active veto by scintillator
← shield / self-shielding / PSD
← very careful washing
← It’s difficult to reduce
have large cross-section for neutron
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Fiducial Volume (FV) for events
cosmic muon External gamma
General ways to reduce BGs in underground experiment
Muon Veto counter Shield (Pb)
(Conceptional fig)
Detector neutron
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double beta decay experiment (CANDLES 3+ Experiment) at Kamioka Observatory.
ambient neutron with Boron shield (~5000 barn for thermal neutron).
spectrum) was not understood well.
measure ambient neutron to demonstrate how difficult to handle neutron as a rare BG.
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for neutrinoless double beta decay using 48CaF2 Scintillator
Photo CANDLES Collaboration
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He-3 Counter Liquid Scintillator Gd-Water Čerenkov
Emulsion Thermal Neutron Very good No Very good No Fast Neutron No sensitivity† Good Good Good Energy Sensitivity No Possible No Possible n/γ rejection Good Sometime Good No Good Internal background Low Sometime bad Low Low Handling Analysis Easy Difficult Difficult Very difficult Detection Efficiency Very good so-so so-so Very good
†Generally.
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Generated neutrons from cosmic muon Spectrum of each source for sample1
100 200 300 400 500 600 700 800 900 1000 Neutron energy(MeV)
16 −
10
15 −
10
14 −
10
13 −
10
12 −
10
11 −
10 /s
3
Number of produced neutrons /MeV /cm
Sample 1 Sample 2 Sample 3
Bin width 10 MeV 9 −
10
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10
2
10 Neutron energy (MeV)
14 −
10
13 −
10
12 −
10
11 −
10
10 −
10
9 −
10
8 −
10
7 −
10
6 −
10
5 −
10
4 −
10
3 −
10
2 −
10
1 −
10 1 10 /s
2
Counts /MeV /cm
Summed spectrum w/o muon , n) α U ( , n) α Th ( U fission
238Muon
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0.05 0.1 0.15 0.2 0.25 0.3
6 −
10 × Energy(MeV) 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 current /cm^2 /MeV /s 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Neutron energy (MeV) 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
6 −
10 × Counts /s /cm^2 /MeV
Example: Differences of simulation tools for transported neutron energy spectrum PHITs Geant4 Thermal neutron Fast neutron PHITs Geant4
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(wt. %) sample1 sample2 sample3
sampleA sampleC
KamRock Si
16.6 15.6 12.0 29.1 27.8 18.5
Ti
0.2 0.0 0.0 0.5 0.5 0.1
Al
5.2 0.3 0.1 7.1 8.3 10.6
Fe
7.6 16.6 13.5 4.6 4.5 1
Mn
0.8 3.5 2.9 0.1 0.1
Mg
0.6 1.1 0.7 2.2 1.3 0.3
Ca
28.0 24.3 29.7 4.5 5.2 1.8
Na
0.0 0.2 0.0 2.4 2.6 3.9
K
0.0 0.1 0.0 1.2 1.5 2.1
P
0.2 0.0 0.0 0.1 0.1 0.1
S
0.0 0.1 1.2 0.0 0.0
Zn
0.0 0.1 4.3 0.0 0.0
Sr
0.1 0.0 0.0 0.0 0.0
Nb
0.0 0.0 0.0 0.0 0.0
Sn
0.1 0.0 0.0 0.0 0.0
Pb
0.0 0.0 0.0 0.0 0.0
O
40.5 37.9 35.6 48.3 48.1 60.7
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10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105 10-2 10-1 100 101 102 103 104 105 106 107
Cross Section (barns) Neutron Energy (eV)
He-3
total elastic capture (n,p)
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used.
the sphere (radius r)/ the area of grate circle(πr2)
the circle (radius r)/ the area (πr2)
use this definition.
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