First Study of Three-body Photodisintegration of with Double Polarizations at HI g S
Measuring the Neutral Current Event Rate in SNO Using 3 He(n,p)t All Neutron Backgrounds (Estimates)...
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Measuring the Neutral Current Event Rate in SNO Using Measuring the Neutral Current Event Rate in SNO Using 3 3 He(n,p)t He(n,p)t All Neutron Backgrounds (Estimates) Photodisintegration Background U in D 2 O (20.0 fg/g) 160 Th in D 2 O (3.7 fg/g) 365 U in NCDs (4.0 pg/g) < 40 Th in NCDs (4.0 pg/g) 180 56 Co in NCDs (after 200 days u.g.) < 150 Muons (tagged) 14000 U Fission (20.0 fg/g U) 9 D(,n)p (20.0 fg/g U) 22 (3.7 fg/g Th) 5 17 O(,n) 20 Ne (20.0 fg/g U) 0.5 (3.7 fg/g Th) 0.02 10 5 210 Po m -2 d -1 35 Antineutrinos CCP < 22 CCD 11 NCD 16 Total Expected Background < 1000 Photodisintegration Background + 2 H p + n, E > 2.22 MeV Sources: 232 Th chain 208 Tl 208 Pb, E = 2.615 MeV 238 U chain 214 Bi 214 Po, E = 2.445 MeV 56 Co 56 Co 56 Fe, E > 2.224 MeV (31%) SNO Detector 238 U, 232 Th in water ’s from PMT’s and their support structure (,p) and (,n) at PMT’s and support structure NCD Detectors 238 U, 232 Th, 56 Co in NCD bodies Diagnostic Techniques Observation of Cerenkov light from associated ’s Radioassay techniques Estimate from NCD signal MEASURING THE NEUTRAL CURRENT EVENT RATE IN SNO USING 3 He(n,p)t R.G.H. Robertson 1 , T.J. Bowles 4 , T.V. Bullard 1 , S.J. Brice 4 , M.C. Browne 4 , P.J. Doe 1 , C.A. Duba 1 , S.R. Elliott 1 , E.I. Esch 4 , R. Fardon 1 , M.M. Fowler 4 , A. Goldschmidt 3 , R. Hazama 1 , K.M. Heeger 1 , A. Hime 4 , K.T. Lesko 3 , G.G. Miller 4 , R.W.Ollerhead 2 , A.W.P. Poon 3 , K.K. Schaffer 1 , M.W.E. Smith 1 , T.D. Steiger 1 , R.G. Stokstad 3 , J.B. Wilhelmy 4 , J.F. Wilkerson 1 , J.M. Wouters 4 1 Department of Physics, University of Washington, Seattle, WA 98195 2 University of Guelph, Physics Department, Guelph, ON N1G 2W1, Canada 3 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 4 Los Alamos National Laboratory, Vectran braid Anchor balls Fused-silica insulator Delay line termination Pinch-off fill tube Nickel endcap body Resistive coupler (cable end only) Readout cable Cable endcap with acrylic spacer neutron capture: 3He(n,p)3H Counter body (3He-CF4 gas) Sudbury Neutrino Observatory (SNO) Water target D2O 1000 t H2O 1,700 t (sensitive volume) Principle Reactions e - + e e - + e (ES) 2 H + e p + p + e - - 1.44 MeV (CC) 2 H + x p + n + x - 2.22 MeV (NC) Expected Signal CC 4350 yr -1 pure e SK flux 11970 yr -1 BP 1998 SSM NC 2030 yr -1 pure e SK flux 4610 yr -1 BP1998 SSM 13,600 yr -1 pure SK flux Neutral Current Detection via 3 He(n,p) 3 H The neutrons produced by the neutral-current dissociation of deuterium can be detected via the 3 He(n,p) 3 H reaction. An array of 3 He–filled proportional counters is being built for installation in SNO. The parameters of the Neutral Current Detector array are: 775 m total length 300 Ni CVD detectors (2 inch diameter) 96 vertical strings on a 1 m square grid Estimated neutron capture efficiency 37% Motivation Separation of charged-current (CC) and neutral-current (NC) events in real time by use of 3 He proportional counters Signal/Background is determined simultaneously Observation of secular variations and supernovae Status of Construction (June 2000) 290 out of 300 counters constructed 233 counters at Sudbury in cooldown underground Radioassay of construction components complete SNO Physics Goals SNO is a high count rate detector, sensitive to e , , Search for Flavor Change NC rate and CC/NC ratio Energy Spectrum Distortion Due to Oscillations CC 8 B+hep energy spectrum Time Dependent Solar Flux Observation of 7% orbital eccentricity Day-night asymmetry Solar magnetic field effects Search for Supernova Flavor sensitivity Direct neutrino mass Relic neutrinos High Energy Neutrinos SNO can resolve the Solar Neutrino Problem, independent of solar models e flux / total flux 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6 0.4 0.2 0.0 e flux / e SSM flux (BP98) 8 B Flux Depressed Oscillation Hypothesis SuperK Proportional Counter Signals Neutrino Signal: Neutron from NC interaction Neutrons capture via 3 He(n,p) 3 H in the NCD and produce 573 keV p + 191 keV t ionization tracks. Distinguishable Backgrounds: Tritium in 3 He 3 H decays deposit on average 6 keV in the gas but pile-up can produce proportional counter signals above threshold. Low-temperature purification of the 3 He has resulted in negligible background levels. Surface and Bulk Alpha Activity 232 Th and 238 U chains in the NCD walls, along with 210 Po surface activity, produce ’s that underlie the neutron capture peak. These events can be rejected by event by event analysis of digitized pulses. (see “Event Identification by Pulse Shape Analysis”) Electrons and Gammas ’s and ’s from the 232 Th and 238 U chains can only deposit 764 keV through extensive multiple scattering. Less than 2x10 -4 fall into the neutron window. High Voltage Microdischarges HV induced surface discharge at the endcap can produce pulses. However, all components have undergone extensive high voltage testing and 100% discrimination is expected by pulse shape analysis. p t 2H n p 3He 3He 3H p e , Eγ=0.7-2.0 Me ν ν or γ, E>2.22 MeV ν Anode Indistinguishable Backgrounds: Photodisintegration Background Gamma rays with E >2.22 MeV can disintegrate deuterons and liberate neutrons. This background is indistinguishable from the neutral- current signal and so must be measured and subtracted. (see “Photodisintigration Background”) To determine the neutron capture rate on 3 He it is necessary to discriminate spurious events. A first cut can be made by measuring the energy of the event (right). This leaves a substantial background. Typical signals (below) look very different. Additional parameters such as rise-time or pulse width help distinguish between pulses. A “background free” window can be drawn in a pulse width vs. energy parameter space. This window rejects alpha and beta events with an approximately 50% cut in the efficiency for detecting neutrons. 1.0 0.8 0.6 0.4 0.2 0.0 1000 800 600 400 200 0 Energy (keV) He(n,p)t Bulk Alpha Compton/Beta 3.0 2.5 2.0 1.5 1.0 0.5 0.0 1000 800 600 400 200 0 Energy (keV) Compton/Beta Bulk Alpha He(n,p)t 14 12 10 8 6 4 2 0 6 4 2 0 -2 Time ( s) 20 15 10 5 0 5000 4000 3000 2000 1000 0 Time (10 -9 s) or n parallel to wire perpendicular to wire 1.5 1.0 0.5 0.0 -0.5 6 4 2 0 -2 Time ( s) 60 50 40 30 20 10 0 5000 4000 3000 2000 1000 0 Time (10 -9 s) n perp. to wire micro- discharge Event Identification by Pulse Shape Analysis Data Acquisition and Electronics 96 NCD `strings' connect to current preamplifiers that produce signals that go to the electronics. The noise level is approximately 2 mV rms in a 30-MHz bandwidth, and the largest signal the preamplifier can deliver is 2.5 V. NCD Event Rates are dominated by neutrons and alpha particles. Neutrons from muon interactions and NC events are expected to be detected at a rate of 15 per day, and alphas 1000 - 10000 per day. The longest duration of the signal (apart from the ion tail) is about 3 s, corresponding to the drift time across a detector. Preamplifier Signals enter 2 parallel buffer amplifiers, one that drives 20-m long cables to the shaper-ADCs that reside in VME, and the other that drives a delay line and a discriminator. The delay line provides a delay of 320 ns. Pulse Digitization is done with two Tektronix 754A 4-channel oscilloscopes. Each scope services all 96 inputs, with the equivalent scope inputs connected in NCD String (1 of 96) VME Controller DAQ Computer Current Preamp Log Amp VME Bus GPIB Shaper ADC 32 Bit differential digital I/O GTID Counter DACs & ADCs NCD MUX/Trig Controller Card SNO MTCD VME ECPU 12 Multiplexer ~300ns Delay VME GBIP Controller Tek 754 Tek 754 Summing Junction NCD DAQ is fully object-oriented, based on the same coding structure as used in the main SNO DAQ. NCD DAQ is currently running on a Macintosh platform, but will soon run on Linux as well. Neutrons/year
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Transcript of Measuring the Neutral Current Event Rate in SNO Using 3 He(n,p)t All Neutron Backgrounds (Estimates)...
Measuring the Neutral Current Event Rate in SNO Using Measuring the Neutral Current Event Rate in SNO Using 33He(n,p)tHe(n,p)t
All Neutron Backgrounds (Estimates)
Photodisintegration Background U in D2O (20.0 fg/g) 160Th in D2O (3.7 fg/g) 365U in NCDs (4.0 pg/g) < 40Th in NCDs (4.0 pg/g) 18056Co in NCDs (after 200 days u.g.) < 150
Muons (tagged) 14000U Fission (20.0 fg/g U) 9D(,n)p (20.0 fg/g U) 22
(3.7 fg/g Th) 517O(,n)20Ne (20.0 fg/g U) 0.5
(3.7 fg/g Th) 0.02105 210Po m-2 d-1 35
AntineutrinosCCP < 22CCD 11NCD 16
Total Expected Background < 1000
Photodisintegration Background
+ 2H p + n, E > 2.22 MeV
Sources: 232Th chain 208Tl 208Pb, E = 2.615 MeV238U chain 214Bi 214Po, E = 2.445 MeV56Co 56Co 56Fe, E > 2.224 MeV (31%)
SNO Detector
238U,232Th in water ’s from PMT’s and their support structure (,p) and (,n) at PMT’s and support structure
NCD Detectors
238U, 232Th, 56Co in NCD bodies
Diagnostic Techniques
Observation of Cerenkov light from associated ’s
Radioassay techniques Estimate from NCD signal
MEASURING THE NEUTRAL CURRENT EVENT RATE IN SNO USING 3He(n,p)t
R.G.H. Robertson1, T.J. Bowles4, T.V. Bullard1, S.J. Brice4, M.C. Browne4, P.J. Doe1, C.A. Duba1, S.R. Elliott1, E.I. Esch4, R. Fardon1, M.M. Fowler4, A. Goldschmidt3, R. Hazama1, K.M. Heeger1, A. Hime4, K.T. Lesko3, G.G. Miller4, R.W.Ollerhead2, A.W.P. Poon3, K.K. Schaffer1, M.W.E. Smith1, T.D. Steiger1, R.G. Stokstad3, J.B. Wilhelmy4, J.F. Wilkerson1, J.M. Wouters4
1Department of Physics, University of Washington, Seattle, WA 98195
2 University of Guelph, Physics Department, Guelph, ON N1G 2W1, Canada
3Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
4Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Vectran braid
Anchor balls
Fused-silicainsulator
Delay line termination
Pinch-offfill tube
Nickel endcapbody
Resistive coupler(cable end only)
Readout cable
Cable endcapwith acrylic spacer
neutron capture: 3He(n,p)3H
Counter body(3He-CF4 gas)
Sudbury Neutrino Observatory (SNO)
Water target
D2O 1000 tH2O 1,700 t (sensitive volume)
Principle Reactions
e- + e e- + e (ES)
2H + e p + p + e- - 1.44 MeV (CC)
2H + x p + n + x - 2.22 MeV (NC)
Expected Signal
CC 4350 yr-1 pure e SK flux 11970 yr-1 BP 1998 SSM
NC 2030 yr-1 pure e SK flux
4610 yr-1 BP1998 SSM 13,600 yr-1 pure SK flux
Neutral Current Detection via 3He(n,p)3H
The neutrons produced by the neutral-current dissociation of deuterium can be detected via the 3He(n,p)3H reaction. An array of 3He–filled proportional counters is being built for installation in SNO. The parameters of the Neutral Current Detector array are:
775 m total length 300 Ni CVD detectors (2 inch diameter) 96 vertical strings on a 1 m square grid Estimated neutron capture efficiency 37%
Motivation
Separation of charged-current (CC) and neutral-current (NC)
events in real time by use of 3He proportional counters Signal/Background is determined simultaneously Observation of secular variations and supernovae
Status of Construction (June 2000)
290 out of 300 counters constructed 233 counters at Sudbury in cooldown underground Radioassay of construction components complete
SNO Physics Goals
SNO is a high count rate detector, sensitive to e , ,
Search for Flavor Change NC rate and CC/NC ratio
Energy Spectrum Distortion Due to Oscillations CC 8B+hep energy spectrum
Time Dependent Solar Flux Observation of 7% orbital eccentricity
Day-night asymmetry Solar magnetic field effects
Search for Supernova Flavor sensitivity
Direct neutrino mass Relic neutrinos
High Energy Neutrinos
SNO can resolve the Solar Neutrino Problem,independent of solar models
e flux
/ t
otal
flux
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.01.00.80.60.40.20.0
e flux / e SSM flux (BP98)
8B Flux Depressed
Oscillation Hypothesis
SuperK
Proportional Counter Signals
Neutrino Signal: Neutron from NC interaction Neutrons capture via 3He(n,p)3H in the NCD and produce 573 keV p + 191 keV t ionization tracks.
Distinguishable Backgrounds: Tritium in 3He3H decays deposit on average 6 keV in the gas but pile-up can produce proportional counter signals above threshold. Low-temperature purification of the 3He has resulted in negligible background levels.
Surface and Bulk Alpha Activity 232Th and 238U chains in the NCD walls, along with 210Po surface activity, produce ’s that underlie the neutron capture peak. These events can be rejected by event by event analysis of digitized pulses. (see “Event Identification by Pulse Shape Analysis”)
Electrons and Gammas’s and ’s from the 232Th and 238U chains can only deposit 764 keV through extensive multiple scattering. Less than 2x10-4 fall into the neutron window.
High Voltage Microdischarges HV induced surface discharge at the endcap can produce pulses. However, all components have undergone extensive high voltage testing and 100% discrimination is expected by pulse shape analysis.
p
t
2H
np 3He
3He3H
p
e
, Eγ=0.7-2.0 MeV
ν
ν or γ, E>2.22 MeV
ν
Anode
Indistinguishable Backgrounds: Photodisintegration Background Gamma rays with E >2.22 MeV can disintegrate deuterons and liberate neutrons. This background is indistinguishable from the neutral-current signal and so must be measured and subtracted. (see “Photodisintigration Background”)
To determine the neutron capture rate on 3He it is necessary to discriminate spurious events. A first cut can be made by measuring the energy of the event (right). This leaves a substantial background. Typical signals (below) look very different. Additional parameters such as rise-time or pulse width help distinguish between pulses. A “background free” window can be drawn in a pulse width vs. energy parameter space. This window rejects alpha and beta events with an approximately 50% cut in the efficiency for detecting neutrons.
1.0
0.8
0.6
0.4
0.2
0.0
10008006004002000
Energy (keV)
He(n,p)t
Bulk Alpha
Compton/Beta
3.0
2.5
2.0
1.5
1.0
0.5
0.0
10008006004002000
Energy (keV)
Compton/Beta
Bulk
Alpha
He(n,p)t
14
12
10
8
6
4
2
0
6420-2
Time ( )s
20
15
10
5
0
Current Amplitude (mV)
500040003000200010000
Time (10
-9
s)
or n parallelto wire
perpendicular to wire
1.5
1.0
0.5
0.0
-0.5
6420-2
Time ( )s
60
50
40
30
20
10
0
Amplitude (mV)
500040003000200010000
Time (10-9
s)
n perp.to wire
micro-discharge
Event Identification by Pulse Shape AnalysisData Acquisition and Electronics
96 NCD `strings' connect to current preamplifiers that produce signals that go to the electronics. The noise level is approximately 2 mV rms in a 30-MHz bandwidth, and the largest signal the preamplifier can deliver is 2.5 V.
NCD Event Rates are dominated by neutrons and alpha particles. Neutrons from muon interactions and NC events are expected to be detected at a rate of 15 per day, and alphas 1000 - 10000 per day. The longest duration of the signal (apart from the ion tail) is about 3 s, corresponding to the drift time across a detector.
Preamplifier Signals enter 2 parallel buffer amplifiers, one that drives 20-m long cables to the shaper-ADCs that reside in VME, and the other that drives a delay line and a discriminator. The delay line provides a delay of 320 ns.
Pulse Digitization is done with two Tektronix 754A 4-channel oscilloscopes. Each scope services all 96 inputs, with the equivalent scope inputs connected in parallel to 24 multiplexed channels. Scopes provide one level of buffering and permit digitization of pairs of events closely correlated in time.
NCD String (1 of 96)
VMEController
DAQ Computer
CurrentPreamp
Log Amp
VME Bus
GPIB
ShaperADC
32 Bitdifferential
digitalI/O
GTIDCounter
DACs& ADCs
NCD MUX/TrigController Card
SNO MTCD
VMEECPU
12 Multiplexer
~300nsDelay
VMEGBIP
Controller
Tek 754
Tek 754
SummingJunction
NCD DAQ is fully object-oriented, based on the same coding structure as used in the main SNO DAQ. NCD DAQ is currently running on a Macintosh platform, but will soon run on Linux as well.
Neutrons/year
