New Efficient Detector for Radiation Therapy Imaging using Gas Electron Multipliers
A New Detector for Electron Antineutrinos
Transcript of A New Detector for Electron Antineutrinos
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F.D. Brooks, University of Cape Town
M. Drosg, University of Vienna
F.D. Smit, iThemba LABS, Somerset West
A New Detector for Electron
Antineutrinos
Colloquium - UCT - 11 April 2012.
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F.D. Brooks, University of Cape Town, South Africa
M. Drosg, University of Vienna, Austria
F.D. Smit, iThemba LABS, Somerset West, South Africa
A Direction-Sensitive Detector
for Electron Antineutrinos
Eleventh International Conference on Applications of Nuclear Techniques
Crete, Greece, 12-18 June, 2011.
(published in AIP Conf. Proc. 1412 (2011) 177-184)
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with thanks to:
Rob de Meijer (EARTH)
Nieldane Stoddart (iTL)
Kerwin Ontong (UCT)
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Interest in νe detection from:
Weak-interaction physics
Astrophysics (next supernova)
Geophysics (geoneutrinos)
Nuclear material surveillance
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Evidence of neutrino oscillations – Lasserre & Sobel (2006)
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Evidence for geoneutrinos – Boroexino data
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Average no. of antineutrino interactions per year in a 1 kiloton detector
(estimated, from all known nuclear reactors)
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Production of plutonium during a typical reactor fuel cycle
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Figure 16: Left: a cutaway view of the plastic scintillator/Mylar
sandwich detector SONGS2. Mylar sheets, covered with a Gd-
doped paint, are interleaved between the 2 centimeter thick plastic
scintillator blocks. Light collection is accomplished with 4
photomultiplier tubes. Right: initial data from the plastic detector
showing sensitivity to the antineutrino signal.
SONGS2 antineutrino detector
for monitoring nuclear reactors
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Neutrinos/antineutrinos
● Postulated by Pauli (1930). (Pauli “apologized” to
physicists for “inventing” a particle that “could not” be
detected!)
● Fermi’s theory, incorporating Pauli’s hypothesis, was
successful in explaining features of beta decay (1934).
● Antineutrino detected by Reines, Cowan et al (1953)
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First detection of antineutrino – Reines and Cowan (1953)
Liquid scintillator
CH, Cd-doped. Built-
in large proton target.
75 cm x 75 cm diam.
90 PM tubes.
νe from Hanford
nuclear reactor
Double-pulse
“signature”.
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νe signature in a Cd-doped scintillator (1)
νe + p → e+ + n (Q = - 0.8 MeV σ ~ 10-43
cm2)
e+ + e- → γ + γ (Q = 1.02 MeV)
sum of pulses from e+ and 2 γ
2) Delay of 1-2 μs while the neutron thermalizes
3) Pulse #2 from neutron capture by Cd:
113Cd + nth → 114Cd* (Q ~ 9 MeV σ = 20 kb)
114Cd* → 114Cd + γ-cascade (Σ Eγ ~ 9 MeV)
sum of pulses from 4-6 γ
1) Pulse #1 from inverse beta decay of the neutron:
Delayed
coincidence
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An improved νe signature (2)
νe + p → e+ + n (Q = - 0.8 MeV σ ~ 10-43
cm2)
e+ + e- → γ + γ (Q = 1.02 MeV)
coinc. of pulses from e+ and 1 or 2 γ
2) Delay of 1-2 μs while neutron thermalizes
3) Pulse #2 from neutron capture by Cd: 113Cd + nth → 114Cd* (Q ~ 8 MeV)
114Cd* → 114Cd + γ-cascade (Σ Eγ ~ 9 MeV)
coinc. of pulses from 2 or more γ
1) Pulse #1 from inverse beta decay of neutron:
Delayed
coincidence
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Reines, Cowan et al (1956): detector #2 (schematic)
2m x 1.5m x 7.5cm deep
solution of CdCl2 in water.
2m x 1.5m x 60cm deep
liquid scintillator.
6 banks of 55 p.m. tubes
2 slabs of Cd solution between
3 slabs of liquid scintillator.
Inverse beta decay at 1 leads to 2
annihilation quanta detected at a.
γ’s from neutron capture by Cd at
2 are detected ~ 1 μs later, at b.
Delayed coincidence (1 followed
by 2) is the signature of νe.
Note: The e+ is not detected at 1.
However, since events 1 and 2
are coincidences, discrimination
against random coincidence
backgrounds is improved.
1 2
a
a
b
νe
e+ n γ e-
b b
b
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Used to detect νe from the
reactor at Savannah River.
CdCl2-in-water solution
Liquid scintillator
Fig. 6: End view
Fig. 7: Light detector (55 p.m. tubes)
at end of liquid scintilltor.
Photographs of antineutrino detector #2 (Reines et al, 1956)
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A large antineutrino detector – KamLand (1980)
1 kiloton of
liquid scintillator
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Super KamioKanda – 50 kilotons water (Cerenkov detector)
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Super KamioKande (Japan)
Photographed in 2000 while being
filled with water (50 kilotons).
11,200 PM tubes detect Cerenkov
radiation from νe νe (elastic
scattering) and other interactions
that release relativistic charged
particles. Note the technicians on
the raft, who are cleaning the PM
tubes as the tank fills up.
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The proposed νe detector is expected to have the following features:-
1) The scintillator will be 10B-doped instead of Cd-doped or Gd-doped.
2) Pulse shape discrimination will be employed in the selection of
double-pulse events.
3) A modular design that can be replicated easily and then assembled
into a large detector will be used.
4) Each module will consist of 19 or more independent scintillators, in
order to obtain a more selective antineutrino signature.
5) It is envisaged that semiconductor-based light sensors will soon
become available, to be used instead of photomultipliers.
6) Data capture will be accomplished by electronics based on up-to-date
techniques such as flash ADCs rather than NIM electronics.
7) Data reduction will be carried out by compact on-line computers.
8) Directional-sensing capability (FWHM ~ 15°).
Initial development and testing is now being undertaken at UCT/iTL,
using neutrons to mimic the antineutrino signature. Further tests are
planned at Koeberg nuclear power station, using antineutrinos.
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νe signature in a 10B-doped scintillator
νe + p → e+ + n (Q = - 0.8 MeV σ ~ 10-43
cm2)
e+ + e- → γ + γ (Q = 1.02 MeV)
coinc. of pulses from e+ and 2 γ
2) Delay of ~ 0.5 μs while neutron thermalizes
3) Pulse #2 from neutron capture by 10B:
10B + nth → 7Li* + α (Q ~ 2.3 MeV)
7Li* → 7Li + γ (0.48 MeV)
coinc. of pulses from 7Li, α and γ
1) Pulse #1 from inverse beta decay of neutron:
Delayed
coincidence
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30-50 cm
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PMT
35 cm
6 cm
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PMT B-doped scintillator
“honeycomb”
single cell
Al-foil
19-cell scintillator module (schematic)
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Container filled with 10B-doped liquid
scintillator NE311
0.2 mm Al foil to
separate cells.
19-cell unit
15-30 cm long cells
2 PM tubes per cell
6 cm
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νe event (1st pulse)
νe + p → e+ + n
e+ + e- → γ + γ
νe
e+
n
γ (0.5)
e-
neutron goes forward
En ≤ 100 keV
Vertex 1
Vertex position is
determined from
cell position (x,y)
and pulse height
division (z)
y
x
z
Ee = Eν – 1.8 MeV
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νe event (2nd pulse)
10B + n → α + 7Li*
7Li* → 7Li + γ
7Li*
α
n
γ (0.5)
e-
Vector from vertex 1
to vertex 2 gives
direction of νe
Vertex 2
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n-event (1st pulse)
n + p → p + n
p
n
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n-event (2nd pulse)
10B + n → α + 7Li*
7Li* → 7Li + γ
7Li*
α
n
γ (0.5)
e- same as for νe event
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Det A
Det B
Pulse #: 1 2
530 ns
2500 ns
Experiments with neutrons
and two small scintillators
n
p α
γ
e-
7Li*
Am-Be or 252Cf
neutron source
Iron
B (NE213) A (boron-doped)
Event 1
Event 2
Pulse #: 1 2
A
B
Discrim
& Coinc
Digital
Scope Trig
A
D
A Laptop
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-10 0 400 800 (ns) 1200 1600
0 400 800 (ns) 1200 1600
40
20
0
(mV)
40
20
0
-10
(mV) Lf L
30 0 240 ns
np (n, α)
γe
after
pulse
Double-pulse events
from a 252Cf source (Inverted pulses from
Detector A). T = 776 ns
T = 520 ns
Lf = fast component (0-30 ns)
L = total light (0-240 ns)
S = “Shape” = 100Lf / L
T = time difference
(1) hadron
(2) lepton
30 0 200 400 600 800 1000
0 200 400 600 800 1000
L1 (keVee)
L1 (keVee)
30
50
100
130
S1
(%)
2
1
0
T
(µs)
PSD from pulse 1
L1 vs S1
2240 events in 2 hr
L1 vs T
( T = time difference)
After-pulses
hadrons
leptons
S1 window
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0 200 400 600 800 1000 L2 (keVee)
2
1
0
T
(µs)
0 100 200 300 400 500 L2 (keVee)
100
50
0
S2
(%)
L2 vs T
PSD from pulse 2
L2 vs S2
After-pulses
After-pulses
n
n
L2-S2 cut
S2 window
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0 200 400 600 800 1000 L2 (keVee)
2
1
0
T
(µs)
L2 vs T after imposing:
window S1;
window S2; and
the L2-S2 cut.
204 events selected
from 2240
n
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Tests using reactor antineutrinos at Koeberg? (proposed)
43 m
Two reactors of 950 Mwe (2700 Mwth). At full power each
reactor produces ~ 1020 antineutrinos per second into 4π.
The test position is directly below reactor 2, 17 m from the
centre of the core, with 6 m of concrete in between. The
estimated antineutrino fluence at this point is 9 x 1012 per
cm2 s. This should produce about 5 inverse beta decays per
day in a detector of volume 1 litre. Thus for a module of
volume 30 litres ~ 150 events/day is estimated.
1 2
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SUMMARY
These tests show that the 10B-doped detector:
should select the antineutrino signature efficiently; and
should reject neutron-induced backgrounds efficiently.
Other tests have shown that the detector should have sufficient
position resolution to achieve a direction-sensing capability.
The next step will be to carry out further tests using larger
detectors with antineutrinos from the Koeberg nuclear reactors.
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SUMMARY
These tests show that the 10B-doped detector:
should select the antineutrino signature efficiently; and
should reject neutron-induced backgrounds efficiently.
Other tests have shown that the detector should have sufficient
position resolution to achieve a direction-sensing capability.
The next step will be to carry out further tests using larger
detectors with antineutrinos from the Koeberg nuclear reactors.
ευχαριστώ !
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