Characterization of neutron signal in Si-CsI telescope and
measurement of the absolute neutron detection efficiency.
E. Bonnet 1 et M. Parlog 2
1
GANIL
2
LPC
For the INDRA-FAZIA collaboration
NFS Workshop, 31 Mars-1 Avril 2014, GANIL
Motivation
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RIB facilities should provide in a (near) future very neutron-rich nuclei to
perform reaction where a lot of free neutrons are expected to be produced.
Next 4π array (FAZIA made of Si-Si-Csi telescopes) dedicated to the
detection of charged particles is under construction and good improvement
in the isotopic resolution of detected nuclei has been made (up to Ca)
To reduce more assumption on missing masses in the reconstruction of
reactions, an estimation of the number of neutrons is needed.
We want :
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to measure the neutron detection efficiency of the Cesium Iodide
material on the energy range provided by NFS (1-40 MeV)
–
validate the procedure to extract neutron signal in a Si-CsI telescope
–
test the response of a new plastic (EJ-299-33) to neutrons and protons
N. Zaitseva et al., Nucl. Instr. Meth. Phys. Res. A 668 (2012) 88
Plan
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How neutron signal is evidenced in INDRA data
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Response of a typical Si-CsI telescope, identification and neutron
extraction
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GEANT simulation used to validate the neutron extraction
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Available cross section values of CsI(n,X) reactions
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Description of the experiment
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Direct measurement (CsI efficiency)
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Coincidence measurement (Validation of the neutron extraction)
CsI(n,X) reactions and neutron
signal
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Neutron interacts in the CsI via (n,X) reaction
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If X is a charged particle, signal is read in CsI
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From analysis of data collected with INDRA
array, candidate for neutron signal is the
following :
Reactions in the CsI(n,X) give
a signal corresponding to the
secondary particle (proton, alpha ... )
Incident
neutron
No energy
deposited
in the Silicon (Si)
Si-CsI telescope :
2 identification methods
INDRA data : 181Ta+66Zn@39MeV/A
Identification cards drawn from energy losses of charged particles
SI_CSI_0705
DeltaE(Si) – E(CsI) matrix
Pulse Shape Discrimination (PSD)
on CsI light signal given a
Fast-Slow CsI identification matrix
Track neutron signal :
How does it work ?
Identification tools of KaliVeda
D. Gruyer, J.D. Frankland
Fast-Slow CsI identification matrix :
Below rel line : electrons, muons
Above red line : proton and heavier charged particles
Track neutron signal
Step1 : We select only particles located above red line in CsI
Track neutron signal
Step2 :
We use Silicon detector has an anti-veto :
we select only particles above red line in CsI AND select “no signal” part in the Silicon
Track neutron signal
Step1
Step1 + Step2
At the end, we consider these particles are produced
by CsI(n,X) reactions.
Track neutron signal
After identification procedure, we can
estimate the ratio between all particles
detected in CsI and the secondary part
produced in CsI(n,X) reactions.
INDRA experimental multiplicities
E613 experiment at GANIL
D. Gruyer thesis, GANIL (2014)
For this case, ratio of detected neutrons respect to hydrogen and helium particles is around 8%
What's needed to go further :
Detection efficiency to extrapolate the real neutron multiplicity.
Check the contribution of second order effects (dead zone, Si(n,X) ... )
GEANT3 simulation has been performed to study secondary proton
from CsI(n,p) reaction.
- Main indication is the key role of the volume of the CsI detector.
- 10% of efficiency looking at the secondary proton
- Multiple scattering contribute less than 10% to this efficiency
Neutron incident
Secondary Proton
CsI
GEANT3 simulation, Thèse J. Benlliure (1995)
(n,p) and (n,alpha) cross section on
127
I and
133
CsI.
Tabulated Cross Sections from http://www.nndc.bnl.gov/exfor/exfor.htm
133Cs(n,p)
127I(n,p)
(n,p) less
than 20 mb
127I(n,alpha)
133Cs(n,alpha)
(n,alpha) less
than 10 mb
Most of data are for neutron energy around 15 MeV
We need to enlarge the energy range
First measurement : Direct measurement
Neutron beam with Fast Chopper producing pulsed beam with a period of 1µs
The CsI detector is put directly in the beam
Flux and
Energy spectra
Monitor
NFS pulsed neutron beam
1-40 MeV
+ Monitoring
CsI
5 meters for TOF measurement
to get the neutron incident energy
Advantage :
measurement allowed at all energies
Disadvantage :
indirect method based on calibrated monitors and
angular distribution knowledge
First measurement : Coincidence measurement
Use neutron beam on CH2 target, and looking at the (n,p) elastic scattering
Neutron properties is deduced from kinematics law :
After detected the proton in one telescope, knowing its energy and angle,
we can deduce the associated neutron energy and angle which should be
detected in the complementary telescope.
The ratio of detected neutrons to protons will give us directly detection efficiency
of CsI.
Advantage :
clean method, fast chopper not needed
Disadvantage :
more difficult to access to the highest
energies for neutron
NFS neutron beam
1-40 MeV
I
Cs
ne
CH2
target
o
utr
n
Si
pr
oto
n
Si
Cs
I
Vacuum chamber
Motor will be needed to move the telescopes at different angles
corresponding to different neutron energies
Second measurement : Coincidence measurement
Use neutron beam on CH2 target, and looking at the (n,p) elastic scattering
We intend to replace the CsI crystal with an EJ-299-33 scintillator in one
of the telescopes, in order to systematically characterize the new plastic
in terms of efficiency and discrimination (p/n) in the whole range of neutron
energies accessible at NFS.
Positive results would stimulate one to
check, further on, the capability of
telescopes in which the silicon is backed
by a thick EJ-299-33 scintillator
to identify charged reaction products in
both the DE-E matrix and via the PSD
procedure in the plastic last stage.
neutron-gamma discrimination
with sources
EJ-299-33 scintillator
N. Zaitseva et al.,
Nucl. Instr. Meth. Phys. Res. A 668 (2012) 88
Thèse M. Sénoville - LPC
First estimation of the expected counting rate
shown it's possible
Telescope 2x2 cm²
at 25 cm
Optimisation between :
distance, angular resolution and thickness of the CH2 target
will be performed ...
Conclusions
We ask to type of measurements with NFS beams:
- Direct measurement
- Correlation measurement using the (n,p) elastic scattering
Absolute neutron detection efficiency of Cesisum Iodide (CsI) cristal and EJ-299-33
plastic will be measure on the energy range 1-40 MeV
In a second step we should be able to extract cross section values for I(n,X), Cs(n,X)
reactions.
Concerning tests on the EJ-299-33 plastic, positive results on discrimination between
neutrons and protons would stimulate one to check, further on, the capability of
telescopes in which the silicon is backed by a thick EJ-299-33 scintillator to identify
charged reaction products in both the DE-E matrix and via the PSD procedure in the
plastic last stage.
Thank you for your attention !