Neutron fluence. X(cm). X(cm). X(cm). (3). n 4. n 3. n. (2). p. n 2. 1.0 mm. 1.2 mm. beam. 1.35 mm. (1). n 1. Z(cm). Z(cm). Z(cm). n. E KIN (MeV). (%). Thr (MeV e equiv. energy). Threshold (MeV e equiv. energy). primary vertex. Shielding (concrete / steel).
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Thr (MeV e equiv. energy)
Threshold (MeV e equiv. energy)
(concrete / steel)
En = 175.7 MeV
En (p) = 126 MeV
Measurement and simulation of the neutron response and detection efficiency of a Pb-scintillating fiber calorimeter
S.Bertoluccia, C. Binib, P. Branchinic, C. Curcenaua, G. De Zorzib, A. Di Domenicob, B. Di Miccoc, A. Ferrarid, P.Gauzzib, S. Giovannellaa, F. Happachera, M. Iliescua, M. Martinia, S. Miscettia, F. Nguyenc, A. Passeric, B. Sciasciaa, F. Sirghia
a Laboratori Nazionali di Frascati, INFN, Italy b Universita’ degli Studi “La Sapienza” e Sezione INFN di Roma, Italy c Universita’ degli Studi “ Roma Tre” e Sezione INFN di Roma3, Italy dFondazione CNAO, Milano, Italy
The overall detection efficiency to neutrons of a small prototype of the KLOE Pb-scintillating fiber calorimeter has been measured at the neutron beam facility of The Svedberg Laboratory, TSL, Uppsala, in the kinetic energy range [5,175] MeV. The measurement of the neutron detection efficiency of a NE110 scintillator provided a reference calibration. At the lowest trigger threshold, the overall calorimeter efficiency ranges from 40 % to 50 %. This value largely exceeds the estimated 8-16 % expected if the response were proportional only to the scintillator equivalent thickness. A detailed simulation of the calorimeter and of the TSL beamline has been performed with the FLUKA Monte Carlo code. The simulated response of the detector to neutrons is presented, as well as a first data-Monte Carlo comparison. The results show an overall neutron efficiency of about 50 %, when no trigger threshold is applied. The reasons of such an efficiency enhancement, in comparison with the typical scintillator-based neutron counters, are explained, opening the road to a novel neutron detector.
The KLOE Pb-scintillating fiber calorimeter
The neutron beam line at TSL – Blue Hall
The KLONE (KLOe Neutron Efficiency) group has measured the neutron detection efficiency of a KLOE calorimeter prototype, at The Svedberg Laboratory (TSL), Uppsala,Oct 2006, performing also the whole simulation of the experiment.
(elastic neutrons scattering on H atoms production of protons detected by the scintillator
itself) efficiency scales with thickness ~1%/cm
an efficiency of 40% for Ekin≤ 20 MeV. An efficiency of 10% would be expected if the
response were only due to the amount of scintillator.
medium-high Z materials, particularly lead, as in the extended range rem counters for
efficiency for photons. If a high neutron detection efficiency were observed, this could also
be the first of a novel kind of neutron detectors.
Neutron detection is important
for the DAFNE-2 program @ LNF:
emitting in the blue-green region: lPeak~ 460 nm.
High sampling structure:
KLOE calorimeter module
178.8 MeV protons on 7Li target. (7Li(p,n)7Be)
The experimental set up and data sets
The measurement of the global efficiency
( 1 )Old prototype of the KLOE calorimeter:
60 cm long, 3 x 5 cells (4.2 x 4.2 cm2), read out at both ends by
( 2 ) Beam position monitor: array of 7 scintillating counters, 1 cm thick.
Full energy spectrum
flive: live time fraction
a: for preliminary measurement,
assume full acceptance and no
Rneutron: incoming neutron rate measured with beam
flux intensity monitors in the TSL Blue Hall
Rtrigger: Detector Trigger rates:
analog sum of 12 PMs/side ,
T1 trig = SA×SB
of 1.5 kHz/cm2, 3.0 kHz/cm2 and 6.0 kHz/cm2
The scintillator efficiency
The calorimeter efficiency
a factor 4 variations of live time fraction
(fLIVE=0.2 0.8) and beam intensity
(1.5 6.0 kHz/cm2).
Results agree with “thumb rule” (1%/cm):
5% for 5 cm thick scintillator (at a threshold of 2.5 MeV)
Agreement, within errors, with previous
published measurements in the same
energy range, after rescaling them to
the used thickness
Very high efficiency, about 4 times
larger than the expected if only the amount of scintillator is taken into account: ~ 8% for 8 cm of scintillating fibers.
Compare with the scintillator efficiency measurement,
scaled by the scintillator ratio factor 8/5
FLUKA simulation of beam-line and calorimeter
Beam line simulation
Response on calorimeter module
Example of a neutron interaction
High probability to have interactions in Lead
The enhancement of the efficiency appears to be due to the huge inelastic production of neutrons on the lead planes.:- produced isotropically; - produced with a non negligible fraction of e.m. energy and protons which are detected in the nearby fibers; - lower energy secondaries( E ≤ 19.6 MeV)→ larger probability of interaction in the calorimeter with further n/p/γ production (62/7/27%).
Study of efficiency dependence on energy
Preliminary measurement by Tof
FLUKA MC prediction
Conclusions and plans
Predicted integrated efficiency ~50% in reasonable agreement with test beam measurements!
New tests to neutron beams at different energies are in program together with new tests of other calorimeter prototipes with different pb-scifi volume ratio.
This work is the starting point for the study and development of a new, compact, chip, fast and efficient neutron detector