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Nuclear Inst. and Methods in Physics Research, A 905 (2018) 112–118
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A
journal homepage: www.elsevier.com/locate/nima
Characteristic of a Cs2 LiLaBr6 :Ce scintillator detector and the responses for
fast neutrons✩
Jianguo Qin, Jun Xiao, Tonghua Zhu, Xinxin Lu ∗, Zijie Han, Mei Wang, Li Jiang, Yunfeng Mou,
Junjie Sun, Zhongwei Wen, Xinhua Wang
Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, MianYang 621900, China
ARTICLE
INFO
Keywords:
CLLB scintillator
Pulse shape discrimination
Fast neutron response
Neutron activation
ABSTRACT
The elpasolite crystal CLLB is proposed to detect both -ray and thermal neutron events with the ability to
distinguish them by pulse shape discrimination (PSD) method. Pulse shapes of -ray, alpha particle, thermal and
fast neutron events were measured and determined that PSD can be performed to separate -ray from alpha and
thermal neutron events with a Figure of Merit (FoM) 1.23. The -ray non-proportional response is less than 2%
in the energy region of 59.6 keV–4438 keV. Fast neutron responses for CLLB scintillator were investigated and
analyzed using deuterium tritium (DT) reaction neutrons. The activity of 511 keV -ray emitted by 78 Br and 80 Br
can reaches up to ∼0.709 Bq⋅n−1 , some high-energy events at 15 MeVee – 18 MeVee were found that generated
according to the reaction 6 Li(n, T)4 He.
1. Introduction
Cerium (Ce3+ )-doped crystal Cs2 LiLaBr6 :Ce is one of the elpasolite
scintillators that have recently attracted considerable interest for radiation detection [1–4]. It can be used as dual neutron/-ray detector
and can distinguish between them. This makes it an attractive option
in nuclear parameter measurement for the integral experiment [5]
and homeland security [1]. Compared with the CLYC crystal, CLLB
crystal has higher density of 4.2 g/cc and higher photo yield of 55 000
ph/MeV [6], this make CLLB has higher -ray detection efficiency and
better energy resolution [2] than CLYC and significantly better than that
of NaI:Tl [7].
Besides the intrinsic radioactive background from Lanthanumcontaining scintillator and the actinium contamination [1], the responses of thermal neutron and fast neutron should be investigated
clearly before it was used in the neutron/-ray mixed fields. Thermal
neutron was detected by the 6 Li(n, )T reaction with Q value of
4.782 MeV, and an electron equivalent energy of ∼3.2 MeVee was
deposited. In addition, fast neutron can also be detected through this nuclear reaction. More importantly, bromine in the Cs2 LiLaBr6 :Ce crystal
has the highest atomic ratio, both 79 Br and 81 Br have considerable fast
neutron reaction cross sections [8], and then the short half-life products
78 Br and 80 Br will result in very high -ray radioactivity. This is a serious
problem for detecting -ray energy spectrum.
In order to investigate fast neutron response of the CLLB scintillator
detector, pulse shapes formed by -ray, neutron and alpha particle,
pulse shape discrimination ability, energy resolution and -ray nonproportional response were characterized firstly. Fast neutron responses
of 6 Li, 79 Br and 81 Br were studied using the deuterium tritium (DT)
reaction neutron, and the activation products 78 Br and 80 Br were
measured and analyzed using a HPGe detector.
2. Experimental methods
The 1.5′′ ×1.5′′ right CLLB crystal containing natural lithium was
produced by Saint Gobain Crystals, of which 6 Li abundance is equal to
7.5%. The crystal was directly coupled to a Hamamatsu photomultiplier
tube (PMT) (R10601-100), all of which were sealed in aluminum casing.
The PMT was biased to −750 V.
Data were acquired using a 4-channel, 10-bit, 1 GHz, USB-based
Flash Analog-to-Digital Converter (FADC) with the waveform digitizer
DT5751 which manufactured by CAEN. Pulse output from the PMT was
digitized directly and the entire waveform was stored on a hard disk via
LabVIEW-based control software.
Pulse height (PH) analysis and pulse shape discrimination (PSD)
are based on the charge integration method. The PSD factor is usually
defined as 1 − s ∕l , where s is a short integration window containing
the fast rise time duration of the pulse, and l is a long integration
window containing both the fast and the slow components of the
pulse [9]. The figure of merit (FoM) associated with PSD performance is
defined as FoM = (P 2 − P 1) / (FWHM 1 + FWHM 2), where P 1 and P 2
are the mean value of the Gaussian function, FWHM 1 and FWHM 2 are
the full width of half maximum of peak 1 and peak 2, respectively [10].
✩ Project supported by the National Natural Science Foundation of China (Grant No. 11575165 and 11575163).
∗ Corresponding author.
E-mail address: xinxinlu@aliyun.com (X. Lu).
https://doi.org/10.1016/j.nima.2018.05.006
Received 4 February 2018; Received in revised form 24 March 2018; Accepted 3 May 2018
Available online xxxx
0168-9002/© 2018 Published by Elsevier B.V.
J. Qin et al.
Nuclear Inst. and Methods in Physics Research, A 905 (2018) 112–118
and/or co-produced by these particles which produced by fast neutron
induced reactions. So we can see that the fast neutron generated
waveforms are located between the waveforms of -ray and alpha
particle.
Firstly, PSD performance for -ray and alpha particle was investigated by measuring the naturally occurring intrinsic background of the
CLLB scintillator, -rays are mainly from 138 La and natural background,
while alpha particles are from the daughter nucleus of 227 Ac as mentioned above. The PSD-PH 2D histogram, PH and PSD figures are shown
in pad 1, pad 2, and pad 3 of Fig. 2. The measuring time is 2171 s.
-rays and alpha particles can be separated easily and effectively using
a simple curve as shown in pad 1, thus the PH spectra of -ray and alpha
were obtained as shown in pad 2. The two distinct peaks in pad 2 (red
line) are 778 keV and 1468 keV (the sum of -ray 1436 keV and X-ray
32 keV) -rays emitted by 138 La. The FoM of -ray and alpha is 1.24 in
the condition of 12 000 <   < 40 000.
Secondly, we use a moderated AmBe neutron source to investigate
the PSD performance between thermal neutron and -ray with a radioactivity of ∼106 s−1 . Pulses were acquired directly by the DT5751 FADC
with a lower threshold of 6 mV, the measured total events is equal to
224 587. Results of PSD and PH performance are shown in Fig. 3.
As can be seen from pad 1 in Fig. 3, the cluster produced by thermal
neutrons is located below the PSD line, while -ray events appear
above the PSD line. The thermal neutrons induced peak (blue line) is
clearly shown in pad 2, while the three peaks of -rays (red line) are
4438 keV from 12m C, single escape (SE) peak and double escape (DE)
peak, respectively. The FoM between -ray and thermal neutron (also
including a small quantity of fast neutron events) is equals to 1.23 in
the condition of 16 000 <   < 20 000, the events is shown in the
rectangle on pad 1 of Fig. 3.
Fig. 1. Waveforms for gamma, alpha, thermal and fast neutron, measured by a
1.5′′ ×1.5′′ right CLLB scintillator and Hamamatsu photomultiplier tube (R10601-100)
at −750 V. (Color online).
-ray and neutron sources were used to investigate the -ray, alpha
particle and thermal neutron responses, including a set of standard -ray
sources 22 Na, 137 Cs, 241 Am, 133 Ba produced by AEA Technology, 24 Na ray source generated by the neutron activation 27 Al(n, ) 24 Na, AmBe
neutron source and the associated 4.438 MeV -ray from 12m C [11],
and also the naturally occurring radioactivity from 138 La. The nonproportionality response (nPR) was also studied using these -rays.
The fast neutron responses of 79 Br and 81 Br were investigated by
using the DT reaction neutron. The CLLB crystal and aluminum housing
as a whole were irradiated, energy spectrum of -ray emitted by the
activated product and the half-life of the corresponding radionuclide
were measured and analyzed based on a GEM60P HPGe detector.
Furthermore, pulsed DT fast neutron source was used to investigate
the 15 MeVee–18 MeVee high-energy events, and the influence of
unexpected decay -rays emitted by 78 Br and 80 Br in experimental
measurements.
3.1.2. -ray response and nPR
Gamma energy spectra of 241 Am, 137 Cs, 24 Na, natural and intrinsic
background, and that from AmBe source are shown in Fig. 4, the energy
was obtained by integrating the time window of 1400 ns with the charge
integration method. Three background -ray emission lines at 1461 keV
from 40 K, 1468 keV from 138 La and 2614 keV from 232 Th can be seen in
the upper pad (black line). -ray peaks at 1368 keV and 2754 keV from
24 Na, the SE and DE of the latter, and the summed peaks are shown as
the purple line. However, 241 Am and 137 Cs energy spectra show only
photopeak and superimposed on the 24 Na energy spectrum. The -ray
peak at 4438 keV from 12m C and the associated DE and SE, thermal
neutron capture event with the electron equivalent energy deposit of
3229 keVee, are shown in the lower pad of Fig. 4.
Accordingly, energy resolution and the corresponding FWHM obtained for -rays are shown Fig. 5. Energy resolution was obtained using
(FWHM/ ) × 100%, where  is the energy of photopeak, energy
resolution is 4.84% at 662 keV, which exhibits much better energy
resolution than commonly used NaI crystal [12]. FWHM is described
as Eq. (1) in the MCNP code [13] and the fitted curve is shown as the
blue dash line in Fig. 5.
√
(1)
FWHM =  +   +  2
3. Results and discussion
3.1. The characteristics of CLLB
In this section, the pulse shapes for gamma-ray, alpha particle,
thermal and fast neutron pulse shapes were derived. And then, the
particle discrimination performance was investigated based on the
waveforms. The gamma-ray response, energy resolution and intrinsic
non-proportionality response were also investigated.
3.1.1. Pulse shape discrimination performance
Pulse shapes for -ray, alpha particle, thermal and fast neutron
events from CLLB are shown in Fig. 1, pulse height were normalized
to 1. Each pulse is obtained averaging 25 pulses of approximately equal
amplitude. The -ray events are from the 2754 keV -ray emitted by
a 24 Na radionuclide, alpha events are from the intrinsic background
of the daughter nuclei from 227 Ac, a contamination of the lanthanum
component. Thermal and fast neutron events are from AmBe and DT
reaction neutron sources, respectively. Pulse rise time from 10% of the
maximum pulse amplitude to 90% is 24.3 ns for -ray event, while
22.1 ns for alpha and neutron events.
In terms of pulses generated by CLLB, electrons induced by -ray
produce a slow decay component that has a greater ratio than the higher
dE/dx particles [3]. Thermal neutron reacts with 6 Li in the CLLB crystal
to produce an alpha particle and a triton, and the waveform for thermal
neutron is co-generated by both particles. Meanwhile, waveform for
fast neutron event maybe generated by alpha, triton, deuteron, proton,
Scintillators have an intrinsic non-proportionality response between
scintillator light yield and photon deposition which affects their energy
resolution. The origin of non-proportional response in scintillator is
extremely complex, which can be affected by factors such as chemical
composition, dopants, rare earth-cation substitution effect and anion effect and so on [14–16]. The nPR can be explained that it originates from
the non-linear interactions of electrons and holes in a tiny excitation
volume leading to a quenching of luminescence [16].
The -ray non-proportionality response can be traced back by means
of experiment. Following the ideas of Pieter Dorenbos [17] and Wahyu
Setyawan et al. [14], a nPR of ∼2% in the energy range from 59.6 keV
to 4438 keV are shown in Fig. 6, all the points were normalized to 1
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J. Qin et al.
Nuclear Inst. and Methods in Physics Research, A 905 (2018) 112–118
Fig. 2. pad 1: PSD-PH 2D histogram of naturally occurring intrinsic background in a 1.5′′ ×1.5′′ CLLB detector by using charge integration method, pad 2: PH spectra of -rays and
alpha particles, pad 3: PSD histogram of the events in the condition of 12 000 <   < 40 000 . (For interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
Fig. 3. pad 1: PSD-PH 2D histogram of thermal neutron and -ray events in a 1.5′′ ×1.5′′ CLLB detector by using charge integration method, pad 2: PH spectra of -rays and thermal
neutrons, pad 3: PSD histogram of the events in the condition of 16 000 <   < 20 000 . (For interpretation of the references to color in this figure legend, the reader is referred to the
web version of this article.)
with respect to 662 keV from 137 Cs. It shows a smaller nPR than CeBr3
crystal 4% measured by Kanai S. Shah [18].
3.2. Fast neutron response
3.2.1. Fast neutron response of  Br and  Br
Bromine used in Cs2 LiLaBr6 (Ce) crystal is composed of 79 Br and
81 Br, with the natural abundance of 50.69% and 49.31%, respectively.
The fast neutron nuclear reaction (n, 2n) cross sections of both 79 Br
and 81 Br are so large that a serious problem formed. Furthermore, the
atom density of bromine in CLLB crystal is the highest 1.7×1022 per
cc, the half-lives of both the activated products 78 Br and 80 Br are as
short as in the order of minutes, and the emission intensity of decay
-ray/ emission intensity are especially high. More importantly, the
detection efficiency for -ray/ particle from the activated products in
CLLB crystal is very high, because of the geometry factor is nearly equal
to 1. As a result, all these factors would lead to a serious problem for ray detection when CLLB was used in fast neutron (n > 12 MeV) field.
Consequently, the fast neutron responses of Bromine in CLLB crystal
must be investigated clearly before it is used in fast neutron field.
The neutron related reaction parameters of 79 Br and 81 Br, and
the decaying constants of associated activated products of Bromine
Fig. 4. The measured energy spectra by CLLB detector, including 241 Am, 137 Cs, 24 Na,
AmBe source, naturally occurring 40 K and 232 Th, the intrinsic background from 138 La,
intrinsic alpha radioactivity of the daughter nuclei from 227 Ac, and the electron equivalent
energy deposit from thermal neutron capture events. (Color online).
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Nuclear Inst. and Methods in Physics Research, A 905 (2018) 112–118
Fig. 7. The -ray spectrum of CLLB detector that irradiated by DT reaction fast neutron,
measured by using a HPGe detector.
Fig. 5. The energy resolution and the FWHM as a function of -ray energy for the CLLB
detector. (Color online).
Fig. 6. The non-proportionality response of the CLLB detector, measured by using -ray
sources.
Fig. 8. Experimental data and the fitted results of two decay constants for 511 keV -rays
that emitted by 78 Br and 80 Br. (Color online).
from CLLB crystal used in this work are shown Table 1. The -rays
and  particles in Table 1 will produce unexpected responses in the
CLLB detector. A verification experiment was carried out by using the
14.75 MeV DT neutrons to validate the effects mentioned above, taking
into account the most influential (n, 2n) neutron reactions of 79 Br and
81 Br.
For convenience, the crystal and aluminum housing of the CLLB
detector were irradiated by DT neutron as a whole. The neutron yields
and irradiation time are about 1×1010 s−1 and two minutes, and the
source–detector distance is about 5 cm. The irradiated CLLB detector
was placed on the top of a GEM60P HPGe detector immediately, and
-ray spectrum was measured automatically and continuously each 30 s
that controlled by a JOB file [20].
The measured -ray spectrum of the irradiated CLLB detector is
shown in Fig. 7, four -ray peaks (511 keV, 614 keV, 617 keV and 666
keV) emitted by 78 Br and 80 Br are clearly shown. Besides these -rays,
there are still three more -ray peaks that produced by 27 Mg, 56 Mn and
24 Na, which were generated by the reactions 27 Al (n, p)27 Mg, 56 Fe (n,
p)56 Mn and 27 Al (n, ) 24 Na, respectively, while 27 Al and 56 Fe are from
the aluminum housing of the CLLB detector.
 = 01 (1 − −1  ) + 02 (1 − −2  )
01 , 02 , 1 , 2 ,  represent the measured net counts of the photopeak,
78 Br and 80 Br atoms at the beginning of the measurement, decay
constants of 78 Br and 80 Br, and the measurement duration, respectively.
Half-lives can then be obtained by the relationship 1∕2 = ln 2∕.
The relationship between net count of photopeak at 511 keV and
measurement time is shown in Fig. 8, the fitted half-lives of 78 Br and
80 Br are 6.38 ± 0.12 min and 17.60 ± 0.32 min, respectively. They are
in good agreement with the reference values in Table 1. In addition,
the half-life of 6.54 ± 0.15 min for 666 keV demonstrated that it was
emitted by 80 Br.
The -rays emitted by fast neutron activated products 78 Br and 80 Br
will cause serious interference to the -ray spectrum to be measured, especially the 511 keV -ray, with a maximum total intensity of ∼0.709 Bq
⋅n−1 . For example, as for prompt -ray experiment in the literature [5],
only the liquid scintillator detector was substituted by a CLLB detector.
The distance between the pulsed (1 MHz) DT neutron source and CLLB
detector is about 10.7 m, -ray time spectrum at 0 deg (with respect to
the direction of deuteron ions) measured by CLLB is shown in Fig. 9,
the red part represents -ray background within 20 ns–60 ns, the green
peak 1 and blue peak 2 represent -rays from the vicinity of the tritium
target (170 ns–210 ns) and the CLLB detector that induced by the pulsed
leakage DT neutrons (340 ns–380 ns), respectively.
Prompt -ray spectrum can be obtained when a depleted uranium
spherical shell was placed, the pulsed DT neutron source was at the
center of the spherical shell, and the inner/outer radii of the spherical
(2)
To further confirm that these four -ray peaks are from 78 Br and
the decay constants of the corresponding -rays were fitted using
a double exponential decay function as shown in formula (2), where ,
80 Br,
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J. Qin et al.
Nuclear Inst. and Methods in Physics Research, A 905 (2018) 112–118
Table 1
The related parameters for neutron reactions of 79 Br and 81 Br and the decay constants, some data were from NNDC [19], including cross section,
half-life, energy and intensity; the others were calculated based on the related parameter of the CLLB scintillator.
1)
2)
Nuclides
Atom density/cc
79
Nuclear reactions
Cross section/barn
Half-life/min
1)
activity/Bq⋅n−1
Emission particles
Energy/keV (intensity %)
79
Br(n, 2n)78 Br
0.976
6.45
0.372

511(185%), 614(13.6%)
81
Br
8.63 × 1021
Br
8.38 × 1021
79
Br(n, n’)79* Br
0.229
0.081
0.09

207(76.3%)
81
Br(n, 2n)80 Br
1.089
17.68
0.408

 2)
511(4.4%), 617(6.7%), 666(1.1%)
2003(85%), 1387(6.2%)
The activities were normalized to one neutron.
The maximum energy of  particle.
Fig. 10. The total, delayed and prompt -ray spectra of a 13.1/18.1 cm depleted uranium
spherical shell induced by pulsed DT fast neutron, which was measured by a 1.5′′ ×1.5′′
CLLB detector using digital ToF technique. (Color online).
Fig. 9. Time spectrum of -rays: the red part means -ray background in the range of
20 ns–60 ns, the green peak 1 and blue peak 2 represent -rays from the vicinity of tritium
target (170 ns–210 ns) and the CLLB detector that induced by leakage pulsed DT neutrons
(340 ns–380 ns), respectively . (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
neutron induced response as shown in pad 3. Interestingly, some highenergy events appeared as shown in the red parallelogram of pad 3. The
discrimination between fast neutron and gamma-ray is not as easy as
between the thermal neutron and gamma-ray. Energy projection of the
events in pad 3 is shown in pad 7. The events in the rectangle of pad
7 are mainly from the ones in the parallelogram, they induced higher
light output.
As for these high-energy events, there have three representative
characteristics as follows: (1) The energy deposited in CLLB detector is
in the range of 15–18 MeVee, which is higher than the incident neutron
energy 14.75 MeV. (2) They are produced only when fast neutrons reach
the CLLB detector. (3) Their PSD factor values are correlated with the
pulse height.
All these three characteristics indicate that these high energy events
should be produced by the reaction of DT fast neutrons with specific
nuclei in CLLB crystal. The (n, p), (n, ) and (n, d) neutron reaction
cross sections are shown in Fig. 12, the top five reaction channels are
79 Br(n, p), 6 Li(n, a)T, 81 Br(n, p) 81 Se, 79 Br(n, a) 76 As and 7 Li(n, d) 6 He,
respectively. They are potential reactions to produce those high-energy
events.
However, considering the quenching factor of the deposition energy
of the reaction products in CLLB detector [1], the Q value of the
reaction must be larger than 4 MeV. Then, reaction 6 Li(n, T) 4 He
is the only potential origin that meets all these requirements. The Q
value of this reaction is 4.782 MeV, the released total energy will
reaches 19.532 MeV if the incident neutron energy added. The total
energy is distributed between the triton and alpha particles, and their
energy varies in the ranges 4.863 MeV–16.857 MeV and 14.669 MeV–
2.675 MeV, respectively. Since the quenching factors of alpha and triton
in CLLB are different, the total energy deposition of them presents a
continuous distribution. Similarly, the pulse shape produced by triton
and alpha is strongly correlated with the energy distribution between
them. Consequently, the PSD factor of these high-energy events will
shell are 13.1/18.1 cm. The measured total, delayed and prompt -ray
spectrum are shown in Fig. 10. From the delayed spectrum we can see
that in addition to the background emitted by 138 La, there is also a
distinct photopeak at 511 keV, which is generated by 78 Br and 80 Br.
Fortunately, under pulsed neutron source conditions, all of these
gamma backgrounds can be deducted by selecting a specific background
time, the blue curve in Fig. 10 is the prompt -ray spectrum with
background subtracted. Whereas, when the DT neutron source was
operated in direct mode, the -rays from 78 Br and 80 Br can hardly be
discriminated and effectively subtracted. As a result, the influence of
the -rays emitted by 78 Br and 80 Br must be considered when the CLLB
detector is used in fast neutron field. Besides the -rays from 78 Br and
80 Br, responses generated by protons from reaction 79 Br(n, p) 79 Se and
 particles from 81 Br(n, 2n) 80 Br should also be considered.
3.2.2. Fast neutron response of  Li
Under the same conditions as mentioned in Section 3.2.1, the 2D
PSD-PH histograms at three different time intervals were measured as
shown in pad 1 to pad 3 of Fig. 11. They are corresponding to the
prompt -ray from DT target at 170 ns–210 ns, the background at 20 ns–
160 ns, fast neutron and the associated -ray responses at 340 ns–360 ns,
respectively. As for pad 1 and pad 2, besides the intrinsic alpha events,
there are still a few environmental scattered neutron events near the
intrinsic events. All these events can be separated from -ray events
easily and effectively, with the FoM of 1.34 and 1.33 in the condition
of 8000 <   < 55 000 as shown in pad 4 and pad 5.
When fast neutron arrives at the CLLB crystal, the reactions with
Li, Br, and La in the CLLB may emit proton, deuteron, triton and alpha
particles, all these ions together with the decay  particles form a fast
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Nuclear Inst. and Methods in Physics Research, A 905 (2018) 112–118
Fig. 11. The measured 2D- and 1D-based PSD histograms by CLLB detector, which irradiated by 1 MHz pulsed DT neutrons, pad 1 to pad 3 are 2D PSD-PH histograms at various time
intervals, pad 4 to pad 6 are the corresponding PSD histograms at various pulse height ranges. Pad 7 is the energy projection of pad 3. (Color online).
induced reaction 6 Li(n, T) 4 He. As a result, the fast neutron responses
must be considered carefully when it was used in fast neutron field.
Acknowledgments
The authors would like to thank the National Science Foundation
of China (Grant No. 11575165, 11575163 and 11775200) for their
funding support in carrying out this work, and we also like to thank
to accelerator engineers at institute of nuclear physics and chemistry of
the China academy of engineer physics (CAEP) for providing deuterium
and tritium reaction fast neutron source.
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Fig. 12. The (n, ) and (n, p) cross sections for 6 Li,
cross section of 7 Li.
79 Br, 81 Br
and
139 La,
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and the (n, d)
vary between the positions produced by pure alpha and pure tritium
particles.
To further identify the origin of these high energy events, the
total number of reaction 6 Li(n, T) 4 He was calculated quantitatively
according to the intensity of incident neutron, reaction cross section, and
the 6 Li atoms in CLLB crystal. The calculated value and the experimental
one (the events in the red parallelogram of Fig. 11, Pad 3) are 552 ± 24
and 573 ± 19, respectively. They are in good agreement within the error
range.
4. Conclusions
Pulse shapes of -ray, alpha particle, thermal and fast neutrons
were investigated. Alpha particle and thermal neutron events can be
discriminated easily using charge integration method with a FoM of
larger than 1.23. The -ray non-proportional response is less than 2% in
the energy region of 59.6 keV–4438 keV.
79 Br and 81 Br are easily activated by deuterium–tritium reaction fast
neutron and produce high level of radioactivity, the radioactivity of 511
keV emitted by 78 Br and 80 Br can reaches up to ∼0.709 Bq⋅n−1 . The highenergy events at 15 MeVee–18MeVee are produced by DT fast neutron
117
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Nuclear Inst. and Methods in Physics Research, A 905 (2018) 112–118
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