Nuclear Instruments and Methods in Physics Research A 647 (2011) 94–99
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in
Physics Research A
journal homepage: www.elsevier.com/locate/nima
New information on the characteristics of 1 in. 1 in. cerium bromide
scintillation detectors
R. Billnert a,b, S. Oberstedt a,, E. Andreotti a, M. Hult a, G. Marissens a, A. Oberstedt b,c
a
European Commission, DG JRC, Institute for Reference Materials and Measurements, B-2440 Geel, Belgium
Fundamental Fysik, Chalmers Tekniska Högskola, S-41296 Göteborg, Sweden
c
Akademi för Naturvetenskap och Teknik, Örebro Universitet, S-70182 Örebro, Sweden
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 March 2011
Received in revised form
2 May 2011
Accepted 4 May 2011
Available online 20 May 2011
In view of highly demanded new and accurate data on prompt g-ray emission in nuclear fission a major
part of investigations is directed towards the selection of suitable detector systems. Here we have studied a
new type of crystal scintillation detectors made from cerium bromide (CeBr3). For the first time a full
characterization of such a detector is presented in terms of energy resolution, pulse-height linearity,
intrinsic activity and intrinsic timing resolution. In particular the latter one is very important for
prompt fission g-ray studies, because the presence of fast neutrons, emitted in fission too, requires the
time-of-flight method for their discrimination. The energy resolution has been found to be comparable to
that of cerium-doped LaCl3:Ce detectors at an efficiency comparable to the one of a LaBr3:Ce detector of the
same size. The intrinsic activity of the CeBr3 crystal was observed to be much lower compared to
lanthanum halide crystals. The intrinsic timing resolution of a coaxial 1 in. 1 in. sized detector was
measured relative to that of a previously characterized LaCl3:Ce detector and found to be (32677) ps at
60
Co energies, which is in between those of a LaBr3:Ce and a LaCl3:Ce detector of same size.
& 2011 Elsevier B.V. All rights reserved.
Keywords:
Prompt fission g-rays
Cerium bromide
Lanthanum chloride
Scintillation detector
Energy resolution
Intrinsic activity
Timing resolution
1. Introduction
Since four out of six nuclear systems identified by the
Generation-IV international forum are fast reactors, a very innovative core design is required in order to respond to the high
performance expected of those future systems. One particular
challenge in modelling new generation reactor neutron kinetics is
to calculate the g-heat deposition in e.g. steel and ceramic
reflectors without UO2 blankets. Thus, requests for new measurements on prompt g-ray emission in the reactions 235U(nth,f) and
239
Pu(nth,f) have been formulated and included in the Nuclear
Data High Priority Request List of the Nuclear Energy Agency
(NEA, Req. ID: H.3, H.4) [1]. However, a major difficulty in such
measurements is, apart from the need to obtain a sufficient mass
resolution for fission fragments, the clear suppression of background g-rays induced by prompt fission neutrons in the
g-detector. A commonly used method here is to discriminate
g-rays and neutrons by their different time-of-flight. The quality
of the discrimination is strongly coupled to the timing resolution
of the detector, which is normally not better than a few ns for
NaI:Tl detectors as used in the past.
A promising step towards better data might be achieved by using
the recently developed lanthanum and cerium halide scintillation
Corresponding author. Tel.: þ 32 14 571 361; fax: þ 32 14 571 376.
E-mail address: [email protected] (S. Oberstedt).
0168-9002/$ - see front matter & 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.nima.2011.05.034
detectors, such as cerium-doped LaCl3 and LaBr3 as well as CeBr3
detectors. The first two have shown to provide an intrinsic timing
resolution well below 500 ps (cf. e.g. Refs. [2–5]), the precise
number depending on crystal size and g-ray energy, together with
a more than up to 60% better energy resolution compared to NaI,
i.e. 3–4% (FWHM) compared to 6.5% at 662 keV (137Cs) [3–10]. At
the same time these materials also possess a significantly higher
efficiency [5,9,11–13] than NaI detectors of same size. However, one
drawback of lanthanum halide detectors is their intrinsic activity
[5,7,9,14,15] due to contamination of the crystal with 227Ac and
227
Th originating from the 235U decay chain. Hence, the price of such
detectors is strongly correlated with the applied purification efforts.
A first report on the properties of the even more recently developed
cerium bromide detectors was provided by Ref. [16]. With most
properties being comparable with those of lanthanum halide
detectors, and the absence of a radioactive isotope like 138La the
intrinsic activity appears to be drastically reduced. In this work we
aim to give a complete characterization of a CeBr3 scintillation
detector in terms of energy resolution, pulse-height linearity,
intrinsic full peak efficiency and timing resolution.
2. Experimental setup
The coaxial CeBr3 crystal used in this work has a volume of
12.87 cm3 1 in. 1 in., was coupled to a Photonis XP6242B01
photomultiplier tube (PMT) and manufactured by SCIONIX
R. Billnert et al. / Nuclear Instruments and Methods in Physics Research A 647 (2011) 94–99
Holland BV [17]. A high-voltage U¼800 V was applied to the PMT.
Since the photomultiplier provided only one output signal, which
is taken from the anode, we split this signal with a 1 kO splitter to
match the input impedance of the amplifier. This is necessary in
order to be able to measure both timing and energy characteristics in a coincidence experiment. One output was connected to a
delay-line amplifier (DLA, Ortec 460) with an integration time set
to 0:25 ms. The second output was fed into a timing filter amplifier
(TFA, Ortec 476), and the output of the TFA served as input for the
ORTEC 935 constant fraction module (CFD) for further use during
the determination of the timing resolution. Energy and timing
information were converted with analogue-to-digital converters
(Canberra 8715) before entering the data acquisition system
DAQ-2000 [19]. Since fission g-rays may have energies up to at
least 10 MeV, the dynamical range of the detector was adjusted to
about 13 MeV. A set of calibration sources, as listed in Table 1,
was used to determine energy resolution, linearity and detection
efficiency as indicated.
For the assessment of the intrinsic activity, the CeBr3 detector
was operated at the HADES underground laboratory [20], hosting
the IRMM Ultra Low-level Gamma-ray Spectrometry (ULGS)
facility [21]. HADES is located 225 m below ground on the
premises of the Belgian Nuclear Research Centre SCK CEN [22].
The sand–clay overburden of about 500 m water equivalent
assures a muon flux reduction by a factor of about 5000. As a
consequence the background count rate of the detectors due to
cosmic rays is considerably reduced. IRMM operates at present
seven HPGe-detectors in HADES, of which two detectors (Ge-6
and Ge-7) are placed face-to-face inside the same shielding, in
order to improve the efficiency by increasing the solid angle
between the sample and the detectors. This spectrometer is called
Table 1
Calibration g-sources used for the characterization of the cerium bromide detector
as indicated by asterisks.
Nuclide
Energy
resolution
Linearity
Full peak
efficiency
22
Na
Mn
57
Co
60
Co
133
Ba
137
Cs
232
Th
Timing
resolution
n
54
n
n
n
n
n
n
n
n
n
n
n
n
n
n
Fig. 1. Schematic view of the experimental setup inside the ‘‘Sandwich’’-spectrometer shield at HADES. All measures are given in mm.
95
‘‘Sandwich’’-spectrometer and it is surrounded by a 18.5 cm lead
shield, of which the inner part is low in 210Pb content (2.0 Bq/kg),
plus an inner lining of 3.5 cm of freshly produced electrolytic
copper. Furthermore, it is covered by a pair of large area plastic
scintillation detectors, operated in coincidence, which reduces the
residual muon contribution to the background by about 30%, cf.
Ref. [21] and references therein. The CeBr3 detector was placed
inside the ‘‘Sandwich’’-spectrometer shielding at HADES, replacing the lower detector (Ge-6), which resulted in a setup as
shown in Fig. 1. In this manner it was possible to operate both the
CeBr3 and the HPGe detector (Ge-7), which were now facing each
other, in coincidence mode.
3. Results and discussion
In the following sections we give a detailed description of the
various steps of the detector characterization, and present and
discuss the results obtained in our studies.
3.1. Energy resolution and pulse-height linearity
For the determination of the energy resolution we used 133 Ba,
Cs, 60Co and 232Th sources in order to cover a g-energy range
from 81 to 2615 keV. Gaussians were fitted to the peaks in the
spectra and their widths (FWHM) relative to the peak energy give
a measure for the energy resolution. Fig. 2 shows the measured
energy resolution as function of g-energy, where the obtained
values were fitted using a power function. It turned out that the
energy dependence exhibited almost exactly the expected E1=2
behavior [23]. For comparison data from Ref. [16] are shown as
well. Our results are also listed in Table 2 together with the
corresponding energies and g-sources.
The linearity of the detector was also studied over the entire
energy range from 81 to 2614.5 keV. In order to perform the energy
calibration, we applied least-squares fits with different functions.
For a linear approach we received a correlation coefficient of
R2 ¼0.99975, while fits with a second order polynomial resulted in
R2 ¼1. Data and fit functions are shown in the lower part of Fig. 3 as
symbols and dashed lines, respectively. In another approach we
employed a sum of an exponential and a linear function (abbreviated by ‘‘exp–lin’’ in Fig. 3), which describes well the initially linear
behavior of the pulse height and takes the increasing non-linearity
(with energy) well into account. This approach leads to the best
description of the calibration energies over the whole energy range
137
Fig. 2. Measured energy resolution for g-ray energies between 81 and 2615 keV
(full circles). The full-drawn line corresponds to a fit of a power function resulting
in FWHM ð%Þ ¼ E0:4993 . For comparison data from Ref. [16] are shown (open
squares) together with the expected E1=2 behavior (dashed line).
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R. Billnert et al. / Nuclear Instruments and Methods in Physics Research A 647 (2011) 94–99
Table 2
Measured energy resolution (FWHM) in percent for different g-energies and
corresponding radionuclides. It should be noted that 232Th refers to all nuclides
of the thorium decay series.
Table 3
Intrinsic full peak efficiency for the 1 in. 1 in. CeBr3 detector characterized in this
work and the 1.5 in. 1.5 in. LaCl3:Ce detector [5] used as reference.
Nuclide
g-Energy (keV)
Nuclide
FWHM (%)
Uncertainty (%)
81.00
238.83
276.40
302.85
336.2
356.01
383.9
510.07
583.19
661.66
911.2
968,97
1173.2
1332.5
2614.5
133
12.61
6.68
5.88
5.98
6.37
5.72
5.27
4.80
5.11
4.37
3.92
3.22
3.27
3.21
2.28
0.03
0.14
0.21
0.08
0.45
0.03
0.28
0.68
0.02
0.01
0.05
0.05
0.01
0.02
0.09
Ba
Th
133
Ba
133
Ba
232
Th
232
Th
133
Ba
232
Th
232
Th
137
Cs
232
Th
232
Th
60
Co
60
Co
232
Th
232
57
Co
Th
Cs
54
Mn
60
Co
60
Co
232
Th
232
137
g-Energy (keV)
122.06
583.19
661.66
834.84
1173.3
1332.5
2614.5
CeBr3
LaCl3
Eintr
Uncertainty
Eintr
Uncertainty
0.656
0.242
0.228
0.198
0.091
0.082
0.048
0.112
0.010
0.007
0.026
0.005
0.003
0.003
0.870
0.280
0.233
0.186
0.110
0.092
0.037
0.018
0.010
0.006
0.006
0.006
0.003
0.007
Fig. 4. Intrinsic full peak efficiency as function of g-ray energy from this work (full
circles) together with the previously published values for a CeBr3 detector of same
size [16] (open squares), a LaCl3:Ce detector [5] (open circles) and a NaI:Tl
detector [23] (line), both of size 1.5 in. 1.5 in.
in the present work. In a forthcoming campaign the energy range
will be extended to higher photon energies in order to confirm the
superiority of this approach with respect to a possible extrapolation
to higher energies. The upper part of Fig. 3 shows the corresponding
relative deviations of the measured energies from the calculated
ones, i.e. the so-called residuals. From this representation it becomes
obvious that for the here investigated energy range the exponential–
linear approach provides the best description, followed by the
quadratic energy versus pulse-height calibration. In contrast, a linear
energy calibration leads to an inadequate description, especially at
low energies with almost 50% deviation at 80 keV.
center of both detector crystals. With the known intrinsic efficiency
of the LaCl3:Ce detector and the number of counts within the known
time interval, we calculated the total amount of g-quanta emitted by
the source. In order to take the natural background from the 232Th
present in the concrete walls into account, a dedicated background
measurement was performed, scaled and subtracted from the
spectrum. The net peak areas were then fitted with the sum of a
Gaussian and a linear baseline. The number of counts under each
peak were then used to calculate the intrinsic efficiency. Further
radioactive sources in use were 54Mn, 57Co, 60Co and 137Cs. The
results are summarized in Table 3 together with the corresponding
values for the 1.5 in. 1.5 in. LaCl3:Ce detector from Ref. [5] and
shown in Fig. 4. There, the results from this work are depicted as full
circles and compared to previously published values for another
CeBr3 detector (open squares) of same size [16] and the LaCl3:Ce
detector (open circles) [5]. In order to make the energy dependency
more obvious, data for a 1.5 in. 1.5 in. NaI:Tl detector from Ref. [23]
are shown as well. Evidently, the efficiency of our CeBr3 detector is of
the same order of magnitude as the larger LaCl3:Ce detector. Since
one may expect a higher efficiency with increasing crystal size (and
thickness), we conclude that CeBr3 detectors have a better intrinsic
full peak efficiency than LaCl3:Ce detectors of same size. In contrast
to that, the values for the similar CeBr3 detector from Ref. [16] are
considerably lower, which is surprising to us.
3.2. Intrinsic full peak efficiency
3.3. Intrinsic activity
The detection efficiency of the CeBr3 detector was determined
relative to the one for a previously characterized LaCl3:Ce detector [5].
For that purpose a 232Th sample of 10 g was placed 25 cm from the
For the assessment of a possible intrinsic activity due to contamination of the crystal with anthropogenic plutonium, which is
chemically homolog to cerium [24], or naturally occurring thorium
Fig. 3. Lower part: Calibration curve (symbols), i.e. relation between pulse height
and g-ray energy obtained by different fits—linear (dashed), quadratic (dotted)
and exponential–linear (full-drawn). Upper part: Residuals for the different
calibration functions as mentioned above.
R. Billnert et al. / Nuclear Instruments and Methods in Physics Research A 647 (2011) 94–99
and uranium, the CeBr3 detector was transferred to the underground
laboratory HADES [20] and measured in coincidence with a highpurity germanium detector. The detector arrangement according to
Fig. 1 allows determining the intrinsic background count rate in the
CeBr3 detector (i.e. crystal and PMT) and, by means of high resolution
g-ray spectroscopy, drawing conclusions about its origin [5,7,9]. Any
contamination of the crystal with actinides, decaying by a-emission
into an excited state in the daughter nucleus, is revealed by
identifying the subsequent g-decay with the HPGe detector in
coincidence with the a-particle registered with the CeBr3 detector.
Fig. 5 shows a two-dimensional representation of coincident events
by their energies, detected with a CeBr3 detector (y-axis) and a HPGe
detector (x-axis). It should be noted that the energies shown here for
the CeBr3 detector are approximate, since only a linear pulse-height
conversion was performed (for details cf. Section 3.1). The rectangular region (with dashed lines) indicates where a-particles were
observed in Ref. [16]. From a measurement that lasted more than
12.8 days, no evidence for an actinide contamination of the CeBr3
crystal was found. However, few coincident events due to Compton
scattered and cascading g-ray s as well as muon-induced pulses are
visible. In the upper part of Fig. 6 the corresponding background
g-ray spectrum taken with the CeBr3 detector is shown. The
dominant g-peak at 1460 keV may be assigned to the decay of 40K,
while the peaks at 1.6, 2.1 and 2.6 MeV are clearly identified as the
decay of 208Tl (full energy, single and double escape peaks, respectively). The peaks at 1764 and 2204 keV are attributed to the decay
of 214Bi. This result is corroborated by a measurement with the HPGe
detector, whose result, together with a background spectrum, is
depicted in the lower part of Fig. 6. At low energies, i.e. below the 40K
peak, the intrinsic spectrum of the CeBr3 detector is obviously
governed by Compton scattering events. Taking the interpretation
of the two-dimensional plot in Fig. 5 into consideration, we conclude
that the a-decays do not take place in the crystals. Hence, this
contribution originates most probably from the photomultiplier and
not from the crystal itself.
From the results presented above, we may conclude that the
count rate in the CeBr3 detector within the investigated energy
range (47–3000 keV) was 0.91 s 1. This number can be considered to be the intrinsic count rate of both crystal and PMT, as all
other background contributions inside the ‘‘Sandwich’’ shield in
HADES are negligible ð o 0:01 s1 Þ. This result is summarized in
Table 4 for the three energy regions of interest. The activity is
mainly due to the decay of 40K and very little from the 232Th and
97
Fig. 6. Upper part: Background energy spectrum of a 1 in. 1 in. CeBr3 detector,
measured during almost 13 days at HADES. Peaks from the decays of naturally
occurring 40K, 208Tl and 214Bi are indicated. Lower part: Corresponding spectrum
of the activity in the CeBr3 detector (dark histogram), together with a spectrum of
the environmental background at HADES (light histogram), taken with a HPGe
detector.
Table 4
Experimentally determined intrinsic background count rate of the CeBr3 detector,
divided in three energy regions. The total measuring time was 12.847 days.
Energy range
(keV)
Origin
Count rate (s 1)
47–1400
1400–1600
1600–3000
Compton scattering
40
K (full energy peak)
232
Th and 238U series (full
energy and escape peaks)
0.87
0.035
0.0022
47–3000
0.91
238
U decay chains, both of which are known to be present in the
construction material of the photomultiplier [17].
Thus, the upper limit for the intrinsic count rate of the crystal
divided by its volume is 0.08 s 1 cm 3. This is a very conservative
estimate, since most of the measured activity appears to come
from the PMT. This is in any case much lower than what we
usually find in lanthanum halide crystals, even when grown from
the purest raw material (cf. 1.79 s 1 cm 3 [7] and 0.45 s 1 cm 3
[18]). In order to definitely verify this interpretation, a high
resolution g-spectrometry measurement of the crystal alone
should be done. This, however, is out of the scope of the present
detector characterization.
3.4. Timing resolution
Fig. 5. Two-dimensional representation of g-energies for coincident events
detected with a HPGe and the CeBr3 detector during 12.8 days. The coincidence
window was set to 5 ms.
The timing resolution of the CeBr3 detector was determined in a
coincidence setup, again with the LaCl3:Ce detector, whose intrinsic
timing resolution as a function of g-energy was determined
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R. Billnert et al. / Nuclear Instruments and Methods in Physics Research A 647 (2011) 94–99
earlier [5]. Since the square of the experimentally determined
coincidence timing resolution equals the sum of the squares of the
intrinsic timing resolution of both detectors, the values for the CeBr3
detector may easily be extracted from the known timing resolution
of the LaCl3:Ce detector.
As radioactive sources we used 22Na and 60Co. Both detectors
were placed in an angle of 251 relative to each other to reduce
detection of the extremely intense 511 keV annihilation radiation
from the 22Na decay as well as possible crosstalk between both
detectors due to backscattering. The distance source–detector
was kept at 25 cm as specified in Section 3.2. With such an
arrangement we measured one annihilation quantum in coincidence with the 1275 keV g-ray from the decaying 22Na nuclei,
between the two decay g-rays from 60Co and all combination
with Compton-scattered g-rays. This allows investigating a wide
pulse-height interval with the same setup as it is required in a
real experiment.
Due to the fact that the timing resolution may vary because of
a pulse-height dependent jitter of the CFD trigger, we investigated
this effect in more detail. After having taken spectra with the
lowest possible CFD threshold, we constructed time spectra for
different low-energy thresholds during offline analysis with the
acquisition program package GENDARC [25], which is based on
the software package ROOT [26]. This threshold was chosen for
the g-energy in steps of 100 keV and applied to both detectors.
The obtained coincidence timing distributions were then calibrated (8192 ADC channels correspond to 50 ns) and fitted with a
Gaussian, whose full-width-of half-maximum (FWHM) gives a
measure for the timing resolution. Fig. 7 shows its dependence
from the selected threshold or cutoff energy.
Beside the expected deterioration with lower threshold three
distinct areas appear in Fig. 7 by kinks in the depicted distributions: one below 300 keV cutoff energy, the other one between
300 and 600 keV, and finally one above 600 keV. In the first two
regions the time distribution is broadened, because both contain
coincidences between the 511 keV annihilation radiation and a
(Compton-scattered) g-ray, and the positron from the 22Na decay
needs some time to find an electron to annihilate with. This effect
results in an exponential tail in the distribution, which causes a
worsening of the coincidence timing resolution. The last region is
not affected by this, because there we detected only coincidences
between two 60Co g-rays, which are emitted practically simultaneously. This is also visualized in Fig. 8. The upper part shows the
coincidence timing spectrum after applying a lower threshold just
below the 511 keV annihilation peak. The deviation from a pure
Gaussian is clearly visible, caused by the exponential decay curve
of the electron–positron annihilation. In the lower part the cut
was applied just below the 1173 keV 60Co g-rays, which implies
that the 22Na decay is excluded from the spectrum. For the latter
cut the description of the distribution with a Gaussian is excellent. The corresponding coincidence timing resolution is determined to be (51474) ps. From the known intrinsic timing
resolution for the LaCl3:Ce detector, the corresponding value for
the CeBr3 detector is calculated to be (326 77) ps (FWHM). This is
a better intrinsic timing resolution than for the LaCl3:Ce detector,
which is 398 ps according to Ref. [5]. However, it is necessary to
remember that the CeBr3 detector is smaller than the LaCl3:Ce
detector, and for a smaller crystal one expects a better timing
resolution. For comparison, for a 1 in. 1 in. LaBr3:Ce detector, a
corresponding timing resolution below 300 ps has been
reported [4]. Putting all that together, this leaves the intrinsic
timing resolution of cerium bromide detectors well competitive
with those based on cerium-doped lanthanum halide crystals.
Fig. 7. Experimentally found timing resolution as a function of low-energy
threshold Eg -cutoff. The light (red) diamonds correspond to the coincidence
timing resolution, while the full and open circles denote the intrinsic timing
resolution of the 1 in. 1 in. CeBr3 detector and the 1.5 in. 1.5 in. LaCl3:Ce
detector, respectively. (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
Fig. 8. Measured coincidence timing spectra and Gaussian fits for g-ray s from the
decays of 22 Na and 60 Co, taken with the 1 in. 1 in. CeBr3 detector and the 1.5 in.
1.5 in. LaCl3:Ce detector. The upper part shows the time distribution with a
threshold just below the 511 keV annihilation peak, in the lower part a threshold
just below the 1173 keV 60Co peak was chosen. The ‘‘tail’’ in the upper spectrum
appears due to the presence of the annihilation radiation.
4. Summary and conclusion
In the present work we have performed a detailed characterization of a 1 in. 1 in. CeBr3 detector. We investigated its energy
resolution, its pulse-height linearity, determined the intrinsic
activity and its intrinsic g-ray detection efficiency. Most importantly, the timing characteristics were investigated as a function
of minimum g-ray energy. The following results were obtained:
(1) The energy resolution at Eg ¼ 662 keV (137Cs) is 4.4%, which is
comparable to the one of a LaCl3 detector [4,5]. Our result is
R. Billnert et al. / Nuclear Instruments and Methods in Physics Research A 647 (2011) 94–99
(2)
(3)
(4)
(5)
much better than the 5.6% reported in Ref. [16] for a similar
detector.
Pulse-height linearity is preserved up to about 1.3 MeV. The
increasing non-linearity at higher g-ray energies can be parameterized with a so-called exponential–linear function, which
allows perfect interpolation for the identification of intermediate peaks. To what extent this approach will allow extrapolation
to higher energies will be subject of a forthcoming investigation.
The efficiency of a 1 in. 1 in. CeBr3 detector is 9% at
Eg ¼ 1173 keV (60Co), which is comparable to or even slightly
higher than the one of a LaBr3 detector of same size (7.3%
according to Ref. [9]). Again, our result is much better than
that previously reported for a similar detector, which is about
6% according to Ref. [16].
The intrinsic activity of the detector turned out to cause a
background count rate of less than 1 s 1. This activity is
mainly due to the decay of 40K and very little from the 232Th
and 238U decay chains. These nuclides are known to be
present in the construction material of a photomultiplier
[17]. From that, we conclude that the upper limit for the
specific intrinsic count rate is less than 0.08 s 1 cm 3. This is
much less than what we usually find in lanthanum halide
crystals, even if grown from the purest raw materials [4].
In terms of timing resolution, CeBr3 detectors turn out to be
highly competitive with lanthanum halide detectors. We find a
timing resolution at 60Co energies of about 330 ps (FWHM),
which is in between the corresponding values for LaCl3 (about
350 ps) and LaBr3 (about 260 ps) detectors of the same size [4].
We may conclude that cerium bromide detectors are excellently suited to meet our requirements for spectral prompt fission
g-ray measurements. Their intrinsic detection efficiency may
allow for an accurate determination of emission characteristics
as a function of fission-fragment mass and excitation energy. In
conjunction with diamond-based fission-event trigger detectors,
excellent separation between prompt neutrons and g-rays may be
expected already at short flight distances, allowing for a compact
and efficient measurement setup. The almost complete nonexistence of any intrinsic activity, in particular the absence of
138
La, makes CeBr3 detectors also highly suitable for environmental g-spectrometry.
Acknowledgments
The authors are very much indebted to SCIONIX Holland BV for
providing the cerium bromide detector for the characterization
performed in this work.
99
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