A technique for the selective detection of neutrons in geological applications
We present a new, combined technique for the detection of fast and thermal neutrons in the presence of accompanying gamma radiation, for geological and radioecological applications. To separate the slow neutron pulses and fast gamma pulses of organic scintillators, we used the method of particle ide...
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irk-123456789-1104032017-01-05T03:02:31Z A technique for the selective detection of neutrons in geological applications Baker, J.H. Galunov, N.Z. Kostin, V.G. Martynenko, E.V. Tarasenko, O.A. Ядернo-физические методы и обработка данных We present a new, combined technique for the detection of fast and thermal neutrons in the presence of accompanying gamma radiation, for geological and radioecological applications. To separate the slow neutron pulses and fast gamma pulses of organic scintillators, we used the method of particle identification by radioluminescence pulse shape. The device has been tested by the combined neutron and gamma radiation sources ²⁵²Cf and ²³⁹Pu-Be, and by a 14.2 MeV D-T source of fast neutrons both in the laboratory, and under real, field conditions as applied at selected sites of the European Union. Розглянуті основні принципи та апаратура для реєстрації швидких і теплових нейтронів для сучасних задач геології й радіоекології. Роздільна реєстрація повільних нейтронних імпульсів і швидких імпульсів гама-випромінювання органічних сцинтиляторів здійснювалася шляхом дискримінації іонізуючого випромінювання за формою сцинтиляційного імпульсу. Атестація апаратури проводилася за допомогою джерел ²⁵²Cf та ²³⁹Pu-Be , а також D-T джерела швидких нейтронів з енергією 14.2 МеВ, як у лабораторних умовах, так і в реальних умовах її застосування в ряді країн Європейського Союзу. Изложены основные принципы и аппаратура для регистрации быстрых и тепловых нейтронов для современных задач геологии и радиоэкологии. Раздельная регистрация медленных нейтронных импульсов и быстрых импульсов гамма-излучения органических сцинтилляторов осуществлялась путем дискриминации ионизирующего излучения по форме сцинтилляционного импульса. Аттестация аппаратуры производилась с помощью источников ²⁵²Cf и ²³⁹Pu-Be , а также D-T источника быстрых нейтронов с энергией 14.2 МэВ, как в лабораторных условиях, так и в реальных условиях ее применения в ряде стран Европейского Союза. 2007 Article A technique for the selective detection of neutrons in geological applications / J.H. Baker, N.Z. Galunov, V.G. Kostin, E.V. Martynenko, O.A. Tarasenko // Вопросы атомной науки и техники. — 2007. — № 5. — С. 126-130. — Бібліогр.: 10 назв. — англ. 1562-6016 PACS: 07.88.+y, 29.40.Mc, 29.25.Dz http://dspace.nbuv.gov.ua/handle/123456789/110403 en Вопросы атомной науки и техники Інститут сцинтиляційних матеріалів НТК "Інститут монокристалів" НАН України |
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Ядернo-физические методы и обработка данных Ядернo-физические методы и обработка данных |
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Ядернo-физические методы и обработка данных Ядернo-физические методы и обработка данных Baker, J.H. Galunov, N.Z. Kostin, V.G. Martynenko, E.V. Tarasenko, O.A. A technique for the selective detection of neutrons in geological applications Вопросы атомной науки и техники |
| description |
We present a new, combined technique for the detection of fast and thermal neutrons in the presence of accompanying gamma radiation, for geological and radioecological applications. To separate the slow neutron pulses and fast gamma pulses of organic scintillators, we used the method of particle identification by radioluminescence pulse shape. The device has been tested by the combined neutron and gamma radiation sources ²⁵²Cf and ²³⁹Pu-Be, and by a 14.2 MeV D-T source of fast neutrons both in the laboratory, and under real, field conditions as applied at selected sites of the European Union. |
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Article |
| author |
Baker, J.H. Galunov, N.Z. Kostin, V.G. Martynenko, E.V. Tarasenko, O.A. |
| author_facet |
Baker, J.H. Galunov, N.Z. Kostin, V.G. Martynenko, E.V. Tarasenko, O.A. |
| author_sort |
Baker, J.H. |
| title |
A technique for the selective detection of neutrons in geological applications |
| title_short |
A technique for the selective detection of neutrons in geological applications |
| title_full |
A technique for the selective detection of neutrons in geological applications |
| title_fullStr |
A technique for the selective detection of neutrons in geological applications |
| title_full_unstemmed |
A technique for the selective detection of neutrons in geological applications |
| title_sort |
technique for the selective detection of neutrons in geological applications |
| publisher |
Інститут сцинтиляційних матеріалів НТК "Інститут монокристалів" НАН України |
| publishDate |
2007 |
| topic_facet |
Ядернo-физические методы и обработка данных |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/110403 |
| citation_txt |
A technique for the selective detection of neutrons in geological applications / J.H. Baker, N.Z. Galunov, V.G. Kostin, E.V. Martynenko, O.A. Tarasenko // Вопросы атомной науки и техники. — 2007. — № 5. — С. 126-130. — Бібліогр.: 10 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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| fulltext |
A TECHNIQUE FOR THE SELECTIVE DETECTION OF
NEUTRONS IN GEOLOGICAL APPLICATIONS
J.H. Baker1, N.Z. Galunov2∗, V.G. Kostin2,
E.V. Martynenko2, O.A. Tarasenko2
1SELOR eeig, Amsterdam, the Netherlands
2Institute for Scintillation Materials of Scientific Technology Center
”Institute for Single Crystals” of NAS of Ukraine, Kharkiv, Ukraine
(Received March 14, 2007)
We present a new, combined technique for the detection of fast and thermal neutrons in the presence of accompanying
gamma radiation, for geological and radioecological applications. To separate the slow neutron pulses and fast gamma
pulses of organic scintillators, we used the method of particle identification by radioluminescence pulse shape. The
device has been tested by the combined neutron and gamma radiation sources 252Cf and 239Pu-Be, and by a 14.2 MeV
D-T source of fast neutrons both in the laboratory, and under real, field conditions as applied at selected sites of the
European Union.
PACS: 07.88.+y, 29.40.Mc, 29.25.Dz
1. INTRODUCTION
Environmental site surveys require accurate, in depth
analysis of potential contaminants in the sub-surface.
Currently this is done by sampling boreholes, sending
samples for analysis, and then interpreting the data,
which often are time consuming. There is a need for
a logging tool, which can rapidly provide this data so
that site assessment can be carried out quickly and
efficiently.
Geological research and mineral investigations on
site also involve time delays between sampling rocks
and getting analytical data. Therefore, the analysis
has to be made on site, thus guiding exploration and
research in a more effective manner. Currently no
such device is available commercially. A number of
electric logging tools exist for water and soil analysis,
but these are not multi-purpose, and the number of
parameters, which can be measured is limited. Pre-
vious neutron logging devices required a radioactive
source, which made them impracticable due to han-
dling and storage safety considerations, and only gave
qualitative analyses of parameters.
In neutron measurements, a scintillator detects
both neutrons and accompanying background gamma
radiation because the neutron detectors based on
solid and liquid scintillators have a high efficiency of
gamma radiation detection. Therefore, a highly ac-
curate experiment is impossible without using a tech-
nique with the selective detection of different types of
radiations.
The problem of selective detection of ionizing ra-
diation, especially the problem of separation of the
neutron spectrum and gamma background is very
important in nuclear experiments. The most effec-
tive method for detection of fast neutrons is based on
the production in organic material of recoil protons.
Therefore, organic detectors with a high content of
hydrogen are the most useful for fast neutron spec-
troscopy.
This work is devoted to the new applied technique
of geological research based on using a combined scin-
tillation method in the detection of fast and ther-
mal neutrons in the presence of accompanying, in-
duced gamma radiation. We have mounted the cir-
cuitry and controlling software with photomultiplier
and other components on a unit that allows operat-
ing the detector system in the research phase of this
work.
2. THEORY
Ionizing radiation in an organic scintillator gen-
erates two types of luminescence referred to as the
prompt radioluminescence and the delayed radio-
luminescence. The formation of the fast compo-
nent of the radioluminescence pulse essentially takes
place outside the region of particle tracks. It has
an exponential decay with time constant of about
10−9 − 10−8 s [1]. The process of scintillation pulse
fast component formation takes place within ”the op-
tical approximation” and practically does not depend
on the specific energy losses dE/dx of a particle. The
slow component of the scintillation pulse arises due
to a triplet-triplet annihilation process that results
in the delayed radioluminescence of the scintillator.
These processes take place only in the regions of high
activation density (e.g. a track of a particle) where
∗Corresponding author. E-mail address: galunov@isc.kharkov.com
126 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, 2007, N5.
Series: Nuclear Physics Investigations (48), p.126-130.
the concentration of ionized and exited molecules is
high, and therefore the influence of dE/dx on the
slow component of scintillation pulse formation is of
primary importance. Due to annihilation nature of
such a process, hyperbolical functions describe the
shape of slow component and its intensity depends
on dE/dx [2]. It is the physical base of the technique
of particle identification by radioluminescence pulse
shape.
3. EXPERIMENT
Js
SIR
PMT D
INT AMP
INV
PFA
C-S
PA
а
d
+
-
n
γ
Spectral
Jf
S
AMP
SUM
INT
Fig.1. Block diagram of the set-up for selec-
tive detection the ionizing radiation with different
dE/dx: SIR is a source of ionizing radiation; S is
a Ø40 mm×40 mm stilbene scintillator; PMT is
a 9272B ETL photomultiplier tube (a is the an-
ode output and d is the next to the last dynode
output); D is a discriminator; INT is an inte-
grator; INV is an inverter; AMP are amplifiers
with adjusted gain; SUM is a summer; C-S PA
is a charge-sensitive preamplifier; PFA is a pulse
former amplifier; n is the neutron spectrum con-
trol output; γ is gamma spectrum control output;
spectral output is the spectrometric output
Fig.1 illustrates the measuring set-up that is
used for above-mentioned method. We used
Ø(40×40) mm stilbene detector optically coupled
with a 52 mm type 9272B Electron Tubes Ltd. pho-
tomultiplier. The signal from the anode output of
the photomultiplier is transmitted to the electronic
part that separates a charge in time intervals from 0
to 50 ns after an excitation and from 50 to 2000 ns,
i.e. the time of the fast and the slow signals, re-
spectively. The electronics integrates the charge ac-
cumulated in the interval from 0 to 50 ns and ob-
tains the Jf -value, as well as integrates the charge
accumulated in the interval from 50 to 2000 ns and
inverts to obtain Js-value. The signals proportional
to Jf and Js are summed in such a way that the
detection of scintillation pulses initiated by neutrons
results in the formation of the positive pulse on the
summation output, whereas the detection of photons
of gamma radiation results in the formation of the
negative pulse. The digital signal appears on a sepa-
rate ”neutron” or ”gamma” output according to the
polarity of the previous signal. The charge-sensitive
preamplifier, followed by the pulse former amplifier,
forms the signal from the next to the last dynode of a
photomultiplier for amplitude analysis. This instru-
ment can work for measurements with separation of
combined spectra of α- and β- scintillations, α- and
γ- scintillations, etc. using the same principle of dis-
crimination analysis.
According to [3], the quality of the discrimi-
nation procedure based on the technique described
above depends on time interval tf of ”complete” de-
cay of the fast component of the radioluminescence
pulse. Single-photon measurements of the radiolumi-
nescence pulse shape give the tf -value.
In our experiments, we used a high output neu-
tron emitting tube that generates 14.2 MeV mono-
energetic neutrons by deuterium-tritium (D-T) reac-
tion. The frequency of bursts is 20 Hz and this source
emits 108 neutrons per second in 4π-geometry. Accel-
erating potential for deuterons was equal to 120 keV
that allows obtaining practically isotropic diagram of
neutrons in a burst [4]. Additionally, for laboratory
tests we used a Pu-Be radionuclide source with neu-
tron flux equal to ∼ 105 neutrons per second, and a
radionuclide 252Cf as fission type source with neutron
flux ∼ 104 neutrons per second.
The dominant type of radiation determines the
choice of scintillation material. Our previous investi-
gations indicate that detectors based on stilbene scin-
tillators are the most effective for the required tasks
of neutron spectrometry. Notwithstanding that, it
is necessary to take into account, that scintillators
based on p-terphenyl have better strength and oper-
ating characteristics [3].
For the detection of thermal neutrons we used a
Ø(20×3) mm detector on the basis of a LiI(Eu) crys-
tal. It contains an element with a high value of ther-
mal neutron absorption cross-section, e.g. 6Li.
For penetrative gamma radiation, a material with
high density is required. Characteristics of some in-
organic materials usually used for the detection of
photons of gamma radiation have been previously
discussed (see [5], for example). Detectors based
on NaI(Tl) crystals have the best characteristics for
high resolution gamma-spectroscopy. The combina-
tion of two of above mentioned scintillation materials
(NaI(Tl) and LiI(Eu), or stilbene and NaI(Tl)) allows
us to detect simultaneously different types of ionizing
radiation.
We have chosen a 25 mm type 9110FLA ETL pho-
tomultiplier for the detection of thermal neutron and
a 52 mm type 9272B ETL photomultiplier for the de-
tection of background gamma radiations. The signal
d (see Fig.1) from the next to the last dynode out-
put was formed for amplitude analysis according to
above-mentioned procedure. In this case the anode
(control) output a did not used.
4. RESULTS AND DISCUSSION
To test the proposed technique of selective de-
tection neutron and gamma radiation (see Fig. 1)
we have carried our a series of measurements of
amplitude spectra from a Ø(40×40) mm stilbene
detector irradiated by the combined neutron and
gamma source (Pu-Be), the mono-energetic D-T neu-
tron source and standard sources of gamma radiation
22Na, 60Co, 137Cs, 152Eu and 232Th.
127
1 2 3 4 5
10
0
10
1
10
2
10
3
10
4
4
2
1
N
u
m
b
er
o
f
p
u
ls
es
E
γ
*
, MeV
3
Fig.2. Scintillation amplitude spectra of a
Ø40 mm×40 mm stilbene detector irradiated
by the sources of ionizing radiation: 239Pu-
Be (curves 1 and 2), 252Eu (curves 3 and 4).
Curves 1 and 3 have been measured without
the neutron control signal, but curves 2 and 4
have been measured with the neutron control
signal
Curve 1 on Fig.2 shows the total recoil protons
and recoil electrons spectrum of stilbene irradiated
by Pu-Be (discrimination is not used). Curve 2 shows
the proton spectrum of Pu-Be (control from neutron
output). Curve 3 shows the recoil electrons spectrum
of stilbene irradiated by 252Eu measured without the
neutron control signal, and curve 4 shows this spec-
trum measured with the neutron control signal, re-
spectively. A negligible number of pulses for curve 4
confirm that discrimination procedure discussed here
is clearly effective. The X-axis is calibrated in the
scale of scintillation amplitudes obtained from pho-
tons of gamma radiation of energy E∗
γ . Compton edge
energies Ecomp for sources with energies Eγ has been
obtained according to a well-known formula [6].
The following expression can used to regenerate
the neutron spectrum with energies En [7] in scale of
scintillation amplitudes:
ϕ (En) = − En
ε (En)
× du (Ep)
dEp
∣∣∣∣
Ep=En
, (1)
where u(Ep) is a recoil proton spectrum (measured
for Ep ≤ En), ε(Ep) is an efficiency of detection of dif-
ferent energy neutrons. Expression (1) does not take
into account the non-linearity of scintillation response
to recoil protons [5]. Expression (1) gives the neutron
spectra ϕ(En) in non-linear En scale. Therefore the
results obtained still hold the information concerning
features of scintillator response, as well as the infor-
mation about ”specific quenching”. The calculation
(1) is inapplicable to the case of study a spectrum
of unknown neutron source, because the non- linear-
ity of scintillation response has to be considered in
such a case. It allows obtaining the scintillation re-
sponse when the neutron source with know spectrum
is used [7]. Therefore we used a radionuclide 239Pu-
Be source. It spectrum is thoroughly studied. See i.e.
the theoretical calculations of the energy spectrum
of Pu-Be neutron source [8], experimental works in
which such a source was tested by stilbene scintilla-
tors and nuclear emulsions [9, 10], etc. The peaks 1,
2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 on Fig. 3 correspond to
well-known energies of neutrons (0.85, 2.0, 3.1, 4.2,
4.9, 6.4, 6.7, 7.3, 7.9, 8.6 and 9.7 MeV respectively
[7-10]) emitted by a 239Pu-Be source.
100 200 300 400 500 600 700 800 900 1000
0
1000
2000
3000
4000
11
1
2
3
4
65 7
8 9
N
u
m
b
e
r
o
f
d
e
te
c
te
d
n
e
u
tr
o
n
s
Channel number
10
Fig.3. Neutron spectra reconstructed from the
recoil proton spectra (see Fig.2, curve 2) of
239Pu-Be source for a Ø(40×40) mm stilbene
detector
We investigated the spectrum of scintillation am-
plitudes of stilbene detector irradiated by a D-
T mono-energetic neutron source using the above-
mentioned procedure of n/γ-discrimination. Fig.4
shows the results of these measurements.
5 10 15 20 25 30
0
250
500
750
1000
1250
1500
1750
2000
b
2
Reactions
(n,n')
E
n
= 14.2 MeV
N
u
m
b
er
o
f
p
u
ls
es
E
n
, MeV
1
a
Fig.4. Scintillation amplitude spectra of a
Ø(40×40) mm stilbene detector irradiated by
a D-T neutron source: curve 1 is the scintil-
lation spectrum of recoil protons, curve 2 is
derived spectrum of 14.2 MeV neutrons
Curve 1 on Fig.4 shows the experimental scintil-
lation spectrum of recoil protons generated by fast
neutrons in the detector. Curve 2 is the neutron
spectrum of a D-T source obtained by the procedure
of numerical differentiation followed by smoothing of
experimental data of curve 1 (see expression 1). The
high-energy peak of curve 2 is the reconstructed neu-
tron signal from 14.2 MeV neutrons. One can see it
splitting on two peaks, a and b. The amplitude rela-
tionship between these peaks is about 1.2 that is in a
good agreement with the value of anisotropy of stil-
128
bene signals obtained during an excitation along and
perpendicular to crystallographic plane ab [3]. In our
experiments, the measuring system was excited along
crystallographic plane ab and this type of excitation
was more probable. The neutrons were scattered by
the neutron shielding excited the crystal perpendicu-
lar to crystallographic plane ab.
Fig.5 shows the scintillation spectra obtained dur-
ing 6LiI(Eu) detectors irradiation by thermal neu-
trons (the sources of fast neutrons in paraffin sphere)
and photons of gamma radiation from a 137Cs ra-
dionuclide source. Neutrons generate monochromatic
α-particles and therefore an α-scintillation spectrum
is obtained. It is accompanied by a γ-spectrum of
background radiation. Amplitude discrimination is
enough to separate these two spectra, because for
thin 6Li(Eu) crystals a γ-scintillation spectrum is
narrow and located in the range of low amplitudes.
500 1000 1500 2000 2500 3000 3500
0
50
100
150
200
250
300
1
2
Neutrons
Threshold
range
Photons of
γ - radiation
T
h
er
m
o
n
eu
tr
o
n
s
N
u
m
b
er
o
f
p
u
ls
es
Channel number
3
Fig.5. Scintillation amplitude spectra from
a Ø20 mm×3 mm LiI(Eu) detector irradiated
by neutron sources have been introduced inside
moderator (a paraffin sphere 15 cm in diame-
ter): 239Pu-Be (curve 1), 252Cf (curve 2) and
irradiated by a source of photons of gamma
radiation 137Cs (curve 3)
5. CONCLUSIONS
We have tested and optimized the set of devices
for fast and thermal neutron detection that can be
used as the basis for measuring a range of parame-
ters including hydrocarbons, heavy metals and other
elements in both geological and environmental ap-
plications. The technique of discrimination of ioniz-
ing radiation by their pulse shape allows the separate
detection and with high degree of accuracy both of
thermal neutrons scattering from the material under
investigation and secondary photons of gamma ra-
diation. These photons are generated in reactions
of inelastic scattering of fast neutrons or radiative
capturing of thermal neutrons, and give information
about the chemical composition of a material [5].
It should be noted that in geological applications
the content of water (one of the most effective mod-
erator of neutrons in nature), difference in density,
porosity of soil, and some other factors might have a
significant effect on the results of any measurements,
especially in the case of quantitative analysis. So, for
complex systems, data processing and interpretation
is a separate task, and therefore has been discussed
separately.
ACKNOWLEDGEMENTS
The Science and Technology Centre in Ukraine
supported this work through grant No. P-130. Addi-
tional financial support was also provided to SELOR
through the Nu-Pulse project of the GROWTH pro-
grammer contract G1RD-CT-200200714 (EU DG-
RTD).
REFERENCES
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Features of scintillation process in organic scintil-
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2. N.Z. Galunov, B.V. Grinyov, O.A. Tarasenko,
E.V. Martynenko. Some aspects of scintillation
mechanism in organic molecular dielectrics //
Journal of the Korean Association for Radiation
Protection. 2005, v.30, p.85-89 (in Russian).
3. N.Z. Galunov, V.P. Seminozhenko. Theory and
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and photons of gamma radiation in geological
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tion Counting, London, ”Pergamon Press”, 1964,
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АППАРАТУРА ДЛЯ РАЗДЕЛЬНОЙ РЕГИСТРАЦИИ НЕЙТРОНОВ
ДЛЯ ГЕОЛОГИЧЕСКИХ ПРИМЕНЕНИЙ
Д.Х. Бэйкер, Н.З. Галунов, В.Г. Костин,
Е.В. Мартыненко, О.А. Тарасенко
Изложены основные принципы и аппаратура для регистрации быстрых и тепловых нейтронов для
современных задач геологии и радиоэкологии. Раздельная регистрация медленных нейтронных им-
пульсов и быстрых импульсов гамма-излучения органических сцинтилляторов осуществлялась путем
дискриминации ионизирующего излучения по форме сцинтилляционного импульса. Аттестация ап-
паратуры производилась с помощью источников 252Cf и 239Pu-Be , а также D-T источника быстрых
нейтронов с энергией 14.2 МэВ, как в лабораторных условиях, так и в реальных условиях ее примене-
ния в ряде стран Европейского Союза.
АПАРАТУРА ДЛЯ РОЗДIЛЬНОЇ РЕЄСТРАЦIЇ НЕЙТРОНIВ
ДЛЯ ГЕОЛОГIЧНИХ ЗАСТОСУВАНЬ
Д. Х. Бейкер, М.З. Галунов, В.Г. Костiн,
Є.В. Мартиненко, О.А. Тарасенко
Розглянутi основнi принципи та апаратура для реєстрацiї швидких i теплових нейтронiв для су-
часних задач геологiї й радiоекологiї. Роздiльна реєстрацiя повiльних нейтронних iмпульсiв i швидких
iмпульсiв гама-випромiнювання органiчних сцинтиляторiв здiйснювалася шляхом дискримiнацiї iонi-
зуючого випромiнювання за формою сцинтиляцiйного iмпульсу. Атестацiя апаратури проводилася за
допомогою джерел 252Cf та 239Pu-Be , а також D-T джерела швидких нейтронiв з енергiєю 14.2 МеВ,
як у лабораторних умовах, так i в реальних умовах її застосування в рядi країн Європейського Союзу.
130
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