- Email: [email protected]
WITHDRAWN: Efficiency of Background Suppression by Tagged Neutron Technology
Accepted Manuscript Efficiency of Background Suppression by Tagged Neutron Technology Maxim Karetnikov, Anatoly Klimov, Sergey Korotkov, Evgeny Meleshko, Igor Ostashev, Timur Khasaev, Guenrikh Yakovlev PII: DOI: Reference:
S0168-583X(07)00954-8 10.1016/j.nimb.2007.04.150 NIMB 54838
To appear in:
Nucl. Instr. and Meth. in Phys. Res. B
Please cite this article as: M. Karetnikov, A. Klimov, S. Korotkov, E. Meleshko, I. Ostashev, T. Khasaev, G. Yakovlev, Efficiency of Background Suppression by Tagged Neutron Technology, (2007), doi: 10.1016/j.nimb.2007.04.150
Nucl. Instr. and Meth. in Phys.
Res. B
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
MS469
Efficiency of Background Suppression by Tagged Neutron Technology Maxim Karetnikov1*, Anatoly Klimov1, Sergey Korotkov2, Evgeny Meleshko1, Igor Ostashev1, Timur Khasaev2, Guenrikh Yakovlev1 (1)
Russian Research Center "Kurchatov Institute", Kurchatov sq., Moscow 123182, Russia (2)
All-Russia Research Institute of Automatics, Suschevskaya st., 22, Moscow 127055, Russia
Abstract The possibility of background suppression by spatial and time discrimination of events stipulates the potentialities of the Nanosecond Tagged Neutron Technology (NTNT) for neutron analysis. For practical application of NTNT, the multi-detector systems and high intensity (up to 1 108 1/s) neutron generator should be used. The total intensity of signals can exceed 1 106 1/s from all gamma-detectors and 1 107 1/s from all alpha-detectors. A preliminary “on-line” data processing by hardware sufficiently facilitates the data transmission interface and computer equipment. The basic criteria of processing (selection of useful events) are the presence of signals from alpha- and gamma- detectors in the certain time interval (tracking interval), range of gamma-ray energy, and absence of foldover of the signals. The suggested architecture of data acquisition and control system is discussed. The basic components of background and factors affecting the total time resolution are examined. The preliminary results demonstrate high efficiency of NTNT for suppression of background by spatial and time discrimination of events. *Corresponding author: Kurchatov sq., Moscow 123182, Russia; Phone: +7 (495) 1969042, Fax: +7 (495) 1966032; Email: [email protected]. PACS Codes: 29.25.Dz, 29.40.Mc, 82.80.Jp, 89.20.Bb
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Keywords: Neutron Generator, Tagged Neutron Technology, LYSO Scintillator, Explosives Detection. 1. Introduction One of basic challenges of neutron technologies of remote control is the high background affecting the accuracy of measurements. Last years, the nanosecond tagged neutron technology (NTNT) has been rapidly progressing [1]. This technology provides effective (by 2-4 orders of magnitude) suppression of background by spatial and time discrimination of events. NTNT is the most effective for solving such tasks as the detection, identification, and localization of chemical explosives. The composition of the object is identified by analyzing the spectrum of gamma-rays induced by inelastic neutron scattering on carbon, nitrogen, and oxygen nuclei (that enter into the composition of explosives). NTNT is based on the following principle. Neutrons are produced at the T(d,n)4He reaction while deuteron beam bombards the tritium target. Vectors of escape of neutron and associated alpha-particle (4He) are uniquely correlated [2]. A multipixel position- and timesensitive alpha- detector measures the time and position of incident alpha-particles. It provides the angle and time of neutron escape (the “tags” of neutron). The fast “tagged” neutrons are directed to an object of interest and induce characteristic gamma rays produced through the inelastic scattering of neutrons. Individual nuclei inside the object are identified by recording energy spectrum of emitted gamma-rays by a gamma-detector array. A data acquisition and control unit traces the number (position) of gamma-detector, gamma-ray energy and recording time, as well as pixel number and recording time of alpha-particle. The speed of 14 MeV neutron is as high as 5.2 cm/ns. Thus, the precision of timing for event localization with the accuracy of several cm should be around 1 ns.
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For practical application of NTNT, the multi-detector systems and high intensity (up to 1 108 1/s) neutron generator should be used [1].The total intensity of signals can exceed 1 106 1/s from all gamma-detectors and 1 107 1/s from all alpha-detectors. The transmission of such stream of data to the computer and its processing might heavily complicate the data transmission interface and computer equipment. Thus, it is reasonable to implement the online preliminary data processing by hardware. The basic criterion of selection of useful events is the presence of signals from alpha- and gamma- detectors in the certain time interval (tracking interval), range of gamma-ray energy, and absence of foldover of the signals. 2. Data acquisition and control system for NTNT The flow block of data acquisition and control system (DAC) system suggested by Russian Research Center “Kurchatov Institute” [2] and then realized in several versions is given in Fig.1. The signals from gamma-detectors come to the gamma-channel units; each unit processes signals from several gamma-detectors. The master is always the signal from gamma-detector. The constant fraction discriminator CFD at the input of each gammachannel generates the logic signal Tγ that starts the time-digital converter TDC and encodes the number of activated gamma-detector (Rγ). The shaping amplifier ShA provides the required resolution of measurements of signal amplitude by analog digital converter ADC. The alpha-channel unit issues a logic signal T (time stamp of alpha-particle recording) and code of the number of activated pixel of alpha- detector (Rα). These signals are transmitted to the timing and address buses of alpha-channels and shared by all units of gamma- channels. As far as the counting rate of gamma-detectors is much less than those
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from the alpha-detector the master is always the signal from the gamma-detector. However, as far as the signal from associated alpha- detector comes first, the delay line DL (several dozens ns) is shifted the time of arriving of the Tα signal to TDC after the Tγ signal for proper timing. The univibrator UVT generates the pulse with duration equal to the tracking interval. If the Tα signal from the alpha- channel comes during the tracking interval, it initiates ADC to measure the amplitude of gamma-signal A and stops TDC that issues the code of time between signals from alpha- and gamma- channels T . After completing the measurements, the codes A , R , R , and T . are packed by the microprocessor and sent to the computer PC. The anticoincidence unit AC and foldover discriminators prevent the writing of the event at the presence of two or more signals from detectors during the tracking interval. The main features of DAC systems developed by this scheme are as follows: Quantization of sampling time: 0.075- 0.2 ns Intrinsic time resolution of hardware: ≤0.3 ns; Digit capacity of time code: 8- 12 bits; Digit capacity of gamma-energy code: 8- 12 bits; Digit capacity of the code of gamma-detector number: 8 bits; Digit capacity of the code of alpha-detector pixel number: 8 bits. Options of the interface for data transmission to the computer: Ethernet; RS-422; RS-422; USB; BlueTooth. Form-factor: Eurocrate; CAMAC (optionally).
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The suggested architecture of DAC system allows alteration of the number of gammadetectors, connection of alpha-detectors with various number of pixels, usage of scintillation units with different crystals. It makes possible to use unified DAC system with different devices utilizing tagged neutron technology for various applications- from explosives detection in sea cargo containers to inspection of luggage. 3. Testing of DAC system The DAC system was tested with the experimental test-bench included the NG-27 neutron generator (NG) manufactured by Dukhov All-Russian Research Institute of Automatics [1] with the built-in 9-pixel semiconductor alpha-detector. The tagged neutrons were directed to the graphite box (7 cm in height, 5 cm in width, 3 cm in thickness). The gamma-rays induced by neutrons were recorded by the LYSO gamma-detector 50 mm in diameter and 50 mm in height coupled to the XP4372 photomultiplier [3]. A configuration of the test-bench and basic dimensions are given in Fig. 2. The signals from the gammaand alpha-detectors were processed by the DAC system described above. During the measurements, the intensity of NG was as high as 2·107 1/s. The time spectrum of alpha-gamma coincidences (upper curve) measured by DAC system is given in Fig. 3. The gamma-detector was shielded from the NG by 8 cm iron bar. The lower curve displays the background spectrum taken when the graphite box was removed. A portion of “tagged” neutrons are scattered at the copper holder of target and the casing of NG inducing background gamma-rays. This peak of “correlated” background (indicated in Fig. 2 as NG peak) is partially suppressed by the iron shielding. Another component of
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“correlated” background (Scattered neutrons peak) is caused by the elastic scattering of tagged neutrons in graphite towards the gamma-detector. The “non-correlated” background includes: Gamma-rays induced by “non-tagged” neutrons (emitted at the high angles about the “tagged” neutron paths; the associated alpha-particle is not recorded by the alpha-detector). Gamma-rays emitted through the reactions other than inelastic scattering (radiative neutron capture, radioactive decay, etc.). It can be seen a good time separation of peak of “useful” events (peak of graphite) from peaks of correlated background. The width (FWHM) of the peak of graphite on the time spectrum diagram can be assessed as τ = τ 02 + τ 2f where
of the measuring system,
f
0
is a total time resolution
is a time of 14-MeV neutron flight through the graphite box. As
far as ≈1.2 ns and f≈0.6 ns, then
0≈1
ns. The time between the peak of graphite and NG
peak corresponds to the time required for 14 MeV neutron to pass the distance between the NG and graphite. As far as the events beyond the tracking interval are rejected by the DAC system, these components of “non-correlated” background are highly reduced as can be seen in Fig. 3 (lower curve). Fig. 4 displays the time spectrum of alpha-gamma coincidences when the iron shielding was removed. It can be seen the increase of NG peak and “non-correlated” background, however, the peaks are still well separated, and the time resolution is close to 1 ns. The results of these measurements demonstrate that the NTNT based systems can operate without a massive shielding of a gamma- detector. It provides the opportunity to
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develop a portable hand-held neutron- based explosives detector with a sufficiently reduced weight. 4. Discussions It was demonstrated that NTNT provides suppression of background by spatial and time discrimination of events. The efficiency of background suppression increases with the improvement of time resolution of NTNT system. The total time resolution τ0 can be estimated as:
τ 0 = τ i 2 + τ D2 γ + τ D2 α + τ G2 γ + τ G2α , where τi is the intrinsic resolution of DAC hardware; τDα and τDγ are the time jittering of alpha- and gamma detectors; τGα and τGγ are the geometrical factors caused by finite size of alpha- and gamma- detectors. The value of τi for DAC hardware measured using the signals from external pulse generators was as low as 0.3 ns [4]. For the detectors used in the existing NTNT systems [1], the assessed values of τGα and τGγ are less then 0.5 ns. The jittering of gamma-detector τDγ is caused by PMT transit time difference, fluctuations of charge collection, etc. For small crystals (1 inch) the jittering can be as low as 0.5 ns for fast inorganic scintillators [4]. However, the scintillator for NTNT applications should have sufficient cross-section and height for full absorption of gamma-rays with the energy above 1 MeV. The jittering increases with the scintillator volume and active diameter of PMT. Currently, the several types of gamma-detectors based on BaF2, LYSO, and BGO scintllators have been assembled by our group for measurements of time and experimental spectrums of alpha- gamma coincidences with the aim of a choice of the
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proper gamma- detectors for commercial NTNT systems. The diameter of scintillators varies from 50 mm to 60 mm; the crystals are coupled with ultrafast photomultipliers of similar type produced by Photonis Group [3]. The completion of experiments is targeted at the end of 2006. Acknowledgement The authors thank Dr. G.V. Muradyan, Yu.D. Molchanov, and Dr. V.F. Apalin, staff members of the Kurchatov Institute Russian Research Center, for useful discussions. References [1]
V.D.Aleksandrov, E.P.Bogolubov, O.V.Bochkarev et al. Applied Radiation and
Isotopes, 2005, Vol.63, Issues 5-6, pp.537-543. [2]
Karetnikov M.D., Meleshko E.A., Yakovlev G.V. Implementation of Hardware
Processing of Events for Recording of Alpha-Gamma Coincidences at Associated Particle Technology. Proceedings of the International Scientific and Technical Conference “Portable Neutron Generators and Technologies on their Basis”, VNIIA, Moscow, 2004, p. 335. [3]
http://www.photonis.com/Photomultiplier/Catalog.htm
[4]
Karetnikov M.D., Klimov A.I., Kozlov K.N. et al. Hardware&Software Module for
Measuring Time-Amplitude Parameters of Coincidences at the Nanosecond Neutron Analysis. Instruments and Experimental Techniques. 49, n. 4 (2006), 134. Figure Captions Fig 1. Flow block of DAC system. Fig 2. Test-bench for testing the DAC system.
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Fig 3. Time spectrum of alpha-gamma coincidences for the shielded gamma-detector when the graphite box is installed (upper curve) and when the graphite box is removed (lower curve). Fig 4. Time spectrum of alpha-gamma coincidences for the unshielded gamma-detector when the graphite box is installed (upper curve) and when the graphite box is removed (lower curve).
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Fig. 1
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Fig. 2
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Fig.3
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Fig.4
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S0168-583X(07)00954-8 10.1016/j.nimb.2007.04.150 NIMB 54838
To appear in:
Nucl. Instr. and Meth. in Phys. Res. B
Please cite this article as: M. Karetnikov, A. Klimov, S. Korotkov, E. Meleshko, I. Ostashev, T. Khasaev, G. Yakovlev, Efficiency of Background Suppression by Tagged Neutron Technology, (2007), doi: 10.1016/j.nimb.2007.04.150
Nucl. Instr. and Meth. in Phys.
Res. B
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
MS469
Efficiency of Background Suppression by Tagged Neutron Technology Maxim Karetnikov1*, Anatoly Klimov1, Sergey Korotkov2, Evgeny Meleshko1, Igor Ostashev1, Timur Khasaev2, Guenrikh Yakovlev1 (1)
Russian Research Center "Kurchatov Institute", Kurchatov sq., Moscow 123182, Russia (2)
All-Russia Research Institute of Automatics, Suschevskaya st., 22, Moscow 127055, Russia
Abstract The possibility of background suppression by spatial and time discrimination of events stipulates the potentialities of the Nanosecond Tagged Neutron Technology (NTNT) for neutron analysis. For practical application of NTNT, the multi-detector systems and high intensity (up to 1 108 1/s) neutron generator should be used. The total intensity of signals can exceed 1 106 1/s from all gamma-detectors and 1 107 1/s from all alpha-detectors. A preliminary “on-line” data processing by hardware sufficiently facilitates the data transmission interface and computer equipment. The basic criteria of processing (selection of useful events) are the presence of signals from alpha- and gamma- detectors in the certain time interval (tracking interval), range of gamma-ray energy, and absence of foldover of the signals. The suggested architecture of data acquisition and control system is discussed. The basic components of background and factors affecting the total time resolution are examined. The preliminary results demonstrate high efficiency of NTNT for suppression of background by spatial and time discrimination of events. *Corresponding author: Kurchatov sq., Moscow 123182, Russia; Phone: +7 (495) 1969042, Fax: +7 (495) 1966032; Email: [email protected]. PACS Codes: 29.25.Dz, 29.40.Mc, 82.80.Jp, 89.20.Bb
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Keywords: Neutron Generator, Tagged Neutron Technology, LYSO Scintillator, Explosives Detection. 1. Introduction One of basic challenges of neutron technologies of remote control is the high background affecting the accuracy of measurements. Last years, the nanosecond tagged neutron technology (NTNT) has been rapidly progressing [1]. This technology provides effective (by 2-4 orders of magnitude) suppression of background by spatial and time discrimination of events. NTNT is the most effective for solving such tasks as the detection, identification, and localization of chemical explosives. The composition of the object is identified by analyzing the spectrum of gamma-rays induced by inelastic neutron scattering on carbon, nitrogen, and oxygen nuclei (that enter into the composition of explosives). NTNT is based on the following principle. Neutrons are produced at the T(d,n)4He reaction while deuteron beam bombards the tritium target. Vectors of escape of neutron and associated alpha-particle (4He) are uniquely correlated [2]. A multipixel position- and timesensitive alpha- detector measures the time and position of incident alpha-particles. It provides the angle and time of neutron escape (the “tags” of neutron). The fast “tagged” neutrons are directed to an object of interest and induce characteristic gamma rays produced through the inelastic scattering of neutrons. Individual nuclei inside the object are identified by recording energy spectrum of emitted gamma-rays by a gamma-detector array. A data acquisition and control unit traces the number (position) of gamma-detector, gamma-ray energy and recording time, as well as pixel number and recording time of alpha-particle. The speed of 14 MeV neutron is as high as 5.2 cm/ns. Thus, the precision of timing for event localization with the accuracy of several cm should be around 1 ns.
2
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For practical application of NTNT, the multi-detector systems and high intensity (up to 1 108 1/s) neutron generator should be used [1].The total intensity of signals can exceed 1 106 1/s from all gamma-detectors and 1 107 1/s from all alpha-detectors. The transmission of such stream of data to the computer and its processing might heavily complicate the data transmission interface and computer equipment. Thus, it is reasonable to implement the online preliminary data processing by hardware. The basic criterion of selection of useful events is the presence of signals from alpha- and gamma- detectors in the certain time interval (tracking interval), range of gamma-ray energy, and absence of foldover of the signals. 2. Data acquisition and control system for NTNT The flow block of data acquisition and control system (DAC) system suggested by Russian Research Center “Kurchatov Institute” [2] and then realized in several versions is given in Fig.1. The signals from gamma-detectors come to the gamma-channel units; each unit processes signals from several gamma-detectors. The master is always the signal from gamma-detector. The constant fraction discriminator CFD at the input of each gammachannel generates the logic signal Tγ that starts the time-digital converter TDC and encodes the number of activated gamma-detector (Rγ). The shaping amplifier ShA provides the required resolution of measurements of signal amplitude by analog digital converter ADC. The alpha-channel unit issues a logic signal T (time stamp of alpha-particle recording) and code of the number of activated pixel of alpha- detector (Rα). These signals are transmitted to the timing and address buses of alpha-channels and shared by all units of gamma- channels. As far as the counting rate of gamma-detectors is much less than those
3
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from the alpha-detector the master is always the signal from the gamma-detector. However, as far as the signal from associated alpha- detector comes first, the delay line DL (several dozens ns) is shifted the time of arriving of the Tα signal to TDC after the Tγ signal for proper timing. The univibrator UVT generates the pulse with duration equal to the tracking interval. If the Tα signal from the alpha- channel comes during the tracking interval, it initiates ADC to measure the amplitude of gamma-signal A and stops TDC that issues the code of time between signals from alpha- and gamma- channels T . After completing the measurements, the codes A , R , R , and T . are packed by the microprocessor and sent to the computer PC. The anticoincidence unit AC and foldover discriminators prevent the writing of the event at the presence of two or more signals from detectors during the tracking interval. The main features of DAC systems developed by this scheme are as follows: Quantization of sampling time: 0.075- 0.2 ns Intrinsic time resolution of hardware: ≤0.3 ns; Digit capacity of time code: 8- 12 bits; Digit capacity of gamma-energy code: 8- 12 bits; Digit capacity of the code of gamma-detector number: 8 bits; Digit capacity of the code of alpha-detector pixel number: 8 bits. Options of the interface for data transmission to the computer: Ethernet; RS-422; RS-422; USB; BlueTooth. Form-factor: Eurocrate; CAMAC (optionally).
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The suggested architecture of DAC system allows alteration of the number of gammadetectors, connection of alpha-detectors with various number of pixels, usage of scintillation units with different crystals. It makes possible to use unified DAC system with different devices utilizing tagged neutron technology for various applications- from explosives detection in sea cargo containers to inspection of luggage. 3. Testing of DAC system The DAC system was tested with the experimental test-bench included the NG-27 neutron generator (NG) manufactured by Dukhov All-Russian Research Institute of Automatics [1] with the built-in 9-pixel semiconductor alpha-detector. The tagged neutrons were directed to the graphite box (7 cm in height, 5 cm in width, 3 cm in thickness). The gamma-rays induced by neutrons were recorded by the LYSO gamma-detector 50 mm in diameter and 50 mm in height coupled to the XP4372 photomultiplier [3]. A configuration of the test-bench and basic dimensions are given in Fig. 2. The signals from the gammaand alpha-detectors were processed by the DAC system described above. During the measurements, the intensity of NG was as high as 2·107 1/s. The time spectrum of alpha-gamma coincidences (upper curve) measured by DAC system is given in Fig. 3. The gamma-detector was shielded from the NG by 8 cm iron bar. The lower curve displays the background spectrum taken when the graphite box was removed. A portion of “tagged” neutrons are scattered at the copper holder of target and the casing of NG inducing background gamma-rays. This peak of “correlated” background (indicated in Fig. 2 as NG peak) is partially suppressed by the iron shielding. Another component of
5
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“correlated” background (Scattered neutrons peak) is caused by the elastic scattering of tagged neutrons in graphite towards the gamma-detector. The “non-correlated” background includes: Gamma-rays induced by “non-tagged” neutrons (emitted at the high angles about the “tagged” neutron paths; the associated alpha-particle is not recorded by the alpha-detector). Gamma-rays emitted through the reactions other than inelastic scattering (radiative neutron capture, radioactive decay, etc.). It can be seen a good time separation of peak of “useful” events (peak of graphite) from peaks of correlated background. The width (FWHM) of the peak of graphite on the time spectrum diagram can be assessed as τ = τ 02 + τ 2f where
of the measuring system,
f
0
is a total time resolution
is a time of 14-MeV neutron flight through the graphite box. As
far as ≈1.2 ns and f≈0.6 ns, then
0≈1
ns. The time between the peak of graphite and NG
peak corresponds to the time required for 14 MeV neutron to pass the distance between the NG and graphite. As far as the events beyond the tracking interval are rejected by the DAC system, these components of “non-correlated” background are highly reduced as can be seen in Fig. 3 (lower curve). Fig. 4 displays the time spectrum of alpha-gamma coincidences when the iron shielding was removed. It can be seen the increase of NG peak and “non-correlated” background, however, the peaks are still well separated, and the time resolution is close to 1 ns. The results of these measurements demonstrate that the NTNT based systems can operate without a massive shielding of a gamma- detector. It provides the opportunity to
6
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ACCEPTED MANUSCRIPT
develop a portable hand-held neutron- based explosives detector with a sufficiently reduced weight. 4. Discussions It was demonstrated that NTNT provides suppression of background by spatial and time discrimination of events. The efficiency of background suppression increases with the improvement of time resolution of NTNT system. The total time resolution τ0 can be estimated as:
τ 0 = τ i 2 + τ D2 γ + τ D2 α + τ G2 γ + τ G2α , where τi is the intrinsic resolution of DAC hardware; τDα and τDγ are the time jittering of alpha- and gamma detectors; τGα and τGγ are the geometrical factors caused by finite size of alpha- and gamma- detectors. The value of τi for DAC hardware measured using the signals from external pulse generators was as low as 0.3 ns [4]. For the detectors used in the existing NTNT systems [1], the assessed values of τGα and τGγ are less then 0.5 ns. The jittering of gamma-detector τDγ is caused by PMT transit time difference, fluctuations of charge collection, etc. For small crystals (1 inch) the jittering can be as low as 0.5 ns for fast inorganic scintillators [4]. However, the scintillator for NTNT applications should have sufficient cross-section and height for full absorption of gamma-rays with the energy above 1 MeV. The jittering increases with the scintillator volume and active diameter of PMT. Currently, the several types of gamma-detectors based on BaF2, LYSO, and BGO scintllators have been assembled by our group for measurements of time and experimental spectrums of alpha- gamma coincidences with the aim of a choice of the
7
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proper gamma- detectors for commercial NTNT systems. The diameter of scintillators varies from 50 mm to 60 mm; the crystals are coupled with ultrafast photomultipliers of similar type produced by Photonis Group [3]. The completion of experiments is targeted at the end of 2006. Acknowledgement The authors thank Dr. G.V. Muradyan, Yu.D. Molchanov, and Dr. V.F. Apalin, staff members of the Kurchatov Institute Russian Research Center, for useful discussions. References [1]
V.D.Aleksandrov, E.P.Bogolubov, O.V.Bochkarev et al. Applied Radiation and
Isotopes, 2005, Vol.63, Issues 5-6, pp.537-543. [2]
Karetnikov M.D., Meleshko E.A., Yakovlev G.V. Implementation of Hardware
Processing of Events for Recording of Alpha-Gamma Coincidences at Associated Particle Technology. Proceedings of the International Scientific and Technical Conference “Portable Neutron Generators and Technologies on their Basis”, VNIIA, Moscow, 2004, p. 335. [3]
http://www.photonis.com/Photomultiplier/Catalog.htm
[4]
Karetnikov M.D., Klimov A.I., Kozlov K.N. et al. Hardware&Software Module for
Measuring Time-Amplitude Parameters of Coincidences at the Nanosecond Neutron Analysis. Instruments and Experimental Techniques. 49, n. 4 (2006), 134. Figure Captions Fig 1. Flow block of DAC system. Fig 2. Test-bench for testing the DAC system.
8
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Fig 3. Time spectrum of alpha-gamma coincidences for the shielded gamma-detector when the graphite box is installed (upper curve) and when the graphite box is removed (lower curve). Fig 4. Time spectrum of alpha-gamma coincidences for the unshielded gamma-detector when the graphite box is installed (upper curve) and when the graphite box is removed (lower curve).
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Fig. 1
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Fig. 2
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Fig.3
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Fig.4
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