A digital method for pulse-shape discrimination between particles

Results from experimental and theoretical investigations of a digital technique for pulse-shape discrimination are presented. Pulses from a scintillation (stilbene-based) detector are recorded by a digital oscilloscope and transmitted to a computer for carrying out particle identification. For a stilbene scintillation detector irradiated by neutrons and γ rays, the γ-ray suppression factor is ～0.5 × 10³?10⁴ and the neutron identification efficiency is ～0.70-0.90 over an energy range of ～30–500 keV at a counting rate up to ～10⁵ pulse/s. It is shown that this technique can form the basis for developing a detector unit that comprises a fast ADC and a digital signal processor and provides online identification of particles by scintillation pulse shape.     

A digital method for pulse-shape discrimination between neutrons and γ rays at a high counting rate and a low energy of detected radiation

A digital method for pulse-shape discrimination between neutrons and γ rays was used in measurements at counting rates of up to ～10⁶ counts/s in the energy range of ～2–800 keV. Pulses produced by neutrons and γ rays in a stilbene-based scintillation detector were digitized by a digital oscilloscope and transmitted to a computer for carrying out particle identification. Identification was performed for radiation of radionuclide sources and a pulsed neutron generator operating in a repeated triggering mode. Amplitude spectra of pulses identified as neutrons and γ rays of radiation from the generator were measured. At a detector counting rate of ～8.5 × 10⁵ counts/s, ～90% of all recorded pulses were recognized as neutrons. In the energy range of ～30–800 keV, the γ-ray suppression factor was ～10⁴–10³ at counting rates of ～1.5×10⁵–5 × 10⁵ counts/s, while the efficiency of identifying neutrons was >0.9. The suppression factor for γ rays with an energy of ～10 keV was ～300, and the neutron identification efficiency was ～0.75.     

A scintillation strip detector for detection of thermal neutrons

A scintillation strip detector designed for precise experiments on the reflectometry of thermal neutrons is described. Test results obtained on the beam of a time-of-flight spectrometer have shown that the detector has a detection efficiency for thermal neutrons close to 100%, a lowered sensitivity to the neutron background, and a low level of intrinsic noise. The coordinate resolution of the detector can be varied in the range 1.5–0.1 mm. The strip is manufactured from a mixture of a ZnS(Ag) scintillator and a ⁶LiF neutron converter.     

First results of use of a scintillating-fiber position-sensitive detector for recording the target image in a 14-MeV neuron beam at the ISKRA-5 facility

The design of the scintillating-fiber detector is described, and the first results obtained in recording the target image in a 14-MeV neutron beam at the ISKRA-5 facility are presented. The scintillating-fiber position-sensitive detector has been designed for diagnosing laser fusion processes by recording the spatial distribution of thermonuclear neutrons escaping from the target. Position-sensitive detection is effected by conversion of neutron radiation into light in a scintillating fiber array. Discrimination of neutrons from γ rays by their time of flight and image intensification are performed with the aid of a frame camera. Images are recorded by a CCD camera. A technique for recording penumbra images is used for imaging at low neutron yields (3 × 10⁸−10¹¹).     

A neutron semiconductor detector based on TIInSe<Subscript>2</Subscript>

A new semiconductor detector of neutron radiation based on a TIInSe₂ crystal has been investigated. The detector is produced from a homogeneous semiconductor sample with two electric contacts and operates in an integrating mode. It is shown that, owing to its high sensitivity (～10^?13 A/(neutron cm^?2 s^?1)) and small size (the volume of the sensitive crystal element is ～7 mm³), the detector is capable of monitoring spatial, time, and intensity distributions of γ rays and neutrons in pulse research reactors.     

Detection of neutrons and γ rays by a xenon pulsed ionization chamber

The applicability of a xenon γ-ray spectrometer based on a high-pressure (50 atm) xenon cylindrical ionization chamber to thermal neutron detection is discussed. The reaction of radiative capture of thermal neutron capture ¹³¹Xe(n, γ)¹³²Xe* followed by emission of 668-keV γ rays detectable by the spectrometer is used. The response of the xenon spectrometer with a sensitive volume of 0.2 L is analyzed. The measured thermal neutron detection efficiency is 0.08%. The advantage of the detector is its capability of simultaneously detecting both thermal neutrons and γ rays, which allows precise and high-efficiency identification of radioactive and fissile materials.     

A method for decreasing the loading on scintillation channels in facilities with pulsed neutron sources

A method is proposed for decreasing the loading on scintillation channels in nuclear material detection and monitoring facilities comprising pulsed neutron sources, neutron moderators, and scintillators with a system for pulse shape discrimination between neutrons and photons. This method is based on the use of composite scintillators containing cylindrical shells of a thermal-neutron absorbing material. Selecting the sizes of zones in a composite scintillator and the absorber type (cadmium and lithium carbonate with different 6 Li content), it is possible to considerably increase the decay time constant for thermal neutrons in a composite scintillator and thereby reduce its load as compared to a homogeneous scintillator over the same time period after a pulse from the neutron source. The sizes of the scintillator component parts and the absorber material are optimized, which provides a means for decreasing the load on the scintillation channel several-fold while maintaining constant detection efficiency for fast fission neutrons. The capabilities of this method for decreasing the load are demonstrated by the example of the operational prototype of the fissile material detection and monitoring facility with a graphite moderator and LS-13 scintillators. The efficiency of the facility used in this method is compared to that of a facility with a deuterium-containing scintillator, in which no radiative capture photons are produced.     

A one-dimensional position-sensitive detector for thermal neutrons

A one-dimensional position-sensitive detector of thermal neutrons has been developed to equip high-efficiency neutron spectrometers at the ИБР-2 research reactor. The detector is based on a multiwire proportional chamber filled with a mixture of ³He + CF₄ and has an active area of 200 × 80 mm and a spatial resolution of 2 mm. The detector has been used to good effect in the REFLEX and HRFD spectrometers of the ИБР-2 reactor, as well as in the diffraction facility of the ИВВ-2M research reactor (Zarechnyi, Russia).     

A neutron tomograph at the IR-8 reactor of the National Research Centre Kurchatov Institute

A transmission neutron tomograph developed by the National Research Centre Kurchatov Institute is described. The tomograph is located at the monochromatic neutron beam of the fifth horizontal channel of the IR-8 research reactor. The neutron wavelength is 1.56 Å, the beam cross section is 50 × 40 mm², the field of view of the CCD-based detector system is 93 × 62 mm², and the spatial resolution at the sample position is ～400 μm. The internal structure of samples having different origin has been investigated.     

Effect of neutron irradiation on the electrodes of a vacuum photoemission detector

The effect of neutron irradiation on Ta-Be photocathodes of a vacuum photoemission detector (VPD) has been investigated. The VPD has been designed for tomography of plasmas using thermal X-ray radiation on the ITER international tokamak reactor. The exposure of VPD electrode samples to neutrons with a fluence of 1.6 × 10¹⁹ neutrons/cm² (E > 0.1 MeV) is shown to change the relative concentration of Ta and Be in the surface layer. As a result, the detector sensitivity in the DT operating mode of the ITER is inevitably altered. Some recommendations concerning selection of materials for the VPD electrodes are presented. The conclusion is drawn that sputtering by thermonuclear neutrons in the ITER may lead to deposition of a conductive film on the insulator surface and that a special shape of insulators must be therefore used to avoid formation of such a coating.     

Testing the neutron attenuator based on <Superscript>6</Superscript>LiH for γ-ray diagnostics of plasmas in the JET tokamak

A ⁶LiH attenuator of a neutron flux incident on a detector is used to reduce the γ-ray background induced by neutrons in the detector material. This attenuator has been tested during experiments with deuterium (DD) plasmas on the JET tokamak. A specimen of the neutron attenuator with dimensions of ?30 × 300 mm has been developed by the Russian Academy of Sciences’ Ioffe Physico-Technical Institute and inserted into a vertical collimator used for γ spectrometry of plasmas. To compare γ-ray spectra recorded with and without the ⁶LiH attenuator being mounted, identical discharges with heating of the DD plasma by a neutral particle beam have been selected. For γ rays with energies of <3 MeV, which are induced by neutrons in the detector material, the suppression factor is found to be ～100. A low attenuation (～2) observed at energies of >3 MeV can be attributed to the transparency of the ⁶LiH attenuator for γ rays. This portion of the spectrum is due to γ radiation of the plasma and γ rays induced by neutrons in the constructional materials of the tokamak. To estimate the efficiency of the ⁶LiH attenuators as a mandatory component of the ITER γ-ray diagnostic system, it is necessary that measurements be taken in deuterium-tritium (DT) discharges.     

An experimental setup for studying neutron-neutron final state interaction on the neutron channel of the Moscow Meson Factory

A setup for measuring the singlet nn-scattering length in the n + d → p + n + n reaction is described. It is composed of a neutron hodoscope with an angular aperture of 12° and a scintillation detector for protons escaping at an angle of 90° with the beam direction. The exit angles and the energies of a proton and both neutrons are measured. The neutron energies are measured using the time-of-flight method. At a time resolution of ∼0.6 ns and a flight base of ∼5.5 m, the accuracy in measuring the neutron energy is ∼1% at an energy of ∼15 MeV. The dependence of the reaction yield on the relative energy of two neutrons is investigated. The neutron-neutron final-state interaction manifests itself as a peak in this distribution.     

A sectioned spectrometer of fast neutrons

Development of a capture gated spectrometer on the basis of a liquid organic scintillator doped with enriched ⁶Li is discussed. Particular interest is evoked by the good pulse height resolution of the spectrometer for 14-MeV neutrons, which is expected to be very high, ～10–15%. This resolution is attained by compensating for the nonlinearity of the light yield in the scintillator owing to the use of separate optically isolated sections, which independently detect scintillations from each recoil proton. The detector is sensitive to fluence rates ranging from 10^?4 to 10² cm^?2 s^?1 above a threshold of 500 keV under conditions of uncorrelated γ-ray background at a level of up to 10² s^?1 (E > 100 keV). A pilot model of the detector based on a scintillator without a lithium dopant has been produced and tested. The detector efficiency is governed by the scintillator volume (～1.2 l); for 3-MeV neutrons, its value is 0.2–0.5%. The response of the pilot detector to neutrons from a Pu-α-Be source with energies of up to 10 MeV has been measured. Initial testing indicates a low threshold at an ～600-keV energy of a recoil proton. A good spectral response is obtained using the criterion that three optical sections of the detector operate at a time. This spectrometer can find application in low-background experiments in basic physics research, as well as in space research and nuclear medicine for measuring the parameters of the neutron flux.     

A method for measuring the energy spectrum of neutrons with energies of 1–15 MeV

The characteristics of the detector prototype for 1–15 MeV neutrons are described. The prototype is a full absorption detector consisting of interlaced plastic scintillators and ⁶Li doped glasses. A neutron incident on the detector deposits all its energy in the plastic scintillator, is moderated to thermal energies, and detected in the lithium glass. The measured time of complete neutron moderation is ～60 μs. Recording two signals in this time interval from the first event of neutron scattering in the plastic scintillator and from the neutron absorption by a lithium atom in the glass, it is possible to effectively suppress background thermal neutrons and γ rays and, therefore, detect low-intensity neutron sources. Owing to the proposed detector design, the direction toward the neutron source can be determined.     

A light-emitting diode monitoring system of the PHOS photon spectrometer in the ALICE experiment on the large hadron collider

A light-emitting diode (LED) monitoring system of the PHOS photon spectrometer in the ALICE experiment on the CERN large hadron collider is described. The spectrometer includes three modules in the form of 64 × 56 matrices consisting of plumbum tungstate (PWO) crystals. As test light signal sources, Kingbright L934SCC superbright green light-emitting diodes with an individual instrumental regulation of light flash intensities in each channel of the spectrometer are used. The system ensures adjustment and monitoring of the electronics at the stage of preparing for the physical trigger of the PHOS modules and is intended to perform special test measurements with the spectrometer without using high-energy particles. In addition, in the course of the experiment, it allows one to promptly monitor each channel of the spectrometer and keep track of temperature variations of the light yield of the PWO crystals. In this case, the long-term relative channel monitoring stability is ensured at a 1.2 × 10⁻³ level.     

Determination of Linear Attenuation Coefficients of Materials by Using Timing Method

Abstract

In this work, gamma-ray linear attenuation coefficients of aluminum (Al) and lead (Pb) materials were determined by using timing method. The used setup is different from the conventional ones. The goal of the presented setup is the fact that it is used the timing technique. The detection system is composed of a 3″ × 3″ NaI(Tl) inorganic scintillation detector and related equipment together with ¹³⁷Cs and ⁶⁰Co radioactive sources. Obtained results are in good agreement with each other.     

Slow-neutron detector based on thin CVD diamond film

A slow-neutron detector based on thin CVD diamond film is discussed. A deep graphitized layer in the diamond film acts as one of the electrodes in the detector. The detector demonstrates low sensitivity to γ radiation, at the background level. The detector is tested with a laboratory neutron source based on the isotope ²⁵²Cf in a moderator. Slow neutrons are detected by means of the boron isotope ¹⁰В and lithium isotope ⁶Li. In both cases, slow neutrons are recorded with about 3% efficiency. The efficiency of slow-neutron recording is also assessed theoretically.     

Calibration of the neutron detectors for the cluster fusion experiment on the Texas Petawatt Laser

Three types of neutron detectors (plastic scintillation detectors, indium activation detectors, and CR-39 track detectors) were calibrated for the measurement of 2.45 MeV DD fusion neutron yields from the deuterium cluster fusion experiment on the Texas Petawatt Laser. A Cf-252 neutron source and 2.45 MeV fusion neutrons generated from laser-cluster interaction were used as neutron sources. The scintillation detectors were calibrated such that they can detect up to 10(8) DD fusion neutrons per shot in current mode under high electromagnetic pulse environments. Indium activation detectors successfully measured neutron yields as low as 10(4) per shot and up to 10(11) neutrons. The use of a Cf-252 neutron source allowed cross calibration of CR-39 and indium activation detectors at high neutron yields (～10(11)). The CR-39 detectors provided consistent measurements of the total neutron yield of Cf-252 when a modified detection efficiency of 4.6×10(-4) was used. The combined use of all three detectors allowed for a detection range of 10(4) to 10(11) neutrons per shot.     

Measuring the 14C isotope concentration in a liquid organic scintillator at a small-volume setup

A low-background scintillation setup situated in the Gran Sasso National Laboratory is described. The facility is composed of nine identical cells, each 2 L in volume. The ¹⁴C content of a PXE-based scintillator has been measured using this setup; the value obtained is R(¹⁴C/¹²C) = (12.6 ± 0.4) × 10^?18. This result can be used for comprehensive investigation of possible ¹⁴C production channels in organic scintillators.