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.     

Suppression of pileup events by pulse shape discrimination using the Gatti filter

An algorithm is proposed that provides reliable discrimination between neutrons and γ rays in mixed fields and reduces the influence of γ-ray pileups at a slight complication of the hardware and the algorithms. The algorithm uses a stepwise Gatti filter for two detection periods (a short period of several hundreds of nanoseconds and a long period of a few microseconds) for the same event. Using mathematical simulation of 12000 neutron and γ-ray events, it has been demonstrated that at particle energies of ~128 keV in the electron equivalent (ee), the algorithm suppresses γ-ray pileups on a level of 10⁴ with a neutron loss of only approximately 1%. Due to the proposed algorithm, the counting ability is of the order of 10⁵ events/s.     

Application of a position-sensitive scintillation spectrometer for measuring the resonance absorption of γ rays in nitrogen-containing substances

A single-coordinate scintillation spectrometer for measuring the γ-ray resonance absorption in nitrogen-containing samples is described. The energy and coordinate characteristics of the spectrometer were measured. The results of experiments on the resonance absorption of γ radiation with an energy of 9.17 MeV in a carbamide sample are presented.     

Fusion product diagnostics planned for Large Helical Device deuterium experiment

Deuterium experiment on the Large Helical Device (LHD) is now being planned at the National Institute for Fusion Science. The fusion product diagnostics systems currently considered for installation on LHD are described in this paper. The systems will include a time-resolved neutron yield monitor based on neutron gas counters, a time-integrated neutron yield monitor based on activation techniques, a multicollimator scintillation detector array for diagnosing spatial distribution of neutron emission rate, 2.5 MeV neutron spectrometer, 14 MeV neutron counter, and prompt γ-ray diagnostics.     

Scintillation γ spectrometers for use at nuclear power plants (review)

In this review, it is shown that out of the 300 scintillators synthesized to date only LaBr₃:Ce, CeBr₃, YAlO₃: Ce, and CsI:Tl crystals with the corresponding silicon photosensors (SiPSs) can be used as detectors in industrial γ-ray spectrometers intended for nuclear power plants. They are superior in their energy resolution and their resistance to mechanical and electromagnetic effects to spectrometers used today with a NaI:Tl crystal and a photomultiplier tube (PMT). A p–i–n photodiode (PD), an avalanche photodiode (APD), and a silicon photomultiplier (SiPM) are promising SiPSs. The properties of various assemblies of listed scintillators and photosensors are analyzed. A PD matches well with any scintillator. A spectrometer does not require LED stabilization of the scale, but its noise level must be reduced by selective PD cooling and the use of a light guide for coupling a massive scintillator and a SiPS with a small area of its sensitive surface. A spectrometer with an APD does not require photosensor cooling; however, LED stabilization of its energy scale is necessary. Application of an SiPM can rule out the use of a light concentrator (which is important for large CsI:Tl scintillators) and selective cooling, but this introduces nonlinearity at a short decay time and a high light yield in the scintillator (LaBr₃:Ce and CeBr₃) and also calls for an LED stabilization system for the spectrometer. The prospects for the development and application of new scintillation γ-ray spectrometers are discussed in this review.     

Characteristics of neutron and gamma radiation in the core of the ΦC-1-4.37.P critical assembly

The characteristics of neutron and γ-ray fields (spectrum, flux density, average energy, cross sections of 23 nuclear reactions, and γ-ray dose rate) and the γ-ray field in the core of the ΦC-1-4.37.P critical assembly of the ΦC-1M critical bench are determined. The results of comparing the characteristics of the neutron fields of the ΦC-1-4.37.P critical assembly and analogous reactors are presented.     

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.     

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.     

An adaptive γ-ray spectrometer with a high event processing rate

A fast γ-ray spectrometer adaptable to the scintillator type is described. This spectrometer is capable of processing a γ-ray energy spectrum (with a resolution of <4% in the energy range from 20 keV to 10 MeV) in a sequence of time intervals in the real-time mode at a counting rate of up to 10⁶ cps. Digitization of the detector signals by a 14-bit ADC with a sampling rate of 64 MHz and real-time data stream processing are used to separate overlapping events and correctly generate energy spectra.     

Energy resolution of gamma-ray spectroscopy of JET plasmas with a LaBr3 scintillator detector and digital data acquisition

A new high efficiency, high resolution, fast γ-ray spectrometer was recently installed at the JET tokamak. The spectrometer is based on a LaBr3(Ce) scintillator coupled to a photomultiplier tube. A digital data acquisition system is used to allow spectrometry with event rates in excess of 1 MHz expected in future JET DT plasmas. However, at the lower rates typical of present day experiments, digitization can degrade the energy resolution of the system, depending on the algorithms used for extracting pulse height information from the digitized pulses. In this paper, the digital and analog spectrometry methods were compared for different experimental conditions. An algorithm based on pulse shape fitting was developed, providing energy resolution equivalent to the traditional analog spectrometry method.     

A differential time-of-flight spectrometer of very slow neutrons

A time-of-flight spectrometer of neutrons with energies of 0.05–2.50 μeV is described. This spectrometer has been tested by measuring the total and differential neutron cross sections for a number of materials—aluminum, copper, silicon, zirconium, polyethylene, ⁶LiF, and fluoropolymers—that are essential for experiments in physics of ultracold neutrons.     

Testing a fiber-optic ionizing-radiation detector

A fiber-optic ionizing-radiation detector is composed of a scintillation sensor, an optical fiber, and a photodetector. Due to the miniature size and the high radiation resistance, the detector is capable of measuring the characteristics of powerful neutron and γ-ray fields with a high spatial resolution. A prototype of the detector has been tested using a ⁶⁰Co γ-ray source with a dose rate as great as 200 R/S. The dynamic range of dose measurements is no less than 10⁵. The detector signal is linearly dependent on the radiation dose rate. The ratio of the useful signal to the background due to radioluminescence of the optical fiber is presented for different types of scintillators.     

Development of a technique for high-speed γ-ray spectrometry

A technique for high-speed γ-ray spectrometry was developed for γ-ray diagnostic experiments on the ITER tokamak and tested at the Ioffe Physico-Technical Institute on the cyclotron and the GLOBUS-M and TUMAN-3M tokamaks. This technique was used to upgrade the γ-ray diagnostic system of the JET tokamak. It was shown by the tests that the new technique compares favorably to the traditional one in that it allows the limiting counting rate of the spectrometer to be increased by at least an order of magnitude without noticeable deterioration of its energy resolution.     

A time-of-flight mass spectrometer for monitoring the inhalational anesthesia concentration in the real-time mode

The use of a medical mass spectrometer for measuring the concentration of the gas mixture components in the breathing circuit of an inhalational anesthesia machine in the real-time mode is described. The resolution of the mass spectrometer is M/ΔM = 200, and the detection threshold in terms of the partial pressure of the analyzed gases is 2 × 10^?12 mbar. The mass spectrometer is capable of measuring the volumetric content of CO₂, O₂, and inhalational anesthetic sevoflurane. The respiratory coefficient (CO₂/O₂) was measured during anesthesia to estimate the patient’s stress reaction to a surgical injury.     

Compact mass spectrometer on permanent magnets

Preliminary results of development and testing of prototype compact mass spectrometer on permanent magnets are presented. The feature of the mass spectrometer is the ability to record mass spectra by mass scanning due to partial shunting of a magnetic flux in the gap of the mass analyzer. Ion-optical scheme of the mass analyzer has an ions deflection angle φ _m = 120° and the radius of the central trajectory r _m = 60 mm. The device can record mass range from 11 to 23 amu, with the accelerating voltage of 1 kV and the resolution of about 200. Inner volume of the mass analyzer chamber with the ion pump is about 500 cm³. Dimensions of the mass spectrometer together with electronic unit (height/length/width)—230 × 450 × 450 mm. The power consumption is not exceeding 60 W, in standby mode (the mode to maintain a high vacuum) is less than 10 W. The weight is 30 kg. The mass spectrometer is designed for educational purposes, however, it can be used as the basis to develop devices for isotopic analysis of the light chemical elements in medicine, geology, agricultural chemistry.     

Development of neutron spectrometer toward deuterium plasma diagnostics in LHD

Neutron spectrometer based on coincident counting of associated particles has been developed for deuterium plasma diagnostics on Large Helical Device (LHD) at the National Institute for Fusion Science. Efficient detection of 2.5 MeV neutron with high energy resolution would be achievable by coincident detection of a scattered neutron and a recoiled proton associated with an elastic scattering of incident neutron in a plastic scintillator as a radiator. The calculated neutron spectra from deuterium plasma heated by neutral beam injection indicate that the energy resolution of better than 7% is required for the spectrometer to evaluate energetic deuterium confinement. By using a prototype of the proposed spectrometer, the energy resolution of 6.3% and the detection efficiency of 3.3×10(-7)?count/neutron were experimentally demonstrated for 2.5 MeV monoenergetic neutron, respectively.     

A Wideband spectrometer for NMR studies

The design of a wideband decimeter-wave (200–900 MHz) spectrometer with a magnetic induction of up to ∼10 T is described. This spectrometer is intended for studying electronic-nuclear oscillations in antiferromagnets at low temperatures (4.2−1.3 K). Critical field H _c = 2.5 ± 0.3 T of a reorientation transition in a noncollinear antiferromagnet Mn₃Al₂Ge₃O₁₂ at temperature T ≈ 1.3 K was determined from a ⁵⁵Mn²⁺ NMR spectrum.     

A prototype of the multipurpose space-based fourier spectrometer

A prototype of the MTsFS multipurpose Fourier transform spectrometer designed for remote sounding of the Earth??s surface is described. The interferometer that is a part of the spectrometer is based on the double-pendulum scheme and has hollow retroreflectors with an aperture of 2.5??. A 4 × 4 cryogenic CdHgTe array and a pyroelectric detector are used as radiation sensors. The interferometer is equipped with a system for scanning transversely to the flight path with the compensation for image smearing caused by spacecraft movement.     

A spectrometer of polarized neutrons

A polarized neutron spectrometer intended for studies of interactions of nuclei and condensed matter with polarized neutrons with energies in the range from thermal energies to several electron volts was designed at the IBR-2 pulsed reactor (JINR, Dubna). Diffraction on magnetized Co(92%)–Fe(8%) single crystals was used to polarize neutrons and analyze the polarization. The attained neutron polarization was ∼95% within the entire energy range.     

Spatial resolution of the multistep avalanche chambers

The spatial resolution of the multistep avalanche chambers is considered. The intrinsic spatial resolution (the full width at half-maximum) of these chambers is 260 μm. The influence of the signal amplitude on the spatial resolution of the chambers under irradiation by β particles is investigated. By analyzing the signal amplitude and selectively measuring the coordinates, or by estimating the signal amplitude and its contribution to the reconstructed image, it will be possible to raise the spatial resolution twofold to 0.5 and 1.0 mm for isotropic radiation of ¹⁴C and ³²P isotopes, respectively. In addition, the spatial resolution can be improved significantly when electrons escaping from solid-state neutron or γ-ray converters are detected.