Counting Detector Research Articles

A study on the optimization of the administered activity in myocardial perfusion SPECT imaging with Tc-99m according to body measurements

PurposeNuclear medicine myocardial perfusion imaging (MPI) in obese patients requires the administration of higher amounts of radioactivity, to compensate for the loss of photons due to the increased attenuation and scatter. The aim of the present study was to investigate whether an administered activity escalation protocol, proposed to yield the same effective dose irrespective of patient’s weight, can also lead to images of comparable count density for all patients. Materials and methods184 pharmacologically induced stress 99m-Tc MIBI and 99m-Tc tetrofosmin SPECT MPI examinations (123 males, 61 females) were included in this study. Body weight, BMI and chest circumference were collected for each patient. The administered activity was adjusted to body weight according to the IAEA protocol. Detector count rate (DCR) from the projection images and normal myocardial count rate (MCR) from the appropriately segmented reconstructed images, with and without attenuation correction, were recorded. ResultsNo statistically significant correlation was found between DCR and any anthropometric parameter. A weak correlation was observed between MCR and BMI and between MCR and chest circumference for male patients only, but even these correlations were eliminated after the application of attenuation correction. The anthropometric parameter that generally correlates more strongly with DCR/MBq and MCR/MBq was body weight for men and chest circumference for women. ConclusionThe IAEA activity escalation protocol used in this study leads to comparable image count densities, irrespective of body weight, for both men and women.

Low‐Resource Technique for Measurement of H+ and O+ in the Terrestrial Magnetosphere

AbstractMeasurement of O+ in the Earth's magnetosphere is important for monitoring and understanding the initiation and evolution of geomagnetic activity. During active times, O+ can be the most abundant ion in the magnetosphere. Furthermore, because O+ and H+ damage exposed spacecraft materials through different processes, measurement and prediction of O+ and H+ fluxes is critical for understanding cumulative damage effects to these materials resulting from the ambient plasma environment of a spacecraft. We describe a simple technique for quantitative, in situ measurement of O+ and H+ fluxes using ultrathin foils. This technique is a low‐resource addition to a standard electrostatic energy‐per‐charge analyzer followed by an array of detectors. H+ and O+ abundances up to a few tens of keV can be determined by comparison of counts in detectors having no ultrathin foil at the detector aperture, in which both H+ and O+ are detected, and adjacent detectors having a foil over the aperture of the appropriate thickness to stop the transmission of O+ but through which H+ can transit. We describe three techniques for implementing this method enabling differentiation of O+ and H+ in an instrument package significantly simpler than traditional mass spectrometers.

SAD phasing of XFEL data depends critically on the error model.

A nonlinear least-squares method for refining a parametric expression describing the estimated errors of reflection intensities in serial crystallographic (SX) data is presented. This approach, which is similar to that used in the rotation method of crystallographic data collection at synchrotrons, propagates error estimates from photon-counting statistics to the merged data. Here, it is demonstrated that the application of this approach to SX data provides better SAD phasing ability, enabling the autobuilding of a protein structure that had previously failed to be built. Estimating the error in the merged reflection intensities requires the understanding and propagation of all of the sources of error arising from the measurements. One type of error, which is well understood, is the counting error introduced when the detector counts X-ray photons. Thus, if other types of random errors (such as readout noise) as well as uncertainties in systematic corrections (such as from X-ray attenuation) are completely understood, they can be propagated along with the counting error, as appropriate. In practice, most software packages propagate as much error as they know how to model and then include error-adjustment terms that scale the error estimates until they explain the variance among the measurements. If this is performed carefully, then during SAD phasing likelihood-based approaches can make optimal use of these error estimates, increasing the chance of a successful structure solution. In serial crystallography, SAD phasing has remained challenging, with the few examples of de novo protein structure solution each requiring many thousands of diffraction patterns. Here, the effects of different methods of treating the error estimates are estimated and it is shown that using a parametric approach that includes terms proportional to the known experimental uncertainty, the reflection intensity and the squared reflection intensity to improve the error estimates can allow SAD phasing even from weak zinc anomalous signal.

Simulation of cosmic rays in the Earth’s atmosphere and interpretation of observed counts in an X-ray detector at balloon altitude near tropical region

The study of secondary particles produced by the cosmic-ray interaction in the Earth’s atmosphere is very crucial as these particles mainly constitute the background counts produced in the high-energy detectors at balloon and satellite altitudes. In the present work, we calculate the abundance of cosmic-ray generated secondary particles at various heights of the atmosphere by means of a Monte Carlo simulation and use this result to understand the background counts in our X-ray observations using balloon-borne instruments operating near the tropical latitude (geomagnetic latitude: ~14.50°N). For this purpose, we consider a 3D description of the atmospheric and geomagnetic field configurations surrounding the Earth, as well as the electromagnetic and nuclear interaction processes using Geant4 simulation toolkit. Subsequently, we use a realistic mass model description of the detector under consideration, to simulate the counts produced in the detector due to secondary cosmic-ray particles.

Hard X-ray Bremsstrahlung of relativistic Runaway Electrons in JET

One of the main requirements to the Disruption Mitigation System (DMS) in International Thermonuclear Experimental Reactor (ITER) is a reliable capability to avoid/suppress a detrimental runaway electron (RE) generation during disruptions. An understanding of the physics of RE is a key factor for design of ITER DMS with necessary properties on RE suppression. RE interacting with plasma particles and hitting the plasma-facing components (PFCs) produce a bremsstrahlung in MeV energy range (hard X-rays (HXR) and γ-rays) and photo-neutrons. Measurements of produced HXR/γ-rays and photo-neutrons provide detailed information on RE generation and serve as a main tool for runaway physics study in JET. This report presents recent progress in development of the JET diagnostic techniques for registering of the HXR/γ-rays emission and improvement of HXR data analysis methods for RE studies. The HXR spectra have been measured with the sets of HXR spectrometers. This data was numerically processed using special de-convolution procedure allowing a study of evolution of the RE Distribution Function (REDF). Maximal and mean energies of RE populations have been calculated. As well, the detection of spatial distribution of HXR sources in JET plasmas with the JET neutron/γ-rays profile monitor allowed the mapping of RE beams spatial evolution during RE plateaus. In order to increase the HXR/γ-rays diagnostic performance in future JET experiments, the vertical slow spectrometers will be replaced by high-speed LaBr3(Ce) spectrometers allowing measurements with counting rate up to 5*106 sec−1. Also spectrometer with tangential LoS will be replaced by a couple of LaBr3(Ce) and CeBr3 spectrometers. CsI(Tl) detectors in γ-cameras will be substituted by LaBr3(Ce) and CeBr3 crystals coupled with up-to-date SiPM light detectors, which allowed increasing the counting rate of the γ-camera detectors by an order of 10.

SIXTE: a generic X-ray instrument simulation toolkit

We give an overview of the SImulation of X-ray TElescopes (SIXTE) software package, a generic, mission-independent Monte Carlo simulation toolkit for X-ray astronomical instrumentation. The package is based on a modular approach for the source definition, the description of the optics, and the detector type such that new missions can be easily implemented. The targets to be simulated are stored in a flexible input format called SIMPUT. Based on this source definition, a sample of photons is produced and then propagated through the optics. In order to model the detection process, the software toolkit contains modules for various detector types, ranging from proportional counter and Si-based detectors, to more complex descriptions like transition edge sensor (TES) devices. The implementation of characteristic detector effects and a detailed modeling of the read-out process allow for representative simulations and therefore enable the analysis of characteristic features, such as for example pile-up, and their impact on observations. We present an overview of the implementation of SIXTE from the input source, the imaging, and the detection process, highlighting the modular approach taken by the SIXTE software package. In order to demonstrate the capabilities of the simulation software, we present a selection of representative applications, including the all-sky survey of eROSITA and a study of pile-up effects comparing the currently operating XMM-Newton with the planned Athena-WFI instrument. A simulation of a galaxy cluster with the Athena-X-IFU shows the capability of SIXTE to predict the expected performance of an observation for a complex source with a spatially varying spectrum and our current knowledge of the future instrument.

Combining Cherenkov and scintillation detector observations with simulations to deduce the nature of high-energy radiation excesses during thunderstorms

We present co-observations of three strong count-rate enhancements associated with thunderstorms observed over 17 April 2015 to 23 September 2015 by the High Altitude Water Cherenkov (HAWC) array, and a suite of small scintillation detectors comprising the Gamma-ray Observations During Overhead Thunderstorms (GODOT) instrument. Because the HAWC array is most sensitive to ionizing radiation at high energies ($g100\text{ }\text{ }\mathrm{MeV}$), and the small scintillation detectors are most sensitive to ionizing radiation at low energies ($3--20\text{ }\text{ }\mathrm{MeV}$), we investigate using the ratio of these detector counting rates variations to infer spectral characteristics of these enhancements, and understand the physics behind these thunderstorm accelerator mechanisms. We consider two extreme mechanisms that can produce these enhancements: a point source of relativistic runaway electron avalanches (RREA), and modification of the background cosmic-ray spectrum (MOS) from an electric field profile that is everywhere below the RREA threshold. We simulate the responses of HAWC and the GODOT $12.7\text{ }\text{ }\mathrm{cm}\ifmmode\times\else\texttimes\fi{}\ensuremath{\oslash}12.7\text{ }\text{ }\mathrm{cm}$ NaI(Tl) scintillator and show that their ratio can discern between the two models, and that the observed thunderstorm rate enhancements are incompatible with the spectra from a point source of RREA, but consistent with our model of MOS for thunderstorm potentials within the range of $\ensuremath{-}250$ to 250 MV.

Noise in boson sampling and the threshold of efficient classical simulatability

We study the quantum to classical transition in Boson Sampling by analysing how $N$-boson interference is affected by inevitable noise in an experimental setup. We adopt the Gaussian noise model of Kalai and Kindler for Boson Sampling and show that it appears from some realistic experimental imperfections. We reveal a connection between noise in Boson Sampling and partial distinguishability of bosons, which allows us to prove efficient classical simulatability of noisy no-collision Boson Sampling with finite noise amplitude $\epsilon$, i.e., $\epsilon = \Omega(1)$ as $N\to \infty$. On the other hand, using an equivalent representation of network noise as losses of bosons compensated by random (dark) counts of detectors, it is proven that for noise amplitude inversely proportional to total number of bosons, i.e., $\epsilon=O(1/N)$, noisy no-collision Boson Sampling is as hard to simulate classically as in the noiseless case. Moreover, the ratio of ``noise clicks" (lost bosons compensated by dark counts) to the total number of bosons $N$ vanishes as $N\to \infty$ for arbitrarily small noise amplitude, i.e., $\epsilon = o(1)$ as $N\to \infty$, hence, we conjecture that such a noisy Boson Sampling is also hard to simulate classically. The results significantly relax sufficient condition on noise in a network components, such as two-mode beam splitters, for classical hardness of experimental Boson Sampling.

A study of PFBR auxiliary neutron source strength activation and its variability with respect to the neutron spectrum and 123Sb capture cross section

In fast reactors, the inherent neutron source strength is often insufficient for monitoring the reactor start-up operation with ex-core detectors. To increase the subcritical neutron flux, an auxiliary neutron source subassembly (SSA) is generally used to overcome this problem. In this study, the estimated neutron source strength and detector count rate of an antimony–beryllium-based SSA are obtained using the deterministic transport code DORT and Monte Carlo calculations. Because the antimony activation rate is a critical parameter, its sensitivity to the capture cross section and neutron flux spectrum is studied. The reaction cross section sensitivity is studied by considering data from different evaluated nuclear data files. It is observed that, because of the variation in the cross sections from different evaluated nuclear data files, the values of the saturation gamma (> 1.67 MeV) activity and neutron strength predicted by ORIGEN2 lie within ± 2%. The obtained antimony activation rate and sensitivity to the neutron flux are partially validated by irradiating samples of antimony in the KAMINI reactor. The average one-group capture cross sections of bare and cadmium-covered 123Sb samples obtained by the ratio method are 4.0 and 1.78b, respectively. The results of the calculation predicting the activated neutron source strength as a function of operating time and sensitivity to the neutron spectrum in the irradiation region are also presented.

Investigation of the chance structure of the fission cross section of 238U by neutrons in energy range from 14 to 18 Mev using the delayed neutrons

In the present work, delayed neutrons are used for the investigation of the chance structure of the fission cross section. For this, time parameters of delayed neutron precursors emitted from the fission of 238U by neutrons with the energies from 14 to 18 MeV have been measured. The T(d,n) reaction was used as a neutron source. The experimental data have been processed to account the effect of degradation of detector counting rate in high intensity neutron flux and the effect of concomitant neutron source D(d,n) caused by implanted deuterium ions in neutron target. The data obtained based on the time parameters of delayed neutron precursors have been used in the analysis of the chance structure of the fission cross section of the 238U.

Measurements and Monte Carlo Simulations of 241Am Activities in Three Skull Phantoms: EURADOS-USTUR Collaboration.

An international intercomparison was organized by Working Group 7, Internal Dosimetry, of the European Radiation Dosimetry Group in collaboration with Working Group 6, Computational Dosimetry, for measurement and Monte Carlo simulation of Am in three skull phantoms. The main objectives of this combined exercise were (1) comparison of the results of counting efficiency in fixed positions over each head phantom using different germanium detector systems, (2) calculation of the activity of Am in the skulls, (3) comparison of Monte Carlo simulations with measurements (spectrum and counting efficiency), and (4) comparison of phantom performance. This initiative collected knowledge on equipment, detector arrangements, calibration procedures, and phantoms used around the world for in vivo monitoring of Am in exposed persons, as well as on the Monte Carlo skills and tools of participants. Three skull phantoms (BfS, USTUR, and CSR phantoms) were transported from Europe (10 laboratories) to North America (United States and Canada). The BfS skull was fabricated with real human bone artificially labeled with Am. The USTUR skull phantom was made from the US Transuranium and Uranium Registries whole-body donor (case 0102) who was contaminated due to an occupational intake of Am; one-half of the skull corresponds to real contaminated bone, the other half is real human bone from a noncontaminated person. Finally, the CSR phantom was fabricated as a simple hemisphere of equivalent bone and tissue material. The three phantoms differ in weight, size, and shape, which made them suitable for an efficiency study. Based on their own skull calibration, the participants calculated the activity in the three European Radiation Dosimetry Group head phantoms. The Monte Carlo intercomparison was organized in parallel with the measurement exercise using the voxel representations of the three physical phantoms; there were 16 participants. Three tasks were identified with increasing difficulty: (1) Monte Carlo simulation of the simple CSR hemisphere and the Helmholz Zentrum München high-purity germanium detector for calculating the counting efficiency for the 59.54 keV photons of Am, in established measurement geometry; (2) Monte Carlo simulation of particular measurement geometries using the BfS and USTUR voxel phantoms and the Helmholz Zentrum München high-purity germanium detector detector; and (3) application of Monte Carlo methodology to calculate the calibration factor of each participant for the detector system and counting geometry (single or multidetector arrangement) to be used for monitoring a person in each in vivo facility, using complex skull phantoms. The results of both exercises resulted in the conclusion that none of the three available head phantoms is appropriate as a reference phantom for the calibration of germanium detection systems for measuring Am in exposed adult persons. The main reasons for this are: (1) lack of homogeneous activity distribution in the bone material, or (2) inadequate shape/size for simulating an adult skull. Good agreement was found between Monte Carlo results and measurements, which supports Monte Carlo calibration of body counters as an alternative method when appropriate physical phantoms are not available and the detector and source are well known.

A water tank muon spectrometer for the characterization of low energy atmospheric muons

Abstract In this work, a water tank muon spectrometer was designed, assembled and operated to measure the energy distribution of low energy atmospheric muon flux induced by cosmic-rays at sea level in the energy range 100–500 MeV. The principle of this experiment is to use water as muon moderator inserted between two coincidence detectors to select the cutoff energy below which muons can no longer be detected. The differential and integral muon spectra are then derived from successive measurements by varying the liquid height within the water tank. The instrument was entirely characterized and modeled in terms of detector efficiency, cutoff energy and counting rate. Experimental data are reported for the energy distribution of muon flux at sea level (43 ∘ N of latitude) and finally compared with literature survey.

TRIFIC: The TRIUMF Fast Ion Counter

Abstract The TRIUMF Fast Ion Counter (TRIFIC) is a tilted-grid gas counter detector for identifying the impurities in radioactive ion beams (RIBs). Placed at zero degrees downstream of a primary reaction target at the TRIUMF ISAC-II facility, TRIFIC provides accurate Z identification of beam species on an event-by-event basis at a rate of up to 5 × 1 0 5 particles per second and functions as a beam composition monitor at rates up to 5 × 1 0 7 particles per second. With this additional level of diagnostics, RIB experiments at TRIUMF are able to reach levels of sensitivity not previously possible. Details regarding the construction and instrumentation of TRIFIC as well as results from the commissioning of the detector are presented.

Preanalysis of Neutron Activation Measurements in Shielding Penetrations at JET

In the present work, the preanalysis of activation foil experiments to determine neutron fluence rates along JET hall ducts and labyrinths is discussed. Simulations were performed using computational codes MCNPX and FISPACT-II and a detailed model of the JET hall, including the tokamak, biological shield and penetrations. The induced activity and detector count rate were predicted for activation foils placed at selected positions within the JET hall for Deuterium-Deuterium and Deuterium-Tritium JET plasma sources. The results of the calculations showed that satisfactory counting statistics can be obtained with the use of activation detectors and therefore activation analysis offers an unbiased and robust cross-benchmarking tool for comparison against other experimental and computation techniques applied in neutron streaming studies at JET.

The development of solar neutron search method with PAMELA neutron detector

With the help of the PAMELA magnetic spectrometer continuous measurements of the cosmic-ray fluxes were carried out on board the RESURS-DK1 satellite during 10 years from the end of the 23rd solar activity cycle to the minimum of 24 cycle. The satellite was launched on June 15, 2006 into an elliptical orbit of 350-610 km height. The background channel of the neutron detector which was the part of the spectrometer and served for improving the separation between electrons and protons detected in the calorimeter. Simultaneously it was possible to monitor neutron fluxes in orbit. The technique for processing neutron detector data was developed to reduce the fluctuations of their counting rates associated with instrumental effects. The analysis of the latitudinal dependences of the neutron detector counting rates was donefor various geomagnetic cut-off intervals from 0 to 16 GV during the time from 2006 to 2016. The new technique of data handling was applied for 29 solar proton events. Time dependencies obtained revealed the number of features that require further analysis.

Measurement of incomplete fusion cross sections in Li6,7+U238 reactions

Background: Incomplete fusion (ICF) in reactions involving weakly bound projectiles is understood to play an important role in enhancing the ratio of asymmetric to symmetric fission at $E\ensuremath{\le}{V}_{b}$, widening the fission fragment folding angle distribution at $E\ensuremath{\le}{V}_{b}$ and suppressing the complete fusion (CF) cross section at $Eg{V}_{b}$. Experimental cross sections for individual ICF channels are necessary to obtain quantitative estimates of the above effects.Purpose: Measurement of the cross sections for individual transfer-induced or ICF-fission channels in $^{6,7}\mathrm{Li}+^{238}\mathrm{U}$ reactions to explain quantitatively the difference in the ratio of asymmetric to symmetric fission for total fission and CF fission.Methods: Triple coincidence measurement of two fission fragments and one light charged projectilelike fragment (PLF) is carried out using two multiwire proportional counter (MWPC) detectors and an array of CSI(Tl) scintillation detectors at energies near the Coulomb barrier. By calculating the efficiency of the detectors by Monte Carlo simulation and fission probability by GEF code, the angle-integrated ICF cross sections corresponding to p, d, t, and $\ensuremath{\alpha}$ emission are obtained. Mass distributions for total fission are calculated by adding the distributions for CF fission and all ICF fissions with weight factors proportional to the measured cross sections.Results: ICF cross sections corresponding to $\ensuremath{\alpha}$ emission are found to be the highest in both the reactions. The relative contribution of ICF to total fusion at the lowest measured energy is found to be $\ensuremath{\approx}70%$ and it decreases with increasing projectile energy, consistent with the systematics of several reactions involving the same weakly bound projectiles. The simulated mass distributions for total fission are found to reproduce the experimental mass distributions.Conclusions: Deuteron (triton) capture is observed to be the major ICF channel in the reaction involving $^{6}\mathrm{Li}\phantom{\rule{0.28em}{0ex}}(^{7}\mathrm{Li})$ projectile. The ratio of the sum of ICF to total fusion cross section for the present systems are consistent with the systematics. The difference in the ratio of asymmetric to symmetric fission between total fission and CF fission is explained quantitatively.

The GlueX Start Counter Detector

The design, simulation, fabrication, calibration, and performance of the GlueX Start Counter detector are described. The Start Counter was designed to operate at integrated rates of up to 9 MHz with a timing resolution in the range of 500 to 825 ps (FWHM). The Start Counter provides excellent solid angle coverage, a high degree of segmentation for background rejection, and can be utilized in the level 1 trigger for the experiment. It consists of a cylindrical array of 30 thin scintillators with pointed ends that bend towards the beam line at the downstream end. Magnetic field insensitive silicon photomultiplier detectors were used as the light sensors.

Polarization-entangled photon pairs from a single molecule

Photonic entanglement is one of the key resources in modern quantum optics. It opens the door to schemes such as quantum communication, quantum teleportation, and quantum-enhanced precision sensing. Sources based on parametric down-conversion or cascaded decays in atomic and atom-like emitters are limited because of their weak interaction with stationary qubits. This is due to their commonly broadband emission. Furthermore, these sources are commonly in the near-infrared such that quantum emitters in the blue spectral region, such as ions or many defect centers, cannot be addressed. Here, we present a sodium-resonant (589.0 nm) and narrow-band (14 MHz) degenerate entanglement source based on a single molecule. A beam-splitter renders two independently emitted photons into a polarization-entangled state. The quality of the entangled photon pairs is verified by the violation of Bell’s inequality. We measure a Bell parameter of S=2.26±0.05. This attests that the detected photon pairs exceed the classical limit; it is reconfirmed by quantum-state tomography and an analysis of the raw detector counts, which result in a value of S=2.24±0.12. The tomography shows fidelity of 82% to a maximally entangled Bell state. This work opens the route to background-free solid-state entanglement sources which surpass the probabilistic nature of the commonly used sources and are free from unwanted multi-photon events. The source is ideal for combination with stationary qubits such as atoms, ions, quantum dots, or defect centers.

Preface to measurement, specification and forecasting of the Solar Energetic Particle (SEP) environment and Ground Level Enhancements (GLEs)

The Sun emits energetic particles following eruptive events such as solar flares and Coronal Mass Ejections (CMEs). Solar Energetic Particles (SEPs) arrive in bursts known as Solar Particle Events (SPEs), which penetrate into the Earth’s magnetosphere. SEPs with large enough energy induce a complicated atmospheric cascade, which secondary particles lead to an enhancement of count rate of ground-based detectors e.g. Neutron Monitors (NMs). This class of SEPs is therefore referred as Ground Level Enhancements (GLEs). The characterisation of the high-energy SEPs environment with corresponding space weather effects is important for space flights, aviation, and satellite industry. In this topical issue recent developments, addressing important user needs in the space radiation environment domain are published. Some articles are relevant to the specification of the SEP environment whilst others focus on space weather prediction of SEP fluxes. Catalogues based on measurement and processing of SEPs including ground-based data, and modelling of aircrew radiation exposure during major events are also presented.

Research of the Single Crystal and Multilayer Composite Detectors Response Under Irradiation by Fast Neutrons

The object of this work was to study the response of the detectors based on the oxide scintillators under irradiation by a flux of fast neutrons from 239Pu-Be source by counting photomultiplier tube pulses. In the process of the research the counting efficiency of the detectors was measured in units of (pulse×s-1×cm-2)/(neutron×s-1×cm-2) for single-crystal and multilayer composite detectors ZWO (ZnWO4), CWO (CdWO4), BGO (Bi4Ge3O12, composite). The measured response for ZWO detector was ~ 64 pulse/neutron, for CWO ~ 36 pulse/neutron, for BGO ~ 0.44 pulse/neutron. The detectors response was registered by a fast preamplifier with the operation speed of up to 500 MHz, based on high-speed operational amplifiers with voltage feedback. The statistical error of measurement for the neutron registration efficiency by the broadband channel made 7% for the detectors with the effective thickness of ~ 40-50 mm, which is due to the spherical geometry of the experiment. The formation of the detector response is affected by the following parameters of neutron reactions: cross section of inelastic and resonant scattering of scintillator nuclei, density of composite nuclei levels, resonance region width, lifetimes of long-lived states and their number. The measured values of the counting efficiency of fast neutrons registration are accounted for the fact that the inelastic scattering reaction for some nuclei is the starting point that triggers the cascade process of the nuclear states discharge. The registration of the cascade of the discharge gamma-quanta, ranging from nanoseconds to a few microseconds, causes an increase in the detector counting efficiency and, as a consequence, an increase in the detector sensitivity to neutron detection. The observed increase in the counting efficiency of secondary gamma quanta is realized when the neutrons are slowed down in the detectors having sufficiently noticeable thickness and appropriate isotopic composition.