Калибровка нейтронных счетчиков токамака Глобус-М2

The paper discusses the results of the calibration of two corona neutron counters used to measure the total neutron yield from the plasma of the Globus-M2 tokamak. The calibration was carried out in the experimental hall of the Globus-M2 facility using an AmBe source. During the calibration, the source moved uniformly around the central solenoid in the equatorial plane of the vacuum chamber, and one of the detectors was gradually moved away from the tokamak along a line with a constant toroidal angle. The values of the calibration coefficient obtained depending on the distance of the detector from the tokamak axis are presented. The calibration technique made it possible to separate in the detector signal the contributions from the direct neutron flux emitted by the plasma and from the flux of neutrons scattered on the elements of the experimental hall.

Determination of Monitor Doses in Neutron Therapy Using the U-120 Cyclotron

Purpose Analyze the various methods for determining the monitor doses in neutron therapy using the U-120 cyclotron and to choose the monitoring method that provides the highest accuracy in dose delivery to the tumor. Material and methods The distributions of the absorbed dose of the therapeutic beam from the U-120 cyclotron were measured in a tissue-equivalent medium using the differential method, in which two ionization chambers with different sensitivity to neutron radiation were used. A comparison of radiation effects on tissues using various techniques of determining the monitor doses was made. The linear-quadratic model was used to assess responses to ionizing radiation. Results Dosimetry studies revealed that the therapeutic beam of the U-120 cyclotron contains concomitant gamma radiation, the contribution of which to the total neutron-photon dose increases with increasing depth of the irradiated medium. The presence of gamma radiation in the neutron beam dictate the need to find the correct method for monitoring neutron therapy. A comparison of radiation effects on the tumor tissue using different techniques of determining the monitor doses was made. It was found that at equal neutron-photon doses, the neutron dose in the tumor changed depending on its depth. It can lead to an incorrect conclusion about the effectiveness of neutron therapy depending on a single dose as well as in relation to various dose fractionation schedules. Conclusion The analysis of the results obtained showed that the problem can be most accurately solved using a technique in which the monitor coefficient and monitor doses are determined from the distribution of the neutron dose, taking into account the contribution of the gamma radiation dose to the total neutron-photon dose.

Assessment of neutrons from secondary cosmic rays at mountain altitudes – Geant4 simulations of environmental parameters including soil moisture and snow cover

Ground-based measurements of neutrons from secondary cosmic rays are affected by environmental parameters, particularly hydrogen content in soil. To investigate the impact of these parameters, in particular snow cover, Geant4 Monte Carlo simulations were carried out. In a previous study the model used for the Geant4 Monte Carlo simulations was already validated by measurements performed with an extended-range Bonner sphere spectrometer (ERBSS) at Zugspitze, Germany, and at Jungfraujoch, Switzerland. In the present study a sensitivity analysis including different environmental parameters (i.e. slope of mountain, snow height, and soil moisture) and their influence on the flux of neutrons from secondary cosmic rays was performed with Geant4. The results are compared with ERBSS measurements performed in 2018 at the Environmental Research Station Schneefernerhaus located at the Zugspitze, Germany. It is shown that the slope of the Zugspitze mountain reduces the neutron flux from secondary cosmic rays between about 25 % and 50 % as compared to a horizontal surface, depending on neutron energy and snow cover. An increasing height of snow cover, simulated as snow water equivalent (SWE), reduces the total neutron flux exponentially down to a factor of about 2.5 as compared to soil without any snow cover, with a saturation for snow heights greater than 10 to 15 cm SWE, depending on neutron energy. Based on count rates measured with the individual spheres of the ERBSS, SWE values were deduced for the whole year 2018. Specifically, mean SWE values deduced for the winter months (January to March) are between 6.7 and 10.1 cm or more, while those for the summer months (July to September) are between 2.1 and 3.6 cm. Soil moisture of 5 % water mass fraction in limestone leads to a decrease of the total neutron flux by about 35 % compared to dry limestone. It is concluded that the measurement of neutrons from secondary cosmic radiation can be used to gain information on the height of snow cover and its seasonal changes, on soil moisture, and on local geometry such as mountain topography. Because the influence of such parameters on neutron flux from secondary cosmic rays depends on neutron energy, analysis of the whole neutron energy spectrum is beneficial.

Time-resolved secondary triton burnup 14 MeV neutron measurement by a new scintillating fiber detector in middle total neutron emission ranges in deuterium large helical device plasma experiments

A middle-sensitivity scintillating fiber detector (hereafter middle Sci-Fi detector) that works at a deuterium-tritium neutron flux of ~105-107 cm−2s−1 was utilized to measure secondary deuterium-tritium neutron emission rates with high temporal resolution at a total neutron emission rate of 1013 to 1015 n/s, where strong magnetohydrodynamic (MHD) instabilities were observed in the large helical device deuterium plasma experiments. The gain and angular characteristics of the middle Sci-Fi detector were evaluated in an accelerator-based deuterium-tritium neutron source in the intense 14 MeV neutron source facility at Osaka University. Observation of 1 MeV triton transport due to MHD instability was performed by a middle Sci-Fi detector whose deuterium-tritium neutron counting rate was approximately 20 times higher than that of the conventional Sci-Fi detector. Fusion-born triton transport due to energetic-particle-driven MHD instability was observed using the middle Sci-Fi detector due to its high detection efficiency and high discrimination ability of deuterium-tritium neutrons from the sea of deuterium-deuterium neutrons.

Assessment of neutrons from secondary cosmic rays at mountain altitudes – Geant4 simulations of environmental parameters including soil moisture and snow cover

Ground based measurements of neutrons from secondary cosmic rays are affected by environmental parameters, particularly hydrogen content in soil. To investigate the impact of these parameters, Geant4 Monte Carlo simulations were carried out. In a previous study the model used for the Geant4 Monte Carlo simulations was already validated by measurements performed with an Extended Range Bonner Sphere Spectrometer (ERBSS) at Zugspitze, Germany, and at Jungfraujoch, Switzerland. In the present study a sensitivity analysis including different environmental parameters (i.e., slope of mountain, snow height, soil moisture, and range of albedo neutrons) and their influence on the flux of neutrons from secondary cosmic rays was performed with Geant4. The results are compared with ERBSS measurements performed in 2018 at the Environmental Research Station “Schneefernerhaus” located at the Zugspitze, Germany. It is shown that the slope of the Zugspitze mountain reduces the neutron flux from secondary cosmic rays between about 25 % and 50 % as compared to a horizontal surface, depending on neutron energy and snow cover. An increasing height of snow cover, simulated as snow water equivalent (SWE), reduces the total neutron flux exponentially down to a factor of about 2.5 as compared to soil without any snow cover, with a saturation for snow heights greater than 10 cm to 15 cm SWE, depending on neutron energy. Based on count rates measured with the individual spheres of the ERBSS, SWE values were deduced for the whole year 2018. Specifically, mean SWE values deduced for the winter months (January to March) are between 6.7 and 10.1 cm or more, while those for the summer months (July to September) are between 2.1 and 3.6 cm. Soil moisture of 5 % water mass fraction in limestone leads to a decrease of the total neutron flux by about 35 % compared to dry limestone. At a height of 1.5 m above ground, 86 % of the total albedo neutron fluence at the detector position are from a ground area with a radius of about 75 m. It is concluded that measurement of neutrons from secondary cosmic radiation can be used to gain information on height of snow cover and its seasonal changes, soil moisture, but also information on local geometry such as mountain topography. Because the influence of such parameters on neutron fluence from secondary cosmic rays depends on neutron energy, analysis of the whole neutron energy spectrum is beneficial.

Bulk and Confined Benzene-Cyclohexane Mixtures Studied by an Integrated Total Neutron Scattering and NMR Method

Herein mixtures of cyclohexane and benzene have been investigated in both the bulk liquid phase and when confined in MCM-41 mesopores. The bulk mixtures have been studied using total neutron scattering (TNS), and the confined mixtures have been studied by a new flow-utilising, integrated TNS and NMR system (Flow NeuNMR), all systems have been analysed using empirical potential structure refinement (EPSR). The Flow NeuNMR setup provided precise time-resolved chemical sample composition through NMR, overcoming the difficulties of ensuring compositional consistency for computational simulation of data ordinarily found in TNS experiments of changing chemical composition—such as chemical reactions. Unique to the liquid mixtures, perpendicularly oriented benzene molecules have been found at short distances from the cyclohexane rings in the regions perpendicular to the carbon–carbon bonds. Upon confinement of the hydrocarbon mixtures, a stronger parallel orientational preference of unlike molecular dimers, at short distances, has been found. At longer first coordination shell distances, the like benzene molecular spatial organisation within the mixture has also found to be altered upon confinement.