Spectra of neutrons inelastically scattered on U238

The spectra of neutrons, inelastically scattered on U²³⁸ have been measured with a Wilson cloud chamber. The neutron source was a heavy-ice target, bombarded by accelerated deuterons. The mean initial neutron energies were 2.5 and 3.5 Mev. The scatterer was a spherical layer of impoverished uranium 18 mm thick. The target was centered in the scatterer. The energy distribution for the inelastically scattered neutrons was measured in the energy range from 100 to 1,300 key and is in agreement with the statistical theory. The most probable energy for the scattered neutrons is about 275 kev for neutrous with an initial energy of 2.5 Mev and about 375 kev for neutrons with an initial energy of 3.5 Mev.     

Spectra of neutrons inelastically scattered on U238

The spectra of neutrons, inelastically scattered on U²³⁸ have been measured with a Wilson cloud chamber. The neutron source was a heavy-ice target, bombarded by accelerated deuterons. The mean initial neutron energies were 2.5 and 3.5 Mev. The scatterer was a spherical layer of impoverished uranium 18 mm thick. The target was centered in the scatterer. The energy distribution for the inelastically scattered neutrons was measured in the energy range from 100 to 1,300 key and is in agreement with the statistical theory. The most probable energy for the scattered neutrons is about 275 kev for neutrous with an initial energy of 2.5 Mev and about 375 kev for neutrons with an initial energy of 3.5 Mev.     

Neutron-capture therapy with ultra-cold neutrons

The status of neutron-capture therapy of malignant tumors and its problems – damage to healthy tissue as a result of neutron transport to the irradiation location and presence in the therapeutic beam of a background consisting of γ rays and fast neutrons – are presented. To solve these problems, the authors have proposed using ultracold neutrons with energy less than 10^–7 eV, whose unique capability is to undergo total reflection from the surface of a condensed substance at any angle of incidence. Numerous works have demonstrated that such neutrons can be transported along neutron guides. The cross section for inelastic scattering of neutrons by hydrogen-containing substances – water, ethyl alcohol, and biological tissue – has been measured in an IR-8 beam of ultracold and very cold neutrons. At temperature 200–300 K, the experimental data are in very good agreement with calculations, but as temperature decreases further a discrepancy appears, which could be due to the inaccuracy of the model spectra of the oscillations hydrogen-containing substances used in the calculations. The use of ultracold neutrons opens up new possibilities of neutron-capture therapy for treating malignant tumors localized in body cavities or organs.     

导管中冷中子传输过程的数值模拟

中子导管是利用中子全反射原理将中子束以很小的传输损失传递到远离中子源处的物理装置。利用蒙特卡罗方法模拟中子在导管中输运过程,在中子导管的设计和实验应用中可发挥重要作用。某座反应堆上正建设包括有3束导管的冷中子导管系统,以蒙特卡罗方法为基础,开发出该导管系统的数值模拟程序,并利用该程序计算得到该导管各个输出口的中子注量率及能谱分布,为布置在导管周围的中子散射谱仪和其它应用装置的设计提供了必要的输入条件。     

中子照相∑定量测量方法

本文描述了一种利用中子照相进行定量分析的方法,介绍了该方法的基本原理,并应用粒子输运程序MCNP模拟分析样品内部散射中子随样品与探测器之间距离变化对中子成像的影响.为削弱散射中子对中子透射成像图像信息的影响,对穿透样品的厚度进行了定量分析.     

Space Dependent Neutron Spectra in the Prisms of Crystalline Media

In an effort to elucidate the space dependent spectral behavior of thermal and cold neutrons in crystalline media, calculations in lead and graphite prisms were carried out using the successive collision method based on the integral transport theory, and also using the successive inelastic scattering method based on the distributed source diffusion theory. The results were compared with experiments to measure the space dependent energy spectra in a lead prism generated by the “thermal” and the “cold” sources.

The space dependent spectra in small crystalline media are modified below the Bragg cut-off energy by the deep penetration of neutrons and acquire the characteristic sharp peak. Above the Bragg cut- off energy, near Maxwellian spectra are generated in graphite prisms, while in small lead prisms the spectra are strongly affected by the neutron penetration below about 0.01 eV.

Calculations by the distributed source diffusion theory showed good approximate spectra.     

Angular distribution of elastic and inelastic scattering of 2.34 Mev neutrons from chromium, iron, and lead

Spectra are obtained for neutrons with initial energy E₀=2.34 Mev scattered by chromium, iron, and lead nuclei, and the corresponding differential cross sections for elastic and inelastic scattering are measured for angles from 30 ° to 135 °. The neutrons were obtained from the D (d, n) He³ reaction with an initial deuteron energy of 1 Mev and a neutron emission angle of 110 °. Nuclear photographic emulsion was used as the detectorspectrometer and as the monitor of the incident neutron flux. The scatterers were 2.8 cm diameter spheres. In calculating the cross sections for elastic and inelastic scattering, corrections for self-absorption and multiple scattering were introduced to the incident neutron flux in the scatterer. The angular distribution of inelastically scattered neutrons from chromium and iron, as well as from lead when the 0.53 Mev level was excited, was found to be isotropic within the limits of the experiment. Inelastic scattering from lead when the 0.805 and 0.890 Mev levels are excited cannot be considered isotropic.This work was carried out during 1953–1955; the results were partially reported at the International Conference on the Peaceful Uses of Atomic Energy in Geneva, 1955.The author expresses his gratitude to Acting Member of the Academy of Sciences of the Ukrainian SSR A. I. Leipunsky for constant interest in the work, and to Candidates of Physical-Mathematical Sciences O. D. Kazachkovsky and I. I. Bondarenko for valuable discussion oi the results.     

Angular distribution of elastically and inelastically scattered 2.9-Mev neutrons

A hydrogen ionization chamber and annular geometry are used to measure the angular distribution of elastically and inelastically scattered 2.9-Mev neutrons, as well as inelastically scattered neutrons associated with excitation of various levels or groups of levels of iron, copper, lead, and bismuth nuclei. The integral cross sections for elastic and inelastic scattering are presented, as are the transport cross sections. The experimental results are compared with theoretical calculations based on the optical model. It is noted that the angular distribution of elastically scattered neutrons from atoms with almost equal atomic weights may be quite different.     

Deuterated liquid scintillator (NE230) as a fast neutron detectorfor cold-fusion and other research

Deuterated scintillators (NE230) can provide, without time-of-flight, usable neutron energy spectra for neutrons E _n⩾1 MeV. The authors have assembled and calibrated several of these detectors and used them in experiments searching for d+d fusion-neutron emission (E_n, 2.5 MeV) in Pd+D ₂O electrolysis and Ti+D₂ adsorption at LN temperatures. The detectors yielded direct fusion-neutron spectra and set limits in the Pd+D and Ti+D experiments of <7×10^-24 fusion n/s/dd pair and <3×10^-24 fusion n/s/dd pair respectively. In addition, these detectors have been used for in-beam accelerator experiments requiring coincidence between fast neutrons and scattered ions     

Measurement of neutron spectra through composed material block bombarded with D-T neutrons

A 2-dimensional composed material assembly made of the iron and hydric block has been established. The neutron spectra from the assembly bombarded with 14-MeV neutrons at neutron generator have been obtained using the proton recoil technique with a stillbene detector. The detector positions were selected at the 60°, 120°, 180° on the surface of the iron spherical shell. The background neutron spectra consisted of background and room return radiation were subtracted with combination of methods of experimental shielding and MCNP calculation. The uncertainty of results was 6.3-7.4%. The experiment results were analyzed and simulated by MCNP code and two data library. The difference is integral neutron flux (background neutron subtracted) of measured results greater than calculations with maximum of 21.2% in the range of 1-16 MeV.     

CTOF measurements and Monte Carlo analyses of neutron spectra for the backward direction from a lead target irradiated with 200-1000 MeV protons

A calorimetric-time-of-flight technique was used for real-time, high-precision measurement of neutron spectra at an angle of 175^o from the initial proton beam direction, which hits a face plane of a cylindrical lead target of 20 cm in diameter and 25 cm thick. A comparison was performed between the neutron spectra predicted by the MARS, RTS&T, MCNP6, and the MCNPX 2.6.0 transport codes and that measured for 200, 400, 600, 800, and 1000 MeV protons. Neutron spectra were measured within the energy range from 0.7 to 250 MeV almost continuously. The transport codes tested here describe with different success the measured spectra, depending on the energy of the detected neutrons and on the incident proton energy, but all the models agree reasonably well with our data.     

Angular distribution of elastically and inelastically scattered 2.9-Mev neutrons

A hydrogen ionization chamber and annular geometry are used to measure the angular distribution of elastically and inelastically scattered 2.9-Mev neutrons, as well as inelastically scattered neutrons associated with excitation of various levels or groups of levels of iron, copper, lead, and bismuth nuclei. The integral cross sections for elastic and inelastic scattering are presented, as are the transport cross sections. The experimental results are compared with theoretical calculations based on the optical model. It is noted that the angular distribution of elastically scattered neutrons from atoms with almost equal atomic weights may be quite different.In conclusion the author thanks Acting Member of the Academy of Sciences, USSR, A. I. Leipunskii for directing the work, Candidate of Physical-Mathematical Sciences, A. N. Serbinov who operated the high-voltage apparatus, and V. S. Stavinskii for discussing the results.     

Measurement of neutron spectra in the thermal column of the reactor of a power station

Knowledge of neutron spectra In nuclear reactors allows comparison of various theories of the slowing down of neutrons with experiment, and also allows carrying out reactor calculations which are based on actual neutron distributions therein. In this paper is described a neutron intensity monochtomator Intended for the measurement of neutron spectra in the energy interval 0 to 0.5 ev.Results are given for measurements for neutron spectra in the thermal column of the reactor of an atomic power station. Discontinuities in the neutron flux were discovered at neutron velocities of 600, 1000 and 1650 m/sec; an analysis is given of the causes of discontinuities of the neutron flux; an evaluation is made of the inelastic scattering cross section for neutrons in graphite. By the method of least squares, the temperature of the neutron gas was found, being equal to 354 ° K at a graphite temperature of 304 ° K.In conclusion we consider it our duty to express gratitude to A. K. Krasin and B. G. Dubovskii for interest and help in the work and F. L. shapiro for valuable interpretation of previous results.     

Distribution of fast fission neutrons along straight,cylindrical ducts in water

A study was made of the transmission of neutrons from the BR-5 reactor inside straight, cylindrical ducts, 144 and 90 mm in diameter, located in water. Sulfur and aluminum threshold detectors were used to detect the neutrons.Data was obtained for the attenuation along the axis of straight, cylindrical ducts of the fast neutron flux from disc, and plane, infinite monodirectional sources of fission neutrons; the effect of displacement on the attenuation of neutron radiation in the ducts was studied. The information obtained can be used to calculate the transmission of neutron radiation along stepped ducts.Translated from Atomnaya Énergiya, Vol. 20, No. 5, pp. 416–418, May, 1966.     

Study of the spectra and doses created in the iron-water shielding of a monoenergetic neutron source

Many-group calculations were made for the penetration of neutrons, emitted from monoenergetic sources, through water, iron, andwater-iron systems of finite dimensions; the results of these calculations are presented. The neutron spectra resulting from the passage of such neutrons through water and iron shielding layers were calculated on the twenty-group diffusion-transport approximation, Detailed attention was paid to the high-energy part of the spectrum; certain peculiarities in neutron migration and moderation processes in shielding of the type in question were elucidated. Dose curves D(r) were plotted for neutrons of various energies.By using the superposition principle, the results enable the neutron spectrum to be determined for sources having any arbitrary spectrum.Translated from Atomnaya Énergiya, Vol. 21, No. 1, pp. 27–35, July, 1966.     

Calculation of the spectra of fission neutrons emitted at angles of 0, 45, and 90° to the direction of flight of the fragments

The evaporation model is used to solve the problem of the spectrum of neutrons emitted by fission Fragments at angIes of 0, 45, and 90° to the direction of flight of the fragments. It is assumed that the neutrons are emitted isotropically in a coordinate system associated with the fragment. The spectra calculated are in good agreement with the experimental data.Translated from Atomnaya Énergiya, Vol. 13, No. 6, pp. 530–533, December, 1962     

Neutron spectra emitted in the fission of U235 at 0, 45, and 90 ° to the direction of motion of the fragments

Neutron spectra emitted at 0, 45, and 90 ° to the direction of motion of the fragments in the fission of U²³⁵ by 14.3 Mev neutrons have been measured. The angular distribution of the fission neutrons was found to be N(0 °): N(45 °): N(90 °) = (3.23 ± 0.12): (1.75 ± 0.07): 1.00. The experimental data are compared with spectra calculated on the assumption of an isotropic Maxwellianneutron distribution in the center-of-mass system of the fragment.     

Spectra of fast pile neutrons in passage through polyethylene

A single-transducer fast-neutron spectrometer was used to measure the spectra of fast pile neutrons after passing through polyethylene layers of different thicknesses. The results of measurements at E_n>3 MeV show excellent agreement with data computed by the method of moments. At E_n<3 MeV, the discrepancies are accounted for by the difference in the geometry and in the original spectra. Problems involving the correct procedures to be folIowed in setting up experiments of this type are discussed.Translated from Atomnaya Énergiya, Vol. 15, No. 1, pp. 20–22, July, 1963     

Measurements of Time Dependent Energy Spectra of Neutrons in a Small Graphite Assembly

The time-dependent energy spectra of neutrons have been measured in a small 30×30×30 cm³ graphite assembly by means of the linac-chopper method, with a view to establishing experimental evidence that there is no asymptotic spectrum in such a small assembly, and in order to study the non-asymptotic behavior of neutrons.

The arrangement of a polyethylene pre-moderator adjacent to the assembly made the measurements possible with the improvement obtained thereby of the neutron counting statistics. It was indicated from calculation that the presence of the pre-moderator had little effect—at least above the Bragg cut-off energy—on the evolution in time of the energy spectra of neutrons in the graphite assembly.

The experimental results indicated very probable disappearance of asymptotic spectra, and revealed significant enhancement of trapping at Bragg energies with the lapse of time. This is consistent with the results of pulsed neutron experiments in small assemblies conducted by Takahashi et al., and falls in line with de Saussure's approximation.

The spectra in the graphite assembly showed significant space dependence, the spectra becoming harder with increasing distance from the pre-moderator. This hardening may be attributed to the relatively faster propagation of higher energy neutrons.