Nuclear information obtainable from low energy neutron spectroscopy

The results of measurements of thermal-neutron cross sections, level distributions in the resonance region, ratios, and determinations of the effective nuclear radius from potential:.scattering of slow neutrons are considered.A discrepancy in the results of measurements of the thermal-neutron fission cross secticn in U²³⁵ is noted. The distribution of levels exhibits a deficiency in small spacings as compared with a random distribution, i. e., there seems to be a repulsion of levels. The dependence of on atomic number A is nonmonotonic, in accordance with the complex-potential model of the nucleus; however there is a considerable discrepancy between the experimental data and theory for atomic numbers in the neighborhood of 100. The effective radius determined from potential scattering of slow neutrons indicates a nonmonotonic dependence on A, in agreement with the model of a semi-transparent nucleus with smeared-out edges.     

Density Profiles in the Levitated Dipole Experiment

A multi-chord interferometer (center frequency 60 GHz) has been constructed to measure the electron density profiles of plasmas in the Levitated Dipole Experiment (LDX). Theoretical considerations suggest that the density of a dipole-confined plasma will vary with radius as 1/r ⁴. Measurements have been made for LDX plasmas, where the dipole-field was produced by a coil that was not levitating but rather suspended from a central column by thin supports. A ray-tracing code has been written to fit the chord data, which are line-integrated densities, to azimuthally-symmetric electron density profiles n _e (r, t). Initial analysis has focused on the model , where A(t) and α(t) are free parameters; α(t) is referred to as the “steepness exponent.” The density profiles are observed to exhibit dynamics due to ECR heating and neutral-gas fueling. The model-fit, meant only to serve as a rough approximation, suggests that LDX plasmas have steepness exponents in the range of 1.5–4. The density at the location of the 2.45 GHz ECRH resonance is reconstructed and found to be of the same order of magnitude as the heating cut-off .     

Chemical potential of oxygen of UO2 close to stoichiometry

Conclusions A closed solid electrolyte cell, permitting reliable values of to be obtained up to –775 kJ/mole, using a ceramic oxygen pump of stabilized ZrO₂, was developed. The temperature dependence of of uranium dioxide was determined for O/U=2.0039; 2.0021; 2.0018; 2.0012; 2.0009, and 2.0006. Coulometric titration of uranium dioxide was performed in the range of O/U from 2.0039 to 1.9991, and the influence of the degree of nonstoichiometry on was studied at 1273°K. A very strong dependence of at 1273°K was demonstrated in the range of O/U from 2.0001 to 1.9999. A change in O/U by 0.01% causes a 70% decrease in .Translated from Atomnaya Énergiya, Vol. 51, No. 4, pp. 228–230, October, 1981.     

Dosimetry method for β radiation based on investigations of the electron spectra in the fields of β emitters

A method has been developed for -ray dosimetry based on the investigation of the effective electron spectra in the fields of emitters. The spectra was investigated with the help of a scintillation spectrometer. It was shown, that the value of the dose , where N is the number of particles penetrating an infinitesimal volume around the point being considered; is the value of the ionization loss averaged over the spectrum. It was established that the quantity is determined by the maximum energy of the spectrum of the isotope and may be considered to be independent of the depth of the medium and of the source diameter. Curves of depth doses for S³⁵, Tl²⁰⁴, Y⁹¹, and Ce¹⁴⁴ + Pr¹⁴⁴ are given and criteria for selecting isotopes to provide optimal conditions of irradiation are established.     

Spheromak Formation and Current Sustainment Using a Repetitively Pulsed Source

By repeated injection of magnetic helicity (K = 2φψ) on time-scales short compared with the dissipation time (τ_inj << τ _K ), it is possible to produce toroidal currents relevant to POP-level experiments. Here we discuss an effective injection rate, due to the expansion of a series of current sheets and their subsequent reconnection to form spheromaks and compression into a copper flux-conserving chamber. The benefits of repeated injection are that the usual limits to current amplification can be exceeded, and an efficient quasi-steady sustainment scenario is possible (within minimum impact on confinement). A new experiment designed to address the physics of pulsed formation and sustainment is described.     

Measurement of the effective number of secondary neutrons from Pu239 in the incident neutron energy region from 7 to 30 ev

Measurements have been made of the energy dependence of the quantity (wherer is the average number of fast neutrons per fission event, _f is the fission cross section and _a is the absorption cross section) in Pu²³⁹ for the energy region ranging from 7 to 30 ev. A knowledge of this quantity is of interest both for practical reactor calculations and in the theory of nuclear fission. The measurements consist of counting the number of fast fission neutrons emitted from a sample of Pu²³⁹ with slow neutrons incident upon it. A higher resolving power in the neutron collector has made it possible to measure the ratio for the separate resonances. In this connection it is assumed thatv remains constant over the entire measurement region. From the data of the present work it is found that the fission widths of ten levels in Pu²³⁹ vary strongly from one to another and that they may be grouped.The authors are indebted to S. Ya. Nikitin for advice and continued interest in the present work.     

The distribution of ionization along a beam of γ-radiation and the determination of radiation dose with normal ionization chambers

It was established that the ionization effect, measured in normal ionization chambers for determining the dose in a region of -radiation, must be referred to a point in space, displaced by a distance of about from the center of the measuring electrode of the chamber towards the source. The corrections for displacement of the measuring volume for the -radiation of Cs¹³⁷ and Co⁶⁰, respectively, equal 0.996 and 0.992.     

Deformation systems of α-zirconium

The deformation systems of -zirconium iodide have been studied in coarse-grained polycrystalline specimens deformed by upsetting. The orientation of the grains was determined from Laue patterns obtained in a special back-reflection camera using a small-diameter beam. The indices of the deformation systems were determined by the two-surface method and by the pole locus method.It was found that -zirconium is deformed by slip along the plane in the direction and along the plane. A number of twinning systems have been discovered In -zirconium: a) K₁ , 1 , K₁ , ₂ and s=0.173; b) K₁ , ₂ [1126], K₂ (0001), ₂ [1120] and s=0.629; c) K₁ (1122), ₁ [1123] and in one case, d) K₁ , ₁ .     

Analytic representation of the fission neutron spectra of235U and252Cf

Analytic representations of the spectra in two forms—in the form of a model spectrum and as a sum of nine model spectra , where α_i=4.2.1.333.1.0.0.8.0.4.0.2.0.05. and 0.01-are obtained on the basis of representative sets of integral cross sections for the fission neutron spectra of²³⁵U due to thermal neutrons and spontaneous fission spectra of²⁵²Cf.2 tables. 5 references. Translated from Atomnaya énergiya, Vol. 88, No. 4, pp. 299–303, April, 2000.     

On M1-transitions from highly excited states

This article is concerned with the probabilities of Mi-transitions from states created by the capture of thermal neutrons for even-odd and odd-odd emitting nuclei with A from 20 to 60. In the single-particle model, such transitions are forbidden with respect tol. A comparison with the probabilities of E1-transistions shows that in even-odd nuclei, the probabilities of forbidden Mi-transitions which we observed, did not differ much from the probabilities ofl-allowed M1-transitions for lighter nuclei.In the case of odd-odd nuclei, certain M1-transitions are characterized by a large number of quanta per single neutron capture and a large value of      

Pulsational characteristics of two-cassette model of boiling-water reactor

Conclusions On a large-scale two-cassette model of the natural-circulation loop of a reactor with vertical dimensions and reduced hydraulic-drag coefficients of the basic loop elements that are close to the full-scale values, an experimental investigation has been conducted, with the following conclusions:With design parameters of the heat carrier, the specific thermal stress of the fuel elements, and the discrepancy coefficients of the pile power, the zone of hydrodynamic instability is characterized by the values ; liquidation of total-loop pulsations of the heat-carrier flow rate entails vapor condensation under the water level in the reactor; total liquidation of the pulsations requires, in addition, the introduction of disks at the input to each pile; the reduced hydraulic-drag coefficient _re of the disk must be no less than 0.8 of the sum of _re for the pile and the ITS.Translated from Atomnaya Énergiya, Vol. 69, No. 2, pp. 87–92, August, 1990.     

Problem of the iodine method of purification of zirconium

A method is proposed for the determination of the equilibrium constantsk and k' for the reactions Zr+2I₂–ZrI₄=0 and 2I–I₂=0, which is based on the measurement of the amount of iodine or zirconium liberated in the decomposition of zirconium tetraiodide on a heated surface in the process of establishing equilibrium. The decomposition of the tetraiodide was carried out at 900–1600C on a tungsten filament. The temperature distribution between filament and vessel walls was neglected.The dependence of the sum of atomic and molecular iodine pressures on zirconium tetraiodide pressure was determined at 1430C, and on temperature for 50 mm Hg. The values of kk'² 35 (mm Hg)³ at 1430C and k0.07 mm Hg at 400C, found from the results, differ substantially from known thermodynamic data, but give good agreement between the authors' formula [1] and experimental results on the iodide process of zirconium purification.     

Simulation of nuclear-fuel solvent-extraction reprocessing 7. Separation of macroscopic amounts of plutonium and uranium by displacement reextraction of plutonium in reprocessing fast-reactor fuel (section 1)

Conclusions These data have been obtained from simulating displacement reextraction in a system with two inputs (system for reprocessing a fast-reactor fuel), and they show that it is possible to obtain a uranium extract with not more than 100 g Pu/kg U in a counter current system with 18 stages to provide partial separation of the uranium and plutonium by reprocessing of an organic solution containing U⁺ Pu (10 1) with 64% saturation in the sum of the metals to produce reextract containing plutonium with U : Pu3 and over 99.99% extraction of the uranium; this requires 90 g/liter of uranium in the reextractant and the parameters n=2.06–2.00 ( =0.3 M); n=1.82–1.87 ( =0.5 M); n=1.61–1.78 ( =1.0 M).Full data obtained from the simulation are to be found in [5], from which one can extract the parameters of the working state of the extractor and other data on the separation of uranium and plutonium, e.g., for other specifications for the plutonium level in the uranium. The next part of the present study will be concerned with engineering solutions that can extend the range of conditions that provide the appropriate output parameters within specified ranges and thereby improve the reliability in operating the process in the optimal region.Translated from Atomnaya Énergiya, Vol. 47, No. 6, pp. 377–381, December, 1979.     

Statistical method for studying the behavior of an ensemble of charged particles under the influence of their inherent magnetic field

The stationary solutions for the statistical distribution function of the charged particles in a discharge in an ionized gas contracting about its own axis of symmetry under the influence of the inherent magnetic field are given. An isothermal plasma at a very high temperature is considered (completely ionized gas). An exact solution is carried out in the case of cylindrical symmetry. The density distribution depends on an arbitrary constant C which is determined by the experimental conditions. At large r the solution has the asymptotic form      

Accelerators with similar orbits

We obtain the conditions that must be satisfied by a magnetic system in order that the frequencies of radial and vertical betatron oscillations be independent of the particle momenta (in this case the orbits are called dynamically similar). In such systems mere should in principle be no excitation of betatron oscillations associated with synchrotron oscillations and other phenomena. A magnetic field with n₀ = const produces both geometric and dynamic similarity of the orbit. In weak-focusing accelerators with segments (race tracks) and in strong-focusing proton synchrotrons, the orbits are not dynamically similar. In order to obtain this kind of similarity in the first case, in addition to n₀ = const it is necessary that the magnet sectors have a common center. Different types of annular synchrocyclotrons are considered. In the first type the centers of neighboring magnet sectors are located on different sides of the doughnut and in the second type at the same point (at the center of the accelerator). In the second type the orbits are dynamically similar, unlike those of the first. It is shown mat it is possible to design an annular synchrocyclotron in which the particles can move with stability simultaneously in both directions within the doughnut.     

Using the method of moments to calculate the space-energy distribution of neutron density from flat and point sources in an infinite medium

A method is given for calculating the space-energy distribution of neutron densities from flat and point sources in an infinite medium.The neutron density (x, E) is sought in the form · To a large degree the form of the function K(x) is arbitrary; its selection is based on physical principles. From the 2N space moments of the function (x, E), 2N parameters a_i, b_i are found. The neutron density distribution is found in hydrogen and water. The calculations for water are compared with experimental data. A comparison with the accurate solution of Wick [1] in the case of retardation of neutrons by hydrogen shows that from four moments the suggested method can, with sufficient accuracy, find the spatial distribution of neutrons at distances up to 20 free path lengths.     

Some data on the spontaneous fission of Cm244

The average kinetic energy of the fission fragments, , the distribution width at half the height, E_k = 24.8 ± 2.5 MeV, and the average number of prompt neutrons per fission, = 2.71 ± 0.04, are found for the spontaneous fission of Cm²⁴⁴. The variation of and as functions of the nucleonic composition of the fissionable nucleus is considered in connection with the experimental results. Attention is drawn to the correlation of anomalies in these functional relationships as the most probable fragment mass varies. The assumption that the observed effects are related to a variation in the elastic properties of the fragments produced is discussed.Translated from Atomnaya Énergiya, Vol. 17, No. 1, pp. 28–34, July, 1964     

Average energies of electron and positron β spectra

The average energies of electron and positron spectra were calculated for various values of the atomic number Z of radioactive nuclei and the timiting energy E₀ of the spectrum. The calculations were carried out for the case of allowed transitions and unique transitions of the first order of forbiddenness. The report contains tables and graphs of the values of and = f(E₀, Z) which may be used in evaluating the thermal effects of various radioactive specimens, nuclear reaction products, and products resulting from the fission of dements under the action of slow neutrons and high-energy nucleons, in calorimetric measurements of radioactive sources, and in calculating certain dosimetric characteristics of specimens which emit radiation. The authors give a brief survey of the methods of determining the average energies of spectra and the values of these quantities obtained up to the present time for various radioactive isotopes.Translated from Atomnaya Énergiya, Vol. 17, No. 1, pp. 9–17, July, 1964     

Calculating the transient temperature field in a reactor tube and the thermoelastic stresses in the fuel element cladding

Approximate analytic methods are given for calculating the transient temperature field in the fuel elements and the coolant temperatures at any point along the reactor tube, as well as the transient thermoelastic stresses in the cladding of a cylindrical fuel element. The coolant temperature at the input to the tube is constant, and the coolant undergoes no changes in state of aggregation. The approximate methods are illustrated by examples.Results are given, for comparison, of accurate calculations of the same examples made with a rapid calculating machine.List of symbols time - r; z coordinates (radius, distance along tube) - r₁; r₂ internal and external radii of fuel element cladding respectively - H total active length of fuel element - a₁; ₁;c _{1 1} coefficients of temperature conductivity, heat conductivity, specific heat capacity and specific gravity of fissionable material respectively - a₂; ₂; C_p2; ₂ cladding parameters - a; ; c_p; coolant parameters - mean cladding radius - f:f₂ cross-sectional area of tube for coolant and cladding respectively - w coolant velocity - coefficient of heat release to coolant - t (r, ); (); () fuel temperature, mean temperature over cross section of cladding, and coolant temperature at pointz. along tube respectively - qv() specific volume of coolant at pointz - values averaged overz - quantities at the initial instant of time - ₃ delay time - _n time required for coolant to go from z=0 to the point in question