Some characteristics ofγ-ray scattering at the boundary of two media

The characteristics of -ray scattering (0.33 E 1,25 MeV) at the boundary between two media were experimentally investigated. It was established that the scattered radiation was produced mainly by a narrow beam of primary radiation. The effective scattering area was contained within a region with a radius r 10h (for h z). The contribution to the total energy from radiation scattered by the medium increased for angles of incidence of the primary narrow beam up to 85–88 °, and then decreased monotonically.An estimate was made of the effective dimensions of the area from which scattered quanta were emitted into the backward half-space when an isotropie source was located at the surface of the scatterer.The energy flux of the scattered radiation was measured with a gas counter which had a practically constant sensitivity for -rays of different energies.The authors are deeply grateful to Prof. O. I. Leipunskii and to A. S. Strelkov for assistance and for discussions of the results.     

γ-Ray spectra excited in inelastic scattering of fast neutrons on manganese,aluminum, iron,copper, tin,and antimony

The study of inelastic scattering of fast neutrons is an important problem of both theoretical and practical interest. From the theoretical point of view the importance of this work lies in the possibility of obtaining data concerning levels in stable nuclei. The practical value arises in connection with the important role played by inelastic scattering of neutrons in fast-neutron reactors as well as the fact that the extension of reactor theory to fast-neutron reactors requires data on the spectra of inelastically scattered neutrons [1, 2]. In this connection the necessity for developing a neutron spectrometer for fast neutrons and-spectroscopy for inelastic neutron scattering is obvious. In the last 5–7 years a great deal of work has been devoted to this problem.The present work reports on measurements of-ray spectra excited in inelastic scattering of 2.8 Mev neutrons by manganese, aluminum, iron, copper, tin and antimony. The measurements were carried out with a scintillation spectrometer consisting of an NaI(Tl) crystal, a FEU-1B photomultiplier and a 50-channel pulse-height analyzer with a magnetic-drum memory. The spectrometer resolution was 6.5–7% for-rays from Co⁶⁰.-Rays of the following energies (Mev) were found: in manganese 0.97, 1.41, 1.92, 2.3; in aluminum 0.84, 1.00, 1.80, 2.16; in iron 0.84, 1.25, 1.46, 1.70; in copper 0.63, 0.78. 0.96, 1.12, 1.38, 1.46, 1.72, 2.03; in tin 0.84, 1.16, 1.50, 1.80, 2.16; in antimony 1.04, 1.50, 1.84, 2.16.Abbreviated version of a paper appearing in the Ukrainian Journal of Physics.The authors wish to take this opportunity to thank L. M. Beliaev and G. F. Dorbrzkanskii of the Institute of Crystallography, Academy of Sciences, USSR for making the NaI(TI) crystal and for kndly allowing us to use it in carrying out the present work.     

Corrections for multiple scattering in spherical and circular geometries

In this paper a method is considered of introducing corrections for multiple scattering into the results of measurements of angular distributions of elastically scattered neutrons. It is assumed that the mean path of the neutron in the sample in which scattering takes place is comparable with the neutron free path.In the first part, using direct calculation of the integrals, we find the probability for double scattering and estimate the probabilities for triple and higher-order scattering for a sphere and for a ring of circular and rectangular cross section in the case of isotropic neutron scattering. In the case of anisotropic neutron scattering, at neutron energies of the order of several million electron volts the cross section may be given as a sum () = ₁ () + ₂ (), where ₁() is the forward peak and ₂() is more or less isotropic. Using this representation all elastic scattering events may be provisionally divided into two groups while all double scattering events can be divided into four groups. The probabilities of double scattering for all four are calculated on the basis of results obtained for isotropic scattering. Triple and higher-order scattering are evaluated in similar fashion.     

Stationary transport of monoenergetic neutrons in inhomogeneous media

The passage of monoenergetic neutrons from a stationary source in an inhomogeneous medium is considered; this may be described by means of a Boltzmann equation with fluctuating coefficients. An equation is derived for the flow of neutrons (neutron flux) averaged over the fluctuations in the medium. A solution is obtained for this equation in limiting cases in which the characteristic dimension of the inhomogeneity 1_s ⁰ (free path in relation to scattering in a homogeneous medium) and 1_s ⁰. In both cases 1L₀ (diffusion length of neutrons in a homogeneous medium). By way of an example of an inhomogeneous medium, the periodic lattice of a reactor is considered.Translated from Atomnaya Énergiya, Vol. 22, No. 4, pp. 271–276, April, 1967.     

Resonance scattering of γ-rays in Mg24

Resonance scattering of -rays With energies E₁=1.38 Mev, corresponding to the transition to the ground state in Mg²⁴. have been observed in metallic magnesium. The energy given off by the -ray (E₁=1.38 Mev) in emission and collision with the nucleus, is compensated for by the energy obtained due to recoil associated with the emission of the preceding -ray with an energy E₂ = 2.76 Mev. Using a fast coincidence method and amplitude discrimination, coincidences were recorded between the -rays with energies E₁=1.38 Mev and E₂=2.76 Mev. Scattercrs of magnesium and aluminum were alternately placed in the path of the 1.38 Mev -rays. The source was radioactive Na²⁴ in a water solution of NaOH. At an angle of 120 ° between the -rays a strong attenuatlon of the 1.38 Mev -rays was observed; this is attributed to resonance scattering. When the angle between the -rays was varied by 5 °. the strong attenuation of the flux disappeared. The width of the level at 1.38 Mev in Mg²⁴ has been estimated at > 1.6· in^–4 Mev.     

Immobilization of Radionuclides in Irradiated Reactor-Graphite Blocks

The immobilization of radionuclides in samples of GR-280 reactor graphite by the fixative atomik is described. A graphite block extracted from RBMK masonry after 17 years of operation is used for the investigations.The investigations showed that the strength of the fixative samples increases only with irradiation doses above 15000 Mrad. The radiation–chemical yield of gaseous products of radiolysis from samples of the fixative under irradiation in vacuum is 12·10^–10 cm³/(g·rad). , , and -emitting nuclides are leached from the samples of irradiated graphite; this process proceeds continually. When the irradiated graphite samples are permeated with the fixative atomik, no release of radionuclides is observed at 20°C for 2 yr.     

Neutron yield of the reactions Li6(t,n) and Li7(t,n)

The differential cross section is determined for the formation of neutrons at an angle of 0 ° in the reactions Li⁶(t,n) and Li⁷(t, n) in the 0.175–2.4 Mev triton energy range. In the reaction Li⁶(t,n) resonance in the neutron yield is observed at E_t = 1.875 Mev, corresponding to a Be⁹ excitation level of 18.936 Mev.Two resonances are detected in the neutron yield of the reaction Li⁷(t, n): at E_t = 0.765 Mev and E_t = 1.735 Mev, which indicates the presence of Be¹⁰ nucleus excitation levels of 17.78 and 18.46 Mev, respectively. The cross section of the reaction Li⁶(t, n) in resonance is d/d(0 °)_res = 37.2 mb/sr; for the reaction Li⁷ (t, n) the cross section at the first resonance is d/d(0 °)_res = 95 mb/sr; at the second resonance d/d(0 °)_res = 159 mb/sr.The angular distributions of neutrons are given for the interval of angles 0–135 ° (every 15 °) for triton energies of 0.358, 0.559, 1.006, 1.218, 1.370, 1.572, 2.123 Mev.The total cross section for the formation of neutrons at E_t = 2.123 Mev in the reaction Li⁶ (t,n) is equal to 324±32.3 mb in the reaction Li⁷ (t, n) to 1332±83.3 mb.     

Nuclear fusion from crack-generated particle acceleration

Summary In summary, the high-voltages necessary to accelerate deuterons to energies sufficient to produce modest numbers (10⁴–10⁵/sec) of d-d neutrons appears to be possible as a result of cracking or fracture of the metal lattice in the cold fusion experiments.This mechanism requires neither massive electrons nor exotic nuclear reactions to explain the apparent cold fusion d-d neutron production results. Instead, it is possible that high voltage electrostatic fields, known to be associated with cracking, can reside across a crack gap long enough for the deuterons to be accelerated to sufficiently high energy to produce the d-d reactions. Interestingly, the electrostatic acceleration is quite similar to that of laboratory accelerators except for its submicron scale. Clearly, much work is still required to determine whether such a crack-generated acceleration mechanism, a quasi-particle mechanism, some combination of these, or some other, as yet unidentified mechanism is responsible for the nuclear effects seen in cold fusion experiments.Presented at the Workshop on Cold Fusion Phenomena, Sante Fe, New Mexico, May 23–25, 1989.     

Transmission of neutron radiation from a reactor through hydrogen-free media

The results of experimental and theoretical investigations into the transmission of neutrons through hydrogen-free, uniform materials and mixtures are discussed. The relaxation lengths obtained for neutrons of different energy groups are discussed. It is shown that under certain assumptions the mag 7 nitude of the flux attenuation for neutrons of the upper energy group (E_n 3 MeV) in a hydrogen- free medium can be obtained from very simple empirical expressions by using well-known constants: the removal cross section Ore m, the cross section obtained from the reciprocal of the relaxation length (₁/) and the asymptotic cross section _as. Values are derived for these constants.Translated from Atomnaya Énergiya, Vol. 18, No. 4, pp. 350–357, April, 1965     

Albedo of Co60 and Au198 γ-rays from various substances

Absolute values are obtained in the present investigation for the energy albedo of the -radiation of Co⁶⁰ (1.17, 1.33 Mev) and Au¹⁹⁸ (0.410 Mev) from various substances, at angles of 0 °, 45 °, and 60 ° from the original beam.The dependence of the magnitude of the albedo on the effective atomic number and thickness of the scattering material was investigated; in addition, the angular distribution of the intensity of the scattered radiation and its spectral composition were determined.The energy flux of the primary radiation was determined by use of an ionization chamber and Roentgen KH-5 photographic film. The intensity of the scattered radiation was measured with a gas-filled counter with a practically constant sensitivity to -quanta of different energies. The spectral composition of the scattered radiation was determined by the method of absorption in lead.This work was performed at the suggestion of Professor O. I. Leipunskii, whom the authors sincerely thank for his scientific guidance. The authors are deeply grateful to N. Ia. Buben and A. S. Strelkov for help in the work and a discussion of the results.     

14 MeV neutron yields from D-T operation of the MIT Cockcroft-Walton accelerator

As part of our fusion-product diagnostic development program, we have begun a series of experiments with 14 MeV neutrons generated in a Cockcroft-Walton accelerator. Two different detectors have been used to measure the neutron yield: a silicon SBD and a Cu foil. The energy of the emitted neutrons has been determined by using two spectrometers: the SBD and a³He proportional counter. The reaction rate is monitored, with about ±5% accuracy, by detecting the particles from D + T n +. The neutron yields obtained from the Si detector and the Cu activation had associated uncertainties of about ±15% and agreed well with the predicted values from measurements.     

Coherent effects during the interaction of slow neutrons with liquids

The total cross sections of liquid nitrogen and oxygen and the total cross section of gaseous nitrogen for neutrons with wavelengths in the 4 to 15-A range were determined in the VVR-M reactor of the institute of Physics, Academy of Sciences, Ukr.SSR. The cross sections of gaseous oxygen and nitrogen rise monotonically with increasing wavelength, while those of the liquids begin to fat1 at 5–5.5 A. Apparently this effect is connected with the existence of short-range order in the liquids; in nature, it is similar to the scattering of neutrons in polycrystalline material for wavelengths close to = 2d_max. The existence of coherent effects in the total cross section of heavy water is considered.Translated from Atomnaya Énergiya, Vol. 18, No. 5, pp. 452–455, May, 1965     

Substantiation of the Choice of Threshold Parameters for the System Monitoring the Fuel-Containing Materials in the Object “Cover”

A substantiation is given for the choice of threshold values of the neutron flux density (threshold-1 – Attention and threshold-2 – Danger), and formulas are derived for calculating these values for systems which are being designed and are currently in operation for monitoring the state of fuel-containing materials in the object Cover at the Chernobyl nuclear power plant.     

Scattering of medium-energy neutrons

Conclusion A study of inelastic-scattering processes as a function of neutron energy and the number of nucleons in the nucleus has enabled us to observe and investigate the effects of the nuclear shells in inelastic scattering. Experimental data on the inelastic-scattering cross sections have been used to check the optical model of the nucleus with a diffuse edge [23].The values of nuclear-physical constants (_e,_tre, ) obtained from the measured angular distributions of elastically-scattered neutrons may be used for calculating multigroup constants [24] required for physical calculations of nuclear-power systems and biological protection (shielding). The experimental material on the angular distributions of elastically-scattered neutrons has enabled us to verify the applicability of the optical model for describing elastic-scattering processes at energies below 1 MeV.Part of the information obtained on the elastic- and inelastic-scattering cross sections and the angular distributions of elastically-scattered neutrons has been included in handbooks on nuclear-physics constants [25–27].Translated from Atomnaya Énergiya, Vol. 20, No. 1, pp. 8–17, January, 1966     

Measurement of neutron emission from Ti and Pd in pressurized D2 gas and D2O electrolysis cells

Experiments using high-efficiency neutron detectors have detected neutron emission from various forms of Pd and Ti metal in pressurized D₂ gas cells and D₂O electrolysis cells. Four independent neutron detectors based on³He gas tubes were used. Both random neutrons (0.05–0.2 n/s) and time-correlated neutron bursts (10–280 n) of 100-s duration were measured using time-correlation counting techniques. The majority of the neutron burst events occurred at –30°C as the samples were warming up from the liquid nitrogen temperature.     

Calculation of neutron and gamma-ray energy spectra for fusion reactor shield design: Comparison with experiment-II

Measured and calculated neutron and gamma-ray energy spectra resulting from the transport of 14 MeV neutrons through a 0.30-m-thick lithium hydride slab and through a 0.05-m-thick lead slab followed by 0.30 m of lithium hydride are compared. Also reported are comparisons of the measured and calculated neutron energy spectra behind an 0.80-m-thick assembly comprised of stainless steel type 304 and borated polyethylene. The spatial dependence of the gamma-ray energy deposition rate measured using thermoluminescent detectors is compared with calculated data. The calculated data obtained using two-dimensional radiation transport methods and ENDF/B-IV cross-section data are in good agreement for all of the experimental configurations. Calculated integral neutron energy spectra agree with the measured data within 5 to 20% depending on neutron energy for the LiH and Pb plus LiH assemblies. The gamma-ray spectra agree within 20% for these slabs. The measured and calculated neutron energy spectra behind the SS-304-borated polyethylene assembly agree within 5% except at neutron energies below 5 MeV where background radiation influences the measured spectra. The gamma-ray energy deposition rates as a function of depth agree within a factor of two at all detector locations.     

The use of an integrating coincidence γ-spectrometer for analyzing a mixture of radioactive isotopes

The integrated -coincidence method is used for the selective detection of radioactive isotopes emitting cascade -quanta. This method enables the quantitative content of the isotopes to be determined, whose -radiation comprises 3–4% of the -radiatlon from the mixture, and also to be determined the quantitative content of the radioactive isotopes whose decay is accompanied by the emission of a positron, with subsequent emission of a -quantum.Translated from Atomnaya Énergiya, Vol. 19, No. 4, pp. 342–346, October, 1965     

Interpretation of Threshold Fission Chamber Signals

The total thermonuclear-neutron fluxes in the two energy groups 1.4–6.5 and 6.5–14.2 MeV are determined by mathematical analysis of the signal from a fission chamber with ²³⁸U using two proposed values of the effective fission threshold cross sections _eff1 and _eff2 in these groups and the generally accepted effective threshold cross section _eff encompassing both of these energy groups.It is shown that for the real ITÉR spectrum and for model spectra of thermonuclear neutrons, where the signals from a fission chamber with ²³⁸U remains constant and are distinguished from one another by the ratio of the fluxes in these groups, the two effective threshold cross sections _eff1 and _eff2 remain constant, while the generally accepted effective threshold cross section _eff varies from one model spectrum to another.Using two fission chambers, one with ²³⁸U and the other with ²³⁷Np, makes it possible to expand the energy range and to determine the total neutron fluxes in the three energy groups.     

Absorption and outgassing of helium during He+ ion bombardment of niobium

Conclusions The capute and outgassin of helium during bombardment by He⁺ ions of energy up to 15 KeV of a niobium target witha temperature of 290–1800°K have been studdied. It has been shown that as the temperature during irradation, T_b, is increased the coefficient of gaseous emission, , increases, while the number of injected atoms, N₀, and the capture coefficient decrease. For temperature greater than 1500°K practically 100% of the bombarding atoms are released to the vacuum. As the dose is increased, and N₀ increase and falls. An increase in to unity indicates saturation of saturation of theniobium by helium. The irradiation dose at which this saturation sets in and its level decrease with the temperature T_b.As a result of an analysis of the outgassing spectra, it has been shown thatthe release of helium occurs in three stages, each of which is due to one of the following causes: diffusion of individual atoms dissolved in the lattice; relase of helium from gas bubbles located in the volume of the metal; release of gas due to bursting of the shells of surface blisters. The last process has a basic role in outgassing at large irradiation doses.Translated from Atomnaya Énergiya, Vol. 38, No. 3, pp. 152–155, March, 1975.     

Drawbacks of the Classical Theory of the α-Rossi Method and Its Alternative

Certain contradictions and inaccuracies in the classical theory of the -Rossi stochastic neutron method are pointed out. An alternative theory which is almost free of contradictions and deficiencies of the classical theory is presented.A new implementation regime for the method is proposed to eliminate any influence of the prestart dip on the correlated amplitude in the -Rossi method using modern time-delay analyzers – the scaled start regime, consisting in triggerings of the time-delay analyzer scaled by two, three, or more signals from the starting neutron detector. It is shown that the correlated amplitude contains the ratio of the first and second moments of the number of prompt neutrons in a chain.A new expression is obtained for taking account of the spatial-energy effect in the -Rossi method. The effect differs from the well-known one not only by the energy component but also by a large range of possible values.The possibilities of the -Rossi method for determining the physical parameters of multiplying and nonmultiplying media are considered: , k _p, k, _eff, F, F _s, and D.