Uranium Fission Fragments Research Articles

Statistical Computational Model of Fission Products Composition of Irradiated Nuclear Fuel and Their Contribution to Gas-aerosol Emissions of Nuclear Power Plants

Based on the assumption that the radionuclide composition of gas-aerosol emissions from nuclear power plants (NPPs) into the environment is determined by the composition of the fuel in the reactor (but not identical to it), an analysis of the probability of the occurrence of various isotopes in possible emissions is conducted in this paper. It is confirmed that the activity of nuclear fuel, and consequently the emissions, are determined by uranium fission fragments, proving that the decay rate of radionuclides is proportional to the probability of the appearance of radionuclides with certain mass numbers. It is also shown that there is no functional relationship between the mass yield of radionuclides and their atomic mass, as the variability (fluctuations) in the content of radionuclides in VVER-440 reactor fuel and consequently in NPP emissions reaches 20 orders of magnitude, which prevents the application of computational methods for processing the results. This paper proves that, in order to determine the yield of radionuclides from their observable activity, applying a Zipf-Mandelbrot type distribution in “rank - size” coordinates, it is possible to carry out the mathematical modeling based on the appropriate processing of the obtained results.

Nuclear-excited source of coherent and incoherent radiation with direct nuclear pumping

Uranium fission fragments, as well as the products of 3He(n,p)3H and 10B(n,α)7Li nuclear reactions were utilized in the nuclear reactor for gas ionization and excitation. However, the 6Li(n,α)3H nuclear reaction was less examined. The use of lithium-6 as a surface source of excitation of the gas medium, due to the long path length of tritium nuclei in the gas, allows to excite large volumes of gas as opposed to using 235U or 10B.While investigating the luminescence of noble gases in the core of the IVG.1M research reactor, we noted an appearance of alkali metal lines and a sharp increase in the intensity of these lines at temperatures above 570 K. It was determined that the population of levels of lithium atoms has practically no effect on the population of the 2p-levels of atoms of noble gases. The selectivity of p- and s-levels deactivation by lithium atoms implies the possibility of creating inversion of population at 2p-1s transitions of noble gas atoms. Successful experiments to study the luminescence of gases upon excitation by 6Li(n,α)3H nuclear reaction products allow us to proceed to experiments to achieve the laser action threshold and study the lasing characteristics of gas mixtures at the IGR pulsed nuclear reactor with thermal neutron flux density up to 7∙1016 n/cm2s. For this purpose, an experimental device designs were proposed to perform experiments on the IGR reactor. A step-by-step procedure of fabrication of a nuclear-excited source for excitation of gas mixtures is provided. The results of reactor experiments aimed at determining the spectral and temporal characteristics of optical radiation during excitation of gas mixtures by 6Li(n,α)3H nuclear reaction products are presented.

Study Results for Intensity of Sputtering of Thin Carbon Films by Uranium Fission Fragments

Study Results for Intensity of Sputtering of Thin Carbon Films by Uranium Fission Fragments

Characteristics of the Active Element of a Nuclear-Pumped Cadmium-Vapor Laser

The influence of the active-element characteristics on the efficiency of a cadmium-vapor laser pumped by uranium fission fragments was studied experimentally. The 441.6 nm laser radiation of the cadmium ion was studied. An aluminum tube with diameter ~15 mm and an inner coating of U3O8 with thickness 3 mg/cm2 served as the active element. The neutron source was the BARS-6 pulsed, fast, aperiodic, self-extinguishing reactor. A comparison of the efficiency of the laser with similar data previously obtained under the same conditions for a 48 mm in diameter active element with a ~10 mg/cm2 thick uranium metal coating shows that a three-fold reduction of the diameter of the active element and uranium coating thickness results in a 2.5-fold increase of the laser efficiency. This confirms the hypothesis of internal losses of laser radiation in the active element of a fission-fragment pumped laser which are due to the scattering of light by transverse sound waves of the gas density which appear during a pumping pulse because of the radial non-uniformity of the energy input.

Revisiting the Analysis of the Isochronous Mass Measurements of Uranium Fission Fragments at the ESR

The re-analysis of experimental data on mass measurements of ura- nium fission products obtained at the ESR in 2002 is discussed. State-of-the-art data analysis procedures developed for such measurements are employed.

Laser Beam Transmission by Inorganic Liquid Activated by Neodymium and Uranyl in Pulsed Excitation by Uranium Fission Fragments

The transmission of 1.054 μm probing laser radiation by laser liquid $$ {\mathrm{POCl}}_{3^{\hbox{--} }}{{\mathrm{SnCl}}_{4^{\hbox{--}}}}^{235}{\mathrm{UO}}_2^{2+}\hbox{--} {\mathrm{Nd}}^{3+} $$ excited by uranium fission fragments was measured. It is shown that for liquid pressure 10.1 MPa the transmission of the liquid does not exceed 1. It is found that the transmission of the liquid in the active element with aperture 25 mm is approximately 4 times lower than in an element with aperture 10 mm. A qualitative explanation of the observed effect is proposed on the basis of the assumption that light was scattered by radial acoustic density waves in the liquid. This effect can serve as one of the primary reasons for the absence of lasing during nuclear pumping of the liquid under discussion. Methods of reducing the influence of this effect are examined.

New results from isochronous mass measurements of neutron-rich uranium fission fragments with the FRS-ESR-facility at GSI

Masses of uranium fission fragments have been measured with the FRagment Separator (FRS) combined with the Experimental Storage Ring (ESR) at GSI. A 410-415 MeV/u 238U projectile beam was fast extracted from the synchrotron SIS-18 with an average intensity of 109/spill. The projectiles were focused on a 1g/cm2 beryllium target at the entrance of the FRS to create neutron-rich isotopes via abrasion-fission. The fission fragments were spatially separated with the FRS and injected into the isochronous storage ring ESR for fast mass measurements without applying cooling. The Isochronous Mass Spectrometry (IMS) was performed under two different experimental conditions, with and without B $\rho$ -tagging at the high-resolution dispersive central focal plane of the FRS. The evaluation has been done for the combined data sets from both experiments with a new method of data analysis. The use of a correlation matrix has provided experimental mass values for 23 different neutron-rich isotopes for the first time and 6 masses with improved values. The new masses were obtained for nuclides in the element range from Se to Ce. The applied analysis has given access even to rare isotopes detected with an intensity of a few atoms per week. The novel data analysis and systematic error determination are described and the results are compared with extrapolations of experimental values and theoretical models.

Efficiency and rate capability studies of the time-of-flight detector for isochronous mass measurements of stored short-lived nuclei with the FRS-ESR facility

A time-of-flight (TOF) detector is used for Isochronous Mass Spectrometry (IMS) with the projectile fragment separator FRS and the heavy-ion storage ring ESR. Exotic nuclei are spatially separated in flight with the FRS at about 70% of the speed of light and are injected into the ESR. The revolution times of the stored ions circulating in the ESR are measured with a thin transmission foil detector. When the ions penetrate the thin detector foil, secondary electrons (SEs) are emitted from the surface and provide the timing information in combination with microchannel plate (MCP) detectors. The isochronous transport of the SEs is performed by perpendicular superimposed electric and magnetic fields. The detection efficiency and the rate capability of the TOF detector have been studied in simulations and experiments. As a result the performance of the TOF detector has been improved substantially: (i) The SE collection efficiency was doubled by use of an optimized set of electric and magnetic field values; now SEs from almost the full area of the foil are transmitted to the MCP detectors. (ii) The rate capability of the TOF detector was improved by a factor of four by the use of MCPs with 5μm pore size. (iii) With these MCPs and a carbon foil with a reduced thickness of 10μg/cm2 the number of recorded revolutions in the ESR has been increased by nearly a factor of 10. The number of recorded revolutions determine the precision of the IMS experiments. Heavy-ion measurements were performed with neon ions at 322MeV/u and uranium fission fragments at about 370MeV/u. In addition, measurements with an alpha source were performed in the laboratory with a duplicate of the TOF detector.

Моделирование прямого преобразования кинетической энергии осколков деления урана в энергию лазерного излучения в аргон-ксеноновой пылевой плазме с наночастицами урана

Моделирование прямого преобразования кинетической энергии осколков деления урана в энергию лазерного излучения в аргон-ксеноновой пылевой плазме с наночастицами урана

Spontaneous and induced emission of excimer molecules under pumping of and gas mixtures with a low content by fast electrons and uranium fission fragments

The spontaneous and induced emission of excimer molecules upon excitation of and gas mixtures with a low content by high-energy charged particles [a pulsed high-energy electron beam and products of neutron nuclear reaction ] has been experimentally studied. The electron energy was , and the pump current pulse duration and amplitude were and , respectively. The energy of fission fragments did not exceed , the duration of the neutron pump pulse was , and the specific power contribution to the gas was about . Electron beam pumping in a cell long with a cavity having an output mirror transmittance of 2.7% gives rise to lasing on the transition in the molecule with a gain and fluorescence efficiency . Pumping by fission fragments in a -long cell with a cavity formed by a highly reflecting mirror and a quartz window implements amplified spontaneous emission (ASE) with an output power of and a base ASE pulse duration of .

Prospects for the nuclear pumping of a VUV laser

The possibility of using nuclear emissions (in particular, uranium-fission fragments) to create a powerful source of stimulated VUV radiation is analyzed. The starting point in the analysis is provided by the results of recent investigations of a krypton–xenon mixture in an extended dc discharge, which indicate that continuous lasing is possible in the VUV region. Experience in transforming the kinetic energy of nuclear particles into the laser radiation of inert gases (in the visible and near-IR regions) makes it possible to homogeneously pump extended volumes of inert gases at atmospheric pressures and to transfer 20–30% of the embedded energy into spontaneous VUV excimer radiation. According to our estimates, the power of the quasi-continuous laser VUV radiation can reach 1–2kW∕L in this case.

Population kinetics of laser levels of neodymium ions in POCl3—SnCl4—235UO22+—Nd3+ excited by fission fragments

The population kinetics of laser levels of neodymium ions in the uranium-containing POCl3—SnCl4—235UO22+—Nd3+ laser liquid irradiated in a BARS-6 pulsed reactor is studied experimentally and theoretically. The relations between the populations of the upper and lower laser levels are studied at different time moments with respect to the pump pulse. An inverse population of laser levels is observed and found to be directly proportional to the pump power. The efficiency of pumping of the upper laser level of neodymium ions in the laser medium by uranium fission fragments is determined, and quantitative information is obtained on the inverse population, gain, and their dependences on the pump power.

Successive composition of two laser channels upon excitation of He—Ar—Xe (2.03 μm) and Ar—Xe (1.73 μm) mixtures by uranium fission fragments

The operation efficiency of the scheme with successive composition of two laser channels upon excitation of the active medium by uranium-235 fission fragments is studied experimentally and numerically. For the He:Ar:Xe = 380:380:1 mixture (at a pressure of 1 atm and the lasing wavelength λ = 2.03 μm) the maximum lasing power of a double channel (1 kW) is almost twice that of a single channel (540 W). Calculations show that in the case of ideal composition (without losses on mirrors) the lasing power of the double channel can be increased to 1.2 kW. For the Ar:Xe = 380:1 mixture (the pressure is 0.5 atm, λ = 1.73 μm) the maximum lasing power of the double channel (620 W) is slightly above that of the single channel (520 W), which is caused by the losses on aluminum mirrors employed for channel doubling and by a negative effect of optical inhomogeneities. In the case of ideal composition, the lasing power can be increased to 830 W.

Ion-optical layout of a powerful next-generation pre-separator for in-flight separation of relativistic rare isotopes

Rare isotope beams can be efficiently produced at relativistic energies via projectile fragmentation and projectile fission. Magnetic rigidity analysis in combination with atomic energy loss (Bρ–ΔE–Bρ method) in profiled matter placed at dispersive focal planes represents the tool for spatial separation in flight. The next-generation in-flight separators at high energies will consist of multiple degrader stages to provide intense monoisotopic fragment beams of all elements up to uranium. The pre-separator layout with the first degrader system holds many technical challenges, e.g. to handle the high-power primary beams characterized by a large range in time structure, from a DC beam to very short bunches. The latter requirement is particularly necessary for high-intensity primary beams bunched in short pulses (50ns) for experiments with storage-rings. Large acceptance and high-separation power for uranium fission fragments and for exotic nuclei far from stability are the keys to serve the nuclear structure and astrophysical research at the frontiers. Consequently, large aperture magnets have to be applied to handle the inevitable large phase-space volume. The correction of higher-order image aberrations is a challenge and essential to achieve a high-separation power for the Bρ–ΔE–Bρ method.

Gas Dynamics in Nuclear-Pumped Laser and Luminescent Cells with Buffer Volumes

A nonstationary gasdynamic model of sealed laser and luminescent cells pumped by uranium fission fragments is developed. This model extends the earlier 1D model of gas dynamics in cells of flat geometry to the case of cells with buffer volumes and allows analysis of gasdynamic processes for the energy deposition step distribution over the laser cell length.

Laser study of the time dependence of induced absorption in a liquid excited by uranium fission fragments

The results of 1.05-μm laser measurements of optical properties of the POCl3 — SnCl4 — UO22+ liquid containing vapour bubbles generated by the fission fragments of 235U nuclei formed upon irradiation of this liquid by neutrons in a BARS-6 pulsed reactor are presented. The average size of a bubble and its mean lifetime are obtained from experiments. The effect of pressure on the bubble size is studied. It is found that the lifetime of a bubble increases with increasing the concentration of molecular chlorine in the liquid due to its radiolysis induced by fission fragments.

The effect of simultaneous temperature, pressure and stress on the experimental annealing of spontaneous fission tracks in apatite: a brief overview

Tracks made in minerals by the electronic stopping of uranium fission fragments provide a modern geological dating tool, and are believed also to yield specific information on the low-temperature thermal history of rocks. Experimental work showing that the damaged crystal lattice along a fission track recovers primarily as a function of temperature ignored the fact that the basic theory of atomic diffusion requires an exponential decrease in the intrinsic diffusion coefficient with increasing pressure. Here, fission track recovery was experimentally investigated in basic apatite under the simultaneous influences of temperature, pressure and stress. We show that track fading is a complex recovery mechanism responding to several environmental physical parameters simultaneously. In particular a strong decrease in the track recovery rate was observed as a function of increasing pressure. And a nearly temperature-independent recovery was observed in samples under stress.

Interferometric technique for determining the energy deposition in gas-flow nuclear-pumped lasers

An interference technique is developed for determining the energy deposition in gas-flow lasers pumped by uranium fission fragments. It is shown that four types of interference patterns may be formed. Algorithms are presented for determining the type of interference and for enumerating the maxima in interference pattern.

Modelling the length distribution of etched tracks taking into account fragmentation due to partial annealing

Fission track length measurements on apatite minerals are of great interest in thermo-chronology studies. RBS analyses on Durango apatites irradiated by Krypton ions have previously shown the progressive fragmentation of tracks by annealing. This study made for different irradiation energies corresponding to those of uranium fission fragments has been completed by TEM and AFM on etched tracks. In all cases, segmentation figures have been observed, that clearly necessitates to introduce fragmentation of latent tracks to model the length distribution of uranium etched fission tracks. This presentation concerns the case of a homogeneous population of tracks with partial amorphization. The next step will consist in considering multiple sub-populations with different segmentation rates. This algorithm is a new aspect to be included in our model, which already takes into account diffusion and crystallography in the track etching process.

Properties of HTS for successful U/n processing

Insertion of uranium into HTS precursor powders prior to texturing, and irradiation with thermal neutrons after texturing is called U/n processing. Damage caused by uranium fission fragments has been extensively studied for pinning center behavior in Y123, and Ag-BiSCCO tape. In both HTS systems results for J c, anisotropy, etc. are excellent. We consider the chemical and physical conditions under which U/n processing is successful, including spacing, S, and size of deposits of U compounds, and neutron absorption by the HTS. If δ=length of the quasi-columnar fission fragment defects, we find S<2δ ∼5.4μm is needed for the best U/n results and, thus, if deposits of U compounds exist, sub-micron size is desirable. Application of these conditions is considered to Y123, Ag-BiSCCO tape, Nd123, Sm123 and Gd123. Studies in progress of Nd123 and Sm123 are reported.