Energy Of Fission Fragments Research Articles

Fission Fragment Transport Effects on Heat Transfer in Fissioning Gases

Direct energy transfer by fission fragments near the wall of a cavity containing fissioning gas is studied in plane and cylindrical geometries. Analytical formulas are derived for the fission fragment energy flux. Heat transfer equations are solved for optically thick fissioning gases by taking into account the fission fragment energy transport effect. The results are applied to a heat transfer analysis of the fuel assemblies of a heterogeneous gas core reactor. The energy transfer mechanism in the fissioning gas is essentially nonlinear. Thus, the cooling effect due to direct fission fragment energy loss to the container walls does not become significant until the stopping range considerably exceeds the characteristic dimensions of the container. For example, when the ratio of the stopping range to the container dimension λ/δ is equal to 3, 45% of the energy flux at the container walls is due to the fission fragments; yet the maximum fuel temperature decreases by only l0%. If the ratio λ/δ is ∼100, fission fragments account for 95% of the energy flux to the walls, and the gas temperature decreases by 50%.

Study of fission fragments channeling in silicon monocrystals

Abstract The research results of 235U fission fragments channeling in silicon semiconductor detectors of heavy ions are reported. The analysis of the pulse height defect enabled to obtain the experimental relationship between energy losses in silicon due to nuclear collisions and the energy of fission fragments in LSS-units. The experimental values obtained more than twice exceed the computed ones given by Heines and Whitehead based on Lindhard's theory.

Fission fragment velocities, masses, and energies from 232Th(n, f) in the resonance-energy region

Fragment velocities, masses, and energies from neutron-induced fission of 232Th were measured at various neutron energies in the subthreshold-resonance region around E n ≅ 1.6 MeV and above threshold with good neutron-energy resolution. These quantities were obtained by three different methods using two different types of detectors, namely parallel plate avalanche counters for time of flight, and surface-barrier detectors for time of flight and pulse height measurements. Comparison of the different results and a careful error analysis clearly exhibit the limitation in resolution due to methodical uncertainties. Within these limits, none of the measured quantities shows dependencies on neutron energy.

New nuclide 263Ha.

A new nuclide $^{263}\mathrm{Ha}$ was produced in the bombardment of a $^{249}\mathrm{Bk}$ target with 93-MeV $^{18}\mathrm{O}$ ions. It was detected via spontaneous fission counting and was shown to have a half-life of about 0.5 min. This activity was also separated from the reaction products by automated rapid chemical separations using cation-exchange chromatography in 0.05M \ensuremath{\alpha}-hydroxyisobutyric acid. After chemical separation, $^{263}\mathrm{Ha}$ was found to decay by spontaneous fission (${57}_{\mathrm{\ensuremath{-}}15}^{+13}$%) and by \ensuremath{\alpha} emission (${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=8.35 MeV, 43%) with a half-life of ${27}_{\mathrm{\ensuremath{-}}7}^{+10}$ s. The spontaneous fission fragment energy spectrum is compatible with an average total kinetic energy of about 200 MeV.

Energy Production Using Fission Fragment Rockets

Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: Approximately twice as efficient if one can directly convert the fission fragment energy into electricity; by reducing the buildup of a fission fragment inventory in the reactor one could avoid a Chernobyl type disaster; and collecting the fission fragments outside the reactor could simplify the waste disposal problem. 6 refs., 4 figs., 2 tabs.

A time-of-flight spectrometer for unslowed fission fragments

The one-armed time-of-flight spectrometer mounted in a vertical experimental port of the research reactor at the Moscow Engineering Physics Institute (MEPhI) was designed for measuring mass-energy distributions of unslowed fission fragments. The study of rare fission modes in the yield regions up to 10 −6 is carried out having a target location near the reactor core and an electrostatic particle guide system installed, which increases the efficiency ratio of the spectrometer by a factor of 50. The special “heavy ion generator” operation mode of the spectrometer can be used for studies of fast (∼ MeV/amu) heavy ion interaction with matter. The fission fragment energy is measured by an ionization chamber or a semiconductor detector. The negligible angular divergence of the fragment beam enables fission fragment detection in a channeling registration mode to improve the energy resolution of semiconductor detectors. The fragment velocity is determined by the time of flight between two time pick-off microchannel plate detectors. A new procedure using unseparated fission fragments was developed to obtain the correct value for the time resolution of the system.

Energy calibration of the time-of-flight fission fragments spectrometer

Abstract A new method of the fission fragment energy detectors calibration is proposed, based on the fast heavy ion channeling effect in crystals. The calibration procedure uses the particle velocity as an additional measured parameter by extrapolating linearly the amplitude distribution peak positions in the two-dimensional spectrum “energy-time-of-flight” of unseparated fission fragments to the infinite electric field strength value in the detector. The calibration coefficients are determined via approximation of the extrapolated values by a bilinear function of fission fragment mass and energy.

Investigation of neutron shell effects and fission channels in the spontaneous fission of the PU-isotopes

The fission fragment energy and mass distributions of the spontaneously fissioning 236, 238, 240, 242, 244pu isotopes have been studied. These characteristics are an ideal data set for the investigation of shell effects and fission channels under identical conditions, i.e. constant Z, I π = 0 + and zero excitation energy. The important variations observed in the distributions are discussed in terms of the scission point model (Wilkins et al.) as well as in terms of the fission channel model with random neck-rupture (Brosa et al.).

Mass, energy and nuclear charge distribution of fission fragments

The most recent data on fission fragments distributions are reviewed with special emphasis put on the nuclear charge. The range of fissile nuclei extends from 229Th to 249Cf for thermal neutron induced fission. The features of the nuclear charge distribution are discussed and the fine structures on the yields and on the kinetic energy are shown to yield valuable informations on the latest stages of the process.

Symmetric and asymmetric fission of nuclei lighter than radium

Recent studies of the mass and energy distributions from fission of nuclei lighter than Ra at low and moderate energies are reviewed in order to inquire into problems related to the boundaries of the fission asymmetry, distinct fission modes, complexity of the fission fragment mass and energy distributions.

Comparison of different methods for the determination of fission fragment velocity, mass, and energy distributions for 232Th(n, f)

Average velocities, masses, energies, and respective variances of fragments from 232Th(n, f) at E n ≈ 1.7 MeV are determined from double velocity, double energy, and from velocity/energy measurements. The results are compared with respect to methodical differences and uncertainties on an absolute scale. It is argued that systematic errors limit the accuracy for velocity, mass, and energy measurement to ±0.1 mm/ns, ±1 u, and ±1.5 MeV, respectively.

Fission-Fragment Energy Deposition in Argon

The gas-dynamic response of argon to fission-fragment energy deposition is simulated, for the first time explicitly including the coupling between the gas density, which is spatially and temporally varying, and the power density. In simulations of three experiments with different initial fill pressures of argon, good agreement was found between calculated and observed pressure rises, after the experimental pressure rise data from one case were used as a calibration. However, in each case, the calculated thermal energy deposition corresponding to the experimental pressure data was about half the fission-fragment kinetic energy release into the gas predicted by neutron and fission-fragment transport calculations. Also, the experimental pressure data exhibited a decay not seen in the simulations, which did not incorporate an energy-loss mechanism.

Detection of Heavy Ions and Fission Fragments Using MOS Sensors

A prerequisite to the application of MOS sensors for measurement in neutron fields is the investigation of detection of heavy ions and fission fragments using these sensors. The detection efficiency of MOS sensors for heavy ions and fission fragments depends on the angle of incidence and the energy of incident particles. Therefore, investigations were carried out for measurement of the pulse rate-voltage characteristics for different angles of incidence of heavy ions and fission fragments and for different energies of fission fragments slowed down in air. From these characteristics the angular dependence of detection efficiency and the registration threshold to the specific ionization losses of fission fragments as a function of operation voltage were determined. The experiments described in the paper were performed with 129Xe ions and 232Cf fission fragments.

Dependence of the mean kinetic energy of fission fragments on the excitation energy of the fissile nucleus

Dependence of the mean kinetic energy of fission fragments on the excitation energy of the fissile nucleus

Sputtering of monocrystalline and polycrystalline gold by multiply charged ions (fission fragments)

The sputtering coefficients S of ultradispersed gold layers were in [i] obtained with multiply charged ions with a high specific energy loss, e.g., fission fragments, and amount to 103-104 atoms per fragment, provided that the size of the gold grains is ~30-50 nm (nonperforated islandlike layers). It follows from the energy dependence of S for such ultradisperse gold layers[2] that abnormally large S values msst result from inelastic interactions of the multiply charged ions with the gold atoms because S decreases in proportion to the decrease in the fission fragment energy, i.e., in proportion to the decrease in the specific ionization losses of energy. The possible mechanisms of such "inelastic" sputtering were considered in [3].

Measurement of prompt neutrons emitted from thermal neutron-induced fission of uranium-233 by double-energy double-velocity method.

A new double-energy double-velocity measurement system for the thermal neutron-induced fission fragments was developed. In this system, the energies of fission fragments were measured by silicon surface barrier detectors (SSB) and the velocities of them by time-of-flight method utilizing thin film detectors as start detectors and SSBs as stop detectors. With this system, the energies and the velocities of the thermal neutron-induced fission fragment of 233U were measured. The prompt neutron distribution was determined from the experimental data.

Selection of objects for radiolytic production of secondary energy carriers

The design of a homogeneous nuclear reactor filled with an aqueous solution of uranium sulfate is described in [I]. During the operation of this reactor some of the nuclear energy is converted into molecular hydrogen, which in this case is a secondary energy carrier. A detailed calculation of the reactor was carried out assuming that the radlolytic yield of hydrogen G (H2) may be ~.6 molecules per i00 eV of absorbed energy of 235U fission fragments.

Spatial distribution of uranium on a thin target foil by external beam PIXE analysis

Measurement of fission fragment kinetic energies requires the use of a very thin uniform fission foil in order to minimize the kinetic energy loss incurred by the fragments in traversing the foil. A study of the thermal neutron-induced fission process in 235U, using nominally uniform uranium foils of 1 mg cm −2 thickness, displayed greater than expected degradation of the recorded fission fragment energy spectra indicating a non uniformity in deposition. The spatial distribution of the uranium deposition on the foils has been measured using an external proton beam for particle-induced X-ray emission (PIXE) analysis, which has identified a nonuniformity of the uranium deposition by greater than 50% from the average with 0.5 mm spatial resolution and provided an independent and nondestructive means of determining the average foil thickness.

Variation of Kinetic energy distributions of fission fragments with bombarding energy in 4HE induced fission of 238U at medium energies

The kinetic energy and mass distributions of fission fragments in 4He induced fission of 238U were studied in the bombarding energy range of 32 to 56 MeV. The variation in the average fragment kinetic energy E k with bombarding energy has been obtained as a function of fragment mass. It is seen that E k increases strongly with bombarding energy and the slope d E k / dE α has a strong dependence on the fragment mass. This result indicates that both the shell effects and the saddle to scission dynamics may play a role in determining the scission configuration at these excitation energies.

235U(n, f) Fragment mass-, kinetic energy- and angular distributions for incident neutron energies between thermal and 6 MeV

Fission fragment energies and emission angles have been measured for 235U(n, f) in the neutron energy range from thermal to 6 MeV in steps of 0.5 MeV. The pre-neutron emission mass distributions were evaluated and described by a five-gaussian representation. The resulting parameters show a sudden change in their neutron energy dependence between 1.5 and 2.0 MeV, which might be due to pair breaking. From the total kinetic energy the sum of the deformations of the two fragments was evaluated. Clear proton pairing effects are visible since the even-proton fragments are less deformed than neighbouring odd-proton fragments. The present data confirm also that the TKE averaged over all fragments drops with excitation energy above 4 MeV. This behaviour is mainly due to drastic changes in TKE as function of mass split. At a yield level of 10 −6 per MeV of the light fragment kinetic energy cold fragmentation was observed for light fragment masses 87 to 110. In this mass region the light fragments are prolate and have a ground state electric quadrupole moment larger than ≈1 b. The angular distributions of fission fragments showed no mass dependence.