Energy Of Fission Fragments Research Articles

Fission fragment energy spectrum determination with solid state nuclear track detectors

Attempts are described to optimize the spectrometric response of a number of solid state nuclear track detectors (SSNTD), including fused silica, soda-lime glass and phosphate glass. Diameters of the etch pits resulting from normally incident beams of fission fragments from a 252Cf source in vacuum have been measured, by both optical and scanning-electron microscopy, as functions of the period of etching and of the thickness of Al absorber introduced in the path of the beam. The best resolution of the heavy and light fission fragment groups, as inferred from the diameter distributions, is obtained with phosphate glass SSTND covered with ≈5 μm Al foil during irradiation.

A Study of Fission-Fragment-Induced Nucleation of Bubbles in Superheated Water

AbstractThis paper reports a study of bubble nucleation by fission fragments in superheated water. The experimental work was conducted using a small bubble chamber especially built for the program. The minimum superheat necessary for nucleation of visible bubbles by fission fragments (the threshold) was measured at temperatures between 380 and 440°F.Predictions of the threshold are based on comparison of the energy and linear energy transfer (LET) of fission fragments with the values required for bubble nucleation. Because of the variation in fission-fragment energy, the comparison is made on the basis of the median, 80’th percentile, and maximum energy and LET of the fragments present in the experiment.The data indicate that the LET comparison is the appropriate basis for prediction of the threshold. Using an empirically adjusted value of the LET required for nucleation, the calculated threshold agrees reasonably well with the data but becomes increasingly discrepant with increasing temperature. Reasons ...

A Review of Nuclear Sources of Non-Fossil Chemical Fuels

Abstract Energy derived from nuclear sources can be utilized either in the form of high-energy radiation, thermal energy or electrical energy. Each of these energy forms can be employed to produce non-fossil chemical fuels by transformation of available non-fossil substances. As a general definition, available non-fossil fuel substances are all resources other than coal, petroleum, or natural gas. Thus the substances that can serve as raw materials for nuclear-energy conversion to non-fossil chemical fuels are basically the substances found in water, air, and minerals. High-energy radiation from nuclear fission can be utilized either directly as fission-fragment energy in a chemonuclear reactor, or indirectly as neutron, gamma, and beta energy from isotopic sources. Fission-fragment energy is actually the only radiation-energy source that can be generated in sufficient quantity and at low enough cost to be considered for production of fuels. The two basic fuels that can be generated are hydrogen from water and carbon monoxide from carbon dioxide. The hydrogen and carbon monoxide can be used as fuels or can be subsequently converted to high-BTU gas or other liquid hydrocarbons. The main difficulties with fission-fragment chemonuclear systems are obtaining sufficiently high yields of fuel gases and demonstrating that a fuel essentially free of radioactive fission fragments can be produced. Thermal energy from nuclear fission in the form of steam or a high-temperature gas stream such as helium can, conceivably, be used to crack water to hydrogen and carbon dioxide to carbon monoxide. Carbon dioxide can be derived from thermal decomposition

Calculation of the Prompt Gamma Energy of Individual Fission Fragments from the Prompt Neutron Numbers

Approximate calculations of the prompt )I-ray energies of fission fragments and the total kinetic energies of different fragment pairs have been made on the basis of a liquid-drop model. In addition, reliable estimates� of the quantum energy for collective quadrupolar vibration have been used to calculate the number of prompt )I-ray quanta emitted by the fragments from the thermal-neutron-induced fission of 235U. There seems to be good agreement with the available experimental data. About 30 pairs of fission fragments from the thermal-neutron-induced fission of 233U, 235U, and 239Pu and the spontaneous fission of 252Cf have been included in this preliminary treatment.

Fission fragment energy loss and spectrum parameter changes for 252Cf sources overcoated with carbon and gold

The self-transfer properties of 252Cf sources in a vacuum environment necessitates the use of thin cover layers if the 252Cf sources are to be used in fission fragment experiments or if the amount of 252Cf on the sources is determined by low geometry alpha or fission fragment counting. The thin cover layers prevent the transfer of the 252Cf to surrounding areas without seriously degrading the fission fragment spectrum. This paper describes how thin carbon and gold cover foils affect the fission fragment energy, fission fragment spectrum parameters, and transfer rates from 252Cf sources.

Correlation entre les energies d'excitation des deux fragments complementaires dans LA fission spontanee de 252Cf

The correlation between the excitation energies of complementary fission fragments has been determined as a function of mass ratio. Contrary to results published by other authors the present data show that these energies are completely uncorrelated for most mass pairs.

Correlation of the most probable kinetic energy of fission fragments and ηp

This paper presents the investigation of correlating the most probable kinetic energy 〈 E k 〉 of the fission fragments and the Coulomb energy Z 2/A sol1 3 Further correlation of the average number of prompt neutrons emitted per fission_, vs. 〈 E k 〉 and Z 2/A sol1 3 , respectively, is also established. For comparative study, a new parameter Z 2√ A, as suggested by Okolovich et al. (1963), is employed for correlating 〈 E k 〉 and v ̄ p . It is found that this parameter Z 2√ A gives better consistency, when compared with experimental values of (Ek) and η p, for each family of isotopes in the present study by considering the logarithmic derivative 1/〈 E k 〉 d〈 E k 〉/d A. Six sets of semi-empirical polynomial equations have been derived for the correlation as mentioned above. The data for both 〈 E k 〉 and v ̄ p , are based on the most recent experimental investigations in this field. The formulae presented herein may be utilized to predict the values of ν p for the new isotopes produced in nuclear reactors with emphasis on the heavy nuclides which have no experimental data available. The range of atomic mass numbers under study is from 228–256.

252Cf Fission Fragment Energy Loss Measurements in Elementary Gases and Solids as Compared with Theory

Energy loss of 252Cf fission fragments in 15 gases and solids, representing a wide range of atomic numbers throughout the periodic system, has been measured using a calibrated Si surface barrier heavy ion detector. The data are used for a detailed and systematic comparison with existing theoretical treatments of the electronic energy loss mechanism showing that none of them gives overall good agreement for all stopping substances.The Bohr expression for heavy stopping substances, which shows consistent deviation from experiment for the entire range of stopping media, suggests that based on this approach, a semi-empirical modification can be derived.

Semi-Empirical Approach for Fission Fragment Energy Degradation in any Elementary Medium

A semi-empirical equation for the electronic energy loss of fission fragments has been derived by fitting the theoretical approach of Bohr, specifically developed for heavy stopping materials, to experimental data in gases and solids in a wide range of atomic numbers. The fitting procedure was performed by choosing a different expression for the number of electrons of the medium taking part in the stopping process, which includes empirical parameters obtained by fitting to experiment.The equation enables the energy loss of fission fragments in substances of any Z2, regardless of their physical state, to be predicted to a good degree of accuracy down to energies of approximately 20 MeV.

Fragment kinetic energies in MeV neutron-induced fission of 232Th

In a two-parameter experiment the kinetic energies of fission fragments from the reaction 232Th(n, f) were measured with semiconductor detectors. The neutron energies were 1.90, 2.97 and 4.81 MeV. From the data, mass and energy distributions along with the correlations between energy and mass were calculated. The mass distributions exhibit the well-known double-humped curve, with the peak-to-valley ratio decreasing from 510 1 , 122 1 to 45 1 for neutron energies E n = 1.90, 2.97 and 4.81 MeV respectively. A fine structure is observed in the mass yield at primary heavy fragment mass numbers A H ∗ = 134 and 141. The mean total primary fragment kinetic energy E K ∗ increases from 169.0 ± 2.0, 169.7 ± 2.0 to 170.4 ± 2.0 MeV for neutron energies 1.90, 2.97 and 4.81 MeV respectively. The errors given include the estimated systematic error, the statistical errors being in the order of 0.05 MeV. The increase in kinetic energy with excitation energy seems to be peculiar for 232Th. It is seen for all masses, except perhaps for the heavy mass numbers A H ∗ = 123 through 126 in the transition region between symmetric and asymmetric mass splits. The results are discussed in terms of channel effects at the saddle point and shell effects at the scission point.

A versatile d E/d x detector for heavy mass nuclear particles

We report herein a significant development in the art of heavy fragment (heavy nucleus) particle detection and identification. Recent improvements in the thin film detector have made it possible to achieve an output pulse responding to the energy loss, ΔE, experienced by the heavy fragment in traversing the scintillator film. Typically, for 252Cf fission fragment energy losses of about 10%, a clear separation between the light and heavy fragment ΔE signals is observed. In recording the ΔE spectrum, peak-to-valley ratios greater than 5:1 are obtained in the best cases. Exploratory experiments on light fragments clearly show the different energy losses experienced by 3He and 4He ions of comparable energies. The signal response (when thicker scintillator films are used) to total energy loss of alpha particles and fission fragments is reported. A preliminary view of the response of the new detector to accelerated 127I ions is also shown. The possible use of these detectors as particle identifiers of heavy mass nuclei is discussed and an attendant wide range of experiments is outlined to which these ΔE detectors might profitably be applied.

Fission fragment mass distributions and kinetic energies for spontaneous fission isomers

Abstract Fission fragment energy correlation experiments have been carried out for spontaneous fission isomers formed in the following reactions: 240 Pu(p, 2n) 239m Am, 239 Pu(d, 2n) 239m Am, 237 Np(d, 2n) 237m Pu, 238 U(d, pn) 238m U and 235 U(d, p) 236m U. The fragment mass distributions, total kinetic energies, and fragment distribution averages and widths are consistent with prompt, low-excitation fission systematics of the actinides. It is argued that fragment configurations, including mass and energy distributions, are determined in the same region of the multidimensional potential surface describing the fission process for both types of fission. Evidence which indicates that this region may begin in the neighborhood of the second barrier is discussed.

Evaluation of epitaxial n-GaAs for nuclear radiation detection

The high purity of n-GaAs grown by the liquid phase epitaxial process makes it suitable for the evaluation of this compound semiconductor in nuclear radiation detection. The wide band gap and high atomic number make it possible to operate surface barrier diodes at room temperature as high resolution detectors. The resolutions (fwhm) at 300 K have been found to be 21 keV for 5.49 MeV α-particles and 2.5 keV for 140 keV γ-rays. The best resolutions observed were 640 eV (130 K) for 59.54 keV γ-rays, 1.3 keV (200 K) for 84 keV conversion electrons and 16 keV (205 K) for 8.785 MeV α-particles. The thickness of the epitaxial region was ≈60 μm with contact diameter up to 3 mm. The energy per electron hole pair for α-particles is 4.27 eV ± 0.05 at 300 K with a linear variation with band gap of 2.7 over the temperature range 87 K to 340 K. The Fano factor for γ-rays is ≤ 0.18 ± 0.04 ( T ≈ 125 K). Variations of capacitance and pulse height with detector bias, as well as etch patterns, indicated a discontinuity in the impurity density profile in the region of the interface between the substrate and the epitaxial layer. Consideration of the theory of excess carrier recombination in direct band gap semiconductors shows that the charge collection efficiency is not expected to be significantly reduced by direct radiative recombination, even in the case of fission fragments. This is confirmed by the experimental observations that 252Cf fission fragment energy deficits of 14.4 and 6.3 MeV are not much larger than have been observed with Si detectors. The advantages of room temperature operation open up a wide field of application for GaAs detectors in both the physical and biomedical fields. For their full exploitation it will be necessary: (a) to grow thicker layers of high purity GaAs by the epitaxial or some other process; (b) to overcome the problem of signal attenuation at the epitaxial-substrate interface; (c) to develop a more rugged form of front contact and of detector encapsulation.

The response of position-sensitive detectors to fission fragments and other heavy ions

Position-sensitive surface barrier detectors have been used for the measurement of energy and angular distributions of fission fragments and other heavy ions. The techniques used to calibrate such detectors are described. It is possible to determine the position of an incident ion with a resolution of about 0.25 mm for a 50 mm detector length, the position response being independent of the energy of the ion. However, the position response curve is non-linear, showing its largest curvature at one end of the detector. The pulse height versus energy calibration was determined for a variety of heavy ions produced by elastic scattering of 32S and 16O. The ions Ni, Ag and Au exhibited pulse-height defects, which were measured as a function of ion energy, and were found to be approximately equal to those for a “heavy ion” type surface barrier detector. The pulse height versus energy calibration is a function of position, but is linear at a given position. In spite of the slow rise time of the pulses, it was possible to obtain fast timing signals, with a resolution of 3.5 nsec (fwhm) at a fixed position and fixed energy. The time dependence on position, however, is very large with about 50 nsec difference between the center of the detector and the ends.

A study of the low-energy transitions arising from the prompt de-excitation of fission fragments

A four-dimensional experiment has been performed in which the energies of coincident complementary fragment pairs, internal conversion electrons, and K X-rays emitted as a result of the spontaneous fission of 252Cf were recorded event by event using a multiparameter analyser. The fission fragment energies were used for mass identification and the X-ray energies supplied precise atomic number identification. The analysis of the conversion electron spectra has resulted in the assignment of numerous transitions to new isotopes, the determination of many transition half-lives, and the procurement of limited information concerning multipolarities. It was concluded, based on the X-ray and conversion electron data, that most of the large number of observed low-energy transitions associated with heavy fragments are attributable to odd-mass or doubly odd nuclei and that surprisingly little contribution to the low-energy spectra is associated with doubly even nuclei in the rare-earth region. Low-energy transitions in doubly even nuclei were found to be more prevalent among the light fragments. Data are presented supporting the assignment of a high intensity 241 keV transition as the 2 + to 0 + transition in 110Ru. An examination of this transition in terms of the energy predicted on the basis of rotational behaviour and with regard to the systematics of neighboring doubly even Ru isotopes reveals evidence which strongly suggests that 110Ru belongs to a new region of stable deformation.

Nuclear-Particle-Track Identification in Inorganic Solids

The unique feature of track-recording plastics which allows them to be used to identify particles is that the chemical rate of attack ${V}_{T}$ along a track is an increasing function of ionization rate. This same characteristic is shown to extend to inorganic dielectric solids. The relation between ${V}_{T}$ and ionization rate has been measured for five different glasses, using fission fragments of different energies. The variation of ${V}_{T}$ is least for ordinary lime glass and much the greatest for a phosphate glass, suggesting that the latter should be useful in resolving atomic numbers and energies of fission fragments and other very heavy, energetic nuclei. Equations are derived that allow the shapes of etched tracks to be calculated as a function of etching time and particle ionization rate. The calculations agree well with recent experimental results.

The diameter of etched fission fragment tracks in solid state nuclear track detectors as a function of the particle energy

Glass and several plastic materials have been irradiated orthogonally with respect to their surfaces by 235U fission fragments of known mass and energy. A correlation between fragment energy and the diameters of the etched fragment tracks is given. For sufficiently long etching times the method is well capable of an energy resolution of about 3 to 5 MeV. A weak mass dependence of this effect is existing. To test the methos a 252Cf fission fragment energy distribution has been measured which is in good agreement with corresponding solid state surface barrier detector.

Energetics and Mass Distribution of Fission Fragments in Triton- and Proton-Accompanied Fission ofCf252

The kinetic energies of the fission fragments and of the light particle emitted in triton- and proton-accompanied fission of ${\mathrm{Cf}}^{252}$ were measured in a four-parameter correlation experiment. Assuming that the average total kinetic energy of the fragments in long-range alpha fission (LRA fission) is 172.9 MeV, this value in triton-accompanied fission was found to be 173.5\ifmmode\pm\else\textpm\fi{}0.3, while in proton-accompanied fission the value of 173.6\ifmmode\pm\else\textpm\fi{}0.5 was obtained. The mass distribution in triton-accompanied fission was found to be very similar to that in LRA fission, while this distribution for proton-accompanied fission is somewhat different from that in both binary and LRA fission. In addition, the degree of correlation between the average total fission-fragment energy and the particle energy was measured.

Measurement of Neutron-Induced, Fission-Fragment Energy Spectra in the Advanced Laboratory

Fission experiments can be profitably performed in the Advanced Laboratory. Measurement of the fragment energy spectrum from a fissile source using a surface barrier detector demonstrates several characteristics of the fission process. Experimental difficulties in such measurements are discussed, and typical results are presented for neutron-induced fission with sources of natural uranium and those enriched in U235. Also shown are the results with the spontaneous fissile source Cf252.

On a simple model explanation of shell effects in nuclear fission

It is shown that shell effects on the deformation energy of fission fragments as derived from Nilsson potentials can account for the observed variation of the kinetic and excitation energy of the fragments as a function of mass. A simple static model of two tangent fission fragments is used, the scission point being determined by the requirement that the sum of deformation energies and the mutual Coulomb repulsion should be a minimum.