Energy Release In Fission Research Articles

Point light detection with UO2

UO2's electrical properties and U's inherently high fission energy release make a UO2-based direct conversion neutron detector a tantalizing possibility, but the evolution of even rudimentary devices is inhibited by the absence of large, high quality single crystals of UO2. Hydrothermally grown UO2 is incorporated into a prototype device here, and laser light is used as a surrogate for neutron-induced fission events. Excitation sources with wavelengths of 325, 488, 532, and 633 nm are incident on the device for a variety of timescales to test the detection responses, resolution, and saturation behaviors. The non-amplified changes in the current are presented, including when the illumination's diameter, power, and location are altered. Photocurrent changes follow a positively correlated linear trend with power and device efficiency is inversely correlated with illumination wavelength. The impact of illumination time on the detection efficiency is discussed. Illumination event detection is independent of illumination surface area size and largely independent of the illumination location. The ramifications of these results with regard to the development of UO2 as a neutron detector are considered.

Total kinetic energy and mass yields from the fast neutron-induced fission of $$^{239}\hbox {Pu}$$

The total kinetic energy (TKE) release in fission is an important observable, constituting over 80% of the energy released in fission (E$_{f}$ $\approx$ 200 MeV). While the TKE release in the $^{239}$Pu(n,f) reaction was previously measured up to 50 MeV incident neutron energy (E$_{n}$), there were features in TKE release at the highest values of E$_{n}$ that were puzzling. There was a marked flattening of TKE release from E$_{n}$ = 30 to 50 MeV, in disagreement with the clearly decreasing TKE observed from E$_{n}$ = 0.5 to 30 MeV. To verify and clarify this trend, TKE measurements at higher values of E$_n$ were made. We present absolute measurements of TKE release in $^{239}$Pu(n,f) from E$_{n}$ = 2.4 to 100 MeV. We used silicon PIN detectors to measure the fragment energies and deduce mass-yield curves using the 2E-method. We also discuss fission asymmetry and the relationships between approximate fission fragment mass and distortion.

Prompt $$\gamma $$-ray characteristics from $$^{235}$$U(n, f) at $${\overline{E}}_{n}$$ = 1.7 MeV

In response to nuclear data requests by OECD NEA, we present here the first results with respect to prompt-fission \(\gamma \)-ray spectra characteristics for fast neutrons on \(^{235}\)U. For that we have analyzed previously taken prompt-fission \(\gamma \)-ray data from the reaction \(^{235}\)U(n, f) induced by fast neutrons of average energy \({\overline{E}}_{n}\) = 1.7 MeV and spectral properties were deduced. It was expected that the values would be somewhat higher than for thermal-neutron induced fission of the same system, which at a first glance turned out to be not the case. However, taking the different prompt time windows relative to the coincidence timing resolution between both measurements into account, this discrepancy could be resolved. The results are an average multiplicity \({\overline{M}}_{\gamma }\) = 7.45 ± 0.48 \(\gamma \) rays per fission and an average total \(\gamma \)-ray energy release in fission \({\overline{E}}_{\gamma ,tot}\) = (6.03 ± 0.47) MeV, which includes an additional relative uncertainty of 4% from the time window correction. The corresponding average energy per \(\gamma \) ray is \({\overline{\epsilon }}_{\gamma }\) = (0.81 ± 0.04) MeV.

ENDF/B-VIII.0: The 8th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, and charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.

Spontaneous fission properties of superheavy elements

Spontaneous fission properties of transuranium isotopes are reviewed. Specific emphasis was laid on brief historical overviews of theoretical descriptions and experimental determination of basic properties as spontaneous fission half-lives, fission barriers, or total kinetic energy release in fission. Experimental spontaneous fission half-lives are compared with the results of recent theoretical predictions. Hindrance factors for spontaneous fission of odd-mass nuclei are discussed in context with the configuration (spin, parity) of the fissioning states and the change in energy of single particle levels at deformation. Kinetic energy release and mass distributions are discussed in the context of different fission modes, as symmetric and asymmetric or fission from elongated or compact shapes of the nascent fission fragments. An overview of recent fission barrier calculations of superheavy elements on the basis of macroscopic-microscopic models or self-consistent calculations is given, and the results are compared for selected examples.

β-delayed fission of192,194At

By using the recoil-fission correlation technique, the exotic process of beta-delayed fission ($\ensuremath{\beta}$DF) was unambiguously identified in the very neutron-deficient nuclei ${}^{192,194}$At in experiments at the velocity filter SHIP at Gesellschaft f\"ur Schwerionenforschung (GSI). The upper limits for the total kinetic energy release in fission of ${}^{192,194}$Po, being the daughter products of ${}^{192,194}$At after ${\ensuremath{\beta}}^{+}/EC$ decay, were estimated. The possibility of an unusually high $\ensuremath{\beta}$DF probability for ${}^{192}$At is discussed.

Cooling of young neutron stars in GRB associated to supernovae

Recent observations of the late ($t=10^8$--$10^9$ s) emission of supernovae (SNe) associated to GRBs (GRB-SN) show a distinctive emission in the X-ray regime consistent with temperatures $10^7$--$10^8$ K. Similar features have been also observed in the two Type Ic SNe SN 2002ap and SN 1994I that are not associated to GRBs. We advance the possibility that the late X-ray emission observed in GRB-SN and in isolated SN is associated to a hot neutron star (NS) just formed in the SN event, here defined as a neo-NS. We discuss the thermal evolution of neo-NS in the age regime that spans from $\sim 1$ minute (just after the proto-NS phase) up to ages <10-100 yr. We examine the key factor governing the neo-NS cooling emphasizing on the neutrino emission. A phenomenological heating source and new boundary conditions are introduced to mimic the high-temperature atmosphere of young NSs. We match the neo-NS luminosity to the late X-ray emission of the GRB-SN events URCA-1 in GRB980425-SN1998bw, URCA-2 in GRB030329-SN2003dh, and URCA-3 in GRB031203-SN2003lw. By calibrating our additional heating source at early times to $\sim 10^{12}$--$10^{15}$ erg/g/s, we find a striking agreement of the luminosity obtained from the cooling of neo-NSs with the late ($t=10^{8}$--$10^{9}$ s) X-ray emission observed in GRB-SN. It is therefore appropriate to revise the boundary conditions used in the cooling theory of NSs, to match the proper conditions of the atmosphere at young ages. Additional heating processes that are still not studied within this context, such as e+e- pair creation by overcritical fields and nuclear fusion and fission energy release, might also take place under such conditions and deserve further analysis. Observation of GRB-SN has shown the possibility of witnessing the thermal evolution of neo-NSs. A new campaign of dedicated observations is recommended both of GRB-SN and of isolated Type Ic SN.

Generalized Energy-Dependent Q Values for Fission

We extend Madland's parameterization of the energy release in fission to obtain the dependence of the fission Q value for major and minor actinides on the incident neutron energies in the range 0 {le} E{sub n} {le} 20 MeV. Our parameterization is based on the actinide evaluations recommended for the ENDF/B-VII.1 release. This paper describes the calculation of energydependent fission Q values based on the calculation of the prompt energy release in fission by Madland. This calculation was adopted for use in the LLNL ENDL database and then generalized to obtain the prompt fission energy release for all actinides. Here the calculation is further generalized to the total energy release in fission. There are several stages in a fission event, depending on the time scale. Neutrons and gammas may be emitted at any time during the fission event.While our discussion here is focussed on compound nucleus creation by an incident neutron, similar parameterizations could be obtained for incident gammas or spontaneous fission.

Investigation of phenomenological models for the Monte Carlo simulation of the prompt fission neutron andγemission

A Monte Carlo simulation of the fission fragment deexcitation process was developed in order to analyze and predict postfission-related nuclear data which are of crucial importance for basic and applied nuclear physics. The basic ideas of such a simulation were already developed in the past. In the present work, a refined model is proposed in order to make a reliable description of the distributions related to fission fragments as well as to prompt neutron and $\ensuremath{\gamma}$ energies and multiplicities. This refined model is mainly based on a mass-dependent temperature ratio law used for the initial excitation energy partition of the fission fragments and a spin-dependent excitation energy limit for neutron emission. These phenomenological improvements allow us to reproduce with a good agreement the $^{252}\mathrm{Cf}$(sf) experimental data on prompt fission neutron multiplicity $\overline{\ensuremath{\nu}}(A)$, $\overline{\ensuremath{\nu}}(TKE)$, the neutron multiplicity distribution $P(\ensuremath{\nu}),$ as well as their energy spectra $N(E)$, and lastly the energy release in fission.

Dynamics and energy release in fission of small doubly charged clusters.

Energetics and dynamics of Coulombic fission of small doubly charged potassium clusters subsequent to the ionization of singly charged ones are investigated experimentally and theoretically. Fission is shown to occur predominantly via ${\mathrm{K}}_{\mathit{n}}^{++}$\ensuremath{\rightarrow}${\mathrm{K}}_{\mathit{n}\mathrm{\ensuremath{-}}3}^{+}$+${\mathrm{K}}_{3}^{+}$ for 5\ensuremath{\le}n\ensuremath{\le}12. The close correspondence between the measured and the calculated kinetic energy release accompanying the fission process allows a deeper understanding of the dynamics and energy redistribution mechanisms in fission of metallic clusters.

Feasibility of a Nuclear Fission Reactor at the Center of the Earth as the Energy Source for the Geomagnetic Field.

Ideas have previously been advanced suggesting the possibility that uranium exists within the Earth's core. In. the present paper, evidence is presented for the existence within the Earth's core of substantial quantities of uranium and thorium. The concept of an accumulation of uranium in the core of the Earth functioning as a nuclear fission breeder reactor is presented. Means for concentrating actinide elements within the Earth's core and for separating actinide elements from reactor poisons are disclosed. Nuclear reactor feasibility is demonstrated by Fermi's k∞ in excess of unity for times in the geological past. The concept that the Earth's geomagnetic dynamo is driven by nuclear fission energy is discussed as is the concept that the frequent, but irregular, polarity reversals of the geomagnetic field have their origins in intermittent nuclear reactor output. Although great uncertainty exists in estimates of the abundances of the actinide elements in the core of the Earth and in details of the chemistry of the core, the results of the present paper indicate if uranium and thorium exist in the core of the Earth as elements or compounds, as evidence indicates, the actinides: (1) would be the most dense matter in the Earth; (2) would tend to concentrate at the center of the Earth; (3) would tend to be separated on the basis of density from less dense reactor poisons; and (4) if accumulated 3000 million years ago, would be able to initiate self-sustaining nuclear fission chain reactions which may continue to the present through fuel breeding reactions. The magnitude of available nuclear fission energy release throughout geological time is of major geophysical importance and is more than sufficient to power the geomagnetic field.

A new systematics of fragment total kinetic energy release in fission

A general fit has been performed to the data on most probable fragment total kinetic-energy release in fission, 〈Ekt〉, for values of parameterZ2/A1/3, of the fissioning nucleus ranging between 42 and 2150. The data result to be rather well fitted to an expression of the type 〈Ekt〉=Z2/(aA1/3+bA−1/3+cA−1) witha=9.39,b=−58.6 andc=226 (all values expressed in MeV−1). For light fisssioning systems the present result provides a trend of 〈Ekt〉 which gives vanishing 〈Ekt〉-values forZ approaching zero, as predicted in liquid-drop model calculations.

Spin-Dependent Calculation of Fission Neutron Spectra and Fission Spectrum Integrals for Six Fissioning Systems

Calculations of fission neutron spectra and fission spectrum integrals for six fissioning systems are reported. The systems studied are thermal-neutron-induced fission of 233U, 235U, and 239Pu; 2-MeV neutron fission of 232Th and 238U; and spontaneous fission of 252Cf The Madland-Nix formalism is used, but is extended to take account of the spin of the fission fragment. Also, more recent values for the average energy release in fission are used. The results of the fission neutron spectrum calculations are given in tabular and graphical form for applied purposes and are compared with experimental data. Similar deviations from a Maxwellian spectrum are seen for each system. The effect on the fission neutron spectra of 233U, 235U, and 239Pu from inclusion of alternative values for the average total fragment kinetic energy is shown.

Energy calibration of surface barrier detectors for fission fragments

The pulseheight, X, delivered in surface barrier detectors by incoming fission fragments of given energy, E, and mass, M, has been studied. Fragments separated as to energy and mass from the 235U(n, f) reaction induced by thermal neutrons were available from the Lohengrin spectrometer of the ILL. The energies on Lohengrin were calibrated by a time-of-flight technique. It could be shown that for the mass and energy ranges of unslowed fragments encountered in nuclear fission there is a linear relationship between E and X for any fixed M, and similarly a linear relationship holds between E and M for any fixed X. The calibration equation, therefore, reads E = ( a + a′ M) X + b + b′ M with a through b′ being constants characterizing the detector. In parallel to the above measurements, the pulseheight spectra from a 252Cf(sf) source were taken. The pulseheights X = P L and X = P H for the light and heavy fragment peaks of this spectrum were determined by a fitting procedure with Gaussians. Several detectors having been tested, it appears that at least for detectors of the same brand, a universal calibration scheme can be set up which correlates the detector constants a through b′ to the Cf spectrum parameters P L and P H. The accuracy of this calibration is sufficient for most practical purposes. The above calibration method has been put forward and in general use since many years [1]. However, the revised constants of the present investigation yield kinetic energies of fission fragments which are lower by about 1–2%. These energies are in excellent agreement with recent independent measurements of the kinetic energy release in fission. Along with the calibration the energy resolution of surface barrier detectors has been studied as a function of bias voltage on the detector and mass or energy of incoming ions.

Systematics of fission fragment total kinetic energy release.

Recent data for the most probable total kinetic energy release in fission $〈{E}_{K}〉$, have been combined with earlier results in order to reevaluate the systematic dependence of these values on the Coulomb parameter $\frac{{Z}^{2}}{{A}^{\frac{1}{3}}}$. A least-squares analysis of the current data base yields $〈{E}_{K}〉=0.1189\frac{{Z}^{2}}{{A}^{\frac{1}{3}}}+7.3$ MeV, where $\frac{{Z}^{2}}{{A}^{\frac{1}{3}}}$ refers to the fissioning nucleus. This expression exhibits a somewhat steeper slope than previous fits.

The fission processes 236U(α, α′f) at Eα = 50 MeV and 235U(d, pf) at Ed = 23 MeV and the total kinetic energy release in fission of excited nuclei

The fissioning nucleus 236U was investigated by two different reactions. Total kinetic energies (TKE) as function of the excitation energy above the highest fission threshold are shown to have different behaviour for E X below the two quasiparticle threshold 2Δ and above. A strong dependence on the mass splitting is observed.

Verification of energy release in fission from power plant calorimetrics and isotopic composition of spent fuel

The reactor of a nuclear power station was treated as a flow calorimeter to evaluate the energy released in fission from a given loading of UO 2. The changes in the inventories of U and Pu isotopes were obtained from reprocessing of the spent fuel and the corresponding total number of fissions was determined. The resulting energy released per average fission in a fuel irradiated to 11·5GWD/MTU was found to be 203·2 ± 6·0 MeV from batch isotopic method, 204·6 ± 6·3 MeV from batch composite method and 204·8 ± 7·2 MeV from 148Nd-analyses. For burnups both higher and lower than this value, the results indicate the presence of a burnup dependence somewhat greater than that expected on the basis of Pu buildup alone. The accuracy of the plant data was found to be limited by the ability to measure the steam generator feed water flow rates.

The use of position-sensitive semiconductor detectors in the study of heavy element nuclear reactions

The application of position-sensitive semiconductor detectors to the study of heavy element nuclear reactions at intermediate energies is described. Experimental procedures and results are presented for the use of these devices in the following types of measurements: (1) binary fission fragment angular correlations; (2) fission fragment angular distributions; (3) kinetic energy release in fission, and (4) spallation recoil product angular distributions. The position-sensitive detectors are found to provide much improved experimental efficiency over normal semiconductor detectors in experiments where the angular dependence of the products is quite strong; e.g. fission fragment angular correlations and spallation recoil angular distributions. For experiments in which the product counting rates vary slowly with angle, such as fission fragment angular distributions, the position detector is much less useful. Although the energy resolution of these devices is poorer than normal detectors, they are advantageous in experiments designed to study fission energetics as a function of reaction kinematics.

Effects of angular momentum on kinetic energy release in fission

Values for the most probable kinetic energy release in fission following compound-nucleus reactions between various targets and ions are reproduced. with a standard deviation of 1.5 MeV. by the expression E K 0 ( MeV) = 0.0042 Z 0 2/A 0 1 3 + 0.075 E 0 . where Z 0. A 0 and E 0 are respectively the atomic number. mass number and the excitation energy of the compound nucleus.

Nuclear systematics of the heavy elements—I energetics and masses

From examination of nuclear decay energy systematics, the mass-energy surface of the heavy elements has been extended to experimentally unknown isotopes. The mass predictions are made by empirical extrapolation of α- and β-decay energies which fit together to form closed cycles. Experimental masses and energies are based upon the most recent work of Wapstra et al. (7) The following quantities are tabulated for nuclei with 54≤ Z≤108 and 139≤ A≤277: nuclidic mass, α- and β-decay energies, and neutron and proton binding energies. In addition the systematic behaviour of the kinetic energy release in fission is examined.