Kinetic Energy Release In Fission Research Articles

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.

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.

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.

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.

Correlation of fission fragment kinetic energy data

Recent measurements of the most probable kinetic energy release in fission are compared in order to study the dependence on nuclear species. Appropriate corrections to data obtained with semi-conductor detectors, particularly with regard to calibration procedures, are discussed and applied. Corrected results are listed in Table I and plotted in Fig. 1. It is found that the most probable kinetic energy release in fission can be simply expressed by the function. <Ek>=0.1071Z2/A1/3+22.2MeV. The corrected <Ek> values are compared with recent liquid drop calculations and good agreement is found for Z2/A less than 35, but not above this value. Effects of mass asymmetry are also briefly discussed. Analysis of the data indicates that the most probable kinetic energy release is essentially independent of excitation energy. Use was made only of results published since 1961. Prior data can be found in the review of Huizenga and Vandenbosch.