Double-lambda compound nucleus and the formation of double hypernuclei

The formation probabilities of single- and double- compound nuclei from ^– following the (K^–, K⁺) reaction are calculated, showing that double- hypernuclei are formed with a fairly large probability through a hyperon compound process involving ^– directly after the (K^–, K⁺) reaction.We dedicate this paper to the late Professor Jan ofka with whom we enjoyed nice friendship and collaboration. We also thank the late Professor H. Bando and Professors K. Yazaki, Y. Akaishi and T. Fukuda for stimulating discussions.     

The lifetime of strongly overlapping compound nucleus levels

We show how to express the lifetime of a compound nucleus in terms of the transmission coefficients. We have derived this result in the absence of doorway states and direct reactions. Our formalism shows that the decay width is then equivalent to the correlation width.     

Entrance channel mass asymmetry dependence of compound nucleus formation

The fusion reactions ⁴⁸Ca + ¹⁵⁴Sm and ¹⁶O + ¹⁸⁶W leading to the same compound nucleus ²⁰²Pb are studied within the framework of an improved isospin dependent quantum molecular dynamics model. The entrance channel mass asymmetry dependence of compound nucleus formation is found by analyzing the shell correction energies, Coulomb barriers and fusion cross sections. The calculated fusion cross sections agree quantitatively with the experimental data. We conclude that the compound nucleus formation is favorable for the system with larger mass asymmetry.     

Microscopic statistical theory of precompound and compound nucleus reactions

Starting from the statistics of the nuclear matrix elements, we derive a generalized master equation which contains the usual master equation for precompound processes, and the Hauser-Feshbach formula, as special cases. Further results, limitations, and possible generalizations of the approach are indicated.     

Fission dynamics of the compound nucleus 213Fr formed in heavy-ion-induced reactions

A stochastic approach based on one-dimensional Langevin equations was used to calculate the average pre-fission multiplicities of neutrons, light charged particles and the fission probabilities for the compound nucleus ²¹³Fr and the results are compared with the experimental data. In these calculations, a modified wall and window dissipation with a reduction coefficient, k _s , has been used in the Langevin equations. It was shown that the results of the calculations are in good agreement with the experimental data by using values of k _s in the range 0.3?≤?k _s ?≤?0.5.     

Isospin dependence of the nuclear level width in the compound nucleus 30P

The excitation functions of ²⁹Si(p, α₀)²⁶Al, ²⁹Si(p, α₁)²⁶Al and ²⁹Si(p, α₂)²⁶Al were measured with high beam energy resolution in order to determine the isospin dependence of the nuclear level width of the composite nucleus, ³⁰P, at an average excitation energy of 19.6 MeV. From an auto-correlation analysis of these excitation functions, the level widths of the T_< = 0 and T_> = 1 isospin states are determined as 81 ± 17 keV and 104 ± 35 keV, respectively. An analysis including isospin mixing is also performed. With the aid of the statistical theory of nuclear reactions, the coherence energies are used to deduce the relative densities of two isospin states. The predictions of the Fermi gas model of level densities including isospin are in good agreement with the obtained results.     

Investigation of the formula for the average of two S-matrix elements in compound nucleus reactions

Recently the problem of calculating the average of two S-matrix elements describing compound nucleus reactions was solved by using the technique of generating functions and grassmann integration. In this paper we analyze the solution, a three-dimensional integral, both analytically and numerically. We study the expansion of the integral in powers of the transmission coefficients and the expansion in inverse powers of the transmission coefficients. The former one, which also contains logarithmic terms, is shown to agree with previous work. The latter one is identical to the expansion obtained with the help of the replica trick. After a suitable change of integration variables the integrand becomes finite everywhere in its domain and numerical integration is without any problem. Earlier Monte Carlo calculations are confirmed. The average of two S-matrix elements at the same energy obtained by a Mexican group using general properties of the S-matrix and the maximum entropy principle is shown to coincide with the microscople result.     

An analysis of runs tests as indicators of nonstatistical structure in the compound nucleus

Runs tests were applied to computer-generated elastic-scattering excitation functions in order to examine their sensitivity to nonstatistical structure in the compound nucleus. The scattering amplitudes were either purely statistical or else they included contributions from additional resonances about 1 MeV broad. Our aim was to determine whether the runs tests could distinguish between the two cases. The tests were successful once trends producing correlations between the datum points were removed. Spurious nonstatistical effects were thus eliminated, demonstrating that if the trend-reduction problem is dealt with propertly, runs tests are effective in searches for nonstatistical structure beneath the compound-nucleus fluctuations in experimental excitation functions.     

Interferometry in the asymmetric mode

A completely automated asymmetric interferometer, useful for temperature dependent (4.2–500 K) complex reflection measurements in the far-infrared region, is outlined. The advantages and disadvantages over other methods are discussed. Results to show the performance of the instrument include a ferroelectric compound (LiTaO₃), an ionic solid which exhibits significant ionic conductivity (Na β-alumina) and a layered semiconductor (GaTe).     

Comparisons between various width fluctuation correction factors for compound nucleus reactions

The exact expression for the width fluctuation correction factor, obtained with the Gaussian orthogonal ensemble (GOE) approach, has been implemented computationally to describe a nuclear reaction for any open channel—elastic, inelastic, capture, and fission. This exact expression is compared with various approximate expressions. It turns out that the approximate expression given by Moldauer is the closest to the GOE value. Since comparison between model predictions and experimental data alone cannot provide the answer concerning the correct approximate method, the present comparison indicates that Moldauer’s model is the one to use in reaction models for practical applications.     

Complex fragment emission from low energy compound nucleus decay to multifragmentation

In the first of these lectures, the experimental emission probabilities of complex fragments by low energy compound nuclei and their dependence upon energy and Z value are compared to the transtion state rates. In the second part, the high energy multi-fragment emission probabilities are shown to be reducible to the single fragment emission probability through the binomial distribution. The extracted one-fragment emission probabilities have a thermal dependence of the formp=e ^–B/T . This suggests that multifragmentation is a sequence of thermal binary decays.Invited lecture given at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Nuclear Physics Division of the US Department of Energy, under contract DE-AC03-76SF00098.     

The structure of Yrast isomers and the nature of γ-rays from a compound nucleus

The unusually large population of yrast isomers in ¹⁵²Dy is theoretically analysed. We also discuss the relation between the structure of the yrast states and the large ?=1 component of γ-rays emitted from a compound nucleus.