The reactions 6Li(n, p) 6He(0) and 6Li(n, n') 6Li(3.56)

doi:10.1016/0375-9474(69)90603-4

Nuclear Physics A

Volume 131, Issue 3, 7 July 1969, Pages 679-697

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Abstract

Integral cross sections have been measured for the two analogous reactions ⁶Li(n, p)⁶He(0) and ⁶Li(n, n')⁶Li(3.56) from the thresholds up to about 7 MeV with an energy resolution between 50 and 200 keV. The excitation functions exhibit annomaly at En = 4.6 MemMeV which is interpreted as due to the lowest T = frcase|3/2 state in the compound nucleus ⁷Li. The data are well fitted by the assumption of two overlapping resonances of the same spin and parity $(32^{−})$ . A two-level resonance analysis yielded the following level parameters: $E_{x}^{(1)} (^{7} Li) = 10.25±0.10 MeV, Γ^{(1)} = 1.40±0.10 MeV, T^{(1)} = 12; E_{x}^{(2)} (^{7} Li) = 11.20±0.05 MeV, Γ^{(2)} = 0.27±0.05 MeV, T^{(2)} = 32$ . Partial widths and reduced widths of the resonances were derived or estimated, and their implications for the structure and isospin purity of the resonant states are discussed.

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Calculation of the 6 Li(n,n ′ γ) 6 Li and 7 Li(n,n ′ γ) 7 Li cross sections up to 20 MeV neutron kinetic energy within a three-body approach
2019, Nuclear Physics A
In this work we numerically calculate cross sections of the reactions ⁶Li $(n, n^{'} γ)$ ⁶Li and ⁷Li $(n, n^{'} γ)$ ⁷Li reactions in the region of neutron kinetic energy $E_{n} = 0.5 - 20$ MeV. Neutron-nucleus interaction is defined in terms of the three-body problem wherein the target-nucleus is a bound two-body system. Dynamics in all two-body segments is described by the coupled Lippman-Schwinger equations with separable potentials. Free parameters of these potentials are chosen based on a fairly good description of elastic scattering phase shifts and radiation cross sections: $t α \to γ^{7}$ Li, $d α \to γ^{6}$ Li, $n d \to γ t$ . The system of three-body strongly interacting particles is described by the Faddeev equations. Radiative relaxation of the excited nucleus is effectively taken into account by the electromagnetic vertex inserted in the three-body scattering amplitude. Total cross sections and also poorly measured double differential cross sections of ⁶Li $(n, n^{'} γ)$ ⁶Li and ⁷Li $(n, n^{'} γ)$ ⁷Li are obtained and briefly analyzed.
Reactions leading to the 7Li and 8Li systems: Shell model and R-matrix calculations
1987, Nuclear Physics, Section A
Level energies and reduced width amplitudes obtained from shell model calculations for ⁷Li and ⁸Li are incorporated into multilevel, multichannel R-matrix calculations of cross sections for reactions leading to these compound systems. With changes to a very few of the large number of parameters obtained from the model calculations, cross sections for eight reactions leading to the ⁷Li system and for five reactions leading to the ⁸Li system are calculated. For reactions where data are available, the calculated cross sections are in good agreement with experimental measurements. Comparisons of the present work to other structure studies are made and suggestions as to possible improvements in the model calculations are given. The applicability of the technique used here to other nuclear structure studies is discussed.
Search for highly excited states in light nuclei with three-body reactions
1985, Nuclear Physics, Section A
Various three-body break-up reactions resulting from the bombardment of ⁷Li with 120 MeV ³He have been measured simultaneously in a kinematically complete experiment. Missing-mass spectra have been deduced for ⁴H, ⁴He, ⁴Li, ⁵He, ⁵Li, ⁶He, ⁶Li and ⁷Li. The ground states of ⁴H and ⁵He are well described as n-t and n-α P-wave final-state interactions, respectively. Evidence is found for relatively narrow states at very high excitation energies in several nuclei. The results are compared with those of other authors and with various theoretical predictions.
Structure of 7li and mechanisms of the low-energy 6Li+n reactions
1983, Nuclear Physics, Section A
The positive-parity states in ⁷Li necessary to explain the properties of the low-energy ⁶Li+n reaction Cross sections using compound nuclear reaction formalism have not yet been identified experimentally, though theoretical model calculations predict them to exist and to be unbound. The present work employs an R-matrix analysis of the ⁷Li system in which the positive- and negative-parity states have been included at excitation energies and with reduced widths consistent with existing model calculations. With this representation, properties of the ⁶Li+n reactions have been properly predicted from thermal neutron energies up to 4 MeV. The positive-parity states are shown to be of necessity broad and will not be observed in the traditional sense as peaks in the ⁶Li+n reaction cross sections. Effects of all states in⁷Li included in the analysis on the cross sections are discussed and detailed comparisons with model calculations are made.
The polarization and differential cross section of fast neutrons scattered from 6Li and an R-function analysis of the interaction below 4 MeV
1981, Nuclear Physics, Section A
The analyzing power of ⁶Li for the elastic scattering of polarized neutrons with energies between 2 and 4 MeV, has been measured at six angles ranging from 25° to 150°. The polarized neutrons were generated from the reactions Pb(γ, n) and ¹²C(n, $n$ ), and their polarization was measured using the double-scattering method. The neutron energies were determined with a nanosecond timeof-flight spectrometer. In addition, the differential cross section was measured at three angles in the same energy range; the cross section was determined relative to the well-known n-¹²C cross section. The present results have been combined with existing data for the neutron total, (n, α), and differential elastic cross sections, in a reduced R-function analysis. Clear evidence of a p-wave triplet of shellmodel states emerges from the analysis.
Neutron-induced charged-particle reactions in 6Li and 9Be
1977, Nuclear Physics, Section A
Angular distributions of tritons from the ⁶Li(n, t)⁴He reaction were measured at E_n = 7.25, 6.77, 6.57, 5.24 and 4.71 MeV. Angular distributions of douterons from respectively, the ⁶Li(n, d)⁵He two-body breakup reaction were measured at E_n = 6.77 and 6.57 MeV, and of protons from the ⁶Li(n, p)⁶He reaction at E_n = 6.77, 5.24 and 4.71 MeV. All these reactions in ⁶Li were analyzed as direct interaction in the formalism of the distorted wave Born approximation. The optical model for the nuclear interaction was found to apply reasonably well to nuclei as light as ⁴He, ⁵He, ⁶He and ⁶Li. In addition, ⁶Li as an alpha-deuteron cluster gives the best bound-state wave function to describe the experimental angular distribution of tritons. The excitation functions at forward angles of the ⁶Li(n, t)⁴He, ⁶Li(n, d)⁵He and ⁶Li(n, p)⁶He reactions were measured for incident neutron energies between 4.4 and 7.3 MeV. It is found that the ⁶Li(n, d)⁵He two-body breakup reaction has a threshold at about E_n = 5.3 MeV. Angular distributions at E_n = 18.3 MeV for tritons and protons from the ⁹Be(n, t)⁷Li and ⁹Be(n, p)⁹Li, respectively, were also measured.

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^†: Present address: AVR (Arbeitsgemeinschaft Versuchsreaktor), Düsseldorf, Germany.

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Nuclear Physics A

Abstract

References (19)

Nucl. Phys.

AWRE Report No. 0-60/64

LA-3765

Nucl. Phys.

Phys. Rev.

Phys. Lett.

Revs. Mod. Phys.

Nucl. Phys.

Phys. Rev. Lett.

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Calculation of the <sup>6</sup> Li(n,n <sup>′</sup> γ) <sup>6</sup> Li and <sup>7</sup> Li(n,n <sup>′</sup> γ) <sup>7</sup> Li cross sections up to 20 MeV neutron kinetic energy within a three-body approach

Reactions leading to the <sup>7</sup>Li and <sup>8</sup>Li systems: Shell model and R-matrix calculations

Search for highly excited states in light nuclei with three-body reactions

Structure of <sup>7</sup>li and mechanisms of the low-energy <sup>6</sup>Li+n reactions

The polarization and differential cross section of fast neutrons scattered from <sup>6</sup>Li and an R-function analysis of the interaction below 4 MeV

Neutron-induced charged-particle reactions in <sup>6</sup>Li and <sup>9</sup>Be