Dieter Kurath

Effective interactions for the 1p shell

Abstract Effective interactions for the 1p shell are obtained by fitting energy data about nuclear levels. Magnetic dipole moments and probabilities for M1 gamma transitions and beta decay are calculated with the resultant wave functions. Comparison of such quantities with experiment provides an important check on the validity of the picture. The properties of the interaction are compared with those found in an earlier calculation and are also compared with the interaction deduced from nucleon-nucleon scattering. For consistency with the scattering potential, one must include a term proportional to ( σ 1 · 1 )( σ 2 · 1 ) as was introduced by Hamada and Johnston.

The particle-hole interaction and the beta decay of 14B

Abstract The last neutron in 14B necessarily occupies an orbit in the sd shell and hence the allowed β-decay to negative parity states of 14C is primarily sensitive to the interaction between nucleons from the p and sd shells (the particle-hole interaction). A particle hole-interaction has been derived which gives a good account of the non-normal parity states of a number of nuclei from 11Be to 16O. The important features of this interaction are that it remains close in character to a realistic G-matrix interaction and that it reproduces two specific characteristics of the nuclear level spectra; (i) the relative separation of the 1 s 1 2 and 0 d 5 2 single particle orbits as a function of mass number which is found to be sensitive to the non-central components of the interaction and is adequately reproduced by the bare G-matrix and (ii) the separation of multiplets of different isospin which is incorrectly reproduced by the bare G-matrix. The failure of the G-matrix in the latter case is remedied by adding a repulsive component to the triplet-odd central force. This interaction is shown to give a good description of the allowed β-decay of 14B to the lowest 1−, 2− and 3− levels of 14C. The unique first-forbidden decay to the 14C ground state is predicted to be weak as the result of a cancellation in the matrix element. No significant strength is predicted for decay to states of 14C which are unstable with respect to neutron emission. It is shown that certain features of the β-decay may be simply understood when the wave functions are expressed in a weak coupling basis and also in a basis classified according to the supermultiplet and SU(3) quantum numbers.

Electroexcitation of non-normal parity states in 11B☆

Abstract The calculation of positive parity states of 11 B is extended to the region of the giant E1 resonance with a complete non-spurious 1ℏ.ω basis. Strengths for longitudinal E1 and transverse M2 transitions to these states from the ground state are compared to the existing (e,e′) data. The calculation results in a strong M2 giant resonance overlapping the E1 resonance. In addition E1 form factors for excitation of low-lying states are given to show that the presence of 0s hole excitation has a drastic effect on the shapes of some of these form factors.

TWO-NUCLEON TRANSFER IN THE 1p SHELL.

Abstract Two-nucleon c.f.p. are given for the 1p shell, based on an earlier effective-interaction calculation. Magnitudes are also given which indicate the strength expected for two-nucleon transfer reactions.

Alpha particle spectroscopic amplitudes in the j--j coupled shell model

Abstract Formulae for calculating spectroscopic amplitudes for α-transfer reactions are developed in the framework of the j - j coupled harmonic oscillator shell model. It is shown that the amplitudes can be written as a sum of coupled two-neutron and two-proton spectroscopic amplitudes, illustrating that many properties of α-transfer reactions can be understood in terms of our experience with two-nucleon transfer reactions.

Three-nucleon transfer for the 1p shell

Abstract Parentage amplitudes for transfer of a (1p) 3 group with spatial symmetry [3] are given for 1p shell targets with initial and final states represented by intermediate-coupling wave functions. Some examples of interference from (1p)(2sd) 2 transfer are given for the upper end of the shell. The selectivity and distribution in energy of such transfer is discussed.

Positive-parity states in mass-13 nuclei

Abstract The strength of coupling between the positive-parity nucleon and the C12 core is investigated. Strong coupling, as implied by using the Nilsson model to generate wave functions, contradicts experiment. A reasonable picture arises from weak coupling with a strength consistent with that derivable from summing the two-body interaction integrals between the positive-parity nucleon and the core.

The positive-parity states of 11B

Abstract The positive-parity states of A = 11 are calculated in a complete iħω representation free of spurious states. Strengths for E1 transitions and for β-decay are examined in a weak coupling representation and found to have strong interference effects. The small 0s hole components are calculated to be extremely important for E1 transitions. The degree of agreement with observed properties indicates a good first-order approximation.

Enhancement of E2 transition probability

Abstract The method of generator coordinates is applied to the calculation of E2 transition probabilities. Complete single-particle states in a deformed well are used as generator functions, and the transition from the first excited state to the ground state of C12 is computed as an example. The degree of enhancement is found to be of a magnitude consistent with experiment. The effect of centre-of-mass motion and other factors affecting the validity of the result are discussed.

The transmission of fast molecular ions through thin foils

Abstract We present new results on the transmission of fast molecular ions through thin foils and propose a mechanism for the transmission process. The main feature of the postulated mechanism is that a finite fraction of the incident molecular beam does not undergo a strong Coulomb explosion while traversing the foil. Because the emerging fragments are at large internuclear separations, there is an enhanced probability for the formation of bound, long-range, excited electronic states following electron capture at the rear surface of the target.