Inelastic scattering of 40 MeV protons fromMg24. II. Microscopic calculations for positive parity states

Abstract

Proton inelastic scattering data at 40 MeV bombarding energy are compared to microscopic distorted-wave Born-approximation'calculations for positive parity states in Mg utilizing shell-model wave functions spanning the full 2sld shell basis. Both empirical forces and forces derived from free nucleon-nucleon potentials are used in the calculations. Except for four transitions for which strong coupling effects are evident, the agreement between theory and experiment is quite good. Enhancement factor's extracted for the natural parity transitions are consistent with the effective charges obtained from electromagnetic transition rates. Levels corresponding to the giant M1 resonance in Mg have been resolved in the present experiment.The fact that the renormalization factor between theory and experiment is close to unity for the 10.713 MeV 1+; T = 1 state indicates that little or no renormalization of the two-body force is necessary for this inelastic transition. It is argued that little renormalization is also involved .for magnetic-type inelastic transitions of multi polarities higher than M1.NUCLEAR REACTIONS Mg(P, P') at 40 MeV to positive parity states. Microscopic DWBA analysis with the full 2sld basis wave functions. Deduced collective enhancement factors.

A Comparison of Spectroscopic Models of Low Excitation 2+ States in 24Mg and 28Si from Inelastic Proton Scattering

“…Thus the mismatch between the analysing power data and the predictions would again appear to be evidence of an incomplete description of the reaction mechanism rather than flaws in the spectroscopy. Indeed, the recent analyses of inelastic proton scattering data by Lombard et al (1978) and Zwieglinski et al (1978) suggest that a coupled channels approach will be required before such discrepancies may be resolved, for quite good results were obtained by using an asymmetric rotational model for the interaction form factors in coupled channels calculations. Even so, a number of problems remained, not the least of which were poor fits to K = 2 band state excitation data in both magnitude and shape, and the need to use a large spin-orbit potential deformation to get fits to the analysing power data for ground state band transitions.…”

“…Even so, a number of problems remained, not the least of which were poor fits to K = 2 band state excitation data in both magnitude and shape, and the need to use a large spin-orbit potential deformation to get fits to the analysing power data for ground state band transitions. However, with 20· 3 MeV incident energy, higher order processes in which the giant resonances of 24Mg act as doorway states (Geramb et al 1975) are significant,and this is evident by the tendency of the analysing powers from weak transitions to have a symmetry about 90° in the centre of mass system, by the large angle enhancement in weak transitions and by the larger scale factors required in the 20· 3 MeV analysis (Lombard et al 1978) when compared with those in the 40 MeV analysis (Zwieglinski et al 1978).…”

“…Recent analyses of 20·3 MeV (p,p') data (Lombard et al 1978) and of 40 MeV (p, p') data (Zwieglinski et al 1978) from 24Mg used a more simplistic model than ours for core polarization, to wit a straight scaling of their chosen two-nucleon interaction strengths. In both of these analyses, the 2t data were used to normalize those scalings against the known B(E2) value and the effective charges required by the nuclear structure calculations to fit that B(E2) value.…”

“…Additionally, however, numerous other transition amplitudes and especially those between p and f orbits are not negligible. Indeed, the 'additional' transition components to those contained solely within the s-d shell will seriously influence predictions of transition rates (Zwieglinski et al 1978); this is evident from the ensuing discussion of the results of our reaction analyses. …”

Probing negative-parity states of Mg24 probed with proton and α inelastic scattering

“…The band structure of 24 Mg has been studied via electromagnetic transitions [1][2][3], and intensively investigated through inelastic scattering of various probes, including electrons [4][5][6][7][8][9][10], pions [11], nucleons [12][13][14][15][16][17][18][19][20][21][22][23], 3 He [24,25], and α [25][26][27][28][29]. For inelastic hadron scattering off 24 Mg, detailed reaction analyses have been performed using the distorted-wave Born approximation (DWBA) and coupled-channel (CC) calculations.…”