Magnetic Dipole Gamma-Ray Strength Function in Deformed Nuclei, and Neutron-Capture Gamma Rays

Abstract

The magnetic dipole gamma-ray strength function for some strongly deformed heavy nuclei is computed on the basis of the Nilsson model, pairing, and a residual spin-spin interaction. The strength of the spin-spin interaction is adjusted to give average agreement with experiment of effective spin g factors for low-energy M1 transitions and moments. Predictions are made for average Ml widths of primary transitions following neutron capture; the predictions are in reasonable agreement with recent data.Existing experimental data on the reduced widths of primary magnetic dipole transitions in the (n, y) reaction have recently been summarized by Bollinger. 1 The reduced widths for yray transitions of 4-to 9-MeV energy are found to be, on the average, some 10 to 20 times larger than "single-particle" estimates. 2 ' 3 It is the purpose of this note to present some results of a simple computation, with no ad hoc assumptions, which can account for some of these results.By reduced width we mean the quantity 3

Electrofission of233U

“…The dotted lines bracketing the curves represent the uncertainties associated with their calculation, as described in the text. of 1.5MeV, in keeping both with theoretical estimates [12] and with the experimental evidence [l 1, 231 for heavy nuclei. We then fit the total M1 strength, given by Bf(Ml), to the experimental points.…”

“…It was found that Bf(M1) = 18 f 5&, with a peak at 6.3 k 0.3MeV. This value of 18 f 5pi compares favorably with a theoretical estimate for 239U of 18.5& [12]. It also should be noted that for the well studied heavy nucleus 208Pb, the result of a recent measurement [25] is 15.6ph.…”

“…While for the GQR the fission-decay process for actinide nuclei is becoming more clear, questions related to the existence and decay of magnetic multipole giant resonances, M1 in particular, in heavy nuclei remain unanswered. Substantial concentration of M1 strength in the fission-decay channel of even-even actinide nuclei has been observed near 6 MeV [ 1 13, which might indicate the presence of a giant M1 resonance (GMDR) for uranium [12].…”