Magnetic dipole <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math>-ray strength functions in the crossover from spherical to deformed neodymium isotopes

The $\ensuremath{\gamma}$-ray strength function is an important input into Hauser-Feshbach calculations of neutron capture in compound nuclear reactions. Experiments suggest an enhancement of the strength function at low energy, but this enhancement has not been reproduced in models of heavy nuclei as conventional shell-model methods become computationally intractable. Using shell-model Monte Carlo methods, the authors have successfully reproduced the low-energy enhancement (LEE) for magnetic dipole transitions in neodymium isotopes, while also illuminating the role of the scissors and spin-flip modes in these $M1$ transitions. If the LEE persists in heavy neutron-rich nuclei, thus significantly enhancing the radiative neutron-capture rates of nuclei near the neutron drip line, it would likely have profound effects on $r$-process nucleosynthesis.