# Restricted spin-range correction in the Oslo Method: The example of nuclear level density and $\gamma$-ray strength function from $^{239}\mathrm{Pu}(\mathrm{d,p}\gamma)^{240}\mathrm{Pu}$

## TL;DR

This paper introduces an iterative correction method for the Oslo Method to accurately extract nuclear level density and gamma-ray strength functions from reactions with limited spin transfer, demonstrated on $^{240}$Pu.

## Contribution

The study develops a novel iterative approach coupling Green's Function Transfer calculations with RAINIER to address spin-parity mismatch issues in the Oslo Method.

## Key findings

- Identified a pronounced enhancement in the gamma-ray strength function between 2-4 MeV.
- Validated the iterative correction method for cases with large spin-parity mismatch.
- Observed the low-energy orbital M1 scissors mode in $^{240}$Pu.

## Abstract

The Oslo Method has been applied to particle-$\gamma$ coincidences following the $^{239}\mathrm{Pu}$(d,p) reaction to obtain the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF) of $^{240}\mathrm{Pu}$. The experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a challenge for the Oslo Method as it can have a significant impact on the extracted NLD and $\gamma$SF. We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's Function Transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code RAINIER. The resulting $\gamma$SF shows a pronounced enhancement between 2-4 MeV that is consistent with the location of the low-energy orbital $M1$ scissors mode.