We have developed an efficient isospin projection method in the shell model Monte Carlo approach for isospin-conserving Hamiltonians. For isoscalar observables this method has the advantage of being exact sample by sample. It allows us to take into account the proper isospin dependence of the nuclear interaction, thus avoiding a sign problem that such an interaction introduces in unprojected calculations. We apply the method to calculate the isospin dependence of level densities in the complete $\mathit{pf}+g_{9/2}$ shell. We find that isospin-dependent corrections to the total level density are particularly important for $N~Z$ nuclei.

• Received 23 September 2008
• Publisher error corrected 1 December 2008

DOI:https://doi.org/10.1103/PhysRevC.78.051304