DATE:

Friday, June 4, 2021

TIME:

3:30 PM

LOCATION:

Virtual Zoom Conference

SPEAKER:

Abraham Flores, PhD Candidate, Computational Science, San Diego State University

ABSTRACT:

For decades the Variational Monte Carlo (VMC) method has been successful in describing nuclear bound states, but it has not yet been extensively used for reactions or scattering. We present preliminary VMC calculations of neutron scattering from tritium, using two different methods to extract scattering information from the wave functions. In both cases our variational ansatz is a particle-in-a-box wave function with a derivative boundary condition at the box surface for each possible set of angular momentum quantum numbers. We optimize our wave functions in accord with the Rayleigh-Ritz variational principle using the COBYLA algorithm to determine parameters. We first apply a direct method to extract scattering information from wave function properties and the minimized energy for each choice of boundary conditions. This method produces results in fair agreement with empirical expectations, but it is limited by the accuracy of the variational ansatz. In the second method we compute a set of amplitudes from integrals over the same variational wave functions found before. When these amplitudes are combined to yield scattering information there is partial cancellation of errors from the variational wave function, so we expect more accurate results compared with the direct method. We see general improvement for all cases when using the integral method compared to the direct method. We have also found that we can compute scattering information over a range of energies through the integral method by using a single optimized wave function and varying only one input parameter to the integrals, greatly reducing human and computer effort. We believe the integral method will have much smaller errors than the direct method for collisions in which nuclei leave with different quantum numbers than they brought in.

HOST:

Jared Brzenski and the SDSU SIAM Student Chapter

VIDEO: