Research Projects - L.W. Townsend

Quantum-mechanical, optical potential descriptions of nuclear collisions for use in predicting nucleon- and nucleus-nucleus total cross sections (elastic and inelastic), elastic differential cross sections, spallation/ fragmentation yields, pion production cross sections, and angular and spectral distributions of secondary neutrons and light ions are being developed. These theoretical models are used for a variety of applications including space radiation protection of astronauts, radiotherapy using heavy charged particles, and production of radioactive ion beams for nuclear structure and reaction studies. I have also developed models of Electromagnetic dissociation of nuclei in these collisions using a modified Weiszacker-Williams approach. [Collaborators: R. K. Tripathi (NASA Langley Research Center), F. A. Cucinotta (NASA JSC), J. W. Norbury (U. Wisconsin - Milwaukee), L. H. Heilbronn (LBNL) and several UT students].

A model to predict the production and decay over time of radioactive ions from nuclear collisions is being developed. Radioactive decays over time are calculated using numerical solutions to the coupled rate equations. A comprehensive database of decay constants for over 2800 nuclides has been developed. This radioactive decay model will be coupled to an optical potential spallation model (see 1. above) originally developed for space radiation protection studies. The spallation model is being extended to heavy nuclei, such as uranium, by incorporating a fission channel. The ion decay model can be used for estimating production yields of exotic nuclear species for fundamental physics studies. It can also be used to assess radiological health requirements for handling radioactive targets.

For about 15 years I was part of the space radiation protection research group at NASA Langley Research Center. During this time we developed the deterministic space radiation transport codes, BRYNTRN and HZETRN, and their extensive nuclear atomic interaction databases. Recently, I have initiated a research project, with NASA funding, to incorporate high energy, heavy ion interaction databases and transport models into the HETC Monte Carlo computer code system for Human Exploration in Space applications for NASA.
[Collaborators: T. A. Gabriel (ORNL), and T. M. Miller (UT student)].

I have spent the past two decades developing methods of estimating doses and equivalent doses received by astronauts in deep space from exposure to galactic cosmic rays (GCR) and energetic solar particle events (SPEs). Present research efforts are focused on estimating dose rates to critical body organs as a function of time during major SPEs. In addition, new, innovative, real-time methods of predicting the buildup of organ doses as a function of time since event onset are being developed using (1) Bayesian inference and (2) a new type of artificial neural network (patent pending) developed for this purpose. The idea is to use several dosimeter readings early in the event to project future doses during the event.
[Collaborators: E. N. Zapp (Lockheed Martin), J.W. Hines (UT), J.L. Hoff (UT student) and J. S. Neal (ORNL)].

Modifications to the ICRP respiratory tract model are being investigated. Present research focuses on calculating dose deposition in the tissues of the ET1 (extra-thoracic) region (nose) resulting from beta decays by airborne sources. The work uses the MCNP4B computer code to estimate the doses. New models of the ET1 region geometry are being investigated.
[Collaborators: K.F. Eckerman (ORNL) and H. Moussa (UT)].

A conceptual design for an economical, safe, modularized, proliferation-resistant, Generation IV light-water reactor plant system is being developed.
[Collaborators: F. M. Mynatt (UT), L.F. Miller (UT), A. Kadak (MIT), and W. Williams and M. R. Williamson (UT students)].

Current research efforts include modeling of secondary neutron production from energetic proton and heavy ion interactions with thin and thick targets using quantum mechanical optical potential methods and development of portable Californium-252 sources for materials science and engineering research, commercial, and medical applications (including development of cold sources.