Zi-Wei Lin
East Carolina University
Dr. Zi-Wei Lin is Associate Professor of Physics at East Carolina University in Greenville, North Carolina. He has a PhD degree in Theoretical Nuclear Physics from Columbia University and has worked at Lawrence Berkeley National Laboratory and University of Alabama Huntsville / Marshall Space Flight Center among other places. Since 2007 he has been a faculty at East Carolina University. His main research interests include transport models for nuclear reactions, radiation physics, and space radiation protection. In 2011 Thomson Reuters ScienceWatch® selected his article, 'Multiphase transport model for relativistic heavy ion collisions' (Physical Review C 72, 064901, 2005), as a featured Research Front Map paper, and an interview was published at http://www.sciencewatch.com/an...
For space missions, solar particle events (SPE) and galactic cosmic rays (GCR) are major sources of space radiation to astronauts and electronics. To calculate the space radiation dose for risk analysis and mitigation, transport codes such as the 1-dimensional deterministic code HZETRN from NASA and the 3-dimensional Monte Carlo code Geant4 from CERN are necessary. Given these multiple transport models, it is worthwhile to study how different the results from these transport models will be in typical space radiation calculations.
In this presentation, I will first review our results from the 1-dimensional HZETRN code with ray tracing. In that study [1], we find that the center of the hemispherical dome on the lunar surface has the largest radiation exposure to blood-forming organs while locations on the inner surface of the dome have the lowest exposure. This reduction in the radiation exposure from the center to the inner edge of the dome can be as large as a factor of 3 or more for the radiation from solar particle events while being smaller for the radiation from galactic cosmic rays. Then I will show our study [2] that compared several transport codes in their predictions of the dose and dose equivalent values as well as the particle spectra inside a spherical shell shielding in typical SPE and GCR environments. Two deterministic codes, HZETRN and UPROP, and two Monte Carlo codes, FLUKA and Geant4, are used. We find that the dose values and particle spectra from HZETRN are in general rather consistent with Geant4 except for neutrons, and results from FLUKA and Geant4 are mostly consistent for the considered cases. In addition, our results from both deterministic and Monte Carlo transport codes [2] show that the dose equivalent inside the spherical shell decreases from the center to the inner surface and this decrease is large for solar particle events; consistent with our earlier study [1] based on a deterministic radiation transport.
[1] Lin, Z.W., Baalla, Y., and Townsend, L.W. (2009). Variation of Space Radiation Exposure Inside Spherical and Hemispherical Geometries. Radiation Measurements 44, 369-373.
[2] Lin, Z.W., Adams Jr., J.H., Barghouty, A.F., Randeniya, S.D., Tripathi, R.K., Watts, J.W., and Yepes. P.P. (2012). Comparisons of Transport Models in their Predictions in Typical Space Radiation Environments. Advances in Space Research 49, 797–806.