[1] Department of Physics, Radiation Dosimetry Laboratory, Oklahoma State University, Stillwater, OK 74078, United States
[2] Space Radiation Analysis Group, National Aeronautic and Space Administration, Johnson Space Center, Houston, TX 77058-3696, United States
[3] Division of Space Life Sciences, Universities Space Research Association, Houston, TX 77058, United States
[4] National Institute of Radiological Sciences, Chiba 263-8555, Japan
[5] Department of Radiation Physics, M. D. Anderson Cancer Center, University of Texas, 1515 Holcombe Blvd., Houston, TX 77030, United States