Characterization of Heavy Ion Beams at the Heavy Ion Medical Accelerator in Chiba Using a Li-drifted 5-mm Silicon Detector

Measurements were taken at the Heavy Ion Medical Accelerator in Chiba, Japan (HIMAC) to characterize accelerator beams to assist in the study of various tissue equivalent proportional counters (TEPCs) designed by Colorado State University (CSU), Oklahoma State University (OSU), and the National Aeronautics and Space Administration (NASA). There were four beams that were part of the HIMAC experiment:

• 290 MeV/nucleon carbon
• 150 MeV/nucleon helium
• 500 MeV/nucleon argon
• 500 MeV/nucleon iron

For the first time ever, a single, 5-mm lithium drifted silicon detector was used to characterize the beam and measure the spectrum of particles striking the TEPCs. If successful, this new methodology can greatly simplify previously used methods and reduce the amount of beam time needed to characterize the beam. Data from the detector was used to yield information on the particle’s species (atomic number) and energy. The data analysis was more complex than the standard analysis performed on Si-detector data due to several complications that became evident during the experiments. The 5mm Silicon detector used to analyze the beams was discovered to have suffered radiation damage from previous experiments. On the night of the Helium run, there was limited time to perform the TEPC measurements, so silicon detector measurements of the beam were not taken. The data for the Argon beam was corrupted, and all information that was taken was lost. In spite of these difficulties, useful data was extracted from the carbon and iron runs.