Fluence spectra of heavy ions on thick targets with model comparison

The problems of high energy heavy ion (HZE) transport in shielding and biological samples are important to the field of space radiation protection. The HZE particles in the galactic cosmic ray (GCR) spectra are responsible for a major portion of the dose equivalent with iron ions being the most prevalent. Therefore iron ions are a natural choice for the study of GCR on shielding material.

The experiment was performed at the Alternating Gradient Synchrotron (AGS) of the Brookhaven National Laboratory as E-898. The AGS provided a beam of ⁵⁶Fe with a target entry energy of 1.05 ± 0.005 GeV/nucleon. This experiment provided a method of collecting data on the presence of secondary radiation behind the target due to nuclear interactions. This information was converted to a fragment fluence spectra using the CERN data analysis program Physics Analysis Workstation (PAW). The fragment fluence spectra of several materials were experimentally determined and compared to a Monte Carlo model resulting in a good, general fit to the data.

The experimental data were compared with the model results by plotting the ordered pairs of the model and experiment for each charge z. For complete agreement the expected slope is unity. A linear regression is applied to the data and the resulting slope is compared to unity by means of a percent error. For the 5 and 10 g/cm² graphite-epoxy targets a slope error value of 10.6% and 7.8% were calculated respectively. For the 3.5g/cm² Heat Shield A target a slope error value of 31.2% was calculated. These results suggest good agreement between the model and the experiment for the given targets.