Measurement of total charge changing cross-section for 5 A GeV Si 14+ ions in polyethylene and CR39 combined medium R. Gupta 1 * and A. Kumar 1 1 Department of Physics, National Institute of Technology, Kurukshetra 136 119 INDIA . * email: renugupta.phy@gmail.com , ashavani@yahoo.com Introduction Interaction of high energy heavy ions (HZE) in various media is a field of great interest in many aspects of fundamental and applied sciences, detection of cosmic rays, shielding design for space-vehicles and hadrontherapy for cancer treatment etc. [1,2]. Nuclear fragmentation in shielding materials generates secondary particles and substantially modifies the radiation field inside the spacecraft. HZE interactions with interstellar gas and fragmentation in interstellar space change the chemical composition of GCR [3]. These radiations may cause health risk to the astronauts. Therefore a good shielding design [4] is required to minimize the radiation risks. In this paper, the total charge changing cross-section of 5 A GeV Si 14+ ion beam on CR39 (C 12 H 18 O 7 ) n and polyethylene (CH 2 ) combined medium has been calculated using CR39 nuclear track etch detectors by cone-height measurements. Experimental A stack composed of CR39 foils of 11.5 cm × 11.5 cm × 0.15 cm in size; two foils upstream and six downstream of 0.6 cm CH 2 target (as shown in Fig.1) was exposed to Si 14+ ion beam of energy 5 A GeV at Brookhaven National Laboratory (BNL), USA in 2005 using Alternating Gradient Synchrotron at normal incidence with total ion density of ~2040/cm 2 . The used CR39 detectors were manufactured by Intercast Europe Co., Parma, Italy using a specially designed line of production [5]. These detectors were covered by a 45 μm plastic film to protect them from exposures to ambient radon and its progeny; these protective layers were removed before etching. From the previous experience of cone-height measurements [6], the chemical etching was performed on one side of the detector in 6N NaOH solution + 1% ethyl alcohol at 70 ˚C for 167 hours in several steps by applying araldite on back surface of the detector to avoid the shadow effects. After etching, the detector was washed in deionized water and then washed for at least one hour in an ultrasonic water-bath to clean up the etchants from inside the pores. After cleaning and drying, the detector was used for scanning under Leica DM6000 M optical microscope. The microscope consists of a CCD camera, a frame grabber and a personal computer (PC) consisting of hardware and software interface. The microscope is equipped with a motorized X/Y stage with an accuracy of better than 1 μm. Fig. 1 Sketch of the stack configuration used for the exposures to 5 A GeV Si 14+ ion beam. Results and Discussion Fig. 2 shows the distribution of cone-height of the etched tracks for Si 14+ ions and their fragments. An area of ~ 4 cm 2 on front face of the CR39 detector was scanned manually by the microscope and the cone-height of each track was measured. The peaks are well separated for the incident beam ions and for the fragments and a charge was assigned to each of these peaks from Z/β = 14.1 down to 6.0 as shown in Fig. 2. Proceedings of the DAE Symp. on Nucl. Phys. 58 (2013) 808 Available online at www.sympnp.org/proceedings