Pergamon Radiation Measurements, Vol. 28, Nos I-6, pp. 495-498, 1997 O 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 1350-4487/97 $17.00 + 0.00 PII: S1350-4487(97)00127-3 EXPERIMENTAL AND SIMULATION STUDY OF NEUTRON DOSIMETRY AT VARIOUS NEUTRON ENERGIES K. JAMIL, S. ALI, I. E. QURESHI, F. REHMAN, H. A. KHAN, S. MANZOOR, A. WAHEED"r AND R. CHERUBINI" Environmental Radiation Group, Radiation Physics Division, PINSTECH, P.O. Nilore, lslamabad, Pakistan *INFN, Laboratori Nazionali di Legnaro, Via Romea 4, 35020 Legnaro (Padova), Italy ABSTRACT A Monte Carlo Neutron Photon (MCNP) transport code has been employed to simulate CR-39 plastic track detector as neutron dosimeter at various neutron energies. In each simulation a monoenergetic neutron source of a particular energy was embedded in the center of a sphere made of CR-39. Surrounding the source there were concentric shells of 2 ~.m CR-39 track detectors. The code, MCNP, was run on personal computer for 7.5xl06 histories. The number of proton recoils in each shell of 2 Bm of CR-39 were determined. The simulation results show that apart from proton recoils (for E, > i.0 MeV), about 50% recoils are due to heavy charged particles i.e. Oxygen and Carbon in CR-39. This indicates that etched tracks are not only due to recoil of protons but also due to recoil of heavy charged particles. The upper limits of the track registration efficiencies have been determined as a function of neutron energies. These simulation results have been experimentally verified using CR-39 track detectors at various known energies of neutrons. The proton and heavy charged particle recoil tracks in CR-39 were made visible by etching in NaOH solution, at 70+1°C for 1.75 hours. KEYWORDS Neutron dosimetry; SSNTD; Monte Carlo simulation; MCNP; detection efficiency; CR-39; track detector. INTRODUCTION Solid State Nuclear Track Detectors (SSNTDs) are widely known for the detection of charged particles. Besides charged particles, neutrons can also leave detectable tracks in these insulating solids through recoiling the constituents nuclei of the detector as charged particles. The measured charged- particle track density can be correlated with the neutron flux and consequently with the absorbed neutron dose. Therefore, SSNTDs have applications in the field of neutron dosimetry (Piesch, 1982, lng and Piesch, 1985). Though some experimental work has been carried out for neutron energy dependent track detection and revelation efficiency in various types of SSNTDs, published data for neutron detection and revelation at various neutron energies are not readily available (Pretzsch, 1982, Matiullah and Durrani, 1987). For this reason, we have employed the method of Monte Carlo simulation. As neutron interactions with matter is stochastic in nature, therefore, Monte Carlo is found to be the most suitable technique to study the neutron interactions with the constituent nuclei of SSNTDs. In this research work, we simulate CR-39, a thermoset plastic, as a neutron dosimeter. The simulation has been carried out while using a reliable and tested Monte Carlo Neutron Photon (MCNP) transport code (Thomson, 1990). Some of the simulation results have been tested experimentally using available neutrons of various energies. r Permanent Address: Physics Department, Gomal University, D.I. Khan, Pakistan 495