Spectrometry and Dosimetry for Accelerator Based In-Vivo Measurements

Abstract

The neutron irradiation facility developed at the McMaster University 3 MV Van de Graaff accelerator will be employed to assess in vivo elemental content of aluminum and manganese in human hands. These measurements will be carried out to monitor the long-term exposure of these potentially toxic trace elements through hand bone levels. This thesis addresses two important issues regarding in-vivo neutron activation (IVNAA) of the hand; the first relates to the optimization of operating conditions at the McMaster University 3 MV KN Van de Graaff accelerator to produce neutrons via the ⁷Li(p, n)⁷Be reaction for in-vivo neutron activation analysis and the second relates to the evaluation of the total dose equivalent delivered to the patient hand undergoing irradiation using a 1/2" diameter tissue equivalent proportional counter (TEPC). The operating conditions at the 3 MV KN Van de Graaff accelerator have been optimized by employing a long counter designed for this study to monitor the neutron fluence and a NaI(TI) detector to measure the ⁷Be activity produced as a result of (p, n) interactions with ⁷Li. It was observed that inefficient target cooling and the presence of oxide layers on the target surface resulted in lower measured yields than those calculated. The computational method described in this work to estimate the average radiation dose equivalent delivered to a patient's hand during irradiation employs the neutron and gamma doses measured using a 1/2" diameter TEPC and the quality factor of the neutron beam calculated by using the Monte Carlo radiation transport code, MCNP4B. Based on the the estimated doses delivered to a patient's hand, the proposed irradiation procedure for the IVNAA measurement of manganese in human hands (Med Phys 29(11) (2002) 2718) with normal (1ppm) and elevated manganese content can be carried out with a reasonably low dose of 31 mSv to the hand which is less than the recommended maximum permissible dose equivalent limit (50 mSv) for such diagnostic procedures. 63% of the total dose equivalent is delivered by the non-useful fast neutron group (>10 keV); the filtration of this neutron group from the beam will further reduce the dose equivalent to the patient's hand.