Measurement of Radial and Longitudinal Dose Distribution in a Water Phantom Irradiated with a 10 Gev Electron Beam*

The radial and longitudinal distribution of absorbed dose in a water phantom irradiated with 10 GeV electrons has been measured. The electron beam was well focussed, and the current was measured accurately with a toroid. Detector plates, containing arrays of thermoluminescent 7LiF dosimeters were inserted at different depths in the water tank. The profiles of the dose distribution were measured over six decades. The dose rate at different depths per unit incoming particle flux density will be presented and compared with two different Monte Carlo calculations by Alsmiller2 and Beck. 3 The variation of the integral dose with electron energy is shown, and its possible significance discussed. The whole body dose versus peak dose for the delta-function type beam used in this experiment is shown. Introduction An experiment has been performed to determine the spatial distribution of the energy absorbed in a water tank irradiated by a 10 GeV electron beam. The measurement was done using thermoluminescent dosimeters (7LiF) of various forms, located within a water tank having a total depth of 32.5 cm. A similar experiment has been performed by Teschl in order to study the longitudinal distribution of energy absorbtion in a 30 cm thick tissue equivalent medium. Recent Monte Carlo calculations by Alsmiller2 and Beck3 give the energy deposited at a certain depth (z, AZ) in a semi-infinite water slab. The shape of the measured dose buildup in this experiment as well as absorbed dose to electron fluence conversion factors will be compared with their Monte Carlo calculations. A discussion of the r%diation hazard in the case of a person being accidentally hit by an electron beam will be presented and the concept of integral dose will be treated. Equipment and Dosimetry The lucite water tank was built of l/2” thick lucite and the inner dimensions were 30 cm depth and 60 x 60 cm front area. The dosimeters were arranged in the detector arrays shown in Fig. 1. These are lucite plates with grooves and holes machined to hold Li F detectors. The inner square array holds 81 extruded rodst (1 mm diameter, *Work supported by the U. S. Atomic Energy Commission. tHarshaw Chemical Company, Cleveland, Chio. -l-