Orientation effects on ESR analysis of alanine-polymer dosimeters

Orientation effects during electron spin resonance (ESR) measurement are studied on alanine-polymer dosimeters prepared by different molding procedures (press-molding or extrusion), and also according to different shapes (rods with different lengths and thin-films). The variation in ESR signal amplitude was measured by rotating a dosimeter around the vertical mid-axis and at a right angle to the magnetic field in the ESR cavity, at a temperature of 22oC. Orientation effects for rod dosimeters with both molding procedures (press and extrusion), and with different lengths, were negligible. Thin-film dosimeters molded by extrusion show a pronounced orientation effect when the samples are cut into disks and positioned horizontally (parallel to the magnetic field) during readout in the ESR cavity. Orientation effects on the film dosimeters can be eliminated, however, when they are positioned vertically and parallel to the mid-axis of the ESR cavity. (Author)