The use of photographic film to pinpoint accelerator beam losses.

Following removal of a superconducting wiggler that has a maximum magnetic-field of 7 T in a high-energy synchrotron facility, sufficient lead shielding was placed upstream of the removal point in the normal-conducting electron storage ring to account for any radiation sources from the upstream components. As is customary in such cases, when vacuum has been breached, there is a period of time required for vacuum re-conditioning of the ring. During this re-conditioning phase, poor vacuum contributes to gas bremsstrahlung formation that typically is visualized as an increase in overall radiation exposure from standard operating conditions. However, in this case, new radiation patterns emerged and persisted throughout the re-commissioning phase. Subsequently, additional shielding was then placed upstream but still failed to resolve the source of radiation. The radiation source point consisted of two distinct components: a point parallel to the position originally covered by the wiggler and a strong forward-directed peak (i.e., bremsstrahlung). The only feedback mechanism to track the beam position is the beam position monitors (BPM's). BPM's were located forward and aft of the parallel source point. The BPM's suggested that the beam was in the correct position. To investigate the elevated radiation level, commercial photographic film was used as a monitoring ruler and the focal point of the radiation source was clearly identified using this novel approach. The silver halide grain contained within the film emulsion possessed sufficient cross section and was activated from Ag to Ag, which has a half-life of 2.39 min and emits easily detectable radiation. Further, the exposed film is ready for reuse after 25 min due to the short half-life of Ag. The proposed method proved to be an easy, economic, and effective approach to rapidly and qualitatively identify the location of the beam losses.

Dose rates from a cobalt-60 pool irradiator measured with Fricke dosimeters.

This project used Fricke dosimeters to determine the dose rates at multiple locations in a Co pool irradiator. Fricke dosimetry is widely accepted as a chemical dosimetry method to measure radiation absorbed dose due to its simple recipe, linear response, wide dose range, good reproducibility, ease of measurements, and low operational cost. Calibration measurements were used to determine a molar extinction coefficient of 2,185 +/- 14 L mol cm at 303 nm and 25 degrees C; the molar extinction coefficient is comparable to values from the published literature. The Fricke dosimeters measured the dose rate of a National Institute of Standards and Technology-traceable calibrated gamma radiation field to within 1.2% of the calibrated value. The pool irradiator had the largest dose rates near the middle of the torpedo, with dose rate decreasing as one moved towards the bottom or top of the torpedo. The dose rate across the torpedo is not uniform at each level, because of the non-uniform distribution of source activity around the irradiator. Relative error in the Fricke dosimeter dose rate measurements ranged from 1-2%. The dose rates mapped in this project can be used to plan bulk sample irradiation, although dosimetry measurements should still be obtained to confirm delivered dose.