A high resolution gamma-ray spectrometer based on superconducting microcalorimeters.

Improvements in superconductor device fabrication, detector hybridization techniques, and superconducting quantum interference device readout have made square-centimeter-sized arrays of gamma-ray microcalorimeters, based on transition-edge sensors (TESs), possible. At these collecting areas, gamma microcalorimeters can utilize their unprecedented energy resolution to perform spectroscopy in a number of applications that are limited by closely-spaced spectral peaks, for example, the nondestructive analysis of nuclear materials. We have built a 256 pixel spectrometer with an average full-width-at-half-maximum energy resolution of 53 eV at 97 keV, a useable dynamic range above 400 keV, and a collecting area of 5 cm(2). We have demonstrated multiplexed readout of the full 256 pixel array with 236 of the pixels (91%) giving spectroscopic data. This is the largest multiplexed array of TES microcalorimeters to date. This paper will review the spectrometer, highlighting the instrument design, detector fabrication, readout, operation of the instrument, and data processing. Further, we describe the characterization and performance of the newest 256 pixel array.

The standardization of the potential bone palliation radiopharmaceutical 117mSn(+4)DTPA.

Solutions containing the potential bone pain palliation radionuclide 117mSn, in chloride form and as a diethylenetriaminepentaacetate (DTPA) complex, have been standardized by 4 pi beta liquid scintillation (LS) spectrometry and 4 pi gamma-ray spectrometry. Massic activities of the stock solutions were measured in order to determine dose calibrator settings for the solutions using commercial dose calibrators. Excellent agreement in the measurement of solution massic activity between the two techniques was achieved. The massic activity of 117mSnCl4 stock solution was found to be 38.62 +/- 0.23 MBq g-1 and 38.81 +/- 0.94 MBq g-1 with LS spectrometry and 4 pi gamma-ray spectrometry respectively. The respective values of the massic activity of the 117mSnDTPA stock solution with LS spectrometry and 4 pi gamma-ray spectrometry were 39.35 +/- 0.23 MBq g-1 and 39.70 +/- 0.96 MBq g-1. Impurities were analyzed in several solutions and found to have emission rates on the order of 10(-4) to 10(-6) of the rate of the 117mSn emission at the end-of-bombardment. The largest impurities came from 113Sn and 125Sn, the activation products of isotopic impurities present in the 117Sn target. The relative proportions of the various impurities were found to be highly dependent upon the source of 117Sn target material. The implications of choice of half-life used in the decay correction of 117mSn are discussed.

Measurement standards for strontium-89 for use in bone palliation.

Strontium-89 standards have been prepared for use in calibrating instruments in the measurement chain from production in reactors to administration in the clinic or radiopharmacy. Alternate reactor production schemes were evaluated to yield high purity 89Sr with minimum 85Sr impurity. Following purification to remove radionuclidic impurities, samples of 89Sr were standardized by high-efficiency liquid-scintillation counting with a relative expanded uncertainty (intended to approximate two standard deviations) of 0.48%. A Standard Reference Material, SRM 4426A, was prepared and distributed to radiopharmaceutical manufacturers and other customers. The standard sources of 89Sr were used in different geometries to calibrate high purity Ge semiconductor detectors, re-entrant ionization chambers and commercial radionuclide calibrators. The latter included Capintec dose calibrators and the Capintec beta C NaI(Tl) scintillation counter.

Preparation and Calibration of Carrier-Free 209Po Solution Standards.

Carrier-free 209Po solution standards have been prepared and calibrated. The standards, which will be disseminated by the National Institute of Standards and Technology as Standard Reference Material SRM 4326, consist of (5.1597 ±0.0024) g of a solution of polonium in nominal 2 mol · L-1 hydrochloric acid (having a solution density of (1.031±0.004) g · mL-1 at 22 °C) that is contained in 5 mL flame-sealed borosilicate glass ampoules, and are certified to contain a 209Po alpha-particle emission rate concentration of (85.42±0.29) s-1 · g-1 (corresponding to a 209Po activity concentration of (85.83 ±0.30) Bq · g-1) as of the reference time of 1200 EST 15 March 1994. The calibration was based on 4πα liquid scintillation (LS) measurements with two different LS counting systems and under wide variations in measurement and sample conditions. Confirmatory measurements by 2πα gas-flow proportional counting were also performed. The only known radionuclidic impurity, based on α- and photon-emission spectrometry, is a trace quantity of 208Po. The 208Po to 209Po impurity ratio as of the reference time was 0.00124 ±0.00020. All of the above cited uncertainty intervals correspond to a combined standard uncertainty multiplied by a coverage factor of k = 2. Although 209Po is nearly a pure α emitter with only a weak electron capture branch to 209Bi, LS measurements of the 209Po a decay are confounded by an a transition to a 2.3 keV ( Jπ= 1/2-) level in 205Pb which was previously unknown to be a delayed isomeric state.

External gamma-ray counting of selected tissues from a Thorotrast patient.

Results of gamma-ray measurements of selected tissues from a patient who was injected with Thorotrast almost 36 y ago are reported. The purposes of this study were: 1) to determine the relative tissue distribution and activities of specific radionuclides in the 232Th decay chain, specifically 228Ra (as measured by 228Ac), 212Pb, and 224Ra (measured directly and as measured by 212Pb), and 2) to evaluate the level of radioactive disequilibrium among the daughter products. The spleen and liver had the highest concentrations of radioactivity. Bone also appears to be a long-term sink for 232Th daughter products based on estimates from a small portion of one rib. Larynx and esophagus contained measurable activity, which may have been due to their proximity to the "Thorotrastoma." Radioactivity in the remaining measured tissues were low, as expected. Secular equilibrium could be demonstrated in bone, pancreas, larynx, esophagus, and breast. Significant disequilibrium was observed for spleen, liver, kidney, and red blood cells. Radioactivity measurements reported here will be useful in estimating radiation doses to selected tissues. Such dose estimates are valuable in refining current risk estimates (e.g., liver) and in identifying tissues at risk for further epidemiologic studies. These results, while consistent with other published studies, should be interpreted with caution since measurements were made on only one patient.

The standardization of samarium-153.

Samarium-153 has been standardized by 4 pi beta liquid-scintillation counting, with an uncertainty of 0.4%. The probability per decay for the 103.2-keV gamma ray was measured, using two germanium detectors, to be 0.298 +/- 0.004. The half life, based on liquid-scintillation measurements over 6.4 half lives and pressurized-ionization-chamber measurements over four half lives, was found to be 46.27 +/- 0.02 h. The uncertainties given are one estimated standard deviation (of the mean when applicable) for random and non-random components.