The x-ray spectrometer (XRS) instrument is a revolutionary nondispersive spectrometer that will form the basis for the Astro-E2 observatory to be launched in 2005. We have recently installed a flight spare XRS microcalorimeter spectrometer at the EBIT-I and SuperEBIT facility at LLNL replacing the XRS from the earlier Astro-E mission and providing twice the resolving power. The XRS microcalorimeter is an x-ray detector that senses the heat deposited by the incident photon. It achieves a high energy resolution by operating at 0.06 K and by carefully engineering the heat capacity and thermal conductance. The XRS/EBIT instrument has 32 pixels in a square geometry and achieves an energy resolution of 6 eV at 6 keV, with a bandpass from 0.1 to 12 keV (or more at higher operating temperature). The instrument allows detailed studies of the x-ray line emission of laboratory plasmas. The XRS/EBIT also provides an extensive calibration “library” for the Astro-E2 observatory.
PACS 29.30.Kv, 29.40.Vj, 29.40.Wk, 74.78.Fk, 85.25.Oj Cryogenic Gamma-ray spectrometers operating at temperatures of ~0.1 K provide an order of magnitude better energy resolution than conventional germanium detectors. Ultra-high energy resolution improves the accuracy of non-destructive analysis of nuclear materials, since a better separation of lines reduces statistical errors as well as systematic errors from background subtraction and efficiency correction. We are developing cryogenic Gamma-spectrometers based on bulk tin absorbers and superconducting molybdenum-copper sensors for nuclear forensics and non-proliferation applications. Here we quantify the improvements in accuracy for isotope analysis with cryogenic detectors in terms of detector performance for different cases of line separation, line intensity ratios and background levels. Precise measurements of isotope ratios are crucial in the context of nuclear attribution, since they provide signatures of composition, age, origin, intended purpose and processing history of illicit nuclear materials.1 Introduction Gamma (γ) spectrometry is widely used to determine the isotopic composition of radioactive materials [1]. Upon decay, each radioisotope emits γ-rays with characteristic energies, which provide a fingerprint of the sample's composition. Relative line intensities can then be used to determine isotope ratios and thus infer sample age, origin and processing history. Traditionally, high-purity germanium (HPGe) detectors operating at liquid nitrogen temperatures of T ≈ 77 K have been used for γ-ray analysis, since they combine high energy resolution needed to separate the emission from different isotopes with high absorption efficiency required to measure weak emission lines from dilute samples. Modern analysis routines to extract isotope ratios from the measured spectra can attain a precision of ~1% or better depending on the isotope. Fundamentally, the precision is set by the statistical uncertainty of the measurement, but practically it is often limited by systematic errors in efficiency correction or background subtraction. Precision measurements are therefore based on the analysis of intense γ-lines with similar energies so that the detection efficiency of the spectrometer is similar. Highest precision requires high energy resolution of the spectrometer, because closely-spaced high intensity lines typically have energies below ~100 keV where line overlap affects both statistical precision and background subtraction. Since the attribution of unknown nuclear samples relies on minute differences in isotopic composition, high-resolution spectrometers are essential for nuclear forensics. Cryogenic γ-ray spectrometers operating at temperatures of T ≈ 0.1 K offer an order of magnitude improvement in energy resolution over conventional high-purity germanium (HPGe) detectors [2]. They typically consist of an absorber attached to a sensitive thermometer, both weakly thermally linked to a cold bath (figure 1). A γ-ray with energy E γ will increase the tem...
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