[en] Accelerator Mass Spectrometry (AMS) is an isotope ratio mass spectrometer that quantifies low levels of rare isotopes with half-lives between 10 and 10⁸ years. Typical sensitivities are 10⁶ atoms in a milligram-sized sample. AMS was originally developed for use in the geosciences as a tool to carbon date archaeological artifacts, but has applications in many fields. In the biosciences, the extreme sensitivity of AMS is used to trace nutrients, toxins and therapeutics in humans and animals using less than (micro)g/kg doses containing between 1-100 nCi of ¹⁴C. This sensitivity is used to reduce sample size, reduce chemical exposures to environmental or physiological levels, reduce radiation exposures to subjects, and/or reduce radioactive (and ''mixed'') waste. Compared to decay counting, AMS provides for a much higher measurement throughput for low activity samples. For example, a milligram-sized sample containing 1 dpm of ¹⁴C can be measured to 3% precision in several seconds. That same sample would require approximately 1 week of decay counting to obtain similar precision

[en] Isotope tracer studies, particularly radiocarbon measurements, play a key role in biological, nutritional, and environmental research. Accelerator mass spectrometry (AMS) is now the most sensitive detection method for radiocarbon, but AMS is not widely used in kinetic studies of humans. Part of the reason is the expense, but costs would decrease if AMS were used more widely. One component in the cost is sample preparation for AMS. Biological and environmental samples are commonly reduced to graphite before they are analyzed by AMS. Improvements and mechanization of this multi-step procedure is slowed by a lack of organized educational materials for AMS sample preparation that would allow new investigators to work with the technique without a substantial outlay of time and effort. We present a detailed sample preparation protocol for graphitizing biological samples for AMS and include examples of nutrition studies that have used this procedure

[en] Aluminum-23 was produced in two 40 MeV proton bombardments of Mg targets at LBNL's 88-Inch Cyclotron. Reaction products were transported by helium jet to a detection chamber. They were observed by two low-energy particle-identification telescopes; each consisted of two gas-ΔE detectors, a thin (<70 μm) Si E detector and a 300 μm Si E-reject detector. Contrary to previous measurements, the lowest energy peak in the spectrum was observed at an energy of 246±20 keV with 33±3% of the intensity of the peak at 838±5 keV. Implications for isospin mixing and the proton-capture width of the ²³Al isobaric analog state in ²³Mg are discussed. Other weak beta-delayed proton-decay branches were also observed with energies up to ∼2200 keV

[en] Cavity ring-down spectrometers typically employ a PZT stack to modulate the cavity transmission spectrum. While PZTs ease instrument complexity and aid measurement sensitivity, PZT hysteresis hinders the implementation of cavity-length-stabilized, data-acquisition routines. Once the cavity length is stabilized, the cavity’s free spectral range imparts extreme linearity and precision to the measured spectrum’s wavelength axis. Methods such as frequency-stabilized cavity ring-down spectroscopy have successfully mitigated PZT hysteresis, but their complexity limits commercial applications. Described herein is a single-laser, model-based, closed-loop method for cavity length control. (paper)