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Abstract: The use of helium as a stripper gas for Accelerator Mass Spectrometry (AMS) measurements of heavy ions is presented. At ion stripping energies of about 500keV and below we observe a significant increase of the mean charge state when using helium instead of other gases. Moreover, scattering losses are reduced with helium because of its lower mass compared to other commonly used stripper gases. Thus, highly efficient AMS measurements for 41Ca, 129I and 236U with transmissions through the accelerator in the range of 40–50% are now possible. [Copyright &y& Elsevier]

The energy-sensitive detection of heavy ions with calorimetric low temperature detectors was investigated in the energy range of E=0.1–1 MeV/amu, commonly used for accelerator mass spectrometry (AMS). The detectors used consist of sapphire absorbers and superconducting aluminum transition edge thermometers operated at T∼1.5 K. They were irradiated with various ion beams (13C,197Au,238U) provided by the VERA tandem accelerator in Vienna, Austria. The relative energy resolution obtained was ΔE/E=(5–9)×10-3, even for the heaviest ions such as 238U. In addition, no evidence for a pulse height defect was observed. This performance allowed for the first time to apply a calorimetric low temperature detector in an AMS experiment. The aim was to precisely determine the isotope ratio of 236U/238U for several samples of natural uranium, 236U being known as a sensitive monitor for neutron fluxes. Replacing a conventionally used detection system at VERA by the calorimetric detector enabled to substantially reduce background from neighboring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of 236U/238U=6.1×10-12 could be obtained, representing the smallest 236U/238U ratio measured at the time. In addition, we contributed to establishing an improved material standard of 236U/238U, which can be used as a reference for future AMS measurements. [ABSTRACT FROM AUTHOR]

Abstract: A new time-of-flight (TOF) system has been installed at the recoil mass separator DRAGON at the radioactive beam facility TRIUMF-ISAC in Vancouver, Canada. The addition of a velocity measurement to the existing energy measurement provides an effective separation of heavy ion reaction particles from remaining beam particles reaching the end detector, especially at low beam energies of interest to nuclear astrophysics research. The TOF detector system is based on two electrostatic mirrors equipped with thin carbon foils as a secondary electron emitter, and micro-channel plates for a fast timing signal. The system has been commissioned with stable , and beams in the energy range from 200 to . [Copyright &y& Elsevier]

In previous experiments, diamond-like carbon (DLC) foils which are being produced at Kurchatov Institute, have proven well suited as long-lived stripper foils for high-energy heavy-ion tandem accelerators and ultra-thin secondary-electron (SE) emitting foils for TOF spectrometers. This paper presents the recent advances in DLC targetry with main emphasis given to development and applications of ultra thin foils (maximum diameter up to 70 mm) with high uniformity and minimal possible effective thickness, the latter has been evaluated by measurements of both energy loss and angular scattering of heavy ions transmitting through the foils. Comparative lifetimes of DLC stripper foils irradiated with high intensity (150 μA) He+ beams at 2 MeV are reported, which demonstrate the favorable use of DLC foils as supplemental strippers at RFQ linacs. In conclusion, the attractive results of application of ultra-thin DLC foils to TOF detectors for heavy ion AMS as well as to compact tandem accelerators are presented. [Copyright &y& Elsevier]

Diamond is an attractive alternative to silicon as a heavy ion detector owing to its exceptional radiation hardness and very fast timing. These remarkable properties of diamond allow one to expect that diamond detectors can outperform silicon detectors and ionization chambers for many applications, in particularly, for heavy ion accelerator mass spectrometry (AMS) measurements. However, most reported diamond particle detectors have been based on polycrystalline chemical-vapor-deposited diamond films and exhibited poor energy resolution (due to loss of charge carriers in the grain boundaries) resulting in limited applications, primarily for counting ions at hundreds of MeV/u. In this paper the evaluation of a thin single-crystal natural diamond detector as an energy spectrometer for 13C, 180Hf, and 238U ions in the energy range from 12 to 38 MeV is presented. The influence of “priming” and “polarization” effects is discussed. Initial measurements of energy resolution, stability and radiation hardness of the natural diamond detector have demonstrated its suitability for heavy ion AMS, in spite of some technical problems to be solved. [Copyright &y& Elsevier]

Compared to heavy ion AMS at large tandem accelerators (TV⩾8 MV) and for cases where stable isobar interference is absent, a small facility like VERA (TV=3 MV) is shown to be able to offset the disadvantage of lower ion energy. After testing the system with 210Pb/208Pb isotope ratio measurements, we prove this by a measurement of 236U at natural levels in a material separated before 1918 and therefore free from anthropogenic contamination. An isotopic ratio of 236U/238U=(6.1±0.4)×10−11 was found for this material. [Copyright &y& Elsevier]