Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Upgrading program for the FN tandem and AMS system at PRIME Lab
Abstract
A coordinated upgrading program is underway at PRIME Lab with the goal of permitting isotopic ratio measurements throughout the periodic table with systematic errors below 1%, detection limits at or below 10−15 and a capacity of over 3000 samples per year. The FN tandem upgrade will include spiral-inclined titanium electrode acceleration tubes, dual Pelletron chains, shielded column grading resistors, a longer and larger diameter stripper with both gas recirculation and active pumping, and a 300-foil stripper. The ion source system will provide for tandem injection at energies as great as 130 keV and includes a non-dispersive energy/momentum analysis pair having M/ΔM above 300 together with 5 Hz mass switching. The 90° electrostatic analyzer will have double-focusing spherical geometry. The 90° magnetic analyzer will have two independent poles to provide four curved boundaries for correction of aberrations. An electrostatic quadrupole triplet will prepare the beam for injection into the tandem and correct any distortion. Following the tandem, an electrostatic quadrupole doublet will be substituted for the existing magnetic lens. This lens will be located close to the tank base for improved optical matching of the existing 90° magnet. The pole width of the existing 90° magnet is adequate for allowing masses 35, 36 and 37 to be directed into separate cups at constant field. Computer control will be added to all power supplies to permit polling of all parameters, unattended operation, and rapid conversion between isotopic systems. The upgrade will begin in the fall of 1993, starting with the tandem
References (3)
- D. Elmore et al.
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Control of <sup>36</sup>Cl production in carbonaceous shales by phosphate minerals
2003, Geochimica et Cosmochimica ActaWhen using 36Cl to date very old groundwater in regional aquifer systems, knowledge of the subsurface 36Cl input into the aquifer system is essential. Although 36Cl can be produced through nuclear reactions in the subsurface, in many situations, the input of 36Cl into sedimentary aquifer systems by this avenue of production can be neglected. This is a valid assumption when investigating long-flowpath groundwater systems composed of sandstones, limestones, and shales of typical composition. These rock types are not sufficiently enriched in radioactive elements to produce significant 36Cl in the deep subsurface. Carbonaceous shales, on the other hand, can concentrate the radioactive elements necessary to produce significant 36Cl in the deep subsurface. Chlorine-36 ratios (36Cl/Cl) for a suite of Late Devonian and Pennsylvanian carbonaceous shales were calculated from bulk-rock chemistry as well as measured using accelerator mass spectrometry. The poor agreement between calculated and measured ratios is the result of the assumption of chemical homogeneity used by the calculation algorithm, an assumption that was not satisfied by the carbonaceous shales. In these shales, organic matter, clay minerals, and accessory minerals are heterogeneously distributed and are physically distinct on a micron-order scale. Although organic matter and clay minerals constitute the overwhelming bulk of the shales, it is the phosphate minerals that are most important in enhancing, and suppressing, 36Cl production. Minerals such as apatite and carbonate-apatite (francolite)—by including uranium, rare earth elements (REEs), and halogens—have an important impact on both neutron production and thermal neutron absorption. By incorporating both uranium and fluorine, phosphate minerals act as neutron production centers in the shale, increasing the probability of 36Cl production. By incorporating REEs and chlorine, phosphate minerals also act to shield 35Cl from the thermal neutron flux, effectively suppressing the production of 36Cl. To reconcile the measured 36Cl ratios with the ratios calculated assuming chemical homogeneity, the shales were artificially split into three fractions: organic, clay mineral, and phosphate mineral. Neutron production was calculated separately for each fraction, and the calculation results demonstrated that the phosphate fraction exerted much more control on the 36Cl ratio than the organic or clay mineral fractions. By varying the uranium and chlorine contents in the phosphate fraction, a new, heterogeneous 36Cl ratio was calculated that agreed with the measured ratio for the overwhelming majority of the carbonaceous shales. When using rock chemistry to calculate the 36Cl ratio, rock types that show mineralogical heterogeneity on a micron scale can be divided into bulk fractions and accessory fractions for separate calculations of neutron production and neutron absorption. In this manner, a more accurate, heterogeneous 36Cl ratio can be calculated for the rock as a whole.
PRIME lab AMS performance, upgrades and research applications
2000, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and AtomsThe Purdue Rare Isotope Measurement Laboratory (PRIME Lab) is a dedicated research and service facility for AMS that provides the scientific community with timely, reliable and high quality chemical processing (∼600 samples/year) and AMS measurements (∼3000 samples/year) of 10Be, 14C, 26Al, 36Cl, 41Ca and 129I. The AMS system is based on an upgraded FN (7 MV) tandem accelerator that has recently been modified to improve performance. The precision is 1% for 14C and it is 3–5% for the other nuclides for radioisotope/stable isotope ratios at the 10−12 levels. System background for 10Be, 14C, 26Al, 36Cl and 41Ca is 1–10×10−15 while for 129I the natural abundance limits it to 20×10−15. Research is being carried out in Earth, planetary, and biomedical sciences. Geoscience applications include determination of exposure ages of glacial moraines, volcanic eruptions, river terraces, and fault scarps. Burial histories of sand are being determined to decipher the timing of human expansion and climatic history. Environmental applications are tracing the release of radioactivity from nuclear fuel reprocessing plants, water tracing, and neutron dosimetry. The applications using meteoric nuclides are oil field brines, sediment subduction, radiocarbon dating, and groundwater 36Cl mapping. Radionuclide concentrations are also determined in meteorites and tektites for deciphering space and terrestrial exposure histories.
Status and plans for the PRIME lab AMS facility
1997, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and AtomsThe operation, status, performance, and upgrade plans for the Purdue Rare Isotope Measurement Laboratory (PRIME Lab) are described. The AMS system is in routine operation for all of the commonly-used AMS nuclides. Chemical preparation is being performed for all nuclides measured in many different matrices. Construction of a new injector and terminal stripper system is in progress; a fast-isotope-switching system is in the final design stage.
Detection of <sup>236</sup>U: A possible 100-million year neutron flux integrator
1996, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and AtomsIt is anticipated that accelerator mass spectrometry (AMS) assay of actinides, in particular 236U and 233U in uranium and 229Th and 230Th in thorium, will become valuable for identifying the previous human use of such materials. A discussion is included concerning the possibility of using 236U as a thermal neutron monitor having an integration period of up to 100 million years using AMS to fragment all molecular interferences. Using the detection of at levels below 10−13 as a design goal, a description is provided of the geometry of a proposed broad-range precision AMS spectrometer that includes a 3 MV terminal tandem accelerator and a terminal gas stripper. The elimination of interfering molecular ambiguities and backgrounds is discussed. A post-acceleration stripping procedure for ambiguity elimination is presented. A novel acceleration and fragmentation protocol is also described where molecular fragmentation is carried out at ground, outside of the tandem, rather than by stripper fragmentation at high voltage. It is shown that this new procedure simplifies AMS especially for heavy elements and leads to the possibility of using smaller tandems and analysis components. Multiple scattering during terminal charge changing is considered together with its effects upon accuracy and efficiency.
The Purdue Rare Isotope Measurement Laboratory
1994, Nuclear Inst. and Methods in Physics Research, BPurdue University has brought into operation a new NSF/NASA facility dedicated to accelerator mass spectrometry. Based on a 7.5 MV FN tandem, 10Be, 26Al, and 36Cl are being measured at a rate of 1500 samples per year. Research involves primarily 1) earth science studies using cosmogenic radionuclides produced in the atmosphere and measured in rain, groundwater, and soils, 2) Quaternary geomorphology and climatology studies using in-situ produced radionuclides, 3) planetary science studies using a wide variety of meteorites and radionuclides, and 4) biomedical tracer studies using 26Al.