Stephan Vogt

PRIME lab AMS performance, upgrades and research applications

Abstract The 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 10 Be, 14 C, 26 Al, 36 Cl, 41 Ca and 129 I. 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 14 C and it is 3–5% for the other nuclides for radioisotope/stable isotope ratios at the 10 −12 levels. System background for 10 Be, 14 C, 26 Al, 36 Cl and 41 Ca is 1–10×10 −15 while for 129 I 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 36 Cl mapping. Radionuclide concentrations are also determined in meteorites and tektites for deciphering space and terrestrial exposure histories.

7Be, 10Be, and 36Cl in precipitation

Abstract We have measured the cosmogenic radionuclides 7 Be, 10 Be, and 36 Cl in mid-latitude precipitation collected in West Lafayette, IN. In the period April 18, 1992 to August 31, 1993, 350 samples were collected. A series of samples was collected through each precipitation event with 3 mm resolution. The 7 Be/ 36 Cl and 10 Be/ 36 Cl ratios vary by as much as a factor of 60 with a mean 10 Be/ 36 Cl ratio of 9.1. 7 Be, 10 Be, and 36 Cl concentrations through a single event are correlated and typically decrease from high values at the beginning of an event to lower values at the end. Mean concentrations of 7 Be, 10 Be, and 36 Cl are 1.4 × 10 7 , 1.8 × 10 7 , and 0.2 × 10 7 atoms/l.

Chemical studies of H chondrites: 5. Temporal variations of sources

We report 36Cl (301-kyr half-life) data obtained by accelerator mass spectrometry allowing nominal terrestrial ages to be determined for 39 Antarctic H4–6 chondrites for which contents of volatile trace elements are known. The compositional difference between these Antarctic meteorites and 58 non-Antarctic falls increases with terrestrial age and, using multivariate statistical techniques, becomes highly significant for Antarctic samples with ages >50 kyr. The compositional difference is inconsistent with trivial causes such as weathering and seems to reflect differences in thermal histories of parent sources. Temporal source variations for the H chondrite flux on Earth thus exist not only on a short-term, 40 years, basis (Dodd et al., 1993) but also on a long-term, >50 kyr, basis.

Environmental 90Sr measurements

90Sr (T12 = 28.5 years) is a long-lived radionuclide produced in nuclear fission. Fast radiochemical detection of 90Sr in environmental samples is not feasible using current analytical methods. Accelerator Mass Spectrometry (AMS) measurements of 90Sr were made with the Rehovot 14UD Pelletron accelerator at a terminal voltage of 11 or 12 MV using our standard detection system. Injection of hydride ions (SrH3−) was chosen owing to high beam intensity and low Coulomb explosion effects. 90Sr ions were identified and discriminated from isobaric 90Zr by measuring time of flight, total energy and three independent energy-loss signals in an ionization chamber. A reference sample and a ground-water sample were successfully measured. The detection limit determined for a laboratory blank by the residual counts in the 90Sr region is 90SrSr = 3 × 10−13, corresponding in practice to (2−4) × 10790Sr atoms or about 0.5–1 pCi/L in environmental water samples.

Aluminum 26, 10Be, and 36Cl depth profiles in the Canyon Diablo iron meteorite

The authors have measured activities of the long-lived cosmogenic radionuclides {sup 26}Al, {sup 10}Be, and {sup 36}Cl in 12 fragments of the iron meteorite Canyon Diablo and have constructed production rate-versus-depth profiles of those radionuclides. Profiles determined using differential particle fluxes calculated with the LAHET code system are in good agreement with {sup 26}Al, {sup 10}Be, and {sup 36}Cl experimental data, but the agreement for {sup 36}Cl was obtained only after neutron-induced cross sections were modified. Profiles calculated with lunar particle fluxes are much lower than experimental Canyon Diablo profiles. The cosmic ray exposure ages of most samples are near 540 m.y. 34 refs., 4 figs., 2 tabs.

Status and plans for the PRIME Lab AMS facility

Abstract The 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.

THE 129I AMS PROGRAM AT PRIME LAB

The current status of sample preparation activities and AMS determination of 129II ratios are described. Determination of 129II ratios is being performed routinely at the precision of 3% (at 10−11 level). A system background of 20−80 × 10−15 of 129II ratio has been achieved without a time-of-flight (TOF) detector and without a low-energy electrostatic deflector. An intercomparison of 129II ratios for AgI samples obtained from other AMS facilities and for the round robin exercise by the International Atomic Energy Agency (IAEA) show an excellent agreement. Potential applications of 129I for tracing groundwater and ocean water are discussed.

Chemistry operations at Purdue's accelerator mass spectrometry facility

Abstract The present status of chemistry operations of PRIME Lab, Purdues Accelerator Mass Spectrometry Facility, is reviewed. The capabilities and performance of sample preparation for the three nuclides 10Be, 26Al and 36Cl in a variety of different sample types are found to be adequate for the current performance figures of the AMS facility. Standard materials prepared and in use at PRIME Lab are described. Future plans are directed toward standardization and automation of analytical techniques as well as the addition of the nuclides 14C, 41Ca, and 129I.

Measurements of 41Ca spallation cross sections and 41Ca concentrations in the grant meteorite by accelerator mass spectrometry

Abstract Systematic measurements of spallogenic 41Ca in the iron meteorite Grant and in proton irradiated elemental Ni, Fe and Ti targets have been made by accelerator mass spectrometry using a 14UD Pelletron accelerator. Spallation (p, 41Ca) cross sections, were measured for proton energies between 40 and 600 MeV. For the Grant meteorite 5 samples at various depths, ranging from the post-atmospheric surface to centre, were measured in order to investigate the depth production profile of 41Ca. Using the measured excitation function for 41Ca on Fe, the production rate due solely to primary galactic cosmic rays is estimated and the importance of secondary flux production for 41Ca in a large meteorite is discussed.

Identification of bomb-produced chlorine-36 in mid-latitude glacial ice of North America

Abstract In 1991, the U.S. Geological Survey collected a 160-meter (m) ice core from the Upper Fremont Glacier (43°07′N, 109°36′W) in the Wind River Mountain Range of Wyoming in the western United States [1]. In 1994–1995, ice from this core was processed at the National Ice Core Laboratory in Denver, Colorado, and analyzed for chlorine-36 (36Cl) by accelerator mass spectrometry at PRIME Laboratory, Purdue University. A tritium bomb peak identified in the work by [1] was used as a marker to estimate the depth of bomb-produced 36Cl. Tritium concentrations ranged from 0 tritium units (TU) for older ice to more than 300 TU at 29 m below the surface of the glacier, a depth that includes ice that was deposited as snow during nuclear-weapons tests through the early 1960s. Maximum 36Cl production during nuclear-weapons tests was in the late 1950s; therefore, the analyses were performed on ice from a depth of 29.8 to 32 m. Calculated flux for 36Cl in ice deposited in the late 1950s ranged from 1.2 ± 0.1 × 10−1 atoms/cm2 s for ice from 29.8 to 30.4 m, to 2.9 ± 0.1 × 10−1 atoms/cm2 s for ice from 31.5 to 32.0 m. Ice samples from a depth of 104.7 to 106.3 m were selected to represent pre-weapons tests 36Cl flux. Calculated flux for 36Cl in this deeper ice was 4.6 ± 0.8 × 10−3 atoms/cm2 s for ice from 104.7 to 105.5 m and 2.0 ± 0.2 × 10−2 atoms/cm2 s for ice from 105.5 to 106.3 m. These flux calculations from the Upper Fremont Glacier analyses are the first for bomb-produced 36Cl in ice from a mid-latitude glacier in North America. It may now be possible to fully quantify the flux of 36Cl from nuclear-weapons tests archived in mid-latitude glacial ice and to gain a better understanding of the distribution of 36Cl and other cosmogenic nuclides.