The state of the art in accelerator mass spectrometry (AMS) is reviewed. The review is divided in two parts. The first covers the general methodology, followed by its specific elaborations for the commonly measured long-lived isotopes such as 10Be, 14C, 26Al, 36Cl and 129I, as well as other isotopes with emerging applications. The second part considers the very wide spectrum of applications that now employ AMS, and groups these according to research area rather than isotope. The period up until late 1998 is covered, with an emphasis on post-1990 developments and literature.

/pdf/accelerator-mass-spectrometry-and-its-applications-2vufqdu2hr.pdf

Accelerator mass spectrometry and its applications

Variations in 129I/127I ratios in recent marine sediments: evidence for a fossil organic component

More than a decade has passed since a complete revision was initiated of the radiation doses received by survivors of the Hiroshima and Nagasaki atomic bombings. The new dosimetry system (DS86) was completed in 1986 and adopted shortly thereafter. Overall, DS86 was noted to be a clear improvement over the old dosimetry system. However, based on limited validation measurements, troublesome inconsistencies were suggested for neutrons. Since 1986, a substantial number of additional neutron activation measurements have been made in mineral and metal samples from Hiroshima. Importantly, a large number of measurements have now been made at distances beyond 1 km. Here, inconsistencies between neutron activation measurements and DS86 calculations for Hiroshima are examined using all available measurement data, including new measurements for 36Cl which extend the measurement range to more than 1.7 km from the epicenter, and Monte Carlo modeling calculations for each sample measured. Results show that thermal neutron activation measured beyond approximately 1 km in Hiroshima (at distances most relevant for radiation-risk evaluation) is two to 10, or more, times higher than that calculated based on DS86. Similar trends observed when comparing results by several independent measurement laboratories, using different analytical methods, suggest that the DS86 calculations for low-energy neutrons are in error. Because of the importance of the Hiroshima data in radiation risk evaluation, this large discrepancy is in need of resolution.

Neutron discrepancies in the DS86 Hiroshima dosimetry system.

Large-quantity dilutions of the National Institute of Standards and Technology (NIST) 36Cl standard (SRM 4943) to 36 Cl Cl ratios of 5.000 × 10−13, 1.600 × 10−12, 5.003 × 10−12 and 1.000 × 10−11 have been prepared for AMS standards. Dilutions were made with an estimated uncertainty better than 1% and were then checked in three separate runs using the AMS facility at the University of Rochester. The results show excellent agreement between the gravimetric dilution factors and AMS measurements.

Development of 36Cl standards for AMS

Geochemistry of halogens in the Milk River aquifer, Alberta, Canada

The accelerator mass spectrometry program at Rochester is at present based on measurements of the long-lived radioisotopes 36Cl and 129I, and on the determination of osmium isotope ratios in sub-ppb level samples. This paper describes the present configuration of the instrument and gives a brief overview of the current research program.

Accelerator mass spectrometry at the university of Rochester

The 36 Cl production mechanism in the atmosphere is of interest in understanding the formation of this cosmogenic radioisotope and its applications in geological studies. The 36Ar (n, p) 36 Cl reaction has been suggested by Onufriev as a source of 36 Cl in the atmosphere. Onufriev derived this estmation by assuming the 36 Ar(n, p) 36 Cl reaction to be caused by slow neutrons with a cross section of the same order of magnitude as that of the 14 N(n, p) 14 C reaction [1]. However, no data existed for the slow neutron cross section of 36 Ar(n, p) 36 Cl. We irradiated enriched 36 Ar gas in a reactor and used the AMS technique to detect 36 Cl. We obtained an upper limit for the thermal neutron cross section of 1.5 mb. This value is three orders of magnitude lower than the value assumed by Onufriev.

Measurement of the 36Ar(n, p)36Cl cross section at thermal energies using the AMS technique

Determination of the more common light elements such as nitrogen and chlorine at trace levels is difficult because of their high abundance on sample surfaces, in materials used to build analysis instruments, and in the residual gas of the instrument vacuum. We present here a new approach to analysis of these elements: accelerator mass spectrometry (AMS) combined with neutron activation. The problem of contamination is overcome by using neutron activation to produce long-lived radioisotopes which generally have low concentrations in the environment. For measurement of 14N and 35C1, AMS can provide sensitive background-free measurements of their neutron activation products 14C and 36C1 and, in addition, can provide depth profiles. These are the first results of this new method: depth profiles of nitrogen and chlorine implanted in semiconductor grade silicon.

/pdf/depth-profiles-of-nitrogen-and-chlorine-in-pure-materials-57womp6phc.pdf

Songsheng Jiang

Papers

Accelerator mass spectrometry at the university of Rochester

Measurement of the 36Ar(n, p)36Cl cross section at thermal energies using the AMS technique

Depth Profiles of Nitrogen and Chlorine in Pure Materials Through AMS of the Neutron Activation Products 14C and 36Cl