AMS measurement standards. Accelerator-mass-spectrometer measurements of Be and Al isotope
ratios are made with reference to analytical standards that have been prepared to have a known
Be-10/Be-9 or Al-27/Al-26 ratio. At present several different measurement standards
are in use at various AMS laboratories. When calculating an exposure age or an erosion
rate, the AMS analyses of the samples that are being dated must be referenced to the same standard
that was used for the analyses of calibration samples used to obtain the nuclide production rate.
If one tries to calculate an exposure age from samples measured against one standard and a nuclide production
rate inferred from calibration samples measured against a different standard, the exposure age will
most likely be incorrect.
AMS standards used in the calculators. The nuclide production rates used in the exposure
age and erosion rate calculators are normalized
to Be-10 and Al-26 standards prepared by K. Nishiizumi (see references below), which are the primary standards in use at
the Lawrence Livermore AMS facility as well as several others. Thus, Be-10 and Al-26 concentrations
submitted to the calculators must be normalized to the same standards.
This may involve adjusting measurements made at other AMS facilities. In particular, users of PRIME
Lab have in the past been instructed to multiply Be-10/Be-9 ratios reported by PRIME Lab by a factor
of 1.14 to make them consistent with the Nishiizumi standards and thus with measurements made at LLNL. There is additional information on
this situation at the PRIME Lab website here. If you're unsure what standards
were used for your measurements, check with the AMS lab where your samples were analyzed.
More information on the Nishiizumi AMS standards:
Nishiizumi, K., 2002. Be-10, Al-26, Cl-36, and Ca-41 AMS Standards. AMS-9
Abstracts, Abstract O16-1, 130.
Nishiizumi, K., 2004. Preparation of Al-26 AMS standards. Nuclear Instruments and Methods in
Physics Research B, v. 223-224, pp. 388-392. (external link to ScienceDirect)