Cosmogenic beryllium (10Be)
Beryllium has one stable nuclide (9Be) and two cosmogenic radionuclides, 7Be und 10Be; 7Be has too short a half-life (53 days) to be useful for in situ applications; the half-life of 10Be is 1.36+/-0.07Ma; 10Be can be used for geological applications during the entire Quarternary and Pliocene.
10Be is produced mainly by spallation reactions from oxygen in rocks and minerals close to the surface. In the Earth's atmosphere 10Be is produced by spallation reactions on nitrogen and oxygen. For in situ applications (applications based on cosmogenic nuclides in rocks/minerals) the meteoric component of 10Be has to be removed; a large part of the sample preparation is therefore the complete removal of the meteoric component. In almost all in-situ 10Be applications quartz is used as target mineral. The difficulty of removing meteoric 10Be from minerals other than quartz stands in the way of the widespread use of other mineral phases for in situ 10Be applications. 10Be is the most widely used cosmogenic nuclide for terrestric in-situ applications. An important aspect of sample preparation for 10Be samples for ASMS measurements has to be the removal of boron, whose isotope 10B interferes during AMS measurements on mass 10. Thus, an almost boron-free lab environment is important for the chemical sample preparation.
Cosmogenic aluminium (26Al)
Aluminium has one stable nuclide (27Al) and one cosmogenic radionuclide; the cosmogenic radionuclide 26Al has a half-life of 708+/-17 ka. For geological applications 26Al is used in conjunction with 10Be frequently. Together, the 10Be – 26Al couple is regularly used to constrain complex exposure histories and for burial dating of sediments.
In silicates close to the surface 26Al is mainly produced by spallation reactions from Si. Since a high Al content (>100 ppm) in samples is prohibiting AMS measurements, quartz is mainly used for 26Al. Due to the lack of appropriate target elements in the atmosphere, production of atmospheric 26Al is low. Consequently, meteoric 26Al is usually not a major concern in the application of in situ 26Al.
An important aspect of the determination of 26Al concentrations in geologic samples is the exact determination of stable 27Al in the sample. 26Al concentrations are determined by the measurement of the 26Al/27Al ratio by AMS and the analytically determined 27Al content.
Cosmogenic chlorine (36Cl)
Chlorine has two stable nuclides (35Cl and 37Cl) and a cosmogenic radionuclide 36Cl (half-life of 301+/-2 ka).
In rocks and minerals close to the surface 36Cl is mainly produced by spallation reactions from K and Ca, and, to a lesser extent, from Ti and Fe. In chlorine rich samples, the thermal-neutron flux generated in rocks can also produce 36Cl via the (n,γ) capture reaction. Since the thermal-neutron flux is reactive to the environmental conditions (humidity) and thus not accountable, it is best when samples contain not much stable chlorine (<10-20 ppm). 36Cl is the only cosmogenic nuclide that can be analyzed routinely in carbonates, feldspars and basalts. Carbonates are generally rich in Ca and poor in stable chlorine, therefore precise ages can be determined even for very young samples (couple of 100 years).
Besides the separation of chlorine carrying phases (mineral separation and chemical leaching) is the separation of sulfur important during the chemical preparation of a sample for AMS measurement. 36S interferes on 36Cl determinations.