Nitrogen spallation

Figure 7.22 14C is produced by reaction of cosmic rays with atmospheric atoms such as N2, O2, and others to produce broken pieces of nuclei, which are called spallation products. The reaction between neutrons and nitrogen (14N+n - 14C+p) is the dominant mechanism for the formation of 14C in the atmosphere. (Modified from Broecker and Peng, 1982.)... 

Tritium is produced in the atmosphere by cosmic-ray spallation of nitrogen (Lai and Peters, 1967). Tritium decays to He with a half-life of... 

The observed cosmic ray intensity NP(E) is determined by the competition between escape and spallation. It is important to realize that the numerical values of At and A at 1 GeV/nucleon are of comparable magnitude, for instance Ai 6.5g/cm2 for nitrogen, and 2.3g/cm2 for iron, and, as mentioned, A lg/cm2. While we may take A to be energy independent, A apparently is not. Hence, the measured energy spectrum NP(E) does not necessarily follow the same power law as the source spectrum. 

Regional laboratories that conform to national standards practices perform external QA measures of the network of RASA systems. An international testing procedure assures that the laboratories remain proficient. Randomly selected filters from the network of monitoring stations, automatic and manual, are sent to regional laboratories to determine if the station results are in control. This can be partially accomplished by measuring the level of 7Be (fi/2 = 53.28d), a cosmic-ray spallation product of atmospheric nitrogen and oxygen that is always in the atmosphere and is easily measurable on air filters. 

Fig. 2. Nitrogen isotopic compositions as a function of spallation ages for a suite of 20 Apollo 16 soils. The spallation ages are relative and not absolutely calibrated, but samples exposed longer ago on the lunar surface clearly contain lighter N than those exposed more recently. From Kerridge (1975).

This notation shows the isotope nitrogen-14 reacting with a neutron, n, giving off a proton, p, and forming the carbon-14 isotope other nuclear reactions can be deduced from this notation where x represents nuclear fragments from spallation. 

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