Recoil loss

The fraction of He lost by recoil is a strong function of effective grain size, or more strictly its the surface/volume ratio (Farley et al. 1996 Martel et al. 1990). Low surface area/volume ratios of 0.03 result in 90% retention of He in all but the most 

The mineral-fluid system and diffusive gradient For diffusion to occur there must also be a chemical gradient. For noble gases in a mineral-fluid system this occurs when the noble gas equilibrium concentration in the mineral phase (Cm) is higher than the equilibrium concentration in the fluid phase (Cf), where the mineral-fluid partition coefficient (Kd) is defined as 

In addition to Kd, the diffusion gradient will also be dependent on the mass ratio of solid to fluid, which together govern fluid s ability to provide a suitable sink for the noble gas released. Baxter et al (2001) for example, show that for diffusion gradients to be established  

Mineral transformations during diagenesis (e.g., illite smectite transition), metamorphism (e.g., recrystallization of clay minerals to biotites, amphiboles, etc) or alteration (e.g., serpentinization of mafic minerals) are likely to release the radiogenic noble gases that were produced within their lattices. This assumes that  

While there is robust evidence for the incompatible behavior of all the noble gases 

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P = permanent recoil loss probability from the detector for Pb-214 atom, t = exposure time,... 

Figure 5. Results of an empirical model that calculated, for each low-pressure impactor size range, the percentage recoil losses of Pb-214 [subplot (a)] necessary to produce a calculated Pb-214 distribution is best agreement with the observed distribution [subplot (b)]. Lower Dp limits are arbitrary.

Ott U, Altmeier M, Herpers U, Kuhnheim J, Merchel S, Michel R, Mohapatra RK (2001) Update on recoil loss of spallation products from presolar grains. Meteoritics Planet Sci 36 A155-A156 Okazaki R, Takaoka N, Nakamura T, Nagao K (2000) Cosmic ray exposure ages of enstatite chondrites. 

Equations (2.11) and (2.12) were solved for values of Ri and A that gave the best fit to observed and calculated " Pb size distributions. The various impactor stages are used for deriving the particle size intervals. An example of the results of this model is presented in Figure 2.9. In this calculation, A was assumed to be 0.963 (i.e. 96.3% of the Po was assumed to attach to ambient aerosol particles before decay to " Pb). The best agreement between calculated and measured Pb size distributions was found for the case when calculated recoil losses Ri) of 100, 70, 65, and 35% occurred from the <0.11-, 0.11- to 0.23-, 0.23- to 0.52-, and 0.52- to 0.90-pm size ranges, respectively. In this example, the percentage of the total " Pb that underwent recoil detachment was calculated to be 79.6%, very similar to values predicted in a theoretical analysis (Mercer, 1976) and calculated from experimental data... 

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