With Janet Sisterson (Northeast Proton Therapy Center, NPTC), and   Don Burnett (CIT), we demonstrated in our 2004 study that a spatially uniform distribution of ³He is produced within minerals when irradiated with an energetic (>100 MeV) proton beam produced by cyclotron acceleration.  Essentially all atoms present in a mineral can produce spallation ³He.

For our purpose, a uniform ³He distribution is useful primarily for two reasons:

(i) it enables a stepwise degassing experiment in which the natural ⁴He release fractions are normalized to the proton-induced ³He released in the same step:  the ratio evolution diagram constrains the natural ⁴He distribution within the sample, and

(ii) it satisfies the initial condition from which diffusion coefficients are easily calculated.

In our latest irradiation, we generated 10⁹ atoms ³He/mg with a fluence of 1×10¹⁶ protons/cm² at 220 MeV, accomplished with a beam current of ~280 nA over a single 8 hour period.  This is an enormous concentration of ³He which easily permits single grain analyses.