In beam tests of implanted helium targets

Targets of 3,4He implanted into thin aluminum foils (approximately 100, 200 or 600 μg/cm2) were prepared using intense helium beams at low energy (20, 40 or 100 keV). Uniformity was achieved by a beam raster across a tantalum collimator at the rates of 0.1 Hz (vertical) and 1 Hz (horizontal). Helium implantation into the very thin (80-100 μg/cm 2) aluminum foils failed to produce useful targets due to an under estimation of the range by SRIM code. The range in aluminum predicted by Northcliffe and Shilling and the NIST online tabulation, on the other hand, over estimate this range. An attempt to implant a second layer was also carried out, but did not significantly increase the helium content beyond the blistering limit. Rutherford Back Scattering of 1.0 and 2.5 MeV proton beams and recoil helium from 15.0 MeV oxygen beams were used to study the helium content and profile. The helium content and profile were very stable even after a prolonged bombardment (two days) with moderately intense beams of 16O or 4He. Helium implanted into thin foils is a good choice, for example, for a measurement of the 3He(α,γ)7 Be reaction and the associated S34 astrophysical cross section factor (S-factor). © 2006 IOP Publishing Ltd and SISSA.

Duke Scholars

Author Henry R. Weller Physics