Recent results at the SIRa test bench: Diffusion properties of carbon graphite and B4C targets

Nuclear Charge Radius ofHe8

“…Most strikingly, the rms charge radius decreases significantly from 6 He to 8 He, while the matter radius seems to increase. The larger matter radius of 8 He is consistent with there being more neutrons and more nucleons altogether.…”

“…The uncertainty in the nuclear mass enters as an additional systematic effect via the theoretical mass shift. This effect is the single biggest contribution to the final uncertainty for 8 He, but plays only a minor role for 6 He. Improved mass measurements for both isotopes are in preparation, using Penning trap mass spectrometry [12].…”

“…Low-energy (20 keV) beams of either 6 He or 8 He with yields of around 1 × 10 8 and 5 × 10 5 ions per second, respectively [8], were delivered to an adjacent lowradiation area where the helium ion beam was stopped in a hot, 1 cm 2 sized graphite foil for neutralization. The released neutral, thermal helium atoms were pumped within 250 ms into the atomic beam apparatus resulting in rates of approximately 5 × 10 7 s −1 and 1 × 10 5 s −1 for 6 He and 8 He, respectively.…”

“…This effect was taken into account for the 8 He data, which could only be recorded with signal-to-noise ratios sufficient for single-atom detection, i.e., at ∼ 3 × I sat .…”