Form Factors of the Three-Nucleon Systems 3H and 3He

Abstract

Recently, Schiff1 has discussed the theory of 3H and 3He form factors in connection with experiments being done at Stanford on elastic scattering of high-energy electrons from these nuclei.2 Both 3H and 3He have bound-state spin = ½, and an analysis of the electronscattering data on these nuclei has been made using the Rosenbluth formula, from which one obtains four form factors, namely, charge and moment form factors for 3H and the same for 3He. The experimental results showed that the two moment form factors and the charge form factor for 3H are quite similar to each other, while the charge form factor for 3He falls off somewhat more rapidly. These observations fit in with a simple intuitive explanation in terms of the spatial distributions of the like pairs of nucleons. Since the spins of the like pair (protons in 3He and neutrons in 3H) are primarily opposite, the moment is carried mainly by the odd nucleon in both cases. Also, the charge in the case of 3H is carried by the odd nucleon, while in the case of 3He the charge is carried by the like particles. Thus, the experimental observations suggest a distribution for each of the like pair which is different from that of the odd nucleon. This could be pictured as arising from the different binding of the odd nucleon, which could be bound to each of the like ones by a linear combination of the triplet and singlet interactions that is more strongly attractive than the singlet interaction binding the like pair, thereby accounting for a more extended distribution in space of the like pair than that of the odd nucleon.