In the paper cited below by Tombrello et al. (1961), the nuc leon cluster structure of the mirror nuclei 3-Li-7 and 4-Be-7 was experimentally verified.
In agreement with the Brightsen Nucleon Cluster Model, these two nuclei can be viewed to differ only by transformation of two mass-3 clusters in their outer energy level. The Brightsen Model predicts that 3-Li-7 can have one isodyne structure where a [N-P-N] cluster in the 1p energy shell (with spin = 1/2) is bound to two [N-P] clusters (each with spin = 1) acting as a single phonon structure in the 1s energy shell (not the strongly bound alpha with spin = 0). In this way the spins of the various clusters can form a net spin = 3/2 for the 3-Li-7 nuclei (e.g., spin 2/2 + 2/2 - 1/2 = 3/2). Conversely, the Brightsen Model predicts that 4-Be-7 has a [P-N-P] cluster in its 1p energy shell with balance of spin dynamics. Tombrello & Phillips (1961) conclude that neither 3-Li-7 nor 4-Be-7 are formed by a "free N or P" bound to a 3-Li-6 structure--which confirms the fundamental assumption of the Brightsen Model that free N and P do not exist within beta-stable isotopes. Note also the fact that 4-Be-7 is unstable (undergoes electron capture) while 3-Li-7 is stable. Electron capture by a [P-N-P] cluster in 4-Be-7 is predicted to result in a transformation into a [N-P-N] cluster to form 3-Li-7. This paper by Tombrello et al. may provide an important clue to the cluster dynamics of the Brightsen Model--namely, that a lone [P-N-P] cluster in the 1p energy shell is unstable when bound to two [N-P] clusters that act as a single resonating phonon with spin I = 2 (not the stable alpha structure with spin I =0) in the 1s energy shell. Comments are welcome.
Cluster Nature of Li7 and Be7 Tombrello, T. A.; Phillips, G. C. ; Physical Review, vol. 122, Issue 1, pp. 224-228, 1961
Abstract
Measurements of the capture gamma-radiation processes, mass 3+alpha-->mass 7+gamma and nucleon+Li6-->mass 7+gamma, give information about the cluster structure of the mirror nuclei Li7 and Be7. The cluster model predicts that the ground state and low excited states of these nuclei should have large reduced widths theta3+42 for the configuration mass 3+alpha particle and small reduced widths theta1+62 for the configuration nucleon +Li6. Scattering experiments provide accurate initial, capturing, wave functions, and an assumption of the cluster nature of the final, bound, states allows the electromagnetic capture cross sections to be calculated and compared to experiment. The reduced widths deduced show that theta3+42 is large, theta1+62 is small, and that the ground states and first excited states of Li7 and Be7 are primarily of the two-body cluster form mass 3 + alpha particle.
