The formation and decay of all the gamma-ray emitting states produced in bombarding ${\mathrm{B}}^{10}$ with protons in the energy range $4<~E_p<~12$ MeV has been studied. Re-examination of the gamma-ray decay scheme of ${\mathrm{B}}^{10}$ showed no evidence for the existence of either a 1.74- or a 1.84-MeV transition; the value $\frac{{\Gamma }_{\gamma }}{\Gamma }=0.73\mathrm{}\pm 0.15$ was obtained for the alpha-unstable 5.16-MeV level. Gamma rays from the first excited states of ${\mathrm{Be}}^7$ and ${\mathrm{C}}^{10}$ were also observed; the energy of the latter was determined to be 3.35±0.01 MeV. The formation of the positron-emitting ground state of ${\mathrm{C}}^{10}$ was studied by means of the annihilation radiation. Giant-resonance structures in the region $12<~E_x\left({\mathrm{C}}^{11}\right)<~18$ MeV were observed in the yield curves for all reactions that did not leave the final nucleus in a $T=1\mathrm{}$ state. A strong correlation between maximum cross sections and reaction energies is noted, but this correlation in itself does not appear to be sufficient to explain the marked suppression of the $T=1\mathrm{}$ final states. It is shown that a resonance in the four-particle system $\alpha +\alpha +d+p$ could be responsible for the giant-resonance structures.

• Received 23 December 1965

DOI:https://doi.org/10.1103/PhysRev.145.736