The ¹⁴C(p, γ₀)¹⁵n cross section from E_p = 3.2 TO 7.7 MeV

Abstract

The 60° yield from the ¹⁴C(p, γ₀)¹⁵N reaction has been measured for proton bombarding energies between 3.2 and 7.7 MeV corresponding to ¹⁵N excitation energies between 13.2 and 17.4 MeV. A broad structure is observed at about 15 MeV which corresponds to the so-called pygmy resonance previously observed in the ¹⁵N(γ, p)¹⁴C reaction. In the present work it is seen that this structure exhibits two peaks. Angular distributions measured in the vicinity of these peaks are isotropic. This structure is in the region of the giant dipole resonance. Assuming that the decay is pure E1 implies that these states have J^π values of $\text{1}\text{2}{}^{\mathrm{+}}$. A $\text{T =}\text{1}\text{2}$ assignment is suggested by the fact that a similar structure (previously assigned $\text{J}{}^{\mathrm{\pi }}\text{= (}\text{1}\text{2}{}^{\mathrm{+}}$, $\text{3}\text{2}{}^{\mathrm{+}}$)) is observed in the ¹⁴N(p, γ_o)¹⁵O reaction. These results are not accounted for by a recent shell-model calculation of the dipole states of the mass-15 nuclei.