Gamma rays from resonance neutron capture in 115In

Gamma rays in the range 5.4–6.7 MeV have been studied for 31 s-wave neutron resonances of ¹¹⁵In, selected by time of flight in the range 3–430 eV. In a subsidiary experiment, spin J = 5 has been assigned to 17 and J = 4 to 14 resonances by measuring intensity variations of some strong low-energy transitions. The reduced widths averaged over all initial states of the same spin have been estimated for 41 primary transitions: these values have provided information on the spin and parity of the corresponding ¹¹⁶In final states. Overall mean values of E1 and M1 radiative strength have been calculated. The width distribution has been fitted with a χ² function with ν = 1.10^+0.27_?0.09 degrees of freedom for M1 and ν = 1.42 ^{+ 0.014}_?0.08 for E1 radiation. An estimate of the spin cut-off parameter σ = 3.6_?0.4^{+ 0.8} has been derived. A non-statistical effect already evidenced in previous measurements has been confirmed, consisting of a strong modulation of the radiative strength against resonance energy, correlated also with the local neutron strength function. In addition, it has now been shown that this structure is due to E1 radiation only.