Theoretical studies on recoil nuclear polarisation in ¹⁰B(γ, π⁺)¹⁰Be*

The recoil nuclear polarisation in ¹⁰B(γ, π ⁺)¹⁰Be* (2⁺;1) can be determined completely by measuring the intensity I(θ, ϕ) and the circular polarisation asymmetry A_c(θ, ϕ) of the 3.3 MeV γ radiation emitted by the nucleus, whose spin state is, in general, non-oriented. The tensor parameters t_q^k, k=1, . . . , 4, characterising the residual nuclear system are calculated theoretically using the photoproduction amplitudes of CGLN (Chew et al. 1957) Berends-Donnachie (1975) and Blomqvist-Laget (1977). Numerical estimates in the energy range 160-360 MeV show that the polarisation parameters are quite sensitive to the basic photoproduction amplitudes employed, unlike differential cross sections. The distortion effects more or less cancel while estimating the t_q^k. A minimum number of optimal measurements capable of determining the t_q^k completely are also suggested.