Effect of Nuclear Alignment on the 14-MeV Total Neutron Cross Section ofHo165

The effect of nuclear alignment on the total cross section of the highly deformed ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ nucleus has been measured using 14-MeV neutrons. The aligned ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ target was obtained by cooling a metal single crystal to 0.33°K. A finely collimated beam of 14-MeV neutrons was produced by careful collimation of the alpha particle produced in the ${}_{}{}^3{}_{}{}^{}\mathrm{H}\mathrm{}(d,n)\mathrm{}{}_{}{}^4{}_{}{}^{}\mathrm{He}$ reaction and by detecting it in fast coincidence with its associated neutron. The measured total cross section is 5.29±0.10 b. The fractional change in the total cross section, for our value of nuclear alignment ($f_2=0.31\mathrm{}$), is + (3.52±0.75)%, where the positive sign indicates a larger cross section for nuclei aligned perpendicular to the incident beam than for randomly oriented nuclei. These results are in excellent agreement with the predictions of the optical model using an adiabatic coupled-channel calculation. The optical-model parameters used are in good agreement with those obtained from other measurements, and in particular the value of the deformation parameter $\beta =+0.30\mathrm{}$ is the same as that used in our earlier work. It was also found that 14 MeV is not yet a sufficiently high energy to use the black-nucleus model to interpret our results.