Valence component in the neutron capture cross section of 90Zr

Abstract

The neutron capture cross section of 90Zr has been measured with high energy resolution between 3 and 200 keV using the capture cross section facility at the 40 m station on the Oak Ridge electron linear accelerator. Through the comparison of the present data with the total cross-section and inverse 91Zt(γ, n) data from Toohey and Jackson, complete resonance parameters have been extracted for 37 p 3 2 , 12 p 1 2 and 11 s-wave resonances out of a total of 101 observed resonances. The neutron strength functions extracted from the resonance parameters are S 0 = 0.56 × 10 −4, S 1 = 3.8 × 10 −4, S 1( P 3 2 ) = 4.7 × 10 −4 and S 1( 3 2 ) = 1.9 × 10 −4 . It is noteworthy that the S 1( 3 2 ) strength function is significantly larger than the S 1( P 1 2 ) strength function in agreement with theoretical expectation. A significant correlation ( ρ = 0.58) exists between the reduced neutron widths and the radiative widths for the 37( P 3 2 ) resonances. The data give strong confirmation of the valence neutron model. With standard valence calculations all radiative widths can be calculated reasonably from the associated reduced neutron width. However, to explain the measured correlation coefficient, it has been necessary to include with the valence component, singleparticle transitions to the ground and low excited states of 91Zr, which are uncorrelated with the resonance reduced neutron width. The average capture γ-spectrum for neutron capture in 90Zr between 2 and 80 keV has been calculated from the valence model and the present data and is found to be in very close agreement with published experimental data.