Nuclear Radii by Scattering of Low-Energy Neutrons

Abstract

The potential scattering cross section for slow neutrons, a p , has, been measured for seventeen elements in order to determine the nuclear potential radius and to investigate the predictions of nuclear optical models. The measurements were based on total cross sections resulting from transmission experiments performed with the Brookhaven fast chopper. In the energy region where individual resonances can be resolved and their parameters determined with reasonable accuracy, <r p is obtained by subtracting the resonance contribution, including interference effects, from the measured total cross section. In the kev region, where the chopper resolution permits determination of cross sections averaged over many resonances only, different sample thicknesses are used and ap derived from the slope of the transmission curve.The results in the two energy regions agree, thereby justifying the concept of potential scattering as a cross section constant with energy, once effects of nearby resonances are removed. The variation of potential scattering with atomic weight is compared with predictions of optical models of the nucleus. The data reflect rather strongly the effects of the deformation of the nuclear shape from spherical, and good agreement is obtained for a potential well with a diffuse surface and nuclear deformations corresponding to known quadrupole moments. The radius of the potential (the distance to its half-value) is given by R=roA$, with ro=(1.35±0.04)XlO~" 13 cm. The radius parameter r 0 is thus distinctly larger than the 1.09X10 13 cm obtained from electron scattering experiments.

Slow neutron scattering parameters for stable nuclei with nucleon numbers betweenA=79 andA=96

“…Taking into account the result of this work that there is practically no incoherent scattering by the element and using the measured b and the resonance . 1) spherical model [32], 2) spherical model with surface absorption 1-33], 3) deformable nuclei and vibrational optical model [3,34] parameters of [27] the parameters for bound levels of 85Rb (I=5/2) and aTRB (I=3/2) can be computed to be for 85Rb with R'=7.2 fm:…”

New Evaluation of Neutron Nuclear Data for Zinc Isotopes

“…1, in which the total cross sections of nat Zn produced from the resonance parameters of five Zn isotopes are Doppler-broadened at 300 K. The resonance parameters adopted for these evaluations well reproduce the experimental data [19][20][21][22][23] and are almost consistent with ENDF/B-VII.0 whose data on Zn isotopes are based on the old recommendation by Mughabghab et al 24) However, the large discrepancies between the present results and ENDF/B-VII.0 are found at the energies of 0.5164 and 2.245 keV. The difference at 0.5164 keV comes from the smaller value of À n for 68 Zn isotope in ENDF/B-VII.0.…”

Scattering of slow neutrons by arsenic and selenium isotopes

“…35A1/3(fm). Cal-culations with different optical model parameter sets predict different R'-values between 5 and 8fro [19,20]. In the discussion of the present work we will come back to this question.…”