Properties of Capture Gamma-Ray Spectra ofs-Wave andp-Wave Resonances in Zr, Nb, and Mo

Abstract

The capture gamma-ray spectra of neutron resonances in ${\mathrm{Zr}}^{91}$, ${\mathrm{Nb}}^{93}$, and ${\mathrm{Mo}}^{95}$ have been studied in order to make unambiguous identification of individual resonances resulting from $p$-wave capture. Features of the capture spectra which are expected to be correlated with the parity of the capture state are discussed. For the nuclides studied, $p$-wave capture was detected by observing anomalously high intensities of transitions from the resonant state to a group of low-lying states of positive parity. For ${\mathrm{Mo}}^{95}$, previous measurements have been extended to 1 keV and resonances at 108, 215, 330, and 1010 eV have been assigned negative parity. For ${\mathrm{Zr}}^{91}$, the total intensity of transitions to the ten states with lowest energy in ${\mathrm{Zr}}^{92}$ has been measured for resonances in ${\mathrm{Zr}}^{91}$ below 2050 eV. The total intensities for the resonances at 247 and 448 eV, and at least one resonance at 2050 eV, are approximately 10 times that of the other resonances and have been assigned a negative parity. For Nb, the interpretation of the spectra is complicated by the presence of a $3^{-}$ state at 40 keV in ${\mathrm{Nb}}^{94}$. However, for transitions to states within 700 keV of the ground state of ${\mathrm{Nb}}^{94}$, resonances at 34, 42, 94, 244, and 524 eV have total intensities 5 times that of the remaining resonances and have been interpreted as $p$-wave resonances. From the assignments for ${\mathrm{Nb}}^{93}$, a value of (${4.6}_{-1.6\mathrm{}}^{+7.3\mathrm{}}$)×${10}^{-4\mathrm{}}$ was obtained for the neutron $p$-wave strength function.