Experimental study of the low-lying structure ofZr94with the(n,n'

Abstract

The low-lying structure of 94 40 Zr was studied with the (n, n γ ) reaction, and a level scheme was established based on excitation function and γ γ coincidence measurements. Branching ratios, multipole mixing ratios, and spin assignments were determined from angular distribution measurements. Lifetimes of levels up to 3.4 MeV were measured by the Doppler-shift attenuation method, and for many transitions the reduced transition probabilities were determined. In addition to the anomalous 2 + 2 state, which has a larger B(E2; 2 + 2 → 0 + 1 ) value than the B(E2; 2 + 1 → 0 + 1 ), the experimental results revealed interesting and unusual properties of the low-lying states in 94 Zr. In a simple interpretation, the excited states are classified in two distinct categories, i.e., those populating the 2 + 2 state and those decaying to the 2 + 1 state.

Level Lifetimes in94Zr from DSAM Measurements following Inelastic Neutron Scattering

“…Excellent agreement was demonstrated both between the results obtained with the metallic and oxide scattering samples and with literature values, and is considered a validation of the method. However, for the lifetimes measured for 94 Zr, a discrepancy is apparent compared with the published values from our prior measurements [1,2]; the new values are approximately a factor of two longer than the previous ones. The lifetime of the 1671-keV 2 + 2 state was previously published to be 183 +13 −12 fs, but is now quoted as a weighted average of the metal and oxide measurements (shown in Fig.…”

“…Based on the observation that the 752-keV transition from the second 2 + state at 1671 keV to the first excited state at 919 keV exhibits a large B(M1; 2 + 2 → 2 + 1 ), we identified the second 2 + state as the lowest mixed-symmetry state [1,2]. In addition, these measurements of 94 Zr revealed anomalous behavior not observed in any other nucleus; the B(E2) value for the transition from the second excited 2 + state to the ground state was found to be larger than that from the first 2 + state to the ground state.…”

The Two-Photon Decay of the 11-/2 Isomer of 137Ba and Mixed-Symmetry States of 92,94Zr and 94Mo

“…The angular distributions confirm the J π = 4 + assignment of Refs. [Sin86,Elh08] of the state at 2330 keV. For the state at 2366 keV a tentative J π = 2 + assignment is possible.…”

“…This is the same result as the one of Refs. [ [Elh08]) it was possible to fit the doublet -fixing the peak positions -and measure the angular distributions. The angular distributions confirm the J π = 4 + assignment of Refs.…”

“…If the QPM calculations are correct the (n, n γ)-experiments of Refs. [Fra03,Fra05,Elh08] missed the main fragments of the one-phonon octupole mixed-symmetry states.…”