Medium and high spin structure in the⁹⁴Y isotope produced in fission induced by cold neutrons

Abstract

The level scheme of the neutron-rich 94Y isotope has been extended up to the 5324 keV excitation energy. During the analysis, a structure above the previously known (5+) isomer, at 1202 keV, was extended by employing multifold gamma-ray coincidence relationships measured with the EXILL array. For some of the new states, the spin-parity assignment has been proposed on the basis of gamma angular correlations and shell-model considerations. The newly identified structure is characteristic of spherical or nearly spherical configurations and no evidence for new isomers and rotational patterns was found.

Excited states of 90,92,94Y populated in 90Zr+208Pb multinucleon transfer reaction

“…One clearly sees three strong γ lines which were uniquely attributed to 94 Y: 305.5(1)keV, 583.8(2) keV and 718.7(3) keV. The same γ rays were reported very recently in [27].…”

“…Most of the observed (yrast) levels of 90 Y and 92 Y were so far measured in fusion-evaporation reactions 74 Ge( 18 O, γnp) and 76 Ge( 18 O, γ3np) for 90 Y [44]) or in multinucleon transfer reactions 238 U( 82 Se, Xγ) and 208 Pb( 90 Zr, Xγ) for 92 Y [45]. For 94 Y, very recently several transitions were reported in [27] where the level scheme has been extended up to the 5.3 MeV excitation energy.…”

“…Spectroscopic studies of 94 Y have been limited until very recently to light ion reactions [21][22][23], β − decay [24] or internal transitions [25]. In recent studies 94 Y was produced in 90 Zr+ 208 Pb transfer reactions [26], fission of 235 U induced by cold neutrons [27] and in fission of 238 U accelerated in inverse kinematic on a 9 Be target [28].…”

“…In the fission of 235 U induced by cold neutrons [27] multi-fold (prompt and delayed) γ-ray coincidence relationships together with γ-ray angular correlations allowed to locate γ transitions above the 5 (+) isomer at 1202keV in 94 Y and assign to them spin and parity. In [28], where fission fragments were identified with the VAMOS++ [32] large acceptance spectrometer in coincidence with prompt and delayed γ rays detected with the AGATA [10] and (part of) EXOGAM [9] γ arrays, respectively, the three γ transitions above the 5 (+) isomer for 94 Y were confirmed.…”

Shape transition in the neutron-rich Y nuclei and its evolution across the isotopic chain

“…Inspired by the new results in the 96 Y isotope, our collaboration made an effort to develop the level scheme of the 94 Y nucleus, located 5 neutrons away from the N = 60 boundary. Using data from EXILL (and crosschecked with partially sorted data from FIPPS), the level scheme was extended up to 5 MeV excitation energy [19], however, no evidence of deformed structure in this isotope was found. This is not surprising, taking into account the significant decrease in population of the rotational bands, in comparison with the spherical pattern when further away from N = 60.…”