Excitation energy and deformation of the1/2+[431] intruder band inTc107

Abstract

The already detailed study of 107 Tc nucleus was complemented by a search for microsecond isomers at very low energy. For this purpose, this neutron-rich nucleus was produced by thermal-neutron-induced fission of 241 Pu. We have found a new 30.1 keV microsecond isomeric state which deexcites to the ground state by a strongly-hindered E1 transition. This isomer was identified as the 3/2 + level of the 1/2 + [431] intruder band in 107 Tc and is also the lowest-lying member of the band. The very low energy of the band head suggests a large quadrupole deformation. From a comparison with 105 Tc, where more information is known about the intruder band, it is deduced that the 1/2 + [431] band has a quadrupole deformation, 2 0.35 and a possible triaxial shape, γ ≈ 20 • .

New insights into triaxiality and shape coexistence from odd-mass Rh109

“…and B(E2; 7/2 + → 3/2 + )=136(5) W.u. confirm the enhanced collectivity indicated by previous measurements [57,59,60], lending support to the large deformations suggested in prior studies of the nearby isotopes [44,45,54,58]. These B(E2) values are among the largest in the region [79], comparable to those observed in the strongly-deformed bands found in the Z≤42 isotopes [22,28,29,31,37,38].…”

“…[86]. In the past, only simplistic particle-rotor calculations were performed to study odd-A isotopes in the higher-Z Rh region, with parameters derived empirically to match experimental observations [44,45,53,54]. Such calculations provided some characterization of the shape coexistence and triaxiality in these odd-A systems, but could not say anything regarding the underlying microscopic structure responsible for these phenomena.…”

“…However, such an idea about the occurrence of triaxiality and its role in shape-coexisting mass regions may not be complete, especially considering past measurements of shape coexistence in the Z>42 region, particularly in odd-mass isotopes, combined now with the recent experimental and theoretical works mentioned above pertaining to the isotopes at lower Z. Despite the apparent regularity of triaxiality above Mo, shape coexistence does remain an important feature in the low energy structure of Tc [53][54][55][56], Rh [44,[57][58][59], Ag [60], In [61,62] and to a lesser extent, the even-even isotopes of Ru [63,64], Pd [65], and Cd [66]. As discussed by Heyde and Wood [11], many have attributed this, perhaps erroneously, to specific, deformation-driving single-particle orbitals crossing the Z=50 shell gap, so-called intruder orbitals.…”

“…Such interactions have long been considered a key component for a unified description of shape coexistence [67]. Indeed, the minimum in the highly-deformed intruder configuration of Tc [53,54,56] and Rh [59] isotopes precisely coincides with the deformation maxima elucidated recently for the lower-Z even-even isotopes Sr [35], Zr [38], and Mo [22] providing an important clue about the evolving structure at higher Z. Up to now, there have been no precise measurements of the collectivity exhibited by these lowlying intruder configurations other than a few lifetimes reported for 113,115 Ag in Ref.…”

New lifetime measurements inPd109and the onset of deformation atN=60

“…Refs. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]). The precise origins and evolutions of such phenomena are still not well-understood.…”