Level structure and reflection asymmetry inTh227

The first experimental evidence for the (M1 + E2) mixed character of the 9.2 keV transition in 227Th

“…For the multipolarity determination, thirteen independent experimental values (i.e., obtained from different measurements) of the M-and N-subshell conversion line ratios were used: M 1 /M 2 = 0.031 (11), 0.027(9); M 1 /M 3 = 0.025(9), 0.023 (7); M 2 /M 3 =0.852 (10); M 4 /M 3 = 0.019(6), 0.021(4); M 5 /M 3 = 0.019(4), N 1 /N 3 = 0.02(3), 0.012(13); N 2 /N 3 = 0.84 (7), 0.84(2); and N 5 /N 3 = 0.044 (17).…”

“…However, later the authors [9] came to a conclusion that the 227 Th ground-state spin is consistent with 1/2 (though their data did not strictly exclude spin≠1/2). This was done on the basis of the measurements [3,10] and results of their investigation [9] of the α-decay of 231 U and the angular distribution of α particles in the decay of low-temperature oriented 227 Th. They deduced that the above-mentioned nuclearorientation experiment [8] was in error and thus the only experimental evidence for a 227 Th groundstate spin≠1/2 was eliminated.…”

“…In the second one the nuclear mean field is reflection symmetric but strong octupole correlations in the residual interaction leads to relatively large collective vibrational components in eigenstates of the intrinsic Hamiltonian (see e.g. [10], [30] and citations therein).…”

“…In the case of odd-A nuclei the intrinsic (single-particle and vibrational) degrees of freedom are mixed with rotational ones by means of the Coriolis (K=1) interaction between rotational bands. This mixing is very important for the interpretation of the experimental odd-A nucleus spectrum (see [10], [29], [30]). As concerns nucleus 227 Th, the interpretation in Ref.…”

“…As concerns nucleus 227 Th, the interpretation in Ref. [10] was based on the calculation of the strongly Coriolis mixed rotational bands built on the lowest K=1/2 + , K=3/2 + and K=5/2 + intrinsic reflection symmetric states involving octupole vibrational components. This strong Coriolis mixing together with relatively high positive decoupling parameter for the ground K=1/2 + rotational band lead to the interpretation of the lowest positive parity levels 0.0 keV, 9.2 keV, 77.7 keV and 88.0 keV to be members of the ground rotational band with the non-standard sequence of spins I  = 1/2 + , 5/2 + , 3/2 + , and 9/2 + , respectively, and levels 24.3 keV and 127.3 keV being 3/2 + -and 5/2 + -members of rotational band built on the lowest K=3/2 + intrinsic state.…”