Alpha decay ofU231to levels inTh<

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

“…The interpretation of the level structure of 227 Th is still a major problem mainly due to the lack of experimental information on the low-lying levels of 227 Th and a long-standing controversy [1] about the spin-parity of the 227 Th ground state, which represents the basis for all other level spinparity assignments. Until recently only two excited levels at 9.3 and 24.5 keV were known from the βˉ-decay of 227 Ac [2] and an additional one at 77.7 keV from the α-decay study of 231 U [3] feeding the former two.…”

“…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.…”

“…Fig 3. An example of the N 1-3 and L 3 subshell conversion electron lines of the 9.2 keV and 24.3 keV transitions, respectively, in227 Th.…”

Systematics of the α decay to vibrational2+states

“…In the last decade, this new kind of α-decay spectroscopy was mainly used to investigate 0 + and 2 + excited states in the Pb region by the ISOLDE collaboration [14][15][16][17][18][19][20] and more recently by the Liverpool-Jyväskylä-Helsinki collaboration [21]. There is also an increasing interest in α-decay experiments searching for fine structure in the U region [22]. Moreover, in the related field of proton emission, two papers [23,24] have shown that the influence of surface vibrations on the emission process is very important.…”