Evidence for two-particle core polarization in the isomeric 29/2+ and 21/2? states of the $$\pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^2 } \right)_{8^ + } i_{1 {3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} v\left( {j^{ - 2} } \right)_{0^ + } $$ and $$\pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^3 } \right)v\left( {j^{ - 2} } \right)_{0^ + } $$ configurations in209At

Abstract

Using a-particles in the energy range 42-51 MeV, the 2~ 4n)Z~ reaction was studied with the intention of investigating the properties of excited high spin states in 2~In-beam prompt and delayed gamma-ray and conversion electron spectroscopy reveal two isomeric states at 2 429 and 1428 keV having the half-lives of 875 + 100 ns and 25 _+ 1 ns, respectively. The spins and parities of these states are found to be 29/2 + and 21/2-, respectively. The g-factors of the isomeric states are 1.06__+0.02 and 0.88_+0.06, which, within the experimental errors, are the same as the g-factors of the corresponding states in 211At. This suggests that the isomeric states are due to the n(hZ/2)s + it3/zV(j-2)O + and n(h39/2) v(j-:)o + configurations, respectively. The deviation between the calculated and experimentally found excitation energies of the isomeric levels are -146_+26 and +72_+ 26 keV. This deviation which in cases of a 2~ usually is smaller than 15 keV, is likely to be due to the neglect of the interaction between two particles via the exchange of virtual 2 + phonons in the 2~ core. This two-particle polarization interaction is found to be approximately described by a P2-force.

Low- and medium-spin states in theN=124 isotones208Po and209At

“…4.1. for details. The yrast cascade presented is in agreement with the one reported previously [26,27]. The assignment of AJ values on angular distribution basis turned out to be difficult because many of the y-rays were weak and probably non-streched, and the relatively high spin of the target and the light bombarding particle attenuated the angular distributions of the y-rays.…”

“…The half-lives reported previously in high-spin works [21,26] have been confirmed and more accurate values have been obtained. The greatest discrepancy is found for the 577.6keV 29/2 +-23/2-transition in Z~ where the previously reported [27] value of 680 +75 ns has been redetermined to be 860 4-20ns, cf.…”

“…Some background-subtracted spectra are shown in Fig. 3, exemplifying the data for 2~ In addition to the yrast cascades reported earlier [21,26,27] a large number of non-yrast levels are observed in both nuclides. The older work on 2~176 decay [22] is largely revised, cf.…”

“…The greatest discrepancy is found for the 577.6keV 29/2 +-23/2-transition in Z~ where the previously reported [27] value of 680 +75 ns has been redetermined to be 860 4-20ns, cf. also [13,26]. The experimental half-lives are thus, in 2~ 4.8___0.5ns (6~), 380+50ns (8/) and 8.0 4-0.5ns (11-) and in 2~ 24+_2ns (21/2-) and 860 +_ 20 ns (29/2 +).…”

Decay of theN=126, Fr213nucleus

“…The ground state of 209 At is identified as 9/2 − based on the favored α decay to the 9/2 − ground state of 205 Bi [38]. High-spin states were established in experiments employing fusion-evaporation reactions [39][40][41][42][43]. In addition, several states with angular momenta ranging from 3/2 to 7/2 were observed in the electron-capture decay of the ground state of 209 Rn, which has I π = 5/2 − [44].…”