γ-ray and decay spectroscopy of194,195,196At

Abstract

Excited states of 195 At have been studied by means of in-beam γ -ray spectroscopy and the recoil-decay tagging technique. A strongly coupled rotational band feeding the α-decaying 7/2 − state via unobserved transitions was identified. This band is presumably built on the oblate proton I π = 13/2 + state. Confirming earlier measurements, α decays from the 1/2 + and 7/2 − states were observed. Additionally, an E3 branch competing with the α decay of the 7/2 − state was inferred. Also α decays of the odd-odd isotopes 194,196 At were examined.

Isomeric 13/2+ state in Fr201

“…[2,[14][15][16] and references therein). In the astatine isotopes, consistent with the oblate deformed interpretation, a rotational band has been identified above the 13 /2 + state in the 199,197,195 At isotopes [17,18]. In francium isotopes, the state has been characterized in 205 Fr [10] and 203 Fr [9], the former having a similar rotational band built on the 13 /2 + state, whereas a tentative assignment for the beginning of said band has been made for the latter.…”

“…Data for bismuth isotopes were obtained from Refs [14,[25][26][27][28][29][30][31][32],. for astatine from Refs [4,[15][16][17][18][33][34][35],. and for francium nuclei from this work and Refs [9,10]…”

Experimental study of isomeric intruder 12+ states in At197,203

“…In other words, if these transitions are assumed to be the lowest E2 transitions in a rotational cascades, this would correspond to E(I +4) /E(I+2) ratios of 3.8, 3.6, 3.5 and 3.5 for 197,199,201,203 At, respectively. Ratios this large are unphysical for a rotational cascade, hence the lowest transition above the 1 + band is suggested to be deformed [33]. From Fig.…”

“…It is worth noting that also on the prolate side of the Nilsson scheme the 1 2 [400] and 3 2 [402] orbitals approach the Fermi surface. This might also serve an explanation for the observed 1 [33]. This makes the complete understanding of the picture even more difficult.…”

Prompt and delayed spectroscopy of At203 : Observation of a shears band and a 29/2+ isomeric state

“…As the odd-mass astatine nuclei can be described as an odd proton coupled to an even-mass polonium core, this onset of deformation can be predicted to exist also in astatine nuclei, and indeed the existing spectroscopical studies support this picture (see, for example, Refs. [6][7][8][9][10][11][12]).…”