Recoil-decay tagging study of205Fr

Abstract

The nucleus 205 Fr has been studied through γ-ray and electron spectroscopy using the recoil-decay tagging technique. The resulting level scheme presents a spherical structure built on the 9/2 − ground state and a rotational structure on top of a short-lived isomer. The isomer, with a spin and parity of 13/2 + and a half-life of 80(20) ns, de-excites by an M2 transition directly to the 9/2 − ground state. Another, longer-lived, isomer, with a half-life of 1.15(4) ms, has also been found and assigned a spin and parity of 1/2 +. Transitions populating and de-exciting this isomer have been observed as well.

Nuclear moments and charge radii of neutron-deficient francium isotopes and isomers

“…The nuclear spins of the isomeric states for 206m1,204m1 Fr and 206m2,204m2 Fr were determined to be 7 (+) and 10 (−) , respectively. In the case of 204m1,m2 Fr, the difference in nuclear spin of I = 3 is supported by the L/K ratio from recoil-tagged conversion electron spectroscopy [19]. The tentative spin assignments from α-decay spectroscopy [13] are herewith confirmed.…”

Decay of201–203Raand200–202Fr

“…We note that an isomeric state with spin and parity 13/2 + decaying through an M2 internal transition to the 9/2 − ground state was observed in 203 Fr at E * = 426 keV with T 1/2 = 0.37(5) μs [ 8] and in 205 Fr at E * = 544 keV with T 1/2 = 80(20) ns [9]. The estimated energy range for the excitation energy of the isomer in 201 Fr, ∼(101-300) keV, confirms the trend of the decreasing excitation energy of the 13/2 + isomer with decreasing N in odd-A francium isotopes (see Fig.…”

“…An intruder 1/2 + state was identified in 201,203 Fr using α-decay spectroscopy [7]. Isomeric 1/2 + and 13/2 + states were observed in 203 Fr [8] and 205 Fr [9] using prompt in-beam γ -ray, delayed γ -ray, and electron spectroscopy, in addition to α-decay * zdenka.kalaninova@fmph.uniba.sk studies. Both the 1/2 + and 13/2 + states are assumed to possess oblate deformations and to coexist with the spherical 9/2 − ground state [7][8][9].…”

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

“…Recently it was also observed that a superdeformed band is partially depopulated to the 1 /2 + state in 193 Bi [12]. Also a couple of candidates for the feeding states in 205 Fr are suggested [8]. Our recent study [5] presented the level structures above the 1 /2 + states in 199,201 At.…”

“…The corresponding state is also known in a few francium nuclei. It is an isomeric excited state in odd-mass isotopes [201][202][203][204][205] Fr [6][7][8], and in 199 Fr it may become the ground state [6,9,10]. The level patterns above these states are of interest.…”