First observation of an isomeric state in proton drip-line nucleus²⁶P

Abstract

Abstract. An isomeric state in the proton drip-line nucleus 26 P has been observed by the γ-ray spectroscopy. The γ-ray energy and the half-life are 164.4 ± 0.1 keV and 120 ± 9 ns, respectively. For the isomeric transition of the mirror nucleus 26 Na, the γ-ray energy of 82.40 ± 0.04 keV and the half-life of 4.35 ± 0.16 µs are also revised. Comparing the experimental reduced transition probabilities of 26 Na and 26 P with theoretical ones calculated by the shell model with the USDA interaction, the spin-parity (J π ) of the isomeric state in 26 P is most likely to be 1 + .

Confirmation of the isomeric state in P26

“…The measured half-life of this decay is t 1/2 = 104 ± 14 ns. The energy and halflife of this γ ray are in agreement with the previously reported result by Nishimura et al [16], but the half-life measured in this work is slightly lower. We also determined an isomeric ratio of R = 14 ± 10%, which is much lower than the previously reported one obtained using a different reaction.…”

“…We know from Ref. [16] that the branching ratio for proton emission from this state is at most 13%. The γ-ray and proton partial widths are therefore related as…”

“…In a recent experiment Nishimura et al [16] reported the observation of an isomeric state with J π = 1 + in 26 P. This state is the mirror analog of the low-lying isomer of 26 Na which has an excitation energy of 82.5 ± 0.5 keV [17]. The reported excitation energy and half-life of the 26 P state were 164.4 ± 0.1 keV and 120 ± 9 ns, respectively [16]. In this paper we report confirmation of this isomeric state in an independent experiment [7,18,19] using a different production mechanism and a different setup at a different facility.…”

“…The efficiency ε = (13 ± 2)% was determined using the calibration of Ref. [7] and α tot = 0.0188 ± 0.0003 was estimated using the online calculator bricc [26], under the assumption that the 164-keV transition has an E2 multipolarity [16].…”

“…It is even possible that 26 P is unbound to proton emission, as various mass models predict [13][14][15], but β decays instead due to the Coulomb barrier. In a recent experiment Nishimura et al [16] reported the observation of an isomeric state with J π = 1 + in 26 P. This state is the mirror analog of the low-lying isomer of 26 Na which has an excitation energy of 82.5 ± 0.5 keV [17]. The reported excitation energy and half-life of the 26 P state were 164.4 ± 0.1 keV and 120 ± 9 ns, respectively [16].…”