First measurement of 60Ge $\beta$ -decay

Abstract

Abstract. The N = 28 isotone60 Ge, Tz = −2, was produced and selected among the products of the fragmentation reaction of a 78 Kr beam at 150 MeV/nucleon and a Be target by means of the A1900 fragment separator at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). Its decay was studied for the first time using the optical time projection chamber. The β-decay of 60 Ge was found to be dominated by β-delayed proton emission, with a branching of ≈ 100% and half-life T 1/2 = 20 +7 −5 ms.

First identification of Zn58 β -delayed proton emission

“…A weighted average of the four results gives 38(2) ms. Taking the detection efficiency into account [66(7)%], it was possible to determine the total branching ratio for the β p decay channel, b β p = 90(10)%, in agreement with the previous value of 78 (17)% [15], both consistent with 100%. The reconstruction of the energy for those protons that are stopped into the chamber shows a spectrum characterized by much lower-energy resolution than the one determined in Ref.…”

“…This points to the fact that 58 Zn ions are not fully neutralized in the gas mixture and drift towards the cathode before decaying, as described in Ref. [17]. The drift time from the implantation point to the electrode for the ions is 20(5) ms. During this time the detector is therefore sensitive to protons emitted into the full solid angle.…”

“…The details of the experiment were given in Refs. [16,17] and are summarized in the following. Neutrondeficient Zn and Ge isotopes were produced in fragmentation reaction of 78 Kr beam on a nat Be target and separated from the other reaction products by means of the A1900 separator [18].…”

“…The assignment of the delayed-proton events to the decay of 58 Zn is supported by the fact that the decay products (β p) are correlated in time and space with an implanted 58 Zn ion. Moreover, with the exception of 60 Ge, which is a known β p emitter [17], all other isotopes in the cocktail beam, which enter the chamber and are recorded in the same event, are less exotic. Among them, only 57 Cu has a positive Q value for β p emission, but the energy window for this decay mode is rather small (1443 keV [20]) and its half-life long with respect to the observation window [T 1/2 ( 57 Cu) = 196.3 ms, giving a probability of 30% to observe a 57 Cu decay event].…”

Shell-model study for GT-strengths corresponding to $β$ decay of $^{60}$Ge and $^{62}$Ge

“…Apart from the above, several other experiments have been carried out to investigate the GT strength for the β + decay of 60,62 Ge, some are direct β decay measurements while others are nuclear reactions based. The β decay of 60 Ge was measured at NSCL, MSU, and found with a 100% branching fraction and half-life T 1/2 = 20 +7 −5 ms [11]. Another experiment was performed to study the β decay of 62 Ge at GANIL and determined the half-life (129 ± 35) ms [12].…”