Observation of γ-delayed 3α breakup of the 15.11 and 12.71 MeV states in C

The reactions at 4.9 MeV and at 8.5 MeV have been used to investigate the γ decay of states in ¹²C. By measuring the four-body final state in complete kinematics we are able to detect γ transitions indirectly. We find γ transitions from the 15.11 MeV state in ¹²C to the 12.71, 11.83, 10.3 and 7.65 MeV states followed by their breakup into three α particles. The relative γ-ray branching ratios obtained are (1.2±0.3), (0.32±0.12), (1.4±0.2) and (4.4±0.8)%, respectively, with the remaining (92.7±1.0)% of the γ decays going to the bound states. We obtain Γ_α/Γ=(2.8±1.2)% for the isospin-forbidden α decay of the 15.11 MeV state. From the 12.71 MeV state we find γ transitions to the 10.3 and 7.65 MeV states. The relative γ-ray branching ratios are and , respectively, with the remaining of the γ decays going to the bound states. Finally, we discuss the relation between the β decay of ¹²N and ¹²B to states in ¹²C and the γ decay of the 15.11 MeV analog in ¹²C to the same states.     

Beta-decay of the N = Z nucleus 72Kr

The beta-decay of the N = Z, even-even nucleus ⁷²Kr has been studied at the ISOLDE PSB facility at CERN. Measurements of βγ and βγγ coincidences have enriched the decay scheme of the daughter nucleus ⁷²Br with 27 new low spin levels. A more precise half-life of T _1/2 = 17.1(2) s has been determined. Strong feeding to the ⁷²Br ground state is established yielding an unambiguous J ^π = 1⁺ assignment for this state. Candidates for the ⁷²Br g.s. wave function are discussed in the framework of a self-consistent deformed mean-field calculation with SG2 Skyrme force and pairing correlations. A search for beta-delayed particle emission was made and an upper limit of 10^-6 for this decay branch obtained. The cumulated experimental level density of 1⁺ states has been fitted with the constant temperature formula. The comparison indicates that most likely all 1⁺ levels up to 1.2 MeV have been observed in this investigation. The corresponding nearest-neighbour level spacing does not follow a Poisson distribution. The Gamow-Teller strength distribution is compared, in terms of nuclear deformation, with different calculations made in the framework of the quasiparticle random phase approximation. Received: 7 February 2002 / Accepted: 31 October 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: borge@pinar2.csic.es RID="b" ID="b"Present address: Centre d' Etudes Nucléaires de Bordeaux-Gradignan, Le Haut Vigneau, F-33175 Gradignan Cedex, France. RID="c" ID="c"Present address: University Mentouri, 25000 Constantine, Algeria. Communicated by J. ?yst?     

High-spin states in the vibrational nucleus 114 Cd

High-spin states of the neutron-rich vibrational nucleus ¹¹⁴Cd have been studied using the incomplete fusion reaction ¹¹⁰Pd(⁷Li, p2n) and the GASP spectrometer in conjunction with the ISIS Si ball. About 50 new states with excitation energies up to 7 MeV and angular momentum were observed and for many of them, spin and parity could be firmly assigned. The band-like stuctures in ¹¹⁴Cd are compared to the corresponding ones in the even-even neighbour ¹¹²Cd.Received: 31 October 2002, Published online: 17 February 2004PACS: 23.20.Lv transitions and level energies - 27.60. + j      

Lifetime of levels belonging to the 3p54p configuration of Ar(I)

The lifetimes of nine levels of Ar(I) belonging to the 3p⁵4p configuration have been measured by the delayed coincidence method, with errors in the range from 4 to 7%. The results are compared with other experimental values and with theoretical calculations using jK coupling and intermediate coupling. From cascade components of the 4p levels, decay lifetime values for some levels belonging to the 3p⁵3d and 3p⁵5s configurations have been inferred.     

Transition probabilities of 4p−nd(n = 4, 5, 6, 7) lines of Ar(I)

Relative transition probabilities for 120 lines belonging to the 4p-nd(n = 4, 5, 6, 7) transition arrays of Ar(I) have been determined from emission-intensity measurements. Lifetime data for the 4d levels were used to obtain absolute transition probabilities. We have obtained 32 transition probabilities for 4p?4d lines. Because of the lack of data on 5p?4d transition probabilities, calculations were performed on jK coupling. Our experimental values are compared with experimental and theoretical data given by other authors.     

Search for forbiddenβ-decays of the drip line nucleus12Be

Beta-coincidentγ-rays have been measured from implanted pure samples of¹²Be separated at the LISE3 spectrometer at GANIL. An intensity of 0.040(26) % can be estimated for the branching ratio of the isospin forbidden pure-Fermi transition to the 0⁺ excited state of¹²B and of 0.008(6)% of the transition to the 1^?1 excited state. Both are taken to represent upper limits. The half-life has been re-measured to be 26.1(2.4) ms.     

Isomeric state of 80Y and its role in the astrophysical rp-process

A careful investigation of the isomeric transition of the long-lived state at 228.5 keV excitation energy in ⁸⁰Y has been done. The HIGISOL facility at the Jyv?skyl? isochronous cyclotron has been used. We used the electron magnetic transporter to prepare an appropriate source and to measure the electron spectra in clean background conditions. The measured internal conversion coefficient α_K = 0.50±0.07 allows unambiguous 1^- identification for the 228.5 keV first excited isomeric state in ⁸⁰Y. With a “bare" half-life of 6.8±0.5 s found in this work, this state is strongly populated in the rp-process during X-ray bursts and has therefore to be taken into account in X-ray burst model calculations. However, because of the similarity of the β-decay half-lives of isomeric and ground states, we find a maximum reduction in the effective β-decay lifetime of ⁸⁰Y of only 17±2%. Our results pave the way for a future investigation of the impact of the isomeric state on the “effective" ⁸⁰Y proton capture rate. Received: 14 March 2001 / Accepted: 10 July 2001