Determination of fission barrier height of Fr 210 and Ra 210 via neutron measurement

Fission barrier heights of short-lived nuclei away from line of β stability are not known reliably. Low-energy fission of Fr210 and Ra210, produced by (d,p) and (d,n) transfer reaction on the re-accelerated unstable beam Fr209 was investigated at HIE-ISOLDE. Four Timepix3 pixel detectors were installed on the body of the ACTAR TPC demonstrator chamber. Polyethylene converters were used for the detection of fast neutrons. Since no significant background was observed, it was possible to measure the spatial distribution of emitted neutrons reflecting the fission excitation function. Subsequent simulations employing the results of the talys code and available data on fission fragment distributions allowed to estimate directly the value of the fission barrier height for the neutron-deficient nucleus Fr210. This first direct measurement confirmed the reduction of the fission barrier compared to available theoretical calculations by 15-30%

Isomeric 13/2+ state in 201Fr

We have identified an isomeric state in 201Fr for which we propose a spin and parity of 13/2 +, and interpret it as arising from the π(i13/2 ) configuration. A half-life of 720(40) ns was measured, corresponding to B(M2) = 0.17(2) W.u., in good agreement with those of other 13/2 + → 9/2 − [π(i13/2 ) → π(h9/2 )] transitions observed in other nuclei in the region. The nuclei of interest were produced in a fusion-evaporation reaction and their decay properties were investigated using the GREAT spectrometer at the focal plane of the RITU gas-filled recoil separator.peerReviewe

Evolution from γ-soft to stable triaxiality in 136Nd as a prerequisite of chirality

The level structure of 136Nd has been investigated using the 100Mo(40Ar, 4n) reaction and the JUROGAM II+RITU+GREAT setup. The level scheme has been extended significantly. Many new bands have been identified both at low and high spin, among which are five nearly degenerate bands interpreted as chiral partners. Excitation energies, spins, and parities of the previously known bands are revised and firmly established, and some previously known bands have been revised. Configurations are assigned to the observed bands based on cranked Nilsson-Strutinsky calculations. The band structure of 136Nd is now clarified and the various types of single-particle and collective excitations are well understood.peerReviewe

Lifetime measurements in Re 166: Collective versus magnetic rotation

Lifetimes of excited states in the neutron-deficient odd-odd nucleus Re166 have been measured for the first time using the recoil distance Doppler-shift method. The measured lifetime for the (8-) state; ?=480 (80) ps, enabled an assessment of the multipolarities of the ? rays depopulating this state. Information on electromagnetic transition strengths were deduced for the ?-ray transitions from the (9-),(10-), and (11-) states, and in the case of the (10-) and (11-) states limits on the B(M1) and B(E2) strengths were estimated. The results are compared with total Routhian surface predictions and semiclassical calculations. Tilted-axis cranking calculations based on a relativistic mean-field approach (TAC-RMF) have also been performed in order to test the possibility of magnetic rotation in the Re166 nucleus. While the TAC-RMF calculations predict a quadrupole-deformed nuclear shape with similar ß2 deformation as obtained by using the TRS model, it was found that the experimental electromagnetic transition rates are in better agreement with a collective-rotational description. © 2016 American Physical Society.China Scholarship Council: 201306210205 Academy of Finland Array BioPharma: 131665 Science and Technology Facilities Council Vetenskapsrådet: 621-2010-3694 262010The authors would like to thank the staff at the Accelerator Laboratory of the University of Jyvskyl for their excellent technical support. This work was supported by the Swedish Research Council (Project No. 621-2010-3694), the Academy of Finland under the Finnish Centre of Excellence Programme 2012 - 2017, the UK Science and Technology Facilities Council, and the European Union Seventh Framework Programme Integrating Activities-Transnational Access, Project No. 262010 (ENSAR). Li is supported in part by the China Scholarship Council under Grant No. 201306210205. Additionally, we thank the GAMMAPOOL European Spectroscopy Resource for the loan of the detectors for JUROGAM II array. T.G. acknowledges the support from the Academy of Finland (Contract No. 131665). -

α-decay spectroscopy of the N = 130 isotones 218Ra and 220Th: Mitigation of α-particle energy summing with implanted nuclei

An analysis technique has been developed in order to mitigate energy summing due to sequential short-lived α decays from nuclei implanted into a silicon detector. Using this technique, α-decay spectroscopy of the N=130 isotones 218Ra (Z=88) and 220Th (Z=90) has been performed. The energies of the α particles emitted in the 218Ra→214Rn and 220Th→216Ra ground-state-to-ground-state decays have been measured to be 8381(4) keV and 8818(13) keV, respectively. The half-lives of the ground states of 218Ra and 220Th have been measured to be 25.99(10) μs and 10.4(4) μs, respectively. The half-lives of the ground states of the α-decay daughters, 214Rn and 216Ra, have been measured to be 259(3) ns and 161(11) ns, respectively. Fine structure in the α decay of 218Ra has been observed for the first time, populating the 695-keV 2+1 state in 214Rn. The fine-structure α decay has an α-particle energy of 7715(40) keV and branching ratio bα=0.123(11)%.peerReviewe