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The Hybrid Recoil mass Analyzer (HYRA) operated in gas-filled mode has recently been coupled with the TIFR 4π spin spectrometer at IUAC, New Delhi to carry out spin (or angular momentum) distribution of heavy residues from fusion-evaporation reactions and spin gated GDR measurements. The details of the combined facility, initial experiments on evaporation residue tagged γ-multiplicity and the extraction of average transmission efficiency of HYRA are elaborated.

225Pa nuclei exhibit a fusion-fission mechanism below the fusion barrier energy. Mass angle distribution measurements indicate absence of noncompound events at this bombarding energy. The effect of asymmetric fission mode on mass distribution of fission fragments is visible at low excitation energy (31.8 MeV). [ABSTRACT FROM AUTHOR]

New mass values measured with the TITAN MR-TOF-MS are reported for the short-lived isotopes 24−26Ne, produced at TRIUMF's ISAC facility using a uranium carbide target and cold FEBIAD ion source. A least-squares adjustment within the framework of the Atomic Mass Evaluation was performed and the improved precision of the new mass values is highlighted. The improved mass accuracy in this N = 14 mid-shell region can also point to the refinement in values of the charge radii. By reducing the mass uncertainty of isotopes, their contribution of the mass shift uncertainty in laser spectroscopy can be negated. The work is part of developments for reaching the N = 20 Island of Inversion, where high molecular contamination hinders mass measurements of the neon isotopes. [ABSTRACT FROM AUTHOR]

Pre- and post-scission α-particle multiplicities have been measured for the reaction 16O+194Pt at 98.4 MeV forming 210Rn compound nucleus. α particles were measured at various angles in coincidence with the fission fragments. Moving source technique was used to extract the pre- and post-scission contributions to the particle multiplicity. Study of the fission mechanism using the different probes are helpful in understanding the detailed reaction dynamics. The neutron multiplicities for this reaction have been reported earlier. The multiplicities of neutrons and α particles were reproduced using standard statistical model code joanne2 by varying the transient (τtr) and saddle to scission (τssc) times. This code includes deformation dependent-particle transmission coefficients, binding energies and level densities. Fission time scales of the order of 50-65 ×10-21 s are required to reproduce the neutron and α-particle multiplicities. [ABSTRACT FROM AUTHOR]

Background: Non-compound-nucleus fission in the preactinide region has been an active area of investigation in the recent past. Based on the measurements of fission-fragment mass distributions in the fission of 202Po, populated by reactions with varying entrance channel mass asymmetry, the onset of non-compound-nucleus fission was proposed to be around ZpZt~1000 [Phys. Rev. C 77, 024606 (2008)], where Zp and Zt are the projectile and target proton numbers, respectively. Purpose: The present paper is aimed at the measurement of cross sections and spin distributions of evaporation residues in the 28Si+176Yb reaction (ZpZt=980) to investigate the fusion hindrance which, in turn, would give information about the contribution from non-compound-nucleus fission in this reaction. Method: Evaporation-residue cross sections were measured in the beam energy range of 129-166 MeV using the hybrid recoil mass analyzer (HYRA) operated in the gas-filled mode. Evaporation-residue cross sections were also measured by the recoil catcher technique followed by off-line γ-ray spectrometry at few intermediate energies. γ-ray multiplicities of evaporation residues were measured to infer about their spin distribution. The measurements were carried out using NaI(Tl) detector-based 4p-spin spectrometer from the Tata Institute of Fundamental Research, Mumbai, coupled to the HYRA. Results: Evaporation-residue cross sections were significantly lower compared to those calculated using the statistical model code pace2 [Phys. Rev. C 21, 230 (1980)] with the coupled-channel fusion model code ccfus [Comput. Phys. Commun. 46, 187 (1987)] at beam energies close to the entrance channel Coulomb barrier. At higher beam energies, experimental cross sections were close to those predicted by the model. Average γ-ray multiplicities or angular momentum values of evaporation residues were in agreement with the calculations of the code ccfus + pace2 within the experimental uncertainties at all the beam energies. Conclusions: Deviation of evaporation-residue cross sections from the "fusion + statistical model" predictions at beam energies close to the entrance channel Coulomb barrier indicates fusion hindrance at these beam energies which would lead to non-compound-nucleus fission. However, reasonable agreement of average angular momentum values of evaporation residues at these beam energies with those calculated using the coupled-channel fusion model with the statistical model codes ccfus + pace2 suggests that fusion suppression at beam energies close to the entrance channel Coulomb barrier where populated l waves are low is not l dependent. [ABSTRACT FROM AUTHOR]

High-accuracy mass measurements of neutron-deficient Yb isotopes have been performed at TRIUMF using TITAN's multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). For the first time, an MR-TOF-MS was used on line simultaneously as an isobar separator and as a mass spectrometer, extending the measurements to two isotopes further away from stability than otherwise possible. The ground state masses of ^{150,153}Yb and the excitation energy of ^{151}Yb^{m} were measured for the first time. As a result, the persistence of the N=82 shell with almost unmodified shell gap energies is established up to the proton drip line. Furthermore, the puzzling systematics of the h_{11/2}-excited isomeric states of the N=81 isotones are unraveled using state-of-the-art mean field calculations.

The gyromagnetic factor of the low-lying E=251.96(9)  keV isomeric state of the nucleus ^{99}Zr was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of J^{π}=7/2^{+}, with a half-life of T_{1/2}=336(5)  ns. The isomer was produced and spin aligned via the abrasion-fission of a ^{238}U primary beam at RIKEN RIBF. A magnetic moment |μ|=2.31(14)μ_{N} was deduced showing that this isomer is not single particle in nature. A comparison of the experimental values with interacting boson-fermion model IBFM-1 results shows that this state is strongly mixed with a main νd_{5/2} composition. Furthermore, it was found that monopole single-particle evolution changes significantly with the appearance of collective modes, likely due to type-II shell evolution.