Development of a low-energy radioactive ion beam facility for the MARA separator

A low-energy radioactive ion beam facility for the production and study of nuclei produced close to the proton drip line is under development at the Accelerator Laboratory of the University of Jyväskylä, Finland. The facility will take advantage of the mass selectivity of the recently commissioned MARA vacuum-mode mass separator. The ions selected by MARA will be stopped and thermalised in a small-volume gas cell prior to extraction and further mass separation. The gas cell design allows for resonance laser ionisation/spectroscopy both in-gas-cell and in-gas-jet. The facility will include experimental setups allowing ion counting, mass measurement and decay spectroscopy.     

In-beam γ-ray spectroscopy of <Superscript>190</Superscript>Po: First observation of a low-lying prolate band in Po isotopes

Gamma rays from excited states of ¹⁹⁰Po have been observed using the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated with a collective band which from spin 4 onwards resembles the prolate rotational bands known in the isotones ¹⁸⁸Pb and ¹⁸⁶Hg. This indicates that in ¹⁹⁰Po the prolate configuration becomes yrast above I = 2. The experimental results are interpreted in a two-band mixing calculation and are in agreement with α-decay data and potential energy surface calculations. Received: 10 January 2003 / Accepted: 19 February 2003 / Published online: 7 May 2003     

Recoil-fission tagging of the transfermium nucleus 252No

An in-beam study of the transfermium nucleus ²⁵²No has been performed using the JUROSPHERE II array of germanium detectors coupled to the gas-filled recoil separator RITU. A new technique of recoil-fission tagging was used to extract tagged γ-ray data. Having significant spontaneous fission and α-decay branches, ²⁵²No is an ideal candidate for a comparative study. In a similar manner to α-decay tagging the fission events can be used to obtain γ-ray data. The recoil-fission tagged γ-ray spectrum showed a similar structure to the α-decay tagged γ-ray spectrum. By comparing the α-tagged and fission-tagged spectra and decay curves, it was shown that the spontaneous fission originates from the same initial state as the α decay. This extension of the tagging method allows in-beam spectroscopic data to be obtained from heavy nuclei with significant spontaneous-fission branches.     

Recoil Beta Tagging: Application to the study of odd-odd near proton drip line nuclei, 74Rb and 78Y

We present a study of low-spin states in ⁷⁴Rb and ⁷⁸Y using the new technique of Recoil Beta Tagging. This yielded new information on ⁷⁴Rb and has provided the first evidence for non-isomeric T= 1 states in ⁷⁸Y.     

Kinetics of the Oxidation of Monosaccharides with Acidic Bromate and N-Bromosuccinimide

Abstract

In earlier studies on the oxidation of monosaccharides, we measured the rates of the oxidation of three aldohexoses, two ketohexoses and three aldopentoses with V(V),¹ Ce(IV)²Cr(VI)³ and MII(VII).⁴We now report on the corresponding oxidations with bromate ion and N-bromosuccinimide (NBS) as oxidants. To our knowledge, only kinetic studies of oxidations of ribose with BrO₃-in aqueous H₂O₄ ⁵ and aldoses with NBS in 10% AcOH - H₂SO₄ ⁶ have been reported. Because oxidation of carbohydrates is subject to HSO₄- ion catalysis, HClO₄ was used, as in our earlier studies, in the present investigation to minimize the number of different catalyzing species.     

Isomer-tagged differential-plunger measurements in proton-unbound Ho

The lifetime of an excited state above a weakly populated isomer in the proton-unbound odd–odd nucleus ¹⁴⁴Ho has been measured using the recoil distance Doppler shift method. This measurement represents the first differential-plunger lifetime measurement to utilize recoil-isomer tagging. The first excited Iπ=(¹⁰⁺)$I^{\pi }=({10}^{+})$ state above the two-quasiparticle πh_11/2⊗νh_11/2(⁸⁺)$\pi h_{11/2}\otimes \nu h_{11/2}(8^{+})$ isomer was determined to have a lifetime of τ=6(1) ps$\tau =6(1)\text{ps}$. Potential energy surface calculations, based on the configuration-constrained blocking method, predict the isomeric state to have γ  -soft triaxial-nuclear shape with |γ|≈24°$|\gamma |\approx 24\text{°}$. The lifetime of the (¹⁰⁺)$({10}^{+})$ state can be understood from these calculations if there is a degree of rotational alignment in this band, with the K value being lower than the bandhead spin. However, the validity of the K quantum number with large predicted triaxiality and gamma softness requires further theoretical study.     

Structure of the odd-A, shell-stabilized nucleus 253/102No

In-beam gamma-ray spectroscopic measurements have been made on 253/102No. A single rotational band was identified up to a probable spin of 39/2planck, which is assigned to the 7/2(+)[624] Nilsson configuration. The bandhead energy and the moment of inertia provide discriminating tests of contemporary models of the heaviest nuclei. Novel methods were required to interpret the sparse data set associated with cross sections of around 50 nb. These methods included comparisons of experimental and simulated spectra, as well as testing for evidence of a rotational band in the gammagamma matrix.     

Alpha-decay studies of the new isotopes 191At and 193At

Detailed alpha-decay studies have been performed for the neutron-deficient isotopes ¹⁹¹At and ¹⁹³At. The nuclei were produced in fusion-evaporation reactions of ⁵⁴Fe and ⁵⁶Fe ions with a ¹⁴¹Pr target. The fusion products were separated in-flight using a gas-filled recoil separator and implanted into a position-sensitive silicon detector. The isotopes were identified using position, time and energy correlations between the implants and subsequent alpha-decays. Three alpha-decaying states were identified for ¹⁹³At and two for ¹⁹¹At. The spin and parity of the initial states in the astatine isotopes were deduced based on unhindered alpha-decays to states in the bismuth daughter nuclei. In both astatine isotopes the 1/2⁺ intruder state was determined to be the ground state and a 7/2^- state to be the first-excited state. In ¹⁹³At the alpha-decay of the 13/2⁺ state was observed in coincidence with a previously known gamma-ray transition from the 13/2⁺ state in the corresponding daughter nucleus ¹⁸⁹Bi. In ¹⁸⁷Bi and ¹⁸⁹Bi low-lying 7/2^- states were observed for the first time via alpha-decay of the mother nuclei.Received: 16 December 2002, Revised: 26 March 2003, Published online: 4 August 2003PACS: 23.60.+e Alpha decay - 27.80.+w - 23.20.Lv transitions and level energies - 21.10.Dr Binding energies and masses