P. Taskinen

The ion guide isotope separator on-line, IGISOL

Abstract A new ISOL method, the IGISOL (Ion Guide Isotope Separator On-Line), permits thermalized primary recoil ions produced in nuclear reactions to be run directly through a mass separator without a conventional ion source. It allows a fast (≳ 100 μs) separation of various radioactive isotopes of both volatile and nonvolatile elements. The overall separation efficiencies measured for heavy nuclides produced in light ion induced reactions are up to 10%. The shortest-lived activity identified in an on-line separation is the 182 μs isomeric state of 207Bi.

Ion guide method for on-line isotope separation

Abstract A new ISOL technique, the ion guide method for isotope separation, has been developed. The method is based on thermalization of primary recoil ions from nuclear reactions in helium and on their transfer by helium flow through a differential pumping system into the accelerating stage of an isotope separator. With this approach, separation times in the submillisecond region are achievable for all elements. The ion guide has no ionizer but instead exploits charge exchange mechanisms related to nuclear reactions and recoil thermalization processes. Operation takes place at room temperature and the simple construction involves no components that can wear out. These properties ensure smooth and stable operating conditions. The overall separation efficiencies measured for heavy nuclides produced by light-ion reactions are up to 10%. The shortest-lived activity identified in an on-line separation is the 182-μs isomeric state of 207Bi. The production rate of the mass separated 440-μs isomeric state of 43Sc is ≈ 2 × 103 ions/μC.

COLLECTIVE STRUCTURE OF THE NEUTRON-RICH NUCLEI, RU-110 AND RU-112

Abstract The collective structure of 110 Ru and 112 Ru has been studied at the IGISOL facility through the beta decay of 110 Tc and 112 Tc. Neutron-rich technetium isotopes were produced by the 238 U(p, f) reaction at 20 MeV bombarding energy. The new isotope 112 Tc was found to decay with a half-life of 280(30) ms. The observed energies of the 2 + and 4 + ground state band levels in 108,110,112 Ru are almost the same. However, a steady energy decrease of the proposed gamma band head is observed with increasing neutron number, suggesting importance of triaxiality in these nuclei. In fact, only in 192 Os the second 2 + state has been observed at lower excitation than in 112 Ru. The static deformation of 108,110,110 Ru isotopes has been investigated in microscopic lattice Hartree-Fock calculations. The obtained potential energy surfaces predict that these isotopes are deformed (β ∼ 0.3), with a quasidegeneracy associated with γ-deformation, and suggest that the γ-asymmetry softness increases with the neutron number for neutron-rich ruthenium isotopes.

Levels in 110Pd, 112Pd, 114Pd and 116Pd from the beta decays of the on-line mass separated Rh isotopes☆

Abstract The energy levels of even 110–116 pd nuclei have been studied from β-decays of odd-odd 110–116 Rh isotopes produced at the on-line isotope separator IGISOL. Two β-decaying states with I π = 1 + and I ⩾4 have been identified in all the cases. New level schemes with preliminary spin assignments have been constructed for 112 Pd, 114 Pd and 116 Pd. Similarities with the level structures of their Xe isotones have been pointed out.

Efficiency and delay of the fission ion guide for on-line mass separation

Abstract Efficiency and time distribution of ions passing through an ion guide system, specially designed for on-line isotope separation of products of proton-induced fission, have been studied. This system, unlike the standard ion guide, consists of a separate, plasma-free thermalizing chamber for stopping the isotropically emitted fission fragments. This arrangement reduces the rate of the recombination losses of thermalized ions by the plasma electrons produced by the beam and results in very good and stable operating conditions. The total efficiency of the order of 10−3 has been determined, nearly independent of the atomic number of the separated nuclide. The main reason for the limited efficiency is the inadequate stopping of the fragments in helium. The delay time distribution of the separated ions is measured to be broad, ranging from about 0.1 ms to 10 ms, the lower limit being set by the flight time through the separator. This has made possible the spectroscopy of short-lived beta-decaying nuclei and the discovery of new short-lived isomeric states, with ms half-lives, populated directly in fission.

Beta decay of Tz = −12 nuclides 51Fe and 55Ni: A new approach to on-line isotope separation

Abstract The mirror beta decays of 51 Fe (J π , T = 5 2 − , 1 2 ) and 55 Ni (J π , T = 7 2 − , 1 2 ) have been studied with the ion guide isotope separator on-line-system. The measured half-lives of 310 ± 5 ms for 51 Fe and 208 ± 5 ms for 55 Ni differ significantly from previouslreported values. In the case of 51 Fe, an allowed decay branch with a (5.0 ± 1.3)% intensity to the 7 2 − state at 237 keV in 51 Mn was observed. The deduced Gamow-Teller matrix elements are compared with values calculated using the empirical ( f 7 2 ) n shell model.

Identification and decay of new neutron-rich isotopes 115Rh and 116Rh

Abstract New isotopes 115 Rh and 116 Rh, produced in the proton-induced fission of 238 U, have been identified at the on-line mass separator IGISOL. The half-life of the β decay of 115 Rh was determined to be 0.99±0.05 s. Two β-decaying state with half-lives of 0.68±0.06 and 0.9±0.4 s were observed for 116 Rh. A clear signature of the dominance of the v1 g 7 2 →π1 g 9 2 transition is observed in their β decay. New level schemes with preliminary spin assignments have been constructed for 115 Pd and 116 Pd.

Separation of fission products by the ion guide fed isotope separator, IGISOL

Abstract The performance of the ion guide method in the on-line mass separation of fission products has been investigated. Activity was produced by bombarding nat. U targets with a beam of 20 MeV protons. All the mass chains from A = 95 through A = 120 have been scanned using conventional methods of nuclear spectroscopy. No chemical selectivity in the separation was observed; isotopes of highly nonvolatile elements from yttrium to palladium were produced with efficiencies equal to those for the more volatile ones. The boundary of known neutron-rich nuclides was reached throughout the mass region from A = 106 to A = 118. During the course of this preliminary study the new isotope 116 Rh was observed and its half-life measured to be (1.0±0.2)s. Several other unknown activities were also detected. A fraction of the order of 15% of Y, Zr and Nb activities were present as oxide ions.

Experimental and Shell-Model Study of the Beta Decay of 43Ti

The mirror nuclei in the f 7/2 shell offer an excellent possibility for systematic studies of various nuclear properties. These nuclei decay by a strong mixed Fermi and Gamow-Teller decay to the ground state of the daughter nucleus and by weak Gamow-Teller decays to the excited states. The accurate determination of the Gamow-Teller strength provides a sensitive test for the nuclear shell-model calculations.

First observation of the beta decay of117Pd and the discovery of a new isotope119Pd

In this paper we wish to report the first direct observations of the beta decays of117Pd and of a new isotope119Pd. The measuredβ-half-life is 4.3±0.3 s for117Pd. For119Pd, the existence of two beta-decaying states with the same half-life but of opposite parity cannot be excluded. The measured half-life for119Pd is 0.92±0.13 s. The observed beta half-lifes are in good agreement with the QRPA predictions. The observed level structure of117Ag and119Ag are discussed in the frame of the level systematics of the known odd Ag isotopes closer to stability.