H. Penttilä

Comparative effects of UVA and UVB irradiation on the immune system of fish.

Aquatic organisms can be harmed by the current levels of solar ultraviolet radiation. We have recently shown that exposure of fish to UVB irradiation alters the functioning of the fish immune system, but the effects of UVA radiation are unknown. The present study continues this work by characterizing UVA irradiation-induced immunological changes in fish. Roach, a cyprinid fish, were exposed to a single dose of either UVA (3.6 J/cm2) or UVB (0.5 J/cm2) irradiation. Both irradiations suppressed transiently mitogen-stimulated proliferation of blood lymphocytes. UVA, but not UVB, decreased hematocrit, plasma protein, and plasma immunoglobulin levels and increased the proportions of blood cells classified as unidentified leukocytes, possibly consisting of UVA-damaged lymphocytes. UVB, but not UVA, altered the functioning of head kidney and blood phagocytes, induced granulocytosis and lymphocytopenia in the blood and increased plasma cortisol concentration. These results imply that both UVA and UVB are potent modulators of the immune defence of fish.

Development of a laser ion source at IGISOL

FURIOS, the Fast Universal laser IOn Source, is under development at the IGISOL (Ion Guide Isotope Separator On-Line) mass separator facility in Jyvaskyla, Finland. This new laser ion source will combine a state-of-the-art solid state laser system together with a dye laser system, for the selective and efficient production of exotic radioactive species without compromising the universality and fast release inherent in the IGISOL system. The motivation for, and development of, this ion source is discussed in relation to the programme of research ongoing at this mass separator facility.

Evolution of the N=50 shell gap energy towards 78Ni.

Atomic masses of the neutron-rich isotopes (76-80)Zn, (78-83)Ga, (80-85)Ge, (81-87)As, and (84-89)Se have been measured with high precision using the Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. The masses of (82,83)Ga, (83-85)Ge, (84-87)As, and 89Se were measured for the first time. These new data represent a major improvement in the knowledge of the masses in this neutron-rich region. Two-neutron separation energies provide evidence for the reduction of the N=50 shell gap energy towards germanium (Z=32) and a subsequent increase at gallium (Z=31). The data are compared with a number of theoretical models. An indication of the persistent rigidity of the shell gap towards nickel (Z=28) is obtained.

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.

Precision mass measurements beyond ^{132}Sn: Anomalous behaviour of odd-even staggering of binding energies

Atomic masses of the neutron-rich isotopes (121-128)Cd, (129,131)In, (130-135)Sn, (131-136)Sb, and (132-140)Te have been measured with high precision (10 ppb) using the Penning-trap mass spectrometer JYFLTRAP. Among these, the masses of four r-process nuclei (135)Sn, (136)Sb, and (139,140)Te were measured for the first time. An empirical neutron pairing gap expressed as the odd-even staggering of isotopic masses shows a strong quenching across N = 82 for Sn, with a Z dependence that is unexplainable by the current theoretical models.

Precise atomic masses of neutron-rich Br and Rb nuclei close to the r-process path

Abstract.The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion-Guide Isotope Separator On-Line (IGISOL) facility at Jyväskylä, was employed to measure the atomic masses of neutron-rich 85-92Br and 94-97Rb isotopes with a typical accuracy less than 10keV. Discrepancies with the older data are discussed. Comparison to different mass models is presented. Details of nuclear structure, shell and subshell closures are investigated by studying the two-neutron separation energy and the shell gap energy.

Status report of the Jyvaskyla ion guide isotope separator on-line facility

The ion guide isotope separator facility IGISOL of the University of Jyvaskyla has been moved to the new K-130 heavy ion cyclotron laboratory. The totally reconstructed facility is described in detail. The primary beams and targets, helium pumping, separator beam line construction and separator beam diagnostics are discussed. The spectroscopy stations are introduced with illustrative examples from the research program, including beta-delayed proton and neutron spectroscopy, gamma-ray spectroscopy with and without arrays, conversion electron spectroscopy, collinear laser spectroscopy and nuclear level lifetime spectroscopy.

β-delayed neutron decay of 104Y, 112Tc, 113Tc and 114Tc: test of half-life predictions for neutron-rich isotopes of refractory elements

Abstract Beta-decay gross properties of neutron-rich isotopes 104Y and 112,113,114Tc produced in 25 MeV proton-induced fission of 238U have been measured. Decays of 104Y with a half-life of 180±60 ms and of 114Tc with a half-life of 150±30 ms are reported for the first time. Beta-delayed neutron emission probabilities of 112,113,114Tc are determined as (1.5±0.2)%, (2.1±0.3)% and (1.3±0.4)%, respectively. Comparison of the observed Pn values with a recent theoretical calculation based on deformed quasiparticle random phase approximation (QRPA) shows good overall agreement for Tc isotopes. However, comparison of beta-decay half-lives of neutron-rich isotopes of Y to Rh with the QRPA model and the refined gross theory shows only modest agreement, pointing to inadequate treatment of structure of these very neutron-rich nuclei lying in a region of rapidly changing deformation.