Penning-trap mass measurements on <Superscript>92, 94-98, 100</Superscript>Mo with JYFLTRAP

Penning-trap measurements on stable ^{92, 94-98, 100}Mo isotopes have been performed with relative accuracy of \(\ensuremath 1\cdot 10^{-8}\) with the JYFLTRAP Penning-trap mass spectrometer by using ⁸⁵Rb as a reference. The Mo isotopes have been found to be about 3keV more bound than given in the Atomic Mass Evaluation 2003 (AME03). The results confirm that the discrepancy between the ISOLTRAP and JYFLTRAP data for ^101-105Cd isotopes was due to an erroneous value in the AME03 for ⁹⁶Mo used as a reference at JYFLTRAP. The measured frequency ratios of Mo isotopes have been used to update mass-excess values of 30 neutron-deficient nuclides measured at JYFLTRAP.     

Mass measurements of neutron-deficient nuclei and their implications for astrophysics

During the years 2005-2010 the double-Penning-trap mass spectrometer JYFLTRAP has been used to measure the masses of 90 ground and 8 isomeric states of neutron-deficient nuclides with a typical precision of better than 10keV. The masses of 14 nuclides -- ⁸⁴Zr , ^{88, 89}Tc , ^90-92Ru , ^92-94Rh , ^{94, 95}Pd , ^{106, 108, 110}Sb -- have been experimentally determined for the first time. This article gives an overview on these measurements and their impact on the modeling of the astrophysical rp -process.     

Overview of the JYFLTRAP mass measurements and high-precision <Emphasis Type="Italic">Q</Emphasis>-values for weak interaction studies

The JYFLTRAP Penning trap set-up at the University of Jyväskylä, Finland is a Penning trap facility that has provided high-precision atomic mass values for short-lived nuclides since 2003. Until now, masses of more than 250 short-lived nuclides have been measured. Since JYFLTRAP is coupled to the chemically insensitive IGISOL mass separator, any element can be accessed. So far, a huge mass surface extending from magnesium (Z = 12) to lead (Z = 82) has been covered.     

Light-ion-induced reactions in mass measurements of neutron-deficient nuclides close to A = 100

A survey of neutron-deficient nuclides which can be produced via proton- and ³He -induced fusion-evaporation reactions in the A = 100 region was made using a Penning trap as a high-resolution mass filter. A comparison of the measured isotopic rates with a statistical model calculation for the proton-induced reactions shows the importance of using the precise binding energy values for the final reaction products. In particular, proton separation energies were found to play an important role in the evaporation process. In addition, accurate masses of 12 nuclides, ^{97-99, 101}Pd , ¹⁰⁰Ag , ^101-105Cd and ^{102, 104}In , were determined with uncertainties of less than 10keV.     

Schottky Mass Measurements of Cooled Exotic Nuclei

Projectile fragments of a ²⁰⁹Bi beam were separated in flight with the fragment separator FRS and injected into the experimental storage ring ESR. In the ESR a beam containing up to about 100 different isotopes was cooled to a relative velocity spread of δv/v=10⁻⁶ by means of the electron cooler. The image currents of the ions induced in a Schottky pick-up probe at each turn were recorded. A subsequent Fast Fourier Transformation of these signals yields the revolution frequencies of the different isotopes stored in the ESR. Unknown masses of more than 150 neutron-deficient nuclides in the element range of 52≤Z≤85 have been measured directly by Schottky Mass Spectrometry and in addition more than 60 new masses have been obtained from α-decay chains. These new mass data allow the location of the one-proton dripline and the prediction of the two-proton dripline for heavy nuclides. The experimental masses are compared with different theoretical predictions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Integrated target-ion source unit for on-line production of radioactive short-lived isotopes

A new version of integrated target-ion source unit (ionising target) has been developed for the on-line production of radioactive single-charged ions. The target is able to withstand temperatures up to 2500 ^°C and acts also as an ion source of the surface and laser ionisation. Off-line and on-line experiments with the ionising target, housing tantalum foils as a target material, have been carried out at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility. The off-line surface ionisation efficiency measured for stable atoms of Li, Rb and Cs was correspondingly 6% , 40% and 55% at the target temperature of 2000 ^°C and 3-10% for atoms of rare-earth elements Sm, Eu, Tm and Yb at a temperature of 2200 ^°C. The off-line measured values of the ionisation efficiency for stable Gd and Eu atoms by the laser beam ionisation inside the target were 1% and 7%, respectively. The radioactive beam intensities of neutron-deficient rare-earth nuclides from Eu to Lu produced by the integrated target-ion source unit have been measured at a temperature of 2500 ^°C. The results of the integrated target-ion source unit use for on-line laser resonance ionisation spectroscopy study of neutron-deficient Gd isotopes have been also presented.     

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

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion-Guide Isotope Separator On-Line (IGISOL) facility at Jyv?skyl?, 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.     

The decay of neutron deficient97Ag,98Ag,and99g,m Ag

The decays of neutron-deficient 21-sec⁹⁷Ag, 44.5-sec⁹⁸Ag, 15-sec^99mAg, and 124-sec^99gAg nuclides have been investigated with the LISOL facility. Sources were produced by the⁹²Mo(¹⁴N, ypxn) reactions on an enriched⁹²Mo target. Positron-, x-, and γ-ray singles spectra have been performed on mass separated samples. The results are consistent with 9/2⁺ ground state in⁹⁹Ag and a high (6⁺ or 7⁺) spin and parity for⁹⁸Ag.     

Mass measurements of neutron-deficient radionuclides near the end-point of the rp-process with SHIPTRAP

Direct mass measurements of nuclides near to the supposed end-point region of the astrophysical rp-process were performed at SHIPTRAP, the Penning trap mass spectrometer at GSI Darmstadt. The masses of 24 nuclides were measured with relative uncertainties between 5 ^. 10^-8 and 2 ^. 10^-7 . Three of them, ¹⁰⁷Sb , ¹¹¹I and ¹¹²I , were determined experimentally for the first time. The data analysis and mass evaluation are presented in detail.     

Search for superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta

Experimental searches for β-active superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta are described. The method of selective off-line mass-separation with scanning of the β-activity distribution on the collector was used. According to π-condensation theory, the long-lived anomalous nuclei are expected to be more neutron-deficient than the usual ones. Moreover, their mass numbers may be significantly nonintegral measured on the normal mass scale, because of unusual binding energy. These predictions guided the present search. No anomalous nuclei were found. The upper limit for Rb nuclei in the range 69 ? A ? 78 is 10^?5 with respect to the yield for ⁸¹Rb; for Cs in the range 112 ? A ? 122 the limit is (5–10) × 10^?6 of the yield for ¹²⁷Cs. These estimations are based on the assumption that the half-life of superdense nuclei equals 5 h.     

Alpha decay studies of tellurium,iodine, xenon and cesium isotopes

Very neutron-deficient isotopes in the trans-tin region were produced by reactions of 290 MeV ⁵⁸Ni ions on ⁵⁸Ni targets, and studied by on-line mass separation at GSI. Twelve α-emitters — ^107–110Te, ^110–113I, ^111–113Xe, ¹¹⁴Cs — were identified. Systematics of Q_α values and reduced α-widths for this new island of α-emission are discussed.     

Target Residues from the Interaction of Indium with 42MeV/nucleon 12C Ions

The cross section is measured for 65 target residues produced from the interaction of indium with 42MeV/nucleon ¹²C ions using nuclear chemistry techniques.The experimental mass yield distribution gives a satisfactory agreement with that calculated from Monte Carlo code GEMINI based on the statistical binary decay model. According to the systematics of isotope distributions,the possibility of the production of new neutron-deficient nuclides far from β stability is discussed in the intermediate energy heavy ion reaction.     

Beta-decay energies and masses of short-lived isotopes of rubidium,caesium, francium,and radium

Total decay energies have been measured for a number of neutron-deficient Rb and Cs isotopes, as well as for some neutron-rich isotopes of Fr and Ra. Mass separated sources were produced at the ISOLDE on-line separator at CERN. By applying two differentβ-γ coincidence methods,Q values or their lower limits were determined for^76–78Rb,⁸⁰Rb,^121–124Cs,²²²Fr,^224–226Fr,²²⁹Ra-²²⁹Ac. For many of these nuclei, the atomic mass excesses could be derived, allowing the comparison of masses of far unstable nuclei with predictions from mass formulae. The odd-odd nuclei⁷⁶Rb and⁷⁸Rb appear to be 1?1 1/2 MeV more strongly bound than expected from the systematics.     

Beta-decay branching ratios of 62Ga

Beta-decay branching ratios of ⁶²Ga have been measured at the IGISOL facility of the Accelerator Laboratory of the University of Jyv?skyl?. ⁶²Ga is one of the heavier T _z = 0 , 0⁺ → 0⁺ β -emitting nuclides used to determine the vector coupling constant of the weak interaction and the V_ud quark-mixing matrix element. For part of the experimental studies presented here, the JYFLTRAP facility has been employed to prepare isotopically pure beams of ⁶²Ga . The branching ratio obtained, BR = 99.893(24) %, for the super-allowed branch is in agreement with previous measurements and allows to determine the ft value and the universal Ft value for the super-allowed β -decay of ⁶²Ga .     

New mass data for the rp-process above Z = 32

High-accuracy mass measurements have been performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The short-lived nuclides ^{70, 71, 72, 73}Se , ^{72, 73, 74, 75}Br , and ^{98, 99, 100, 101, 103}Ag have been measured with an average uncertainty of a few keV. The data are important input for nucleosynthesis calculations of the rp-process beyond Z = 32 .     

Precise half-life measurement of the 26Si ground state

The β-decay half-life of ²⁶Si was measured with a relative precision of 1.4·10^?3. The measurement yields a value of 2.2283(27) s which is in good agreement with previous measurements but has a precision that is better by a factor of 4. In the same experiment, we have also measured the non-analogue branching ratios and could determine the super-allowed one with a precision of 3%. The experiment was done at the Accelerator Laboratory of the University of Jyväskylä where we used the IGISOL technique with the JYFLTRAP facility to separate pure samples of ²⁶Si.     

Double-β decay studies with JYFLTRAP

We have applied JYFLTRAP double Penning trap mass spectrometer to study several double-β decay Q values that could be useful for the search of neutrinoless double-β decay and, hence for the determination of neutrino properties.     

First observation of medium-spin excitations in the <Superscript>138</Superscript>Cs nucleus

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion Guide Isotope Separator On-Line (IGISOL) facility at Jyv?skyl?, was employed to measure the atomic masses of neutron-rich ^70-73Ni and ^{73, 75}Cu isotopes with a typical accuracy less than 5keV. The mass of ⁷³Ni was measured for the first time. Comparisons with the previous data are discussed. Two-neutron separation energies show a weak subshell closure at ⁶⁸ ₂₈Ni₄₀ . A well established proton shell gap is observed at Z = 28 .     

Isospin dependence in the odd-even staggering of nuclear binding energies

The FRS-ESR facility at GSI provides unique conditions for precision measurements of large areas on the nuclear mass surface in a single experiment. Values for masses of 604 neutron-deficient nuclides (30 < or = Z < or = 92) were obtained with a typical uncertainty of 30 microu. The masses of 114 nuclides were determined for the first time. The odd-even staggering (OES) of nuclear masses was systematically investigated for isotopic chains between the proton shell closures at Z = 50 and Z = 82. The results were compared with predictions of modern nuclear models. The comparison revealed that the measured trend of OES is not reproduced by the theories fitted to masses only. The spectral pairing gaps extracted from models adjusted to both masses, and density related observables of nuclei agree better with the experimental data.