Observation of proton radioactivity of the (21+) high-spin isomer in 94Ag

We have observed direct one-proton decay of the (21+) isomer in the N=Z nuclide 94Ag into high-spin states in 93Pd by detecting protons in coincidence with gamma-gamma correlations and applying gamma gates based on known 93Pd levels. Two decay branches have been identified, with proton energies of 0.79(3) and 1.01(3) MeV and branching ratios of 1.9(5)% and 2.2(4)%, respectively. The corresponding partial half-life values are 21(6) and 18(4) s. The Q value of the direct proton decay of the (21+) isomer was found to be 5.78(3) MeV. The very small reduced widths of the observed proton decays might reflect dominating collective configurations in the (21+) isomer, and the fine structure of the proton spectrum might indicate a strong deformation of this state.     

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.     

16+ spin-gap isomer in 96Cd

A β-decaying high-spin isomer in (96)Cd, with a half-life T(1/2)=0.29(-0.10)(+0.11) s, has been established in a stopped beam rare isotope spectroscopic investigations at GSI (RISING) experiment. The nuclei were produced using the fragmentation of a primary beam of (124)Xe on a (9)Be target. From the half-life and the observed γ decays in the daughter nucleus, (96)Ag, we conclude that the β-decaying state is the long predicted 16(+) "spin-gap" isomer. Shell-model calculations, using the Gross-Frenkel interaction and the πν(p(1/2),g(9/2)) model space, show that the isoscalar component of the neutron-proton interaction is essential to explain the origin of the isomer. Core excitations across the N=Z=50 gaps and the Gamow-Teller strength, B(GT) distributions have been studied via large-scale shell-model calculations using the πν(g,d,s) model space to compare with the experimental B(GT) value obtained from the half-life of the isomer.     

Static quadrupole moment of the five-quasiparticle k = 35/2 isomer in (179)w studied with the level-mixing spectroscopy method

The spectroscopic quadrupole moment of the high-spin, high- K five-quasiparticle isomer (K(pi) = 35/2(-), T(1/2) = 750(80) ns, E(i) = 3349 keV) in (179)W has been determined using the level mixing spectroscopy method. A value Q(s) = 4.00(+0.83-1.06)e b was derived, which corresponds to an intrinsic quadrupole moment Q0 = 4.73(+0.98-1.25)e b and to a quadrupole deformation beta(2) = 0.185(+0.038-0.049). These values differ significantly from the deduced ground-state quadrupole moments and are in disagreement with the current theoretical predictions in this mass region.     

Beta decay of 94Pd and of the 71 s isomer of 94Rh

The β decay of ⁹⁴Pd and of the 71s isomer of ⁹⁴Rh was investigated by using total γ-ray absorption techniques. Several levels in ⁹⁴Rh are established, including a new low-lying isomer characterized by a half-life of 0.48(3)μs and a de-exciting transition of 55keV. E2 multipolarity is determined for this transition by measuring the intensities of its γ-rays and the characteristic X-rays from its electron conversion. On the basis of the measured reduced β-decay transition rates to known ⁹⁴Ru levels and shell model considerations, the spin-parity of the 71s and the 0.48μs isomers of ⁹⁴Rh is assigned to be (4⁺) and (2⁺), respectively. The β-decay strength distributions measured for ⁹⁴Pd and the 71s isomer of ⁹⁴Rh yield Q _EC values of 6700(320) and 9750(320)keV for these decays and give evidence for the population of those states below and above the magic N = 50 gap that belong to both components of the 0g spin-orbit doublet.     

Unambiguous identification of three beta-decaying isomers in 70Cu

Using resonant laser ionization, beta-decay studies, and for the first time mass measurements, three beta-decaying states have been unambiguously identified in 70Cu. A mass excess of -62 976.1(1.6) keV and a half-life of 44.5(2) s for the (6-) ground state have been determined. The level energies of the (3-) isomer at 101.1(3) keV with T(1/2)=33(2) s and the 1+ isomer at 242.4(3) keV with T(1/2)=6.6(2) s are confirmed by high-precision mass measurements. The low-lying levels of 70Cu populated in the decay of 70Ni and in transfer reactions compare well with large-scale shell-model calculations, and the wave functions appear to be dominated by one proton-one neutron configurations outside the closed Z=28 shell and N=40 subshell. This does not apply to the 1+ state at 1980 keV which exhibits a particular feeding and deexcitation pattern not reproduced by the shell-model calculations.     

Low-lying excited states of106Ag studied with the103Rh (α,nγ)106Ag and104Pd (α,pnγ)106Ag Reactions

The level scheme of¹⁰⁶Ag has been studied using the¹⁰³Rh(α,nγ)¹⁰⁶Ag and¹⁰⁴Pd(α,pnγ)¹⁰⁶Ag Reactions. The experimental information is taken fromγ-ray coincidence data using Ge(Li)-Ge(Li) and HPGe-planar Ge(Li) configurations andγ-ray angular distributions. With these measurements 126 γ rays have been assigned to¹⁰⁶Ag with 116 deexciting 78 states below 2.26 MeV in excitation. The location of the 8.4-day 6⁺ isomer is established at 89.63±0.09 keV. Many of the low-lying states are interpreted in terms of a slightly deformed rotor model.     

Q value of the superallowed decay of 46V and its influence on Vud and the unitarity of the Cabibbo-Kobayashi-Maskawa matrix

The masses of the radioactive nuclei (46)V and its decay daughter (46)Ti have been measured with the Canadian Penning Trap on-line Penning trap mass spectrometer to a precision of 1 x 10(-8). A Q(EC) value of 7052.90(40) keV for the superallowed beta decay of (46)V is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision. An investigation of an earlier Q-value measurement for (46)V uncovers a set of 7 measurements that cannot be reconciled with modern data and affects previous evaluations of V(ud) from superallowed Fermi decays. A new evaluation, adding our new data and removing the discredited subset, yields new values for G(V) and V(ud). When combined with recent results for V(us), this yields modified constraints for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix and other extensions of the standard model.     

The ground state mass of147Gd from single-neutron-transfer reactions and its impact on derived mass values

Using a¹⁴⁸Gd radioactive target and the (p,d), (d,t), and (³He,α) single neutron pick-up reactions we have measured the¹⁴⁷Gd mass excess as — 75,366(4) keV, which differs by 139(24) keV from the adopted value of the 1983 mass table. From this result, and from recently reported first transfer-reaction mass determinations for¹⁴⁵Eu and¹⁴⁶Eu, we have recalculated the masses of nuclei above¹⁴⁶Gd from a previous shell model analysis of high-spin states.     

A study of the 106Pd(p,d)105Pd and 106Pd(3He,d)107Ag reactions

The ¹⁰⁶Pd(p, d)¹⁰⁵Pd reaction has been studied at 22.9 MeV with an energy resolution of 13 keV. Angular distributions permitted the assignment of l-values and the extraction of spectroscopic factors for 13 states including several previously unresolved l = 2 transitions. The ¹⁰⁶Pd(³He, d)¹⁰⁷Ag reaction has also been studied at 32.8 MeV with a resolution of 20 keV. Angular distributions were obtained, l-values assigned and spectroscopic factors extracted for 14 levels including many not observed previously in a proton transfer reaction. The level structure of ¹⁰⁵Pd and ¹⁰⁷Ag is discussed particularly in terms of quasirotational bands.     

Discovery of a nuclear isomer in 65Fe with penning trap mass spectrometry

A new long-lived isomeric state in (65)Fe has been discovered with Penning trap mass spectrometry and high-precision mass measurements of the neutron-rich isotopes (63-65)Fe and (64-66)Co have been performed with the Low-Energy Beam and Ion Trap Facility at the NSCL. For the new isomer in (65)Fe an excitation energy of 402(5) keV has been determined from the measured mass difference between the isomeric and ground states. The mass uncertainties of all isotopes have been reduced by a factor of 10-100 compared to previous results. In the case of (64)Co the previous mass value was found to deviate by about 5 standard deviations from the new measurement.     

Differentielle Wirkungsquerschnitte für die elastische Streuung niederenergetischer Elektronen an Kalium

The 2.41 min ground state decay of¹⁰⁸Ag has been studied with a Ge(Li) detector. Twelve transitions are observed of which seven have not been reported previously. Five of the new transitions are placed in the level scheme which includes the second 2⁺, 930.4 keV level and a new level at 1539.4 keV in¹⁰⁸Pd.     

Ion detection from beta decay and two-body decay experiments with laser-cooled atoms

Localized and cold samples of atoms produced with laser cooling and trapping techniques are a powerful tool for nuclear β-decay experiments. Recently we have concentrated on measurements of the momentum of the daughter ion produced, which leads to a variety of new observables. Angular distributions of the recoils with respect to the nuclear spin in β ⁺ decay are sensitive to non-standard model interactions. Measurements of the momentum of monoenergetic recoils from either electron capture or isomer γ decay would make it possible to search for particles with masses of 10s of keV.      

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.     

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.     

On theβ − decay of the 2s isomer in98Y and the existence of an intruder band in98Zr

The γ radiation from the ß^? decay of the high-spin isomer in⁹⁸Y has been studied at the separator JOSEF. A main goal was to get insight into the spins of levels in⁹⁸Zr which have been interpreted as members of an intruder band based on the 0₂ ⁺ state at 854 keV. The measuredγ-γ angular-correlations lead to the assignment of spins of 4 and 3 ? to the 2491 and 1844 keV levels, respectively, and contradict their interpretation as the 6⁺ and 4⁺ states of the proposed band. For the 2.0s isomer of⁹⁸Y, the ß{?}-decay properties suggest I=5 with a major configuration [πg_9/2,νs_1/2(g² _7/2)₀].     

On the assignment of high-spin cascades to98Rh and98Pd isotopes

Isotopic assignment of high-spin cascades in⁹⁸Rh and⁹⁸Pd have unambigously been obtained by a suitable combination of the⁹⁶Ru(α, xn yp) and the⁹⁹Ru(d, xn yp) reactions. As a result the band headed by the 841.3 keV line was assigned to⁹⁸Rh and the one headed by the 862.6 keVγ-ray has been found to belong to⁹⁸Pd. In the case of⁹⁸Rh the band is based on the (2⁺) ground state.     

Creation of localized optical waves that Do not obey the radiation condition at infinity

X-ray bursts have been suggested as a possible site for the astrophysical rp-process. The time scale for the process is governed by beta-decay half-lives of several even-even N = Z waiting point nuclei, in particular, N = Z = 40 80Zr. A 4.1(+0.8/-0.6)-s beta(+)/EC half-life for 80Zr was determined by observing delayed 84-keV gamma rays depopulating a T(1/2) = 4-&mgr;s isomer at 312 keV in the daughter 80Y. As this half-life is lower than many previously predicted values, the calculated excessive production of A = 80 nuclides in astrophysical x-ray burst scenarios is reduced, and less extreme conditions are necessary for the production of heavier nuclides.     

Magic nucleus 132Sn and its one-neutron-hole neighbor 131Sn

Prompt and delayed gamma-ray cascades in doubly magic 132Sn and its neighbor 131Sn have been studied at Gammasphere using a 248Cm fission source. Isotopic assignments of unknown gamma rays were based on coincidences with known transitions in A = 112-116 Pd fission partners. The yrast level spectra of both tin nuclei are interpreted using empirical nucleon-nucleon interactions from the 132Sn and 208Pb regions. Results include identification of the (nuf(7/2)h(-1)(11/2))9(+) aligned state in 132Sn and of extensive (nuf(7/2)h(-2)(11/2)), (nuf(7/2)d(-1)(3/2)h(-1)(11/2)) and (nuh(-1)(11/2)x3(-)) multiplets in 131Sn. The previously reported beta(-) decay of an unusual 131In high-spin isomer to levels in 131Sn is also elucidated.     

The decay of 101Ag

The decay of ¹⁰¹Ag have been studied using β- and γ-spectrometers in singles and coincidence modes. A half-life of 11.4 ± 0.3 min was obtained and a decay scheme was proposed. The first excited state was established at 80.3 keV and a half-life of 4.8 ± 0.5 ns was suggested. The resultant level structure of ¹⁰¹Pd is compared to a theoretical calculation with strong band mixing.