L X-ray-gamma angular correlations following the decay of139Ce

A reinvestigation of theL X-ray-gamma angular correlations following the decay of¹³⁹Ce is made by using a Si(Li) semiconductor detector asL X-ray detector. Coincidence measurements at five different angles were made between the 166-keV gamma ray and theL X-ray spectrum. The data were handled in two different ways: (i) the counts under theL _l +L _α+L _β+L _γ peaks were taken; (ii) the counts under theL _l +L _α+L _β peaks were only considered. Chance coincidences as well as coincidences background were taken into account. The results indicate that no anisotropy is to be found within a margin of error of 6×10^?3.     

Gamow-Teller strength in the β+ decay of104In

Theβ-strength function of¹⁰⁴Cd is studied in theβ ⁺/EC decay of mass-separated¹⁰⁴In. The determination of theβ ⁺ feeding and theβ ⁺/β ⁺EC ratio is the result of the simultaneous measurement of beta and gamma rays in one semiconductor beta-spectrometer. Information on the strength function near theQ _EC value is obtained from the detection of high-energyγ rays. The total observedβ strength amounts up to 10% of the Extreme Single-Particle Shell Model value. A strong enhancement in theβ ⁺/EC feeding to a group of levels around 5.6 MeV shows the influence of the Gamow-Teller Resonance.     

The decay of 33 70 Se37

The decay of⁷⁰Se was studied using a 75 cm³ Ge(Li) detector, placed in an anti-compton shield, and a low-energy detector. Of the 36γ-rays observed 31 are placed in a levelscheme of⁷⁰As, based on coincidence- and sumrelations. Conversion electrons of two low energy transitions were observed in order to determine their multipolarity. The halflife is measured (41.1 min). Spins and parities of the excited levels were deduced and compared with shell model predictions and logft values of theEC/β ⁺ branches were calculated.     

Investigation ofβ + β + andβ +/EC decay of106Cd

A low background scintillation detector with a CdWO₄ crystal of 1.046 kg was used to search forβ ⁺ β ⁺ andβ ⁺/EC processes in¹⁰⁶Cd. For the neutrinoless mode the limits T_1/2(0νβ ⁺ β ⁺)≥2.2·10¹⁹ y and T_1/2(0νβ ⁺/EC)≥5.5·10¹⁹ y were obtained with 90% C.L. For the possible two neutrino decay limits of T_1/2(2νβ ⁺ β ⁺)≥9.2·10¹⁷ y and T_1/2(2νβ ⁺/EC)≥2.6·10¹⁷ y have been determined with 99% C.L.     

Search for an isomer in94Rb

Measurements of theβ-ray half-life,γ-ray and X-ray spectra andγ-ray half-lives have been done with a plastic scintillation detector, a high resolution Ge(HP) detector and a 142 cm³ Ge(Li) detector to search for an isomeric state in⁹⁴Rb. Mass-separated activities of⁹⁴Rb were obtained from the He-jet type on-line mass-separator at the Kyoto University reactor. No isomeric transition was found in theγ-ray and X-ray measurements with the upper limits of 3×10^?4 and 8×10^?5, respectively, as compared with the 836.9 keV transition. Half-lives obtained from theγ-ray decay measurements are discussed in the light of classification given byQ _β -value measurements.     

A note on60Co decay

Theγ-rays from⁶⁰Co have been studied with a 30 cm³ Ge(Li) detector. Gamma rays of energies 826.4 and 2,158.9 keV which are expected on the basis of the⁶⁰Co decay scheme were sought but not observed. Their intensities are <0.02% and <0.002%, respectively, of the⁶⁰Co disintegrations. Any direct feeding from the (5⁺)⁶⁰Co ground state to the (2⁺) 2,159 keV level is <0.022%, yielding a logft>12.3 for the 664 keV second-forbidden uniqueβ-transition. Radioactivity⁶⁰Co; measuredE _γ,I _γ.⁶⁰Ni deduced levels, logft. Ge(Li) detector.     

The beta branching ratio and conversion coefficients in the137Cs decay

The decay of¹³⁷Cs has been reinvestigated using several precision counting methods. The emission rate ofβ-particles plus internal conversion electrons was measured by the 4π-proportional counter method using vacuum evaporated sources free of self-absorption and checked by the liquid scintillation method. TheK-conversion coefficient was determined by the electron X-ray coincidence method using a magnetic spectrometer and a high resolution Si(Li) detector. TheK/(L+M+...) conversion ratio and a second less accurate value for the β-branching ratio were obtained from the recorded electron spectra. Theγ-ray emission rate of all sources was determined to within ±0.14%, on the average, with a calibrated NaI(Tl) crystal detector. As results the intensity of theβ-decay to the ground state of¹³⁷Ba could be determined to (5.4±0.3)% of the¹³⁷Cs decays, theK-conversion coefficient to 0.0916±0.0004, and theK/(L+M+...) conversion ratio to 4.41±0.04. From these values the γ-ray emission intensity is (85.1±0.4)% of the¹³⁷Cs decays and theK X-ray emission intensity is (8.13±0.10)% of the emittedγ-rays. All errors are discussed in detail.     

The decay of115 mIn

The decay of^115m In has been investigated using accurate counting methods. The emission rate of conversion electrons plusβ ^?-particles was determined with a 4π proportional flow counter. The total andK-shell internal conversion coefficients of the 336 keVγ-ray in¹¹⁵In were measured by the electron X-ray coincidence method using combinations of a Si surface barrier with a NaI(Tl) detector and of a magneticβ-spectrometer with a high energy resolution Si(Li) detector, respectively. The conversion ratioR=K/(L+M+...) was deduced from electron spectra recorded with the magneticβ-spectrometer. The 336 keVγ-ray emission rate of all used sources was determined with a calibrated NaI(Tl)γ-ray spectrometer. A Ge(Li) detector has been used to determine the relative intensity of the 497 keVγ-ray in¹¹⁵Sn. As results have been deduced the 336 keVγ-ray emission per decay (N _γ1/N ₀=(45.9 ± 0.1)%), the total internal conversion coefficient (α=1.073 ± 0.014), theK-shell internal conversion coefficient (α _K=0.843±0.012), the conversion ratioR=3.63±0.07, theβ ^?-transition per decay going to the ground state (N _β1/N ₀=(5.0 ± 0.7)%) and to the first excited level in¹¹⁵Sn¹¹⁵Sn(N _β2/N ₀=(0.047 ± 0.002)%), and the 497 keVγ-ray emission (N _γ2/N _γ1=(0.103 ± 0.004)%). From the obtained internal conversion data it follows that the 336 keVγ-ray transition is ofM4 character with anE5 admixture of less than (3.5±1.5)%. The half-life of the isomeric state¹¹⁵ mIn has been determined with four different methods. The result isT _1/2=(4.486±0.004) h.     

Investigation of β+β+ and β+/EC decay of 106Cd

A low background scintillation detector with a CdWO₄ crystal of 1.046 kg was used to search for β⁺β⁺ and β⁺/EC processes in ¹⁰⁶Cd. For the neutrinoless mode the limits T_1/2(0νβ⁺β⁺) ≥ 2.2 · 10¹⁹ y and T_1/2(0νβ⁺/EC) ≥ 5.5 · 10¹⁹ y were obtained with 90% C.L. For the possible two neutrino decay limits of T_1/2(2νβ⁺β⁺) ≥ 9.2 · 10¹⁷ y and _1/2(2νβ⁺/EC) ≥ 2.6 · 10¹⁷ y have been determined with 99% C.L.     

The Gamow-Teller transitions in the96Pd→96Rh decay

Using the⁴⁰Ca(4.2 MeV/u) +⁶⁰Ni reaction and on-line mass separation, the decay properties of ₄₆ ⁹⁶ Pd₅₀ were reinvestigated. From a comparison of experimental and theoreticalβ ⁺/(EC +β ⁺) probability ratios, theQ _EC value was deduced to be 3,450 ± 150 keV. The strength was determined for four 0⁺→1⁺ Gamow-Teller beta transitions and found to be quenched as compared to predictions of the single-particle shell model. For⁹⁶Pd and⁹⁴Ru the sources of this quenching are discussed.     

Determination of theL-shell conversion coefficient for the 26 keV Mössbauer transition in161Dy

TheL-shell conversion coefficient of the 26 keV Mössbauer transition in¹⁶¹Dy has been determined to be α_L=2.4 _?0.2 ^+0.3 by coincidence techniques using high resolution Ge(Li) and Si(Li) detectors. With theoretical values for theM- andN-shells the total conversion coefficient is calculated to be α_tot=2.9 _?0.2 ^+0.3 .     

Precise atomic masses of147Eu,147Gd,and151Tb derived from their decay properties

Theβ-decay energies of¹⁴⁷Eu,¹⁴⁷Gd, and¹⁵¹Tb were determined by usingγ-spectroscopical methods. The comparison of experimental with calculatedK-capture probabilities yielded theQ _EC values 1.690( _?16 ⁺²¹ )MeV and 2.203( _?13 ⁺¹⁹ )MeV for¹⁴⁷Eu and¹⁴⁷Gd, respectively. By measuring the ratio of positron decay to electron capture for two branches in¹⁴⁷Eu decay, the decay energiesQ _EC=1.702(13) MeV andQ _EC=1.709(18)MeV were derived. Also fromEC/β ⁺ ratios the valuesQ _EC=2.225(75) MeV for¹⁴⁷Gd, andQ _EC=2.566(12)MeV for¹⁵¹Tb were obtained. Earlier discrepancies in the mass adjustment of these isotopes were removed. In course of the present studiesγ-decay properties of¹⁴⁷Eu and¹⁴⁷Gd were reinvestigated.     

The g-factor and the electric quadrupole moment of the 7/2+ isomer in125Xe

The time differential perturbed angular distribution method (PAD) was used to measure theg-factor and the electric quadrupole interaction in a Cd single crystal for thet _1/2=140 ns,I ^π=7/2⁺ isomer in¹²⁵Xe. Theg-factor isg=+0.264(10) and the quadrupole coupling constante ² Qq/h=122.1 (6) MHz at 552 K. The lifetime of theI ^π=11/2⁺ state was measured to beτ=11.3 (1.1) ps by the recoil distance method (RDM). From an analysis of the spectroscopic data using the triaxial-rotor-plus-particle (TRPP) model the quadrupole moment of the 7/2⁺ isomer is deduced to beQ=1.40 (15) b yielding an electric field gradient (efg)eq=3.6(4)·10¹⁷ V/cm² for XeCd.     

The alpha-branching ratios of the188,190,192Pb isotopes

Theα-branching ratios (b _α ) of^192,190,188Pb are measured using mass-separated sources. Different experimental set-ups are used — one detector as well as two detector set-ups — thereby detecting theα particles from the parent and/or viaα decay formed daughter nuclei, theβ-delayed gamma radiation from the parent and/or viaβ decay formed daughter nuclei and the Tl KX rays from electron capture decay. Values forb _α of 6.2(6) 10^?5 and 4.0(4) 10^-3 were found for^192,190Pb respectively. For¹⁸⁸Pb, limits on theb _α values were obtained: 0.03<b _α <0.10. A careful analysis of the previously reportedb _α values showed that the discrepancies in theb _α values were not due to inadequate correction procedures, as was suggested, but to experimental uncertainties in the efficiency determination of the different detection set-ups and to an unreliableβ-decay scheme for¹⁸⁸Pb. Theb _α obtained in this work show that the leadα decay is not faster than the Hgα decay and that there is no need to assume a disappearance of theZ=82 shell closure halfway betweenN=82 andN=126.     

Solution of the10Li-Puzzle

The mass of¹⁰Li has been measured with two different reactions:⁹Be(¹³C,¹²N)¹⁰Li,E _Lab=336 MeV, and¹³C(¹⁴C,¹⁷F)¹⁰Li,E _Lab=337 MeV. The mass excess of 33.445(50) MeV is deduced from theQ-value measurement.¹⁰Li is found to be particle-unstable with respect to one-neutron emission by 0.42(5) MeV. In the analysis of the first reaction a low lying excited state is found at 0.38(8) MeV. This state and the ground state can be most probably identified as the 1⁺/2⁺-doublet coupled from the [π 1p3/2 ?ν 1p 1/2] configuration, the 1⁺-state being the ground state. The (¹³C,¹²N)-reaction populates the 1⁺-state strongly due to a spin-isospin-flip character of the dominant part of the transition amplitude. The 2⁺-member corresponds to the mass given by Wilcox et al. A second excited state is observed at 4.05(10) MeV with a width of 0.7(2) MeV, it can be associated with theν 1d 5/2-strength. The second reaction is fully supporting the interpretation of the ground state doublet. The excited state at 4.05 MeV is not observed in this reaction and indeed it should not, because the reaction does not populate in first order excited neutron configurations. The levels are well described by mean field calculations including pairing correlations. The lowest resonance in the calculations is theν 1/2^?-configuration, whereas theν 1/2⁺-configuration shows at the neutron threshold a strong non-resonant contribution.     

Quadrupole interaction of8Li and9Li in LiNbO3 and the quadrupole moment of9Li

The quadrupole interaction of nuclear spin polarized⁸Li (I=2) and⁹Li (I=3/2) in LiNbO₃ has been studied at room temperature. The polarization was achieved by optical pumping of a fast atomic beam with circularly polarized laser light. The atoms were implanted into a hexagonal LiNbO₃ single crystal and the quadrupole splitting ofβ-NMR spectra was measured. A ratio of ¦Q(⁹Li)/Q(⁸Li)¦=0.88(4) for the nuclear quadrupole moments was deduced, yielding a new value of ¦Q(⁹Li)¦=25.3 (9) mb for the quadrupole moment of⁹Li.     

Study of the excited 0+ states through conversion electron spectroscopy of neutron rich Zr and Mo fission products

A windowless Si(Li) electron detector has been used in conjunction with the gas filled fission product separator JOSEF to study totally converted transitions in Zr and Mo isotopes. The existence of twoβ-decay modes in⁹⁶Y,⁹⁸Y and¹⁰⁰Nb is confirmed. The half-lives of theβ-decaying levels feeding O ₂ ⁺ states in⁹⁶Zr and⁹⁸Zr are 6.0 ± 0.4 sec and 0.60±0.05 sec respectively. A search for other first excited O ₂ ⁺ states shows that no such states are apparent in¹⁰⁰Zr and¹⁰⁴Mo.     

Thed(7Li,p)8Li cross section nearE cm=0.61 MeV

The absolute cross sectionσ of thed(⁷Li,p)⁸Li reaction near theE _cm=0.61 MeV resonance has been measured using a⁷Li ion beam and a windowless gas target system filled with D₂ gas. The proton yield of the reaction and theβ-delayedα-activity of the residual nuclides⁸Li were observed both concurrently with the elastic scattering yield, relatingσ to the Rutherford scattering cross sectionσ _R. The resulting values,σ (fromp)=143.6±8.9 mb andσ (from⁸Li)=151±20 mb, lead to a weighted mean value ofσ=153±6 mb (x ²=2.26) including all available values andσ=146±5 mb (x ²=0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed.     

Interaction of Li ions with ethylene carbonate (EC): Density functional theory calculations

Electronic structures of Li⁺ ion-ethylene carbonate (EC) complexes were studied by density functional theory. The structural, electronic and dynamical properties of Li⁺-EC complexes were studied for both an isolated EC molecule and clusters including Li⁺ ion. Our structural analysis showed only one type of Li⁺ coordination with EC through Li⁺?OC which was supported by the vibration spectral analysis for interaction between Li⁺ ion and a solvent (EC) molecule. It was analyzed that the solvation energy and Mulliken charge of Li+ ion solvated by EC molecule decrease with increase in number of EC molecule. However, electron affinity shows the opposite change. This analysis with solvation energy, electron affinity and Mulliken charge supported the stabilization of 4-coordinated solvation shell among [Li⁺(EC)_n]_n=1-5 complexes.     

Investigation of the 2νEC/EC Decay of 106Cd

Search for the β⁺β⁺, β⁺ EC, and EC/EC modes of the ¹⁰⁶Cd decay was carried out with the TGV-2 (Telescope Germanium Vertical) low-background multidetector spectrometer installed at the Modane underground laboratory (4800 m w.e.). The measured foil samples ～50 μm thick and 52 mm in diameter were placed between the entrance windows of the neighboring detectors inside the cryostat. The total measurement time for 10 g of ¹⁰⁶Cd enriched to 75% was 8687 h. New limits (at the 90% confidence level, CL) were obtained for the ¹⁰⁶Cd half-lives against various branches of the decay to the ground state 0⁺ and excited states 2⁺ of the ¹⁰⁶Pd daughter nucleus. They are T _1/2(2νβ⁺β⁺) ≥ 6.0 × 10¹⁹ y, and T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 3.0 × 10²⁰ y for the transitions to the 0⁺ ground state of ¹⁰⁶Pd; T _1/2(2νβ⁺β⁺) ≥ 5.7 × 10¹⁹ y, T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 4.2 × 10¹⁹ y for the transitions to the 2⁺, 512-keV excited state of ¹⁰⁶Pd; and T _1/2(2νEC/EC) ≥ 3.1 × 10¹⁹ y for the transition to the 0 ₁ ⁺ , 1334-keV excited state of ¹⁰⁶Pd.