Total β-decay energies and masses of85–89Br

Experimentalβ-decay energies of neutron-rich bromine isotopes are presented. The samples were produced as mass-separated fission products by using the on-line isotope separator technique. By means of a Si(Li)-detector system,β-spectra were recorded in coincidence with differentγ-gates, and {ie173-01}-values for^85–89Br were deduced. The atomic mass excess is derived for these nuclei, and comparisons are made with mass formula predictions. The possibility of delayed-neutron emission is discussed in conjunction with information from the shape of the delayed-neutron spectra.     

Decay of78Br

The decay of⁷⁸Br was investigated with a Ge(Li) spectrometer and Ge(Li)-NaI(Tl) coincidence methods. Accurate energy and intensity determinations of 14 gamma rays have been performed. A level scheme with levels at 614.0, 1,308.1, 1,498.4, 1,758.5, 1,993.7, 2,334.4, 2,538, 3,090 and 3,253 keV is deduced. Spin and parity indications for most of the observed levels are given from electron capture and positon decay considerations and gamma branches.     

Decay properties of76m Br

The remeasured half-life of^76m Br was found to be 1.31±0.02s.γ-ray and conversion electron measurements gave for two cascading transition energy values 57.11±0.02 and 45.48±0.02 keV with multipolaritiesM2 and M1, respectively. The 4⁺ isomeric state at 102.59±0.04 keV is placed in the⁷⁶Br level scheme. The intensity of the cross-over transition is less than 0.8% of isomeric decays.     

Graphs of separation and decay energies

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Electromagnetic decay strengths in the isobars89Nb,89Mo and89Tc

Lifetimes of high spin states in the threeA=89 isobars⁸⁹Nb,⁸⁹Mo and⁸⁹Tc have been measured via the Recoil Distance Doppler Shift technique and the fusion evaporation reactions⁵⁸Ni(³⁵Cl,xnypzα) at 120 MeV beam energy. Reduced transition probabilities for about 50γ transitions were extracted. The experimental branching ratios in⁸⁹Mo and reduced transition probabilities in all three isobars are compared with the predictions of the spherical shell model based on the restrictedπ(p _1/2),π(g _9/2), ν(p_1/2),ν(g _9/2) configuration space with two different types of residual interaction.     

Decay of 14.6 h90Nb

The disintegration of 14.6 h⁹⁰Nb produced by bombarding natural Zr with 13 MeV protons was investigated by methods of γ-ray spectrometry. Results from singles, coincidence and anti-Compton spectrometer measurements are reported. A decay scheme is proposed including excited states in⁹⁰Zr at 1761, 2186.4, 2319.1, 2739.4, 2747.9, 3077.0, 3448.2, 3589.5, 3977.1, 4232.4, 4319.5, 4375.4, 4541.6, 5060.0, 5164.6 and 5432.9 keV. Over 10 γ-ray transitions and several levels proposed in an earlier investigation are shown to be in error.     

Decay of the compound nucleus179Au formed in the cold fusion reaction90Zr+89Y

For the compound nucleus¹⁷⁹Au formed at an excitation energy of 26 MeV in the fusion reaction⁹⁰Zr+⁸⁹Y, the energy spectra of promptly emitted protons,α particles andγ rays were measured in concidence with the evaporation residues. On the basis of the measured total decay energy, the 1p and 1α decay channels were separated from all other evaporation-residue channels. The energy spectra and absolute cross sections, together with previously measured excitation functions for various decay channels, are successfully described by statisticalmodel calculations with the Monte Carlo code CODEX.     

Isomerism,total decay energies,and absolute γ-ray intensities of the heavy Pd and Ag isotopes

The decays of^{113, 114, 115g, 115m, 116}Pd have been studied with an emphasis on the determinations of total decay energies and absoluteγ-ray intensities. The experiments also provided improved data on these quantities for the decays of^{114, 115g, 115m, 116m}Ag. A search for isomeric transitions using a high resolution electron detector resulted in the identification of isomericE3 transitions in¹¹⁵Pd and^{113, 115, 116, 117}Ag. The isomeric branching was determined in all cases. TheQ _β-values of^113–116Pd and^113–116Ag have been measured using aβγ-coincidence method.     

Decay of90m,g Rb

The decay of mass separated⁹⁰Rb has been studied usingβ,γ and conversion electron spectrometers in single and coincidence modes. The half-lives of the ground state and the isomeric level have been confirmed to be 162± 3 and 258±4 s, respectively. Theγ-rays from the decays of ground state and metastable state have been identified by measuring the decay of individual photopeaks using Ge(Li) detectors. The multipolarity of the 106.6 keV isomeric transition has been determined to beM3. Separate decay schemes of the ground and metastable states are presented. The levels of⁹⁰Sr are discussed in terms of the available experimental and theoretical information. Radioactivity.^90m,gRb [from²³⁸U(p, f)]; measuredT _1/2,E _γ,I _γ,γ—γ coin,I _ce,cc,E _β deduced logft,⁹⁰Sr levels, mass separated⁹⁰Rb.     

The beta decay of90g Tc and90m Tc

The level structure of⁹⁰Mo is investigated via the beta decay of^90g Tc and^90m Tc whose half-lives are measured to be 8.7±0.2 and 49.2±0.4 s, respectively. The decay properties are studied by means of beta and gamma spectroscopy techniques. The level structure of⁹⁰Mo populated in the decays of both isomers is proposed with deducedJ ^π values. Theβ-decay energies for^90g Tc and^90m Tc are 8.8±0.3 and 9.3±0.3 MeV, respectively. The structure is discussed in terms of the shell model.     

Decay of a new nuclide:89m Mo

The half-life of the 1/2^? isomer in⁸⁹Mo has been determined in an experiment where an enriched⁹²Mo target was irradiated by 350 or 700 ms bursts of 60 MeV protons. Analysis of the gamma-ray spectra collected as a function of time between irradiations revealed gamma rays at 118.8 and 268.5 keV decaying with a 190±15 ms half-life. The hindrance ofE3 transitions inN=47 andZ=47 nuclides is discussed.     

Energy levels of Kr populated by Br decay

The γ-rays following the β-decay of ⁸²Br have been investigated using a 220 mm³ Ge(Li) detector, an anti-Compton NaI(Tl) spectrometer and a two-dimensional coincidence arrangement. The ⁸²Br was produced by thermal neutron activation of ammonium bromide. The presence of eight, well-known and 11 weak γ-rays has been established. It has been shown through half-life measurements that the newly identified γ-rays belong to ⁸²Br decay and that the high-energy peaks are not to summing effects. All the reported transitions have been incorporated in a level scheme of ⁸²Kr by introducing levels at 0, 776, 1474, 1820, 1953, 2093, 2426, 2554, 2647 and 2828 keV. Limits on probable spin and parity values for the newly-introduced levels have been established. The level introduced at 2828 keV on the basis of a 1008–1043 keV γγ-coincidence must be fed by a weak β-branch of ⁸²Br with an end-point energy of 263 keV and log ft of approximately 6.1.     

Decay energies of the low-spin states of147Tb and148Tb

Using¹¹²Cd(⁴⁰Ar,pxn) reactions andγ-ray spectroscopy, the EC/β ⁺ and EC(K)/β ⁺ probability ratios were determined for individualβ-transitions in the¹⁴⁷Tb(1.6 h)→¹⁴⁷Gd and¹⁴⁸Tb(60 min)→¹⁴⁸Gd decays. Under assumption of applicability of theoretical ratios for allowedβ-decays on the first-forbidden nonunique transitions studied here, the experimental ratios were converted into information on decay energies. Combining the results with the known masses of^147,148Gd andQ _α values of neutron-deficient holmium-to-lutetium isotopes, mass excesses could be determined for¹⁴⁷Tb,¹⁴⁸Tb, low-spin¹⁵¹Ho, low-spin¹⁵²Ho,¹⁵⁵Tm,¹⁵⁶Tm and¹⁵⁹Lu.     

The decay schemes of Y and Y and γ-rays observed in the decay of Y

Active yttrium was separated from ²³⁵U fission products and the decay of ⁹⁴Y, ⁹⁵Y and ⁹⁶Y to the levels of ⁹⁴Zr, ⁹⁵Zr and ⁹⁶Zr, respectively, has been studied with the aid of a 17 cm³ Ge(Li) detector. Gamma-ray energies and intensities were accurately determined. In the decay of ⁹⁴Y four new transitions at 1232.78 ± 0.35, 1324.97 ± 0.35, 1363.48 ± 0.35 and 2467.00 ± 2.75 keV were observed. The data obtained support the level scheme proposed for ⁹⁴Zr by Knight et al. and that deduced from more recent reaction data. Evidence supporting the location of the 0⁺ excited state at 1300 keV is presented. Branching ratios are calculated and a modified level scheme for ⁹⁴Zr is proposed. In the decay of ⁹⁵Y the energies of 13 γ-rays, previously identified with the decay of this nuclide, have been accurately measured and are presented in a partial level scheme for ⁹⁵Zr. The data obtained in this work support the level structure deduced from reaction data by Cohen and Chubinsky and by other workers. New γ-transitions at 550.10 ± 0.23, 1723.30 ± 0.90 and 1805.0 ± 1.0 keV were measured in the decay of ⁹⁶Y.     

Decay asymmetry in non-mesonic weak decay of light Λ -hypernuclei

The proton decay asymmetry, α^NM _p , of the polarized Λ -hypernuclei, ⁵ _ΛHe , ¹² _ΛC and ¹¹ _ΛB , has been investigated to understand the reaction mechanism of the non-mesonic weak-decay process. These Λ -hypernuclei were produced in the highest statistics ever via the (π⁺, K ⁺) reaction at 1.05GeV/c by using the SKS spectrometer at KEK 12GeV PS. The results show that the α^NM _p are very small for these s -shell and p -shell hypernuclei.     

可能合成的超重核的alpha衰变能和半衰期

本文考察和研究了将来可能在实验上合成的超重新元素和新核素的基态性质。研究的重点主要放在原子核的alpha衰变能和半衰期。详细比较和讨论了不同理论模型计算的alpha衰变能和半衰期。通过这些计算和比较,从理论上提出了将来在实验上比较容易合成的超重新元素和新核素的性质。理论计算结果可为将来的超重核实验提供理论参考。     

Alpha decay energies and half-lives for possibly synthesized superheavy elements

We investigate the ground state properties of some superheavy nuclei, which may be synthesized in future experiments. Special emphases are placed on the alpha decay energies and half-lives. The alpha decay energies and half-lives from different theoretical models are compared and discussed comprehensively. Through these calculations and comparisons, the optimal superheavy elements to be synthesized in future experiments are proposed theoretically.     

Complex energies and beginnings of time suggest a theory of scattering and decay

Many useful concepts for a quantum theory of scattering and decay (like Lippmann-Schwinger kets, purely outgoing boundary conditions, exponentially decaying Gamow vectors, causality) are not well defined in the mathematical frame set by the conventional (Hilbert space) axioms of quantum mechanics. Using the Lippmann-Schwinger equations as the takeoff point and aiming for a theory that unites resonances and decay, we conjecture a new axiom for quantum mechanics that distinguishes mathematically between prepared states and detected observables. Suggested by the two signs ±i? of the Lippmann-Schwinger equations, this axiom replaces the one Hilbert space of conventional quantum mechanics by two Hardy spaces. The new Hardy space theory automatically provides Gamow kets with exponential time evolution derived from the complex poles of the S-matrix. It solves the causality problem since it results in a semigroup evolution. But this semigroup brings into quantum physics a new concept of the semigroup time t = 0, a beginning of time. Its interpretation and observations are discussed in the last section.     

A generalized r-matrix interpretation of the 89Y + n total cross section at low incident energies

The resonance structure observed in the ⁸⁹Y(n, n)⁸⁹Y total cross-section measurements in the range of 0.9 to 1.2 MeV neutron energy is investigated using a comprehensive theory of nuclear reactions. A shell-model calculation which formed the initial stage of this study predicts satisfactorily the energies of the negative-parity states that contribute to the observed anomalies. The neutron decay widths for these resonances are evaluated using the model wave functions. The general trends in the energy dependence of the total cross section are satisfactorily reproduced by the theory. The factors that could contribute to the discrepancies between theory and experiment are discussed. The theoretical estimates of the damping widths for the two 1^? anomalies that occur in this region were within 20 to 25% of the experimental values and support the view that these are intermediate-type resonances. Their configurational structure as predicted by the model calculation suggests that they are the parent states of the T_> components of the giant dipole resonance near 21.0 MeV in ⁹⁰Zr. The distribution of E1 widths calculated for a proposed 1^? → 2⁺ (at 0.78 MeV) transition in ⁹⁰Y indicates that an anomaly corresponding to these 1^? states can also be expected in the (n, γ) reaction.