Non-collective oblate states in121Te

Two new neutron-deficient isotopes,²¹³Pa and²¹⁴Pa were produced in complete fusion reactions of⁵¹V-ions with¹⁷⁰Er targets at (5.2–5.6) AMeV. The assignment was based on delayed evaporation residue - - time and position coincidences. The- decay energies of^213,214Pa were measured to be E=(8236±20) keV and E=(8116±20) keV, respectively. The half-lives of^213,214Pa were determined to be T_1/2=(5.3 _–1.6 ^+4.0 ms and T_1/2=(17 ±3) ms, respectively.This article was processed by the author using the LAT_EX style filecljour2 from Springer-Verlag.     

Study of theβ +/EC decay of the neutron deficient nuclei76,78Sr and79Y

The +/EC decay of the neutron deficient nuclei^76,78Sr and⁷⁹Y was studied employing mass separated molecular beams of SrF⁺ and YF₂ ⁺ from the ISOLDE mass separator. The halflives of^76,78Sr and⁷⁹Y were measured as t_1/2=8.9(3)s, 159(8)s and 14.4(15)s, respectively, and decay schemes were established for⁷⁶Sr and⁷⁹Y. In the⁷⁸Sr decay 10 new -ray transitions were identified.     

Half-lives andQ β measurements for new nuclei of89Tc and89mTc

Neutron deficient isotopes of⁸⁹Tc and^89mTc have been produced through the⁶⁰Ni(³²S,p 2n)⁸⁹Tc at 95 MeV and the⁵⁸Ni(³⁵Cl, 2p 2n)⁸⁹Tc reaction at 135 MeV. A rotating catcher foil system was used to collect the activities and transfer them to a measuring position for- spectroscopy. The half-lives of⁸⁹Tc and^89mTc were measured to be 12.8±0.9 s and 12.9±0.8 s, respectively. The total decay energy, Q_EC, for⁸⁹Tc was determined to be 7.51±0.21 MeV.The authors would like to express their thanks to technical staff of the Tandem Accelerator Center at the University of Tsukuba for their operation of the accelerator and assistance during the experiment. This work is partly supported by a Grant-in-Aid from the Japanese Ministry of Education, Grant No. 01790180.     

Evidence for the alpha decay of108I

A Residue Implantation Detection System has been used in conjunction with the Daresbury Recoil Mass Separator in a search for radioactivity from the unknown nuclides¹⁰⁸I and¹⁰⁵Te. In the reaction of 260 MeV⁵⁸Ni ions with a⁵⁴Fe target two new decay lines at energies of 3.730±0.025 MeV and 3.885±0.025 MeV corresponding to cross sections of approximately 0.3 b and 0.4 b respectively were identified in theA=108 region of the separator's focal plane. These decay lines are tentatively assigned to the alpha decays of¹⁰⁸I. No evidence for a proton decay branch of this nuclide could be found. In a second reaction in which a⁵⁰Cr target was bombarded with 230 MeV⁵⁸Ni ions, no alpha decay peak from¹⁰⁵Te could be identified. Cross section dependent half life limits were determined from which correspondingQ-value limits were deduced.RDP, SJB and MF would like to thank the SERC for financial support during the course of this work and all of us would like to thank the crews at Daresbury for providing the⁵⁸Ni beams.     

The new element 111

In an experiment carried out to identify element 110, we have observed an-decay chain, that can be unambiguously assigned to²⁶⁹110. In a scries of preexperiments the excitation functions of the fusion reactions⁵⁰Ti +²⁰⁸Pb²⁵⁸104^* and⁵⁸Fe +²⁰⁸Pb²⁶⁶108^* were measured with high precision in order to get the optimum projectile energies for the production of these heavy elements. The cross-section maxima of the 1n evaporation channels were observed at excitation energies of 15.6 MeV and 13.4 MeV, respectively. These data result in an optimum excitation energy of 12.3 MeV of the compound nucleus for the production of²⁶⁹110 in the reaction⁶²Ni +²⁰⁸Pb²⁶⁹110 + 1n. In irradiations at the corresponding beam energy of 311 MeV we have observed a decay chain of 4 subsequent a decays. This can be assigned to the isotope with the mass number 269 of the element 110 on the basis of delayed - coincidences. The accurately measured decay data of the daughter isotopes of the elements 108 to 102, obtained in the previous experiments, were used. The isotope²⁶⁹110 decays with a hair-life of (270 _-120 ⁺¹³⁰⁰ ) s by emission of (11.132±0.020) MeV alpha particles. The production cross-section is (3.3 _-2.7 ^+6.2 ) pb.     

Analysis of the 33-133-133-1final state in photon-photon collisions

The reactione ⁺ e ^- e ⁺ e ^{- 00}e ⁺ e ^- 6 has been analysed using the full data sample taken with the Crystal Ball detector at the DORIS II storage ring at DESY. The ⁰⁰ invariant mass spectrum is dominated by the ', for which we determine the radiative width (') to be (4.5±0.3±0.5)keV. Near 1.9 GeV/c² we observe a second enhancement in the ⁰⁰ mass distribution. Assuming that these events are created by the production and subsequent decay of a wide resonanceX(1900), we have investigated the decay modes, the invariant mass distributions of the ⁰ and ⁰⁰ subsystems and the angular distributions of the final state mesons. We find that the data is best described byJ ^PC=2. For thisJ ^P assignment the resonance parameters are (X) BR(X)=(0.95±0.27±0.20) keV _tot (X)=(221±92±44)MeV, andM(X)=(1881±32±40) MeV/c².Deceased     

The Β decay of the new isotope79Y

The neutron deficient isotope⁷⁹Y has been firstly identified and the decay properties were studied from-decay measurements in the reaction of⁵⁴Fe(²⁸Si,p2n at 92 MeV. Three rays of 152.5, 177.4, and 1106 keV were observed concerning the decay. The half life and Q_EC value were determined to be 14.9 ± 0.6 s and 7.12 ± 0.45 MeV, respectively. The decay scheme including spin-parity is discussed, and 5/2⁺ assignment for the ground state is proposed.We would like to thank to Dr. Y. Maeda for his valuable advice about the electroplating method of iron targets. We also thank to Mr. T. Maeda and Mr. S. Niiya for preparation of hardware for data-taking.     

The branching ratio ofβ-delayed two-proton emission

The decay of the ⁺-fed isobaric analog state by one- and two-proton emission is calculated in the formalism of compound-nucleus decay. Support is given to the uncorrelated character of the emitted protons in the2p process. The ratio of2p top probabilities is obtained for the isotopes predicted to be2p emitters up to Z=30, i.e.²²Al,^22,23Si,²⁶P,²⁷S,³¹Ar,³⁵Ca,³⁹Ti,⁴³Cr,⁴⁶Mn,^46,47Fe,^49–51Ni, and⁵⁵Zn.     

The influence of shape changes on the alpha decay in the191Bi m,g →187Tl→183Au chain

The¹⁹¹Bi^{m,g 187}T1 ¹⁸³Au a-decay chain has been studied using mass — separated sources. The a — branching ratios have been measured. Out of the reduced a — decay widths, it is clear that the s_1/2 — S_1/2 and h_9/2 h_9/2 transitions are not hindered although they involve strong shape changes.     

The structure of28Si above 10 MeV excitation energy I: gamma-decay modes and radiative widths of levels

The systematics of-decay modes and radiative widths of highly excited states in²⁸Si has been extended by taking-ray spectra on 60 resonances of the²⁷Al(p,) reaction in the range 1097 keVE _p 4492 keV (12643 keVE _x 15915 keV) and on the²⁴Mg(,) resonances atE =3355, 3431, 4003 keV (E _x =12860, 12925, 13 415 keV). The-decay modes of levels in the sub-resonance region (E _x =10–12.5 MeV) were studied with both the²⁷ A1(p, ) reaction and the²⁷ A1(d, n) reaction at E_d=4,5,6 MeV. Information on radiative widths of levels was obtained by measuring the resonance strengthsS =(2I+1) _p / for 52 resonances of the²⁷Al(p, ) reaction with an emphasis on prospective T=1 states.     

The decay of the isotopes179Ir and180Ir

The probability for non-radiative (n.r.) excitations in muonic²⁰⁹Bi was determined from a ( ^–,)-measurement by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The values of P_n.r(3p1s)=(17.9±2.0)% and P_n.r.(3d1s)=(3.0±2.2)% were measured for the first time. The strength of the n.r. decay of the 2p-level was found to be (4.2±2.2)%. The n.r. transition probabilities of two subcomplexes of the (2p1s)-transition leading to different mean excitation energies are (3.2±1.8)% and (5.0±2.0)%, respectively.We are indebted to the following institutes or organizations for financial support: Bundesministerium ffir Forschung und Technologic der Bundesrepubfik Deutschland contract number 06 BN 271 (HP, PD, HH, FR, CR), Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization of the Advancement of Pure Research (NWO) (JK, CTAMdL, WL, AT) and the Schweizer Nationalfonds (LS).     

Lifetime of charged and neutral B hadrons using event topology

The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z⁰ decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1±0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be 1.72±0.08 (stat.) ±0.06 (syst.) ps and 1.58±0.11 (stat.)±0.09 (syst.) ps respectively. The ratio of their lifertimes, _charged/_neutral, was 1.09 _–0.10 ^+0.11 (stat.)±0.08 (syst.). By making assumptions about the B _s ⁰ and _b ⁰ states, the B⁺ and B⁰ meson lifetimes were determined to be _B+ = 1.72 ± 0.08 (stat.) ±0.06 (syst.) ps and _B+ = 1.63 ± 0.14 (stat.)±0.13 (syst.) ps and the ratio of their lifetimes was:_B+/_B0 = 1.06 _–0.11 ^+0.13 ±0.10. The mean B lifetime was also deduced to be <> > = 1.64 ±0.06 (stat.)±0.04 (syst.) ps.     

Beta decay of very neutron-rich110Mo studied at the new IGISOL facility

The decay of the new activity¹¹⁰Mo (t_1/2=0.30(4).s) has been observed at the new IGISOL separator. Multiscaled singles,--t and -y-t coincidences were recorded. The decay scheme suggests I=2⁺ for the ground state of the daughter nucleus¹¹⁰Tc. Three 1⁺ levels are fed with logft values below 5, indicating no drastic change among Mo and Ru decays at the middle of the neutron shell. This experiment confirms the expectation that the new IGISOL facility will allow the identification of one or two new more neutron-rich isotopes per element in this region.Supported by the Academy of Finland.     

Measurement of the forward-backward asymmetry ofe+e?→Z→ b[`(b)]b\bar b using prompt leptons and a lifetime tag

An analysis of inclusive production of K⁰ and the meson resonances K^*±(892), ⁰(770),f ₀(975) andf ₂(1270) in hadronic decays of the Z⁰ is presented, based on about 973,000 multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. Overall multiplicities have been determined as 1.962±0.060 K⁰ mesons, 0.712±0.067 K^*±(892) and 1.21±0.15⁰(770) per hadronic Z⁰ decay. The average multiplicities off ₀(975) for scaled momentum,x _p , in the range 0.05x _p 0.6 and off ₂(1270) for 0.05x _p 1.0 are 0.098±0.016 and 0.170±0.043 respectively. Thef ₀(975) and ⁰(770)x _p -spectra have similar shapes. Thef ₂(1270)/⁰(770) ratio increases withx _p . The average multiplicities and the differential cross sections are compared with the JETSET Parton Shower model. The model with default parameters fails to reproduce the experimental K⁰ momentum spectrum at low momentum, describes the K^*±(892) and ⁰(770)x _p -spectrum shapes, but significantly overestimates their production rates.(CICYT-AEN93-0832)     

DieK-ElektroneneinfangwahrscheinlichkeitPK beim Zerfall von139Ce

TheK-Shell Electron-Capture ProbabilityP _K for the Electron Capture of¹³⁹Ce has been measured using the coincidence method. The detectors used have been a NaJ(Tl)-detector with Be-window for the Lanthan-X-ray, a Ge(Li)- and a 76.2 mm Ø×76.2 mm-NaJ(Tl)-detector for the 166 keV--ray. The escape-effect of the Lanthan-X-ray in the NaJ(Tl)-detector was investigated. The experimental results areP _{K K}= 0.726±0.010 andP _K =0.801±0.034 using _K=0.906±0.026.     

Shell model high-spin states in 67 151 Ho84

In an in-beam study of ₆₇ ¹⁵¹ Ho₈₄ we have established its high-spin states up to 10 MeV and have suggested spin assignments up to (49/2) at 6.2 MeV. The main decay-cascade proceeds through the yrast states of the h³ _11/2f² _7/2 and h³ _11/2f_7/2h_9/2 5-particle configurations, which are predicted with good accuracy in parameter-free shell-model calculations. States with one proton in d_3/2, or involving i_13/2 or f_7/2×3^– excitations were also identified.     

B* production in Z decays

The decayB ^*B has been observed with the DELPHI detector at LEP, where theB ^* meson is produced inZ boson decays. The combination of inclusively reconstructedB mesons with well-measured converted photons yields a measurement of the flavour-averagedB ^*-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c². 95% confidence level upper limits at 6 MeV/c² are placed on both the isospin (i.e.B ⁺-B ⁰) and theB _s -B _ud splitting of the mass difference. The production ratio ofB ^* toB mesons inZ decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excitedB hadron states decaying radiatively are established. The differentialB ^* cross section has been measured to be in good agreement with the averageb fragmentation, yielding an average fractionalB ^* energy of x _E =0.695±0.009 (stat.) ±0.013 (syst.). From the decay angular distribution the relative contribution of longitudinalB ^* polarisation states is measured to be _L/(_L + _T) = 0.32 ± 0.04 (stat.) ±0.03 (syst.).CICYT_AEN93-0832     

Bivariate distributions in statistical spectroscopy studies: IV. Interacting particle Gamow-Teller strength densities and β-decay rates offp-shell nuclei for presupernova stars

A method to calculate temperature dependent-decay rates is developed by writing the expression for the rates explicitly in terms of bivariateGT strength densities (I _O ^H _(GT)) for a given hamiltonianH=h+V and state densities of the parent nucleus besides having the usual phase space factors. The theory developed in the preceding paper (III) for constructing NIP strength densities is applied for generatingI _O ^h _(GT) and thenI _O ^H _(GT) is constructed using the bivariate convolution formI _O ^H _(GT)= _S I _O(GT) ^h,S _O(GT) ^V,S ; _BIV-G . The spreading bivariate Gaussian _O(GT) ^V ;BIV-G, forfp-shell nuclei, is constructed by assuming that the marginal centroids are zero, the marginal variances are same as the corresponding state density variances and fixing the bivariate correlation coefficient using experimental-decay half lifes. With the deduced values of 0.67,-S-decay rates for^61,62Fe and^62–64Co isotopes are calculated at presupernova matter densities=10⁷–10⁹ gm/cc, temperaturesT=(3–5)×10⁹ K and electron fractions Y_e=0.43–0.5. The convolution form forI _O(GT) ^H led to a simple expression for calculatingGT non-energy weighted sum rule strength and it describes (within 10%) the shell model results offp-shell nuclei.The work presented in this paper has grown out of many discussions and correspondence one of the authors (VKBK) has with J.B. French in the last five years and also out of an ongoing project one of the authors (VKBK) is carrying out with J.B. French and R.U. Haq. Thanks are due to K. Kar and S. Sarkar for supplying some of their results before publishing. The authors thank V. Potbhare for his interest in the work presented in this paper.     

Evidence for higher twist mechanisms in highp ⊥π− p events with prompt ρ0 production at 38 GeV/c

The ^– p interactions with at least one charged secondary produced at polar angle 90° in c.m.s. and having the transverse momentum above 1 GeV/c were investigated. The data were obtained using streamer chamber magnetic spectrometer RISK at 38 GeV/c beam from Serpukhov accelerator. The analyzis of associated production in reconstructed events suggests, that if the transverse momentum of a pair of oppositely charged secondaries compensates the trigger particlep practically completely, this pair is the product of the ⁰ decay in marked fraction of such events. We observed a large spin-alignment for the ⁰-mesons selected as described above: the probability of zero spin projection onto the normal to the ⁰ production plane is equal to ₀₀ ^T =0.86±0.23. The enhancement of the number of events, in which the ⁰ picks up practically full momentum transfer carrying by the exchange, and also the enlarged tensor polarization for the ⁰-mesons in these events could be qualitatively explained as manifestation of direct ⁰-production via the QCD higher twist processes in the highp ^– p collisions. At the same time, the observed effects are markedly larger than the values predicted with QCD model in which the higher twist corrections were included.     

Energy inversion of thef 7/2 andh 9/2 neutrons in yrast states of154Yb

The N=84 nucleus¹⁵⁴Yb was investigated through the¹⁰⁶Cd(⁵⁴Fe,2p) reaction. We found the 16⁺ yrast level in this nucleus to be formed by the (h_11/2 ² f_7/2h_9/2) configuration, in contrast to the lower-Z isotones where (h_11/2 ² f_7/2 ²)16⁺ is the yrast state. Manybody shell model calculations with empirical two-body interactions support our conclusion.Dedicated to Prof. Dr. O. Schult on the occasion of his 60^th birthday