SubthresholdK + production in proton-nucleus collisions

We analyzed theK ⁺ production at projectile energies below the free nucleon-nucleon threshold in proton-nucleus collisions and studied the contribution from different reaction channels to this process. It was shown that the secondary pion-nucleon (+N+K ⁺) channel significantly prevails over the direct (p+N+N+K ⁺) one. The momentum and angularK ⁺ spectra were calculated in the framework of different production channels in order to propose experimental measurements which allow to distinguish the mechanisms discussed. We also studiedK ⁺ d correlations and considered the deuteron reabsorption in the nuclear medium as well as the fast deuteron background. The features ofK ⁺ p correlations related to the different production channels were analyzed as well.     

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 low-energyD(α, γ)6Li and6Li+208Pb→D+α+208Pb cross sections

We have calculated theE1 andE2 contributions to the low-energyD(,)⁶Li fusion and to the⁶Li+²⁰⁸Pb D++²⁰⁸Pb Coulomb dissociation cross sections within a multichannel Resonating Group calculation based on many-body deuteron+ configurations and pseudo-states. For both reactions experimentally determined cross sections are reasonably well reproduced. We find that dipole capture contributes noticeably to the fusion cross sections atE500 keV, while it is negligible in the Coulomb dissociation data.     

The proton g9/2 isomer in theN=50 nucleus87Rb and M2 transition rates in85,87Rb

Low-lying states of theN=50 nucleus⁸⁷Rb have been investigated in the (, ') reaction measuring- and delayed-rf-coincidences. A half-life ofT _1/2=6(1) ns was obtained for the level at 1578.1 keV. This experimental result confirms the 9/2⁺ assignment and the proton 1g_9/2 single-particle character of this state. Experimental M2 transition strengths in^85,87Rb are compared with predictions of the shell model and the particle-core coupling model.This work was partly supported by the Bulgarian National Research Foundation.     

Excitations in208Pb nearE x=5683 keV

A search for the recently proposed two-phonon octupole vibrational (2-POV) 4⁺ or 6⁺ state in²⁰⁸Pb at an excitation energy of 5683 keV has been performed using the²⁰⁷Pb(d,p),²⁰⁸Pb (p,p) and (,) reactions at high energy resolution. No evidence for a two-phonon excitation at this energy is found.This work was supported in part by the DFG under contract nr. II C4-Gr 894/2-1 and by the DFG-Graduiertenkolleg Struktur der Hadronen und Kerne under contract nr. Mu 705/3-1.     

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.     

Spin and parity of isomeric and ground states of the doubly-odd nucleus184Au

Low-spin states in doubly-odd¹⁸⁴Au have been populated in the ⁺/EC decay of¹⁸⁴Hg produced by bombarding¹⁸⁴Sm targets with an 185 MeV⁴⁰Ar beam. Radioactive Hg nuclei were transported by a He jet system. A new level scheme has been established from --t and X--t coincidence measurements. Spin and parity values I=5⁺, I =2⁺ and I=3^– were assigned to the ground state and the two isomeric states of¹⁸⁴Au, respectively. The structure of these states is discussed using B(E1) values.     

The new isotope218U

The new neutron-deficient isotope²¹⁸U was produced in the bombardment of¹⁹⁷Au target with²⁷Al ions and identified using the- correlation method. The -decay energy and the half-life of²¹⁸U were determined to be 8625±25 keV and 1.5 _–0.7 ^+7.3 ms, respectively. Evaporation residues recoiling from the target were separated in-flight from the projectiles and from the products of other nuclear reactions by the electrostatic separator VASSILISSA [1].     

Separation and implantation of relativistic86Kr-fragments at the FrS; half-life measurement by ion-β time-correlations

Neutron-rich Co and Fe isotopes produced by⁸⁶Kr projectile fragmentation at 500 MeV/u were separated and identified using the fragment separator (FrS) in a bunched energy mode.⁶⁶Co and⁶⁵Fe ions were selectively implanted in a double PIN-diode array where the-decay signals were measured. The half-lives were deduced from time correlations between implantation and-decay signals. The remeasurement of the⁶⁶Co half-life confirms the isotope identification. The value of the⁶⁵Fe half-life was found to be 0.45±0.15 s.     

Investigation of the40Ca(γ,N) reaction at 60 MeV

The values of the angle-integrated cross section for the decay to various low-lying states in³⁹K following the⁴⁰Ca(,) reaction at a mean photon energy of 60 MeV are reported on, together with the values of the reduced Legendre coefficientsa _i . The⁴⁰Ca(,gp) and⁴⁰Ca(,n) reactions yield the same angular cross-section values and these agree with the corresponding RPA-calculations.Senior Research Associate NFWO     

High-spin states of odd-odd156Ho

High spin states in the nucleus¹⁵⁶Ho have been studied via the fusion-evaporation reaction¹⁴⁰Ce(¹⁹F,3n)¹⁵⁶Ho at the beam energy of 82 MeV.- coincidences, E, I and excitation functions have been measured. With two rotationally-aligned bands identified as [h_11/2] [i_13/2], we found two new bands with a signature splitting, whose structure is believed to arise from either [h_9/2] or [f_7/2] coupled to [h_11/2]. Our placement of rays belonging to these new bands suggests that the previously known level scheme should be corrected. We also found many new low-energy rays in the low excitation energy. As compared to¹⁵⁴Ho, the present nucleus with two more neutrons becomes more collective, and shows well-observed rotationally-aligned bands with a clear signature splitting.Communicated by B. Herskind     

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     

Nuclearg-factors of the 1229 and 2911 keV isomers in143Nd

Nuclearg-factors of the 1229 keV 13⁺/2 and 2911 keV 21⁺/2 level and the half-life of the 1229 keV level have been measured to beg(1229)=0.058(5),g(2911)=0.69(12) andT _1/2 (1229)=6.79(2) ns. The experimental g-factors show that the 1229 keV level has a dominant configuration of (f _7/23^–), and the 2911 keV level has an almost pure (f _7/27^–), configuration.The authors would like to thank the crew of CYRIC for the operation of the cyclotron.     

A pair of excited superdeformed bands in196Pb

Two excited superdeformed bands have been found in¹⁹⁶Pb using the GASP-ray spectrometer array. They are signature-partner bands with a small signature splitting developing at higher frequencies, similar to bands 2 and 3 in the isotone¹⁹⁴Hg. The bands are probably built on an excited neutron configuration. They show an unusual incremental alignment of 1/2 with respect to the¹⁹⁴Pb core.Communicated by: B. Herskind     

On the role of theΔ -isobar in deep inelastic scattering on the deuteron

The role of the nuclear structure effects, viz. the boundness of nucleons and-isobar components, in the deep inelastic scattering of leptons on the deuteron is considered. It is shown that small admixture of the-isobar configurations to the deuteron wave function may lead to significant effects in the spin structure functions of the deuteronb ₁ ^D andg ₁ ^D (x): up to 4% in g ₁ ^D (x) dx and up to 10% ing ₁ ^D (x) at smallx.One of the authors (A.U.) thanks Prof. F.C. Khanna for helpful discussions and for kind offering the information used in our calculations.     

Nuclear structure study of the neutron deficient cadmium isotopes100, 101, 102Cd

The neutron-deficient nuclei^100,101Cd were identified for the first time in — beam following the reactions⁵⁸Ni +^46,48Ti and⁵⁸Ni +⁵⁰Cr at 230 MeV and 245 MeV bombarding energy of the⁵⁸Ni beams. The-decay of the isotopes^100,101,102Cd was studied inp, pp,n, nn, andn prompt and delayed coincidence spectra. Isomers were found with spin and half life {ie1-01}=8⁺, T_1/2=52(5) ns in¹⁰⁰Cd, {ie1-02}=(19/2⁺), T_1/2=4.6(4) ns in¹⁰¹Cd and {ie1-03}=8⁺, T_1/2=56(4) ns in¹⁰²Cd. In a PAD experiment theg-factor of the {ie1-04}=8⁺ isomer in¹⁰⁰Cd was measured to be g=1.24(6). Using the reaction³⁶Ar +⁷⁰Ge at 135 MeV energy of the³⁶Ar beam, theg-factor and the quadrupole moment of the {ie1-05}=8⁺ isomer in¹⁰²Cd were measured to be g=1.29(3) and Q=87(10) fm², respectively. The spectroscopic results are discussed within a shell model approach using a¹⁰⁰Sn core, which accounts well for the electromagnetic properties of the proton aligned isomers. The structure of the spherical neutron states, dominated by the close lying vd_5/2, g_7/2 orbitals, and the gradually developing quadrupole collectivity are reproduced by the shell model calculations.The authors gratefully acknowledge fruitful discussions with K. Heyde and are indebted to him for communicating unpublished theoretical results. The help of N.A.F.M. Poppelier and A.G.M. van Hees in running the RITSSCHIL code is very much appreciated.     

Hard form factors for meson-baryon strong couplings as derived from deep inelastic lepton scattering

As stimulated by earlier attempts for obtaining theNN andN form factors from the deep inelastic lepton scattering data, we extend the analysis by taking into account effects of additional mesons including, , ,K, andK ^*, with the coupling constants fixed by the lowenergy nucleon-nucleon and hyperon-nucleon scattering data. Contrary to an earlier claim that the NN andN form factor must be very soft (e.g., with the cutoff mass less than 500 MeV in the monopole form), we find, for example, that with all form factors parametrized in the dipole form, a universal cutoff mass of 1150 MeV in the/N sector and 1400 MeV in the/ sector yields predictions in excellent agreement with recently published neutrino data on the momentum fractions carried by thes, , and¯d quarks, as well as consistent with the sea-to-valence ratio extracted from the CDHS data and the Femilab E615 experiment. Similar results can also be obtained by using exponential cutoffs for all couplings, or by using monopole forms for some vertices while retaining dipole forms for the rest. The success of the mesonexchange picture in generating the strangeness content in a proton suggests an alternative understanding of the origin of sea quarks in the proton.We wish to thank G. Garvey, K. Holinde, L.-C. Liu, M. B. Johnson, M. Strikman, A. W. Thomas and Jochen Wambach for helpful conversations. W-Y. P. Hwang wishes to acknowledge the Alexander von Humboldt Foundation for a fellowship to visit Jülich for conducting research. His research works was also supported in part by the National Science Council of the Republic of China. The work of G. E. Brown is supported in part by a Humboldt award, in part by NATO Grant RG85/0093, and in part by the U.S. Department of Energy.     

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.     

Search for the 70 keV resonance in17O(p, α)14N

A direct search for theE _R =70 keV resonance in¹⁷O(p, )¹⁴N was carried out using¹⁷O enriched Ta₂O₅ targets in combination with a 1 mA proton beam and suitable detectors of large solid angle. The observed upper limit for the resonance strength is8×10^–10 eV.Work supported in part by Deutsche Forschungsgemeinschaft (Ro429/21-2) and the Science Program SC1-0065 of the European Economic Community     

Decay of the new isotope127Pr

A new isotope,¹²⁷Pr, has been identified and its decay has been studied using on-line isotope separation of⁹⁴Mo (³⁶Ar,p2n) reaction products. The half-life of the isotope was determined to be 7.7(6) s, and a /X-ray spectrum has been obtained. A partial level scheme is proposed for¹²⁷Ce on the basis of-singles,-gated and-coincidence data.The authors would like to thank the TIARA cyclotron crew for their cooperation in generating an intense³⁶Ar beam as well as in operating the cyclotron. This work was partly supported by the JAERI-University Collaborative Research Project.