Showing papers in "European Physical Journal A in 1979"

Production of high current particle beams by low pressure spark discharges

Abstract: On the basis of low pressure spark discharges a new type of a particle accelerator as been developed. It produces pulsed ion as well as electron beams of high intensities in a gas atmosphere at pressures of the order of 1 mbar. The method was used to produce in hydrogene at particle energies of about 70 keV an electron beam with a current density of more than 106 A/cm2 at 140 A total current. It is shown that magnetic confinement by the pinch effect takes place in the discharge. Discharge times smaller than 5 ns and spark frequencies up to 2 MHz can be obtained.

Alpha decay studies of very neutron deficient isotopes of Hf, Ta, W, and Re

Abstract: Very neutron deficient isotopes in the Hf-Re region were produced by bombarding targets of107, 109Ag,nat, 108, 110Pd, and103Rh with58Ni accelerated by the linear accelerator UNILAC at GSI After separation from the projectile beam by the velocity filter SHIP, the fusion products were implanted with their full recoil energy into a silicon surface barrier detector The subsequent alpha decay of the implanted ions was measured with the same detector In some of the experiments the evaporation residues were implanted into a position sensitive silicon surface barrier detector With a newly developed position and time correlation technique parent daughter relationships, half lives, andα branching ratios of a large number of isotopes could be determined In the investigated reactions the eleven new isotopes161–164Re,160W,157–161Ta, and156Hf could be identified The measuredQ α values, half lives, and a branching ratios are discussed Two new high energyα transitions of (7,408±10) keV and (7,804±15) keV were also found with half lives of 27 ms and 052 ms, respectivelyA tentative mass and atomic number assignment givesA=153–156 andZ=70–72 The energies of the excited isomeric states are between 2 MeV and 3 MeV From the systematics of alpha ground state transitions in even nuclei a hindrance of 105 can be deduced for both transitions, possibly indicating orbital angular momenta on the order of 10ħ for the alpha emitting states The isomers are proposed to belong to shell model isomers beyond146Gd

Particle hole yrast states in146Gd and147Gd and the Z=64 shell closure

Abstract: The level structures of146Gd and147Gd have been investigated by in-beamγ-ray ande− spectroscopy with (α, xn) reactions on enriched Sm targets. Detailed level schemes up to ∼4 MeV, which differ radically from earlier schemes, are reported. The energy levels are characterized as particle-hole excitations using empirical single particle energies and two nucleon interactions. Analysis of pure 1p 1h proton excitations demonstrates that theZ=64 andN=82 energy gaps are about equally large.

The reaction 238 U + 238 U at 7.42MeV/u

Abstract: One-particle-inclusive measurements have been performed for the charge, kinetic energy and angular distributions of reaction products from238U +238U at 1 766MeV (7.42MeV/u) incident energy. The deep inelastic products exhibit features similar to those seen in reactions induced by medium heavy nuclei: increasing particle transfer is observed with increasing energy damping, the angular distributions are peaked near the grazing angle, they broaden significantly with increasing energy loss and/or charge transfer. The dominant reaction mechanism, however, is found to be sequential fission of one or both primary reaction products. The reconstructed primaryZ- andQ-value distributions show more particle transfer at a given energy loss than in other systems, i.e. the diffusion process seems to proceed colder in this system. This is confirmed by relatively large cross sections for surviving deep inelastic reaction products belowZ=92. A direct search forα-decay or fission of superheavy nuclei being produced in a deep inelastic reaction and being implanted in a surface barrier detector resulted in an upper cross section limit of 2 ×10−32cm2.

Rotationally inelastic, classical scattering from an anisotropic rigid shell potential of rotation symmetry

Abstract: Rotational excitation in collisions of structureless atoms and diatomic rigid rotor molecules interacting by a rigid potential shell is considered in classical mechanics. The double differential cross sectionJ(u*,θ) for final (over initial) relative velocityu*=ν′/ν and deflection byθ is analytically related to the shell form in the case of vanishing initial molecular rotation.J(u*,θ) exhibits the strong structure of “bulge” scattering or “orientational rainbows” which has been observed in the K−N2 and K-CO systems and is expected to occur in rotationally inelastic collisions of many nonreactive systems under appropriate scattering conditions. The present results elucidate the nature of the sensitive and direct relation of bulge scattering to the anisotropy of the intermolecular potential.

Anisotropy of the repulsive intermolecular potential from rotationally inelastic scattering

Abstract: Structure is observed in recoil velocity distributions of potassium atoms scattered inelastically from N2 and CO molecules at CMS anglesϑ>π/2 and collision energies 0.34≦E≦1.24 eV. It is caused by rotational excitation mainly. Individual rotational transitions are not resolved. The quasi-continuous recoil velocity distributions extend between well defined bounds, the upper corresponding to elastic scattering, the lower marking a largest amount of energy transferred into molecular rotation at givenϑ andE. This maximal transfer increases with angle and — forE≳0.64 eV — in near proportion toE. At allϑ andE it is larger for CO than forN2, amounting to about 0.42E forN2 and 0.64E for CO atϑ=150°. At or very close to each of their bounds the distributions exhibit pronounced maxima. A third intermediate maximum is present for CO, but missing for N2.

Relaxation times in dissipative heavy-ion collisions

Abstract: The classical model introduced earlier for analyzing experimental data on dissipative heavy-ion collisions, is generalized to include effects from the gradual dissipation of radial kinetic energy and from the development of fragment deformations during the collision. Relaxation times for the dissipation of radial kinetic energy (τ R ) and relative angular momentum (τ l ) as well as for the development of deformations (τα) are fitted to the reaction86Kr (8.18 MeV/u) +166Er and applied to three other reactions. A consistent set of relaxation times isτ R = 0.3 · 10−21 s,τ l =1.5 · 10−21 s andτ α = 5 · 10−21 s. Empirical mass transport coefficients are deduced from comparisons with experimental element distributions. Effects from fluctuations in the deflection function are discussed. Evidence is found for the existence of a relaxation time of the order 10−21 s in the mass-drift coefficient.

A theoretical model for the charge equilibration in heavy ion collisions

Abstract: We propose to treat the charge equilibration process as a collective high frequency mode and discuss the implications for the first stages of a heavy ion collision. We show how its dynamics can be treated by means of a quantal master equation. We solve numerically the dynamical equations for a two-dimensional model, using charge excess and mass asymmetry as dynamical degrees of freedom.

Description of even-even Krypton isotopes by the Interacting Boson Approximation

Abstract: Energy spectra andB(E2) values of the even-even Kr isotopes74–82Kr have been analyzed in terms of the IBA-2 model of Otsuka, Arima and Iachello [6, 7]. We can reproduce the variation of collectivity along the isotope chain by means of a consistent set of 5 parameters, essentially only one of them has been varied with neutron number. The low lying 0 2 + states have been found to be strongly influenced by shell effects. Predictions are given for the not yet observed gamma bands of74,76Kr.

Strong Compression Effects in Fast Nuclear Collisions

Abstract: The importance of the impact parameter for compression effects and the reaction mechanism in high energy heavy ion collisions (HEHIC) are investigated within three-dimensional nuclear fluid dynamics. For central collisions of a small projectile (Ne) with a heavy target (U) a Mach shock wave is formed resulting in the sidewards emission of matter with azimuthally symmetric fragment distribution. At intermediate impact parameters the Highly-Inelastic Bounce-Off (HIBO) appears, where the large compression potential leads to the sidewards deflection of the projectile, which then explodes. A large collective transverse momentum transfer to the target leads to azimuthally asymmetric (180° correlated) fragment distributions. The deflection angles, energy losses, mean associated multiplicities as well as the maximum compression and thermal excitation of the system are calculated as a function of the impact parameter.

Direct observation of the transversal Doppler-shift

Abstract: An experiment is reported in which the second order Doppler-shift has been determined by the observation of theHα-line emitted by linearly moving hydrogen atoms of velocities 2.53×108 cm/s−9.28×108 cm/s. In contrast to previous experiments the direct transversal observation has been used for the first time. The coefficient of the second order term in the relativistic approximation is found to be 0.52±0.03 which compares good with the theoretical value of 1/2.

Ion storage technique for very long living states: The decay rate of the 5 D 3/2 state of Ba II

Abstract: The metastable 5D 3/2 state of Ba+ is used to demonstrate the possibility of the ion storage technique for the measurement of extremely long lived states. The ions are confined in a r.f. quadrupole trap and excited by a strong pulsed tunable dye laser to the 6P 1/2 state which partially decays into the 5D 3/2 state. Sampling of the time development of the ground state population leads to the determination of the 5D 3/2 decay rate. Using He as a buffer gas at a pressure of about 10−6 mbar to initially store the ions, varying the gas density and extrapolating to zero pressure, we find for the lifetime $$\tau _{D_{3/2} } = 17.5 \pm 4s$$ .

Hyperfine structure and isotope shifts of neutron-rich 138–146 Cs

Abstract: The 6s2S1/2-7p 2P3/2 transition in138–142Cs (λ=455.5 nm) has been investigated by high-resolution collinear laser spectroscopy in a fast atomic beam. The isotopes are obtained by on-line mass separation of fission products. Nuclear moments and changes of mean-square charge radii are derived from hyperfine structure and isotope shift.

Reorientation effect measurements of even mercury isotopes

Abstract: Reorientation effect and multiple Coulomb excitation measurements have been performed for198, 200, 202, 1204Hg. By measuring particle spectra after Coulomb excitation of an enriched198Hg target with4He and16O beams, a positive quadrupole moment of Q2 = 0.66±0.18 eb (for negative interference) or Q2=0.80±0.18 eb (for positive interference) andB(E2,0→2)=0.991±0.006 e2b2 were obtained. All otherB(E2) values and quadrupole moments were determined relative to these numbers from preciseγ-ray yields obtained from Coulomb excitation of a frozennatHg target with4He and16O projectiles. Oblate shapes of all Hg isotopes were found. The data have been interpreted in terms of triaxial rotation and anharmonic vibrations.

Ground state correlations and the nuclear charge distribution

Abstract: Combining a sum rule approach and the generator coordinate model we evaluate the influence of ground state correlations on the moments of the radial charge distribution. The isotopic and isotonic differences of the moments come out to be particularly sensitive to fluctuations of the ground state correlations due to changes in the low energy spectrum. A comparison with the experimental results for the isotopes of Ca, Fe, Ni and Zn shows a fair agreement and confirms the importance of the ground state correlations for isotopic and isotonic differences of radial moments.

Three-dimensional calculations on the formation of density isomers in high energy heavy ion collisions

Abstract: A three dimensional fluid dynamical model is used to investigate the possibility of forming superdense abnormal nuclear matter (“density isomers”) in fast collisions of heavy nuclei, the dependence of the formation process on the bombarding energy and on the impact parameter An experiment for the detection of such phase transitions in nuclear matter is suggested

A high resolution study of the transitions 4 f 7 6 s 2 →4 f 7 6 s 6 p in the Eu I-spectrum

Abstract: Eight transitions in the Eu I-spectrum connecting the ground state with configuration 4f 7 6s 2 with states of the configuration 4f 7 6s6p were studied with high resolution laseratomic-beam spectroscopy. CW dye lasers operating in the wavelength regions 435–470 nm and 560–630 nm were used for this study. New data for the hyperfine structure in153Eu were obtained as well as new and more accurate values for the isotope shifts between151Eu and153Eu. The existing data for the hyperfine structure in151Eu were reproduced with an exception for the levelz 6 P 7/2.

On the mass distribution in Time-Dependent Hartree-Fock calculations of heavy-ion collisions

Abstract: Structural limitations in the Time-Dependent Hartree-Fock formalism when applied to heavy-ion collisions are discussed. These severely impair the ability of the method to correctly predict mass distributions and mass-to-charge ratios for the resulting fragments.

Delta Electrons: An Atomic Clock for Deep Inelastic Collisions*

Abstract: We calculate the δ-electron distribution resulting from heavy ion collisions with projectile energies above the Coulomb barrier. It is shown that the life time (Δτ≳10−21s) of superheavy composite systems causes pronounced oscillations in the electron spectrum. The width of the oscillations is found to be ΔE=h/Δτ. This effect can be used to measure nuclear sticking times quite accurately.

Core-particle coupling and polarization effects

Abstract: The unpaired particle in an odd-mass transitional nucleus exerts forces on the rest of the system leading to an effective shape which is in general dependent on thej-orbital occupied by the extra particle. To account for this polarization effect we propose to modify the collective matrix elements by a phenomenological polarization factor. This enables us to describe also such band structures by the core-particle coupling model for which the common coupling rules seem to fail. Selecting a typical case the model is applied to123I in order to demonstrate the important role of the polarization. The calculation reproduces fairly well all band structures including theirM1 andE2 decay properties.

Search for low-energy resonances in 25 Mg( p,γ ) 26 Al

Abstract: The reaction25Mg(p,γ)26Al has been investigated atE p (lab)=80-350keV. The existence of the resonance atE p =317keV has been verified and new resonances have been found atE p =198, 255 and 304 keV. TheE p = 304keV resonance represents a new compound state in26A1. Information on branching ratios,Ωγ values, total widths andJ π assignments for the observed resonances as well as upper limits on themy strengths for the expected resonances atE p =97 and 134 keV are given. The astrophysical aspects of the data are discussed in the light of the renewed interest in the precise location of26A1 nucleosynthesis.

Observation of new nuclides37Si,40P,41S,42S produced in deeply inelastic reactions induced by40Ar on238U

Abstract: Atomic numbers and masses have been identified for the fragments 10≦Z≦18 and 20≦A≦45 produced in the reaction40Ar(263MeV)+238U. Four new neutron-rich nuclides,37Si,40P,41–42S have been observed as a result of deep inelastic collisions. The nuclide identification combined two independant time of flight measurements as well as two (Δ E×E) informations and was quite unambiguous.

Jet-like distributions from the weak decay of heavy quarks

Abstract: We consider the production and weak decay of a pair of heavy quarks (mesons) ine+e− experiments and study their effect on the various jet distributions. The relative magnitudes of the two-quark-jet and three-quark-jet final states, in the decay of a heavy quark are estimated in the framework of an SU(2)L×U(1) model. We find that the three quark configuration dominates over the two quark configuration. For the quark jets resulting from the weak decay of the heavy quarks, we calculate the jet distributions in Sphericity, Spherocity and Thrust for the process\(e^ + e^ - \to Q\bar Q \to 6\) quarks. These distributions are compared with the corresponding quantities from the non-perturbative process\(e^ + e^ - \to q\bar q\) and the QCD process\(e^ + e^ - \to q\bar qg\). We find that the weak decay of heavy quarks is the dominant mechanism for jet broadening ine+e− experiments, in the intermediate energy region relevant for PETRA and PEP.

Half-lives, neutron emission probabilities and fission yields of neutron-rich rubidium isotopes in the mass region A=96 to A=100

Abstract: Neutron-rich rubidium isotopes were produced by thermal-neutron induced fission of235U and were isolated by surface ionization and mass separation. The new isotope (51 ±17) ms100Rb was identified. The half-lives of the rubidium isotopes with mass numberA=96 toA=100 were measured using neutron multiscaling or gamma multispectrum analysis. Measurements of the delayed-neutron emission probabilityP n of99Rb and of the fission yields of97Rb,98Rb, and99Rb were performed.

Coulomb capture of muons and atomic radius

Abstract: An earlier theoretical treatment of the Coulomb capture of muons has been extended to take the radius of the (electronic) atom into account. Smaller radii are shown to favor the capture, in agreement with earlier experimental findings.

Changes in nuclear mean square charge radii of stable Krypton isotopes

Abstract: The isotope shifts of stable even Kr isotopes (A=78 throughA=86) in the optical transitions at 432 nm and 557 nm were measured by means of polarization laser spectroscopy. The observed shifts are consistent with earlier results for other transitions. From the isotope shifts the changes in the nuclear mean square charge radiiδ〈r 2〉 were inferred using preliminary muonic isotope shift data. Starting from78Kr, a monotonic decrease of 〈r 2〉 with increasing mass number is found throughout theg 9/2 neutron shell. The effect onδ〈r 2〉 of nuclear deformations as well as possible contributions due to changes in the skin thickness of the nuclear charge distribution are discussed.

Extended measurements of isotope shifts in Mg I

Abstract: The isotope shifts in the Mg I transitionsλ 2,852 A (3s 2 1 S 0-3s3p 1 p 1 P 1) andλλ 3,829, 3,832 and 3,838 A (3s3p 3 P-3s3d 3 D) have been measured for24Mg,25Mg and26Mg. The measurements were carried out using a pressure scanned Fabry-Perot interferometer and separated isotopes excited in hollow cathode discharge tubes. The results are compared to theoretical predictions and an attempt is made to convert measured line shifts into level shifts.

Microscopic, quantal theory of Brownian motion applied to deep inelastic heavy-ion collisions

Abstract: The present understanding of the statistical features of deep inelastic heavy ion collisions can be improved considerably by following the lines of modern molecular theory of Brownian motion. Only a few assumptions are necessary, which are direct consequences of the underlying physical picture. The physical interpretation of these assumptions leads to simple estimates of their validity. The theory is a quantum mechanical, strong coupling, transport theory. Collective vibrations can be included in a simple and straightforward manner.

Spin alignment and polarisation in the (16O,15N) transfer reactions

Abstract: The spin alignment of the15N 3 2/* (6.33 MeV) state was measured in the88Sr(16O,15N)89Y reaction atE L =96 MeV using theγ-recoil method. Angular distributions of excited states in15N and89Y were measured with high accuracy. The analysis in terms of DWBA shows that the spin alignment is correctly described by the usual reaction models. The polarisation of the outgoing15N1/2(GS) and15N 3 2/* (6.33 MeV) is discussed. It is shown that cross section differences for transitions to final states with different configurations are sensitive to a spin-orbit potential of15N. The strength and sign of the spin-orbit potential for15N is determined.

High spin isomers in151Dy

Abstract: Three yrast isomers in151Dy, at 6.03 MeV (I=49/2, T/=15(3) ns), 4.90 MeV (41/2−, 5.5(1.0) ns), and at 2.96 MeV(27/2−, 1.3(6) ns) have been located through152Gd(α,5n) and136Ce(18O, 3n) measurements. Shell model configurations are suggested for them.