Negative parity states and ground state properties of theα—α—n system calculated by different forces

In recent years predictions on the off-shell behavior of composite particles interactions have been made by some theoretical models. The goal of this paper is to test them by using⁹Be nucleus. The bound state problem of⁹Be considered as aα—α—n three-cluster system is solved in configuration space. Several on-shell equivalent local and nonlocal forces for theα—α andn—α interactions are used for calculation of the low lying negative parity spectrum of⁹Be, and also of the charge density, quadrupole moment, and the correlation density of⁹Be ground state. The contributions to the calculated quantities of different partial waves of the two-body forces are examined and discussed.     

The two- and three-cluster fish bone model with saturation

The two- and three-cluster fish bone optical model with hard core correlations is derived from the corresponding resonating group model. The nuclear saturation effect is represented by three different features of inter-cluster interactions:i) by the non-local exchange potential,ii) by a reduced attraction in the region of overlapping clusters,iii) by an effective three-cluster potential. Comparability of the microscopic theory with phenomenological models is established by two off-shell transformations which orthogonalize function bases and avoid appearance of artificial three-body forces.     

Off-shell extension function from a generalised phase-function method

It is shown that the Combined-variable-phase-off-shell scattering theory or the generalised phase-function method provides efficient algorithms to calculate the off-shell extension function which plays a role in the theories of three-particle scattering. In order to assert this we have chosen to work with a model potential for theα-α interaction. The functions which occur in the context of our approach exhibit certain interesting features with regard to effect of the potential in producing on-and off-shell quantities like the phase shift and quasi-phase. Interpolating off-shell extension function is seen to exhibit a discontinuity where the phase function goes through a zero.     

Renormalization effects in a field theory of finite nuclei

In case of thep-α system, the Coulomb exchange potential of the resonating group model and of the fish bone optical model are compared with each other. It is seen that the difference between the two approximations arises mainly from the unrealistic shortdistance behaviour of the proton-protone ²/r potential, which has been assumed in both models. In case of the α-¹⁶O system, it is demonstrated that the importance of the Coulomb exchange potential can be very much reduced by an off-shell transformation.     

Multichannel effective range approach to low energy nucleon-antinucleon interactions

MultichannelM-matrix method is applied to an N¯N-system with taking into account elasticp¯ p-scattering, charge-exchangep¯ p → n¯ n reaction andp¯ p annihilation. The isospin breaking in theM-matrix is discussed. We describe the differential and total cross-sections forp¯ p → p¯ p andp¯ p → n¯ n processes, cross-section σ_tot(p¯ p) and the real-to-imaginary ratio of the forward amplitude of elasticp¯ p scattering. The fitting leads to bound state in thep-wave near thep¯ p-threshold, which elucidates a significant role of this wave at small energies.     

Neutron halo in 8He

The structure of ⁸He is investigated within a three-cluster microscopic model. The threecluster configuration α+² n+₂ n is used to describe the properties of the ground state of this nucleus. The results obtained evidently indicate the existence of a neutron halo in ⁸He.     

Absolute alpha-decay width of212Po in a mixed shell-and-cluster model

We have reproduced the absolute width of theα decay of the ground state of²¹²Po in a model in which the shell model is combined with a²⁰⁸Pb+α cluster model, and found that the amount of core+α clustering in the parent state is ～30%.     

Intrastate γ-transitions: A spectroscopic tool?

In the framework of a potential model we have calculated the various bremsstrahlung cross sections into the⁵Li ground state, includingM 1 andE 2 γ-transitions leading from the high energy wing of the⁵Li ground state resonance into states belonging to the same resonance at lower energy (intrastate transition). Our calculation supports the hypothesis of Schmalbrock et al. [1] that intrastate transitions ofM 1 andE 2 multipolarity exist. While we find a maximum cross section of roughly 1.4 nb for theE 2 transition, we predict the cross sections forM 1 intrastate transition to be less than 3·10^?5nb. An experimental observation of the intrastate γ-ray emission appears to be very difficult due to the dominance of competing resonant (M 1) and direct (E 1) capture processes. Schmalbrock et al. have suggested to deduce magnetic dipole and electric quadrupole moments of resonant states from the measurements of the respectiveM 1 andE 2 intrastate transitions. We will show that theM 1 intrastate cross sections do not yield the appropriate information to determine the magnetic dipole moment. We will also discuss thatE 2 intrastate transitions do not seem to be a suited tool to find the quadrupole moment of an unstable state.     

Effect of hyperon channels in low-energyK − d scattering

Within the framework of a Faddeev formalism and an implicit hyperon channel approximation, we have calculatedK ^? d elastic, total, and reaction cross sections for incident kaon laboratory momenta up to 120 Mev/c. We have used as input two different (slightly modified) multichannelM matrix fits to low-energy¯KN scattering, each of which contains explicitly theπ Y channels, as well as a single channel representation of the¯KN interaction in which the hyperon channels appear only through their contributions to the imaginary parts of the¯KN scattering lengths. TheK ^? d cross sections obtained with the single channel¯KN input differ by only some 10% from those for which we used the multichannel¯KN input. TheK ^? d cross sections calculated using¯KN input parameters from each of the two separateM matrix fits differ across the entire momentum range investigated by 25–35%.     

Zur Isomerie des Tl197

Tl^197m was produced by the (α, 4n) reaction on Au¹⁹⁷ using 49 MeVα particles. The following results were obtained: Half-lifeT _1/2=(0.55±0.02) sec; energy of the isomeric level (607±4) keV, determined directly by summing up the cascade transitions in a well-type scintillator; energy of the isomeric transition (222±2) keV; conversion coefficients of this transitionα _K222=0.41±0.05 andα _tot222=2.1±0.2, indicating anE3 multipolarity; energy of the second transition (385±3)keV; conversion coefficientsα _K385=0.09±0.03 andα _tot385<0.1. This transition was identified asE2 with aM1 admixture of 20 to 30%. Spins and parities are 1/2⁺, 3/2⁺ and 9/2^? for the ground state, the 385 keV state and the 607 keV isomeric state, respectively, in disagreement with the extreme single-particle model. If this model were correct, anotherM1 transition should appear. No furtherM1 transition having an energy greater than theL-shell binding energy of T1 was observed.     

Atomic effects on α-α scattering to the8Be ground state

Theα-α scattering to the⁸Be ground state was investigated in kinematic coincidence for the angle pairs 45?/45? and 30?/60? using the crossing beams technique, with an energy resolution of 26 eV. The nuclear resonance is split into 2 structures, not the 3 structures suggested by earlier work. The atomic physics origin of the splitting, the resonance parameters of the⁸Be ground state, and astrophysical implications are discussed.     

Orbital rearrangement in thesd-shell nuclei

The single particle orbital rearrangement energy is found to lie between 30 and 50% of theBrueckner rearrangement energy in thesd-shell. This calculation shows that the orbital rearrangement energyR _α is in a good approximation equal to half the difference of the single particle energies ?_α in the system withA particles and in the system withA- 1 particles having a hole in the state ¦α〉.     

Nature of resonance states in the 9Be and 9B mirror nuclei

The spectra of low-lying states of the ⁹Be and ⁹B mirror nuclei in the excitation-energy range between 0 and 5 MeV are considered within the microscopic α + α + n(p) three-cluster model, which is a three-cluster variant of the algebraic version of the resonating-group method. Attention is given primarily to studying the nature of resonance states in a three-cluster continuum. A detailed comparison of the results obtained in this way with experimental data and with results of other microscopic calculations is performed.     

Three-body Pauli potential in then p α system

Matrix elements of the three-body Pauli potential are calculated in thenpα resonating group model. They are small (~1%) compared with matrix elements of the two-body subsystem potentials, provided that correct normalization of all relative motion solutions is induced by off-shell transformation of the effective (subsystem) hamiltonians.     

Search for a 11/2−→3/2+ M 4 transition in141Sm

The electromagnetic decay of the 11/2^{? 141m} Sm is investigated. Internal conversion electron and X-ray-conversion electron coincidence measurements indicate that the state undergoesβ ⁺ and electron capture decay with 99.69% strength and the remaining 0.31% goes to a 174.2±0.3 keVM4 transition. TheK/L conversion electron intensity ratio for the transition is measured to be 1.7±0.4. The energy of the 11/2^? is established at 175.8±0.3 keV above the 1/2⁺ ground state in¹⁴¹Sm. Systematics of theM4 transitions in theN=79 and 81 isotones are discussed.     

Three-particle correlations from208Pb+6Li

Three-particle correlations in the reaction²⁰⁸Pb+⁶Li were studied near the Coulomb threshold between \(E_{6_{Li} } = 24\) and 30 MeV. Three reaction mechanisms contribute predominantly to the observed coincidences of the charged particles: 1. Coulomb excitation of the 2.184 MeV,J=3⁺ state of⁶Li, followed by the decay intoα+d, 2. Deuteron pick-up of the⁶Li to the ground state of⁸Be and sequential decay into twoα-particles and 3. Neutron-transfer to the ground state and the first excited states of²⁰⁹Pb:²⁰⁸Pb(⁶Li,αp). The last two reaction mechanisms explain the previously measured large contributions to theα-channel relative to thed-channel.     

On the decay of compound nuclei following alpha-particle and12C induced reactions

Multiple coincidence rates have been measured using a detector system consisting of a Ge(Li) spectrometer and eight NaI(Tl) or eight liquid scintillators. Reactions induced byα-particles with energies of 51–55 MeV and 118 MeV¹²C ions are studied. The data are analysed to give the first and second central moments of the distribution of the number ofγ-rays feeding individual levels in the final nuclei. When these numbers are compared to spin distributions calculated with the statistical model code GROGI the relative importance of dipole and quadrupole deexcitation modes can be ascertained. In particular, in the¹²²Te(α, 4n)¹²²Xe reaction theγ-decay prior to the entry into the ground band is well described as a statistical process proceeding to 50% by dipole and 50% by quadrupole radiation. In the¹⁶⁶Er(α,4n)¹⁶⁶Yb and¹⁹²Os(α,4n)¹⁹²Pt reactions the relative amount of quadrupole radiation is larger and it seems that the dipole and quadrupole decay takes place via separate cascades. In the¹⁶⁴Dy(¹²C, 7-8n) reactions the average multiplicity is independent of spin, suggesting that the nucleus forgets the spin of the entry state before the process enters into the ground band. In the¹⁷⁶Yb(¹²C, 8n)¹⁸⁰Os reaction, finally, the nucleus definitely retains memory of the entry state during the decay. In this last case the multiplicity measurement is combined with aγ-ray singles measurement to give an average excitation energy prior to theα-decay and the average moment of inertia characterising the decay of the high-spin states.     

Konversionskoeffizienten und Fluoreszenzausbeuten beim Zerfall des Ir192m und Co58m

With a proportionalcounter and an anthracene-crystal-spectrometer theL-X-ray- and the conversion-electron-spectra of \(Ir^{192_{m_1 } } \) were measured. TheL-fluorescenceyield of iridium was found to beω _L=0.30±0.04. The partial fluorescence-yields of theL ₂- andL ₃-subshells could be determined:ω _L2 =0.35±0.14 andω _L3 =0.29±0.04. The conversion-coefficients for the isomeric transition of \(Ir^{192_{m_1 } } \) were also measured:α _L =1660±250 andα _L +α _M =2030±230. The spectra of the conversion-electrons of the 25 keV-isomeric transition of \(Co^{58_m } \) were measured with a methane-filled proportionalcounter, and theγ- and X-rays with a Nal-scintillation-spectrometer. The conversion-coefficients for this transition and theK-fluorescence-yield of cobalt were found to beα _K =2000±260,α _L+M =890±150,K/(L+M)=2.25±0.15,α _K =0.34±0.02.     

Ground state bands in142Gd and140Sm

The ground state bands of theN=78 isotones¹⁴² Gd and¹⁴⁰Sm were observed up to the 8⁺ state by bombarding¹⁴⁴Sm and¹⁴²Nd withα-particles of energies between 80 and 130 MeV. Excitation functions,γ-γ coincidences, lifetimes and angular distributions were measured. The ground state band in¹⁴⁰Sm is partially fed by an isomeric state ofT _1/2?17ns. No such isomerism is observed for¹⁴²Gd. The level energies are very similar in both cases and agree well with the predictions of the VMI model.