Dynamics of superheavy system in 86Kr + 208Pb reaction

The dynamics of the excited superheavy system with Z = 118 in the reaction ⁸⁶Kr + Pb at E _Kr = 600 MeV has been investigated. The mass and kinetic energy of binary fragments were measured by the time-of-flight method. Double differential distributions of neutrons and α particles were measured in coincidence with fragments. Neutron and α-particle probes were used for determination of the fragmentation time scale. Evidence of the neck fragmentation was obtained from analysis of double differential α spectra. Properties of the α-particle neck fragmentation component are close to those known from the ternary fission of actinide nuclei, but the multiplicity is much larger. The total kinetic energy distribution of fragments tagged by neutrons or α particles shifts towards lower energies. Fragment yields in the symmetric region increase substantially when fragments are tagged by α particles.     

Binary nuclear molecules of an α-particle and a heavier cluster

A simple nuclear molecule is used as a model to interpret the band structure observed in elastic α-scattering and α-transfer reactions in the sd-shell. As in spectra of halogen acid molecules the bands have even and odd spins and parities. Due to the broadening and fine structure of the rotational levels they are characterized as giant resonances. The big moment of inertia and the line broadening is discussed in terms of performed measurements of scattering and the (α,p) reaction. A fine structure of prominent peaks in the inelastic scattering crosssections hints at the existence of rotational states with an α-particle orbiting an excited core.     

Alpha-cluster states in <Superscript>18</Superscript>O

The excitation function of elastic α-particle scattering on ¹⁴C has been measured in the laboratory energy range 16.3–19.2 MeV using a backscattering technique with a thick target. These data were analyzed together with the old low-energy data of G.L. Morgan et al. in the framework of the R-matrix formalism. Spin-parity assignments were made for 32 states in ¹⁸O in the excitation range 9–20 MeV. The estimates of the widths of the states are also presented. The 0⁺ and 0^?α-cluster bands appeared to be well separated by 5.6 MeV (as in ¹⁶O and ²⁰Ne). We have not found a confirmation of existence of the negative-parity molecular states proposed by M. Gai et al. We observed an effect of a doubling of α-cluster levels in ¹⁸O similar to that found in ²²Ne.     

Resonance States and Alpha Condensation in 12C and 16O

Low density states near the 3α and 4α breakup thresholds in ¹²C and ¹⁶O, respectively, are discussed in terms of the α-particle condensation. Calculations are performed in Orthogonality Condition Model and Tohsaki–Horiuchi–Schuck–Röpke approaches. The ${0_2^+}$ state in ¹²C and the ${0_6^+}$ state in ¹⁶O are shown to have dilute density structures and give strong enhancement of the occupation of the S-state c.o.m. orbital of the α-particles. The possibility of the existence of α-particle condensed states in heavier nα nuclei is also discussed.     

Two-center molecular states in9B,9Be,10Be,and10B

The molecular states in the mass 9 and 10 nuclei, which consist of two α-particles plus one or two valence nucleons (protons or neutrons) are discussed. Arguments for the existence of two-center dimers as excited states in¹⁰Be and corresponding resonances (p+⁹Be) in¹⁰B are given. The latter states are observed as anomalous (non statistical) population in the final state interactions in thep+⁹Be channel in various heavy ion collisions. With the establishment of two-center states (dimers) based on the αα-potential and a localized binding via two nucleons in¹⁰Be, the existence of more extended structures (multimers) by adding (α2n) structures to¹⁰Be* is postulated. Generally clustering intoα-particles and nucleons in terms of molecular states is expected to occur at excitation energies close to the threshold for these substructures in analogy to the clustering rules of Ikeda forα-particle nuclei. Consequences to clustering properties of neutron rich nuclei are discussed.     

α + 12C scattering at 110 MeV: Has exotic 7.65 MeV Hoyle’s state signatures “alpha-condensate” structure?

We present new measurements of the α + ¹²C elastic and inelastic (to the states 4.44, 7.65, and 9.64 MeV) scattering at E _lab = 110 MeV in the wide angular range from ～10° to 175°, which enable us to examine the condensate and cluster properties of the low-lying excited states in ¹²C. We present the diffraction-radius analysis of our data together with a considerable amount of the existing data. The magnitudes of the diffraction radii for the ground and the first excited (4.44 MeV) states are found to be equal, whereas they appear to be enhanced by ～0.6 fm both for 7.65 and 9.64 MeV states. This result shows that the radius of the Hoyle’s 0 ₂ ⁺ , 7.65 MeV state in ¹²C is by a factor of ～1.2–1.3 larger than that of the ground state. It is demonstrated that the direct transfer mechanism of ⁸Be dominates at the largest angles in all four reactions reported here. The configuration corresponding to the transfer of ⁸Be in its ground state (I ^π = 0⁺) with L = 0 turns out to be the most important for the 7.65 MeV state of ¹²C. Evidence of existence of some features of α-condensed structure of the Hoyle’s 0 ₂ ⁺ state in ¹²C was obtained: its enhanced radius and large contribution of α-particle configuration with L = 0.     

Elastic α+28Si scattering — thick target measurements and results

Excitation functions for elasticα-particle scattering from a thick target have been measured. The formalism developed for elemental analysis has been adopted to calculate cross sections. Results fromα+²⁸Si elastic scattering,E _α=6.5?19 MeV, are presented. Spins have been deduced from angular distributions and are shown to form a rotational band with odd and even parities. This result is compared to an old GCM phase shift prediction taken from literature.     

Gas-Like Cluster States in Finite Nuclei

Gas-like α cluster states are investigated in ¹⁶O with the use of 4α OCM (orthogonality condition model) and GEM (Gauss expansion method). α-particle condensed state is found slightly above the 4α threshold as the ${0_6^+}$ state. The candidates of the ${\alpha + {^{12}{\rm C}(0_2^+)}}$ rotational states are also found at a few megaelectron volt above the condensate. The ${0_6^+}$ state is shown to have an analogue structure to the Hoyle state ${({^{12}{\rm C}}(0_2^+))}$ and its relation with the α+ Hoyle-like rotational states is also discussed.     

High energy proton-carbon scattering in the alpha-particle model

We investigate elastic and inelastic 0⁺–2⁺ high energy proton-¹²C scattering in the alpha-particle model. We use a rigid equilateral triangle nuclear wave function with a Gaussian dispersion function allowing theα-particles of the¹²C-nucleus to deviate from their most probable positions at the triangle vertices. Expressions for the differential scattering cross sections are deduced using Glauber multiple diffraction theory. Thus we need thep?α-particle scattering amplitude, which is calculated from a Gaussian nucleon-nucleon profile function. Numerical calculations show that the model reproduces the experimental results onp?α andp-¹²C scattering.     

Selective population of the lowest-lying negative parity states in23Na in the12C(12C,p)23Na reaction

The¹²C(¹²C,p)²³Na reaction was investigated in the vicinity of the Coulomb barrier. The lowest-lying negative parity states in²³Na were found to be preferentially populated at energies for which correlated resonances exist in the excitation functions of theα, p, n andγ exit channels of the¹²C+¹²C reaction. If these negative parity states are assumed to consist of ap _1/2 hole coupled to a²⁰Ne quartet state, this selectivity can be explained with the existence ofα-particle doorway states.     

Double-differential spectra of the secondary particles in the frame of pre-equilibrium model

An approach was developed to describe the double-differential spectra of secondary particles formed in heavy-ion reactions. Griffin model of nonequilibrium processes was used to account for the nonequilibrium stage of the compound system formation. Simulation of de-excitation of the compound system was carried out using the Monte-Carlo method. Analysis of the probability of neutron, proton, and α-particle emission was performed both in equilibrium, and in the pre-equilibrium stages of the process. Fission and γ-ray emission were also considered after equilibration. The analysis of the experimental data on the double-differential cross sections of p, α particles for the ¹⁶O + ¹¹⁶Sn reaction at the oxygen energy E = 130 and 250 MeV were performed.     

New outlook on the possible existence of superheavy elements in nature

A consistent interpretation is given to some previously unexplained phenomena seen in nature in terms of the recently discovered long-lived high-spin super-and hyperdeformed isomeric states. The Po halos seen in mica are interpreted as being due to the existence of such isomeric states in corresponding Po or nearby nuclei that eventually decay by γ or β decay to the ground states of ²¹⁰Po, ²¹⁴Po, and ²¹⁸Po nuclei. The low-energy 4.5-MeV α-particle group observed in several minerals is interpreted as being due to a very enhanced α transition from the third minimum of the potential-energy surface in a superheavy nucleus with atomic number Z=108 (Hs) and atomic mass number around 271 to the corresponding minimum in the daughter.     

Nuclear structure with the dinuclear model

The dinuclear system concept is applied to the explanation of the structure of nuclei. The appearance of a low-lying band with negative parity states near the ground-state band in actinides and other nuclei is described by oscillations of the dinuclear system in the mass-asymmetry coordinate. The results for the parity splitting and electric multipole moments in alternating parity bands of these nuclei are in agreement with experimental data. The ground-state band and the superdeformed band of ⁶⁰Zn are interpreted as being caused by α-particle and Be clusterizations, respectively. Hyperdeformed nuclei are assumed as dinuclear systems which could directly be built up in heavy-ion collisions. Signatures of hyperdeformed states in such reactions could be γ transitions between these states and their decay into the nuclei forming the hyperdeformed nucleus.     

Three-alpha force and the 3-α model of12C

We postulate a Gaussian three-body potential amongα particles and adjust its parameters so that, when it is added to the Ali-Bodmerα-α potential, a good fit to experimental energies of low-lying 0⁺ and 2⁺ states of¹²C is achieved. With these potentials we made a linear variational calculation in a basis of harmonic oscillator functions which are translationally invariant, completely symmetric, and have a definite orbital angular momentum. We study the influence of this three-body potential on elastic and inelastic form factors, transition widths, Coulomb energy and charge radius of the 3-α system. The 3-α potential improved results found with the Ali-Bodmer potential alone. We find the 0 ₂ ⁺ state to be a (non-rigid) linear chain and the ground state to be a triangle ofα particles.     

Evidence for boson-mode excitations in the16O(α,n) and20Ne(α,n) excitation functions

Excitation functions for¹⁶O(α,n) and²⁰Ne(α,n) have been measured from threshold to 26 and 31 MeV compound excitation energy, respectively. The dominating compound states are interpreted as boson excitation modes of nuclei with α-particle structure.     

A study of the (α, t) reaction on 19F, 27Al, 51V and 59Co

The angular distributions of tritons from the (α, t) reaction on ¹⁹F, ²⁷Al, ⁵¹V and ⁵⁹Co nuclei corresponding to the (0⁺) ground states and (2⁺) excited states in the final nuclei have been measured in the angular range between 15° and 170° at α-particle energies of 25 MeV. For reactions on ²⁷Al and ⁵¹V nuclei, the differential excitation functions have also been obtained at different angles of outgoing tritons at E_α from 20 to 25 MeV. The experimental angular distributions are analysed by the DWBA approximation on the assumption of a nucleon stripping mechanism. The analyses of the present results and the data obtained earlier for the (α, t) reaction on the 1 p shell nuclei, A ? 30, reveal that the distinguishing feature of the reaction under study is the presence of backward angle peaks in the reaction cross section, which appear to be associated with exchange processes. For the (α, t) reaction on the heavier nuclei (A > 30), the dominant mechanism is nucleon stripping.     

Elastic scattering and fusion cross-sections in 7Li + 27Al reaction

With an aim to understand the effects of breakup and transfer channels on elastic scattering and fusion cross-sections in the ⁷Li + ²⁷Al reaction, simultaneous measurement of elastic scattering angular distributions and fusion cross-sections have been carried out at various energies (E _lab?=?8.0–16.0 MeV) around the Coulomb barrier. Optical model (OM) analysis of the elastic scattering data does not show any threshold anomaly or breakup threshold anomaly behaviour in the energy dependence of the real and imaginary parts of the OM potential. Fusion cross-section at each bombarding energy is extracted from the measured α-particle evaporation energy spectra at backward angles by comparing with the statistical model prediction. Results on fusion cross-sections from the present measurements along with data from the literature have been compared with the coupled-channels predictions. Detailed coupled-channels calculations have been carried out to study the effect of coupling of breakup, inelastic and transfer, channels on elastic scattering and fusion. The effect of 1n-stripping transfer coupling was found to be significant compared to that of the projectile breakup couplings in the present system.     

Spectroscopy of88Y homologous levels

The⁹¹Zr( $z\bar p$ ,α)⁸⁸Y reaction has been studied at incident energy of 22 MeV using a polarized proton source and a Q3D spectrometer. The differential cross sections and asymmetries for transitions to levels of⁸⁸Y homologous to the lowest excitation energy states of⁸⁷Y have been measured and interpreted both in terms of the experimental differential cross sections and asymmetries of the parent⁸⁷Y states and by means of the finite-range distorted wave Born approximation theory using conventional Woods-Saxonα-particle potential. The advantage of the concept of homology consists in having to deal with a uniquel-transfer, that given by the transition to the corresponding parent state. In order to validate the concept of homology as a spectroscopic tool to identify spin, parity and dominant configuration of highly excited states in ( $z\bar p$ ,α) reaction on odd mass target nuclei, shell model calculations have been performed. Several new attributions of spin and parity for⁸⁸Y residual nucleus are proposed.     

Neutron-emission mechanisms in the <Superscript>115</Superscript>In(<Emphasis Type="Italic">α, xn</Emphasis>) reactions

Spectra and angular distributions of neutrons from the ¹¹⁵In(α, xn) reactions were measured at α-particle energies of 16, 18, 27, and 45 MeV. The measurements were performed with time-of-flight neutron spectrometers at pulsed accelerators of charged particles. The data obtained in this way were analyzed within the models of equilibrium, preequilibrium, and direct reaction mechanisms. The exact formalism of Hauser-Feshbach statistical theory was used in the calculations, level densities in residual nuclei excited in the reactions under consideration being found from the neutron evaporation spectra in the (p, n) reactions on tin isotopes. Contributions from equilibrium, preequilibrium, and direct neutron emission were studied in a wide range of α-particle energies.     

Sequential processes in the14N(τ,pα)12C* reaction

α-particle and proton spectra in coincidence with the 4.44 MeVγ-ray from the¹²C first excited state have been taken atE _τ MeV. Several states in¹³N and¹⁶O are seen to contribute to the decay sequenceα?p andp?α respectively. Estimates are given for the branching of these two decay modes and for a possible simultaneous break-up.