States In 24Mg Research Articles

Investigation of quasimolecular states in 24Mg* through the analysis of the angular dα correlations in the 12C(14N, d)24Mg(α)20Ne reaction

Theoretical analysis of the differential cross sections and angular correlation functions in the 12C(14N, d)24Mg*(α)20Ne reaction at the energy of the incident nitrogen ions E lab=29–42 MeV is performed in the models of the direct transfer of 12C cluster and the compound nucleus. Amplitudes of the reduced widths for the excited quasimolecular states like 12C ⊗ 12C* in the 24Mg nucleus are obtained. The effect of various states of the relative motion of nuclei in the 12C + 12C* configuration on the angular dα-correlation functions is studied.

16O-8Be break-up states and cluster structure of 24Mg

High-spin states of 24Mg produced in the 16O + 12C interaction and decaying into the 16Og.s. + 8Beg.s. channel have been observed in the excitation region between 35 and 52 MeV. Spins have been assigned on the basis of the analysis of the measured angular correlations. Some of these states with positive parity correspond to the known resonances of the 12C( 12C, 8Beg.s.) 16O reaction belonging to the 16O-2α rotational band of 24Mg. Moreover other resonances show up at higher excitation energy with an energy-spin relationship again suggesting a 16O-2α cluster structure for the associated configuration.

The 12C( 16O, 12C 12C) α reaction at Ebeam=75 MeV

The 12C( 16O, 12C 12C) α reaction has been measured at E beam=75 MeV, for 24Mg emission from 0 to 180 degrees. This energy coincides with an enhancement observed in earlier measurements of the 12C+ 16O system. The properties of the angular correlations of the reaction products are found to be consistent with a resonance in 28Si at E x=48.9 MeV, with spin J=17±1. The decay properties of the states in 24Mg, populated following α-decay of the resonance, suggest that the state in 28Si possesses a triaxial structure linked to a ( sd) 8( fp) 4 configuration.

Measurement and analysis of quadruple ( αγγ) angular correlations for high spin states of 24Mg

Measurement and analysis of quadruple ( αγγ) angular correlations for high spin states of 24Mg

Identification of the Iπ = 10+ yrast rotational state in 24Mg

Identification of the Iπ = 10+ yrast rotational state in 24Mg

Target dependence in the resonant12C+12Cbreakup of excited states in24Mg

Target dependence in the resonant<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow /><mml:mrow><mml:mn>12</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">C</mml:mi><mml:mrow><mml:msup><mml:mrow><mml:mo>+</mml:mo></mml:mrow><mml:mrow><mml:mn>12</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">C</mml:mi></mml:math>breakup of excited states in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow /><mml:mrow><mml:mn>24</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Mg</mml:mi></mml:math>

Search for electromagnetic transitions between12C-12C cluster states in24Mg

The superdeformed states in heavy nuclei withA≳60 are characterized by their gamma decay pattern. In light nuclei, this signature is still missing especially for the cluster states formed in light heavy-ion reactions. The aim of the present experiment was thus to search for γ-ray transitions between 10+ and 8+ resonant states formed in the12C +12C reaction. A bombarding energy ofElab = 32.9 MeV has been chosen to populate a known and isolated 10+ resonance. The experiment has been carried out in a triple coincident mode (fragment-fragment-g) with the outgoing binary fragments detected in two position-sensitive Si detectors and the γ rays in the 4π array Château de Cristal. A few events have been observed which we attributed to the γ-ray transitions we searched for. This would be the first time that such transitions have been seen and, under certain assumptions, a radiative partial width of (1.2 ± 0.4) 3 1025 has been deduced for the 10+ resonant state.

Resonances in the12C(12C,8Beg.s.)16O reaction and rotational states in24Mg

The results of a set of experiments on the12C+12 C →8 Beg.s. +16 O excitation function between 20 and 36 MeV cm. beam energy are summarized and discussed. A set of 1 MeV wide resonances shows up in the energy range investigated, all of them following the rotational rule with a coefficient of inertia consistent with a α -16O - α configuration.

Reaction mechanism for the symmetric breakup of 24Mg following an interaction with 12C

Data on the yield of the symmetric breakup of 24Mg as a function of beam energy are presented and compared with detailed calculations of the energy dependence. The 24Mg states seen in symmetric breakup agree with previously observed breakup states having spin and parities J π = 4 +,(6 +),8 +. The data allow the variations of yield for individual states to be judged, as the beam energy is varied. The variation in the yield of the 4 + states is compared in detail with calculations assuming several possible compound nuclear or direct reaction mechanisms. It is concluded that a massive ( 12C) transfer or a simple statistical compound process are unlikely mechanisms, but that each of several other mechanisms is consistent with the data.

Calculations of particle decay widths of hyper-deformed nuclei using prolate spheroidal coordinates

We address the problem of calculating the particle decay widths from hyper-deformed nuclei. To simplify the calculation we treat the deformed nucleus as a prolate spheroid, and the particle-nucleus interaction as sharp-edged. This enables us to describe the deformed nuclear shape as an equipotential surface in a prolate spheroidal coordinate system. We model the particle-nucleus interaction by means of a spheroidal “square well” potential. Next we make the adiabatic approximation. This enables us to consider the deformed nucleus as being fixed in space. We then solve a system of coupled Schrödinger equations which describe the scattering of the particle from the deformed nucleus. These partial differential equations are separable in our chosen coordinate system. We generate prolate spheroidal wave functions to describe the particle both inside and outside the nuclear volume using a matrix diagonalization technique. The scattering problem is then solved by matching appropriate linear combinations of internal and external wave functions, and their first derivatives, at the nuclear boundary and searching for resonances as the Q-value for particle emission is varied. Using this formalism we calculate the alpha-decay widths of the recently discovered α-chain state in 24Mg and of the proposed 16O+ 16O+ 16O configuration in 48Cr.

Resonances in 24Mg revealed in the 12C(20Ne,12C12C)8Be reaction

A study has been made of the 12C(20Ne, 12C12C)8Be reaction. The reaction is found to proceed via sequential breakup of states in 24Mg probably excited by alpha transfer onto the 20Ne projectile. The breakup occurs from a series of discrete narrow states at high excitation in 24Mg which appear to correlate with those previously observed in the 12C(24Mg,12C12C)12C reaction.

Geometry and collectivity in the Bloch-Brink α-cluster model

We investigate α-cluster geometries and collectivity in the Bloch-Brink α-cluster model. We find in many cases that the geometrical arrangements of the α-clusters can be derived from relaxed atomic and metallic “cluster” structures. The α-cluster model has a large number of collective degrees of freedom related to this geometrical structure. The most important are quadrupole and octupole deformations and we explain how these arise naturally in the model. Three other collective degrees of freedom are those associated with rotations in the three dimensional internal space defined by Buck et al. and Morinigo. Such rotations enable us to discuss mixing between different α-cluster configurations in a compact and elegant way. We speculate on the relevance of mixing to the excitation of the 6α-chain state in 24Mg.

Systematics of 2-dimensional α-cluster configurations in 4 N nuclei from 12C to 44Ti

The recent discovery of the six-alpha chain state in 24Mg suggests that alpha-cluster configurations may extend to much higher excitation energies and have much larger deformations than has previously been believed possible. The systematics of alpha chain states (one-dimensional alpha-cluster states) have recently been published. Here we present systematics of a second class of highly deformed alpha-cluster states which arise from two-dimensional configurations.

The solution of the nonlinear static Hartree-Fock eigenvalue equations by means of the Lanczos algorithm

In order to avoid large diagonalizations seemingly implied in the solution of the Hartree-Fock equations, an algorithm based on the Lanczos method has been developed to sequentially determine the single-particle eigenstates. This algorithm is computationally more cost effective than the traditional diagonalization technique, since it approximates only the occupied single-particle orbitals and requires only small matrix diagonalizations. The present algorithm is compared with the imaginary time step method for a numerical calculation of the ground state of24Mg and is found to be more rapidly convergent with considerable saving in the computational work required.

Spin measurement for symmetric fission states of 24Mg. A new angle on the 12C + 12C interaction

A new high resolution measurement of the 12C( 24Mg, 12C 12C) 12C breakup reaction has been performed. Sequential breakup is observed from specific states in 24Mg at excitation energies ranging from 20 to 26 MeV. Angular correlation measurements indicate that states with spins ranging from J=4 to 8 are populated. These states are consistent with superdeformed shape isomeric bands predicted by cranked cluster model and Nilsson-Strutinsky calculations.

States of 25Al between 6 and 8 MeV

Polarized protons were scattered from 24Mg in 20 keV steps at laboratory energies between 4 and 6 MeV, corresponding to excitation energies in 25Al between 6 and 8 MeV. Cross sections and analyzing powers were measured at 14 angles for elastic scattering and for inelastic scattering to the first excited state in 24Mg. A phase-shift analysis was done for the elastic scattering data. The energy dependences of the extracted phase shifts were used to determine excitation energies, spins, parities and widths of levels of 25Al.

EXPERIMENTAL VERIFICATION OF THE 11.528MeV STATE IN 24Mg

This work gives the experimental verification about the existence of the 11.528 MeV state in 24Mg which was newly discovered with the recoil-coincident technique in HI reaction. Resonant γ-ray absorption method has been used. Several dips have been observed in the resonance absorption transmission curve and recognized to be the fine structure around the 11.528 MeV excited energy level. The excitation energy and level width were deduced for each sub-level and the total width of energy level 13.321 MeV in emitting nucleus 28Si was also obtained from data fitting procedures.

Measurements of Γ γ/Γ for states of 24Mg in the excitation region 10< Ex< 12MeV

Measurements of Γ γ/Γ have been carried out for about 40 states of 24Mg in the excitation region 10 to 12 MeV using a recoil-coincidence technique. The information obtained has been combined with known values of ωγ to determine Γ γ, and Γ α. Widths of the order of 0.01 to 100 eV can be determined accurately using this method. Some previous data on levels in this excitation region are discussed. Excitation energies and electromagnetic transition rates are compared with theoretical predictions. Two notable conclusions are the observation of a considerable excess in E2 strength in the 10 to 12 MeV region compared with that predicted by the shell model, and the identification of the 4 + 11.219 MeV level as possibly being a member of a collective band based on the 0 +, 6.432 MeV level.

Excitation of Jπ=2 + resonances in 24Mg by the 23Na(p, 12C) 12C reaction

Angular distributions of the 23Na(p, 12C g.s.) 12C g.s. reaction were measured at energies on top of resonance-like structures or close to them in the range E p=8−18 MeV and were analysed using parametrized S-matrix elements. Partial cross sections proceeding through compound nuclear states of 24Mg with various spin J were derived. In was found that the resulting cross sections for J=2 exhibit correlated structures with the “fissioning resonances” recently observed by the 12C( 12C, λ 0) and 24Mg(α, α') 12C g.s + 12C g.s. reactions.

Cluster structure in the highly-excited states of 24Mg

We propose a μ-truncation method for the multi-cluster orthogonality condition model (OCM) to reduce the large number of basis states. The cluster structures in the highly-excited states of 24Mg are discussed on the basis of solutions obtained by the 16O+2α OCM.