Search

A study of the 12 C( 24 Mg, 12 C 12 C) 12 C reaction has revealed discrete states at excitation energies between 20 and 30 MeV in 24 Mg. Angular correlation analyses of some of the lower energy states confirms the report by earlier authors of monotonically increasing spin values consistent with a rotational sequence. Comparison with breakup observed in the 12 C( 20 Ne, 12 C 12 C) 8 Be reaction suggests that the same states in 24 Mg are populated, while the difference in laboratory cross sections in the two reactions is interpreted as evidence for the association of the breakup states with a prolate hyper-deformed configuration appearing in theoretical calculations for 24 Mg.

The breakup of {sup 23}Na nuclei into {sup 11}B+{sup 12}C and of {sup 24}Mg nuclei into {sup 12}C+{sup 12}C has been studied using the reactions {sup 12}C({sup 23}Na,{sup 11}B{sup 12}C){sup 12}C and {sup 12}C({sup 23}Na,{sup 12}C{sup 12}C){sup 11}B. Clear evidence was found for the breakup of the {sup 23}Na and {sup 24}Mg nuclei into the ground states of both fragments. The yieldrotect from the {sup 12}C({sup 23}Na,{sup 11}B{sub g.s.}{sup 12}C{sub g.s.}){sup 12}C{sub g.s.} reaction was concentrated in the region of excitationrotect energy in {sup 23}Na between 24 and 28 MeV and fragmented among a number of states. Therotect {sup 12}C({sup 23}Na,{sup 12}C{sub g.s.} {sup 12}C{sub g.s.)}{sup 11}B{sub g.s.} reaction was found to proceed chiefly via broad states at 22.1 and 23.9 MeV in {sup 24}Mg.

Some experimental techniques used in the measurement and analysis of inverse kinematic reactions are described and applied to a kinematically complete

In several recent measurements the symmetric fission of 24 Mg has been reported. In this paper the results of a search for similar processes in 28 Si and 32 S are presented. In contrast to the results for 24 Mg, no evidence is seen for the fission of 28 Si to 16 O+ 12 C or 32 S to 16 O+ 16 O following inelastic excitation. However, these processes are observed to occur following pickup onto 24 Mg. The results are consistent with a simple model of the fission process developed by Harvey and suggest the existence of large scale cluster structure in all three nuclei.

A new high resolution measurement of the 12 C( 24 Mg, 12 C 12 C) 12 C breakup reaction has been performed. Sequential breakup is observed from specific states in 24 Mg 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.

A search has been performed for large cluster breakup from 40Ca following inelastic scattering. No evidence is seen for breakup to the 12C+28Si, 16O+24Mg or 20Ne+20Ne channels.

Small area chemically-milled parallel-grid avalanche counters (PGAC) with isobutane counter gas and thin entrance and exit windows, have been developed as transmission timing detectors for use in heavy-ion experiments. The performance of the counters has been investigated with α particles and elastically scattered 35Cl ions. To optimize the PGAC capabilities it is best to operate at pressures greater than 14 Torr where good timing and efficiency are available well below the breakdown threshold. A system timing resolution, using a silicon surface barrier stop detector, of 360 ps was achieved.

We report the operation and performance of a compact, high-efficiency 8Be detector designed for use in breakup reaction studies. It offers a number of advantages over previous detectors in allowing accurate kinematical identification of 8Be excited states and scattering angle as well as allowing large solid angle coverage.

The breakup of {sup 25}Mg has been studied using a beam of 180 MeV {sup 25}Mg with a {sup 12}C target. The main reaction channels investigated are the near-symmetric breakup into {sup 12}C+{sup 13}C and symmetric breakup into {sup 12}C+{sup 12}C following neutron transfer to the target. The symmetric breakup into two {sup 12}C nuclei is observed to occur from states at high excitation in {sup 24}Mg. The yield is, however, about two orders of magnitude smaller than that observed in a similar experiment using a {sup 24}Mg beam.

Mass, energy, charge and angular distributions from fully damped reactions of the 40 Ca + 40 Ca system have been measured at 197 and 231 MeV, in both singles and coincidence. The data display features of compound nucleus fission. Comparison with similar, but asymmetric systems, however, shows an entrance-channel dependence which invalidates a fusion-fission description. A discussion in terms of fission barriers calculated using the finite-range liquid drop model suggests a fast-fission mechanism. Re-analyses of systems studied in the literature are presented in terms of the finite-range liquid drop model, indicating fast fission — a process previously assumed only to be relevant for heavier systems — to be significant in most cases. Furthermore, using the finite-range liquid drop model, we find that the systematic behaviour of the mass distributions from systems where complete fusion-fission is expected to be dominant is well described in terms of the revised locus of the Businaro-Gallone transition from symmetric to asymmetric fission.

The use of online Hypertexts, like "Les Chants de Maldoror" (Lautréamont), is a mean for literary research, of course, but also a mean for thinking and creating exercices for Learning of French as a second Language. Some examples in this paper may help to concieve the interest of these possibilities. The exercices we give as examples, with morpho-syntaxic or semantic purpose, are depending on the needs of the students and on their reactivity in the use of computers. Please Note : This paper contains some dynamic links, mainly to the Lautréamont hypertext.

The α-transfer reaction 12C(16O, 20Ne∗)8Be has been studied at a bombarding energy of 150 MeV in a search for high-spin α-cluster resonances in 20Ne. Angular correlations were measured for states in 20Ne which α-decay to the ground state of 16O. A broad 10+ resonance was located at E x ( 20 Ne )∼27.5 MeV , but no definite evidence was found for any 10+ strength at lower excitation energy.

Fundamental constructive theorems on the existence and uniqueness of the solution to the nonlinear Boltzmann transport equation for the isotropic field free case are utilised to set up a numerical solution process of controlled accuracy based on a functional iteration process arising directly from the theorems. It is demonstrated how a tabulation scheme describes the evolution of any reasonable initial distribution in velocity, space and time. Extensions are indicated for the particular problem of non-linear sputtering effects.

States with excitation energy > 15 MeV populated in the reaction 12C(16O, αγ)24Mg have been studied using a total energy γ-ray spectrometer for E lab ( 16 O ) between 40 and 67 MeV. A previously unknown state has been identified at 16.904 ± 0.003 MeV with Γγ/Γ=0.13±0.02, mean lifetime

A simple kinematic coincidence technique is described for separating γ-decaying states from particle decaying states populated in two-body reactions. The method is especially suited to the discovery and further study of γ-decaying states at high excitation energies in light nuclei, but has not previously been widely exploited. Experimental applications using the reactions 12 C( 16 O, α) 24 Mg and 12 C( 6 Li, d) 16 O are presented and these illustrate the range of results obtainable. In particular, the method provides an excellent means of measuring the probability for γ-decay, Γ γ /Γ, of individual excited states. The general properties of reactions suitable for use with the coincidence technique are discussed.

We have observed a gross structure resonance in the reaction 12 C( 12 C, 8 Be) 16 O leading to the 11.09 MeV 4 + state in 16 O at E cm =25 MeV. Using a triple coincidence technique we suggest J π =16 + for this resonance in agreement with other work. We interpret these results in terms of recent theoretical calculations for 24 Mg.

High spin states in 80 Sr have been studied using the techniques of in-beam γ-ray spectroscpy. The ground state band has been investigated up to (26 + ) and three new side-bands have been discovered. The deduced level scheme is compared with cranking model calculations; the predicted transformation to mostly non-collective excitations of an oblate shape is not observed. The behaviour of the J (1) and J (2) moments of inertia is discussed and presented as evidence for γ-softness in the light Sr isotopes.

16O+8Be breakup of 24Mg has been identified following inelastic scattering of 24Mg projectiles. The spectrum of states observed is compared to that previously measured in the 12C+12C breakup channel to obtain information on the partial decay widths.

The α-decay of states in 19F has been studied in the sequential breakup reaction 12 C ( 19 F , 19 F ∗ → 15 N α) at laboratory energies of 82 and 144 MeV. Double differential cross sections have been obtained for 20 excited states in 19F. The correlations show a systematic dependence on the reaction angle θ c.m. ∗ which allows the transferred angular momentum to be deduced. Using this result we present evidence for two new states (J π = 5 2 − or 7 2 − ) at excitation energies of 7740 keV and 8277 keV and two parity assignments for states at 7245 keV ( 3 2 + ) and 9287 keV ( 7 2 + , 9 2 + ) . Comparisons with shell model calculations suggest the two new states probably have J π = 5 2 − and 7 2 − respectively. The double differential cross sections have been analysed with a strong absorption model which allows extraction of qualitative information on the reaction mechanism.

Symmetric fission into two 12 C nuclei has been observed from states at high excitation energy in 24 Mg excited in inelastic scattering. Fission to the 10 B+ 4 N channel has also been observed and indirect evidence for the 16 O+ 8 Be channel noted. The same experiment also reveals fission into 16 O+ 12 C from states in 28 Si populated by alpha-particle pickup onto the 24 Mg projectile. The correlation of the states in 24 Mg observed in this experiment with those previously observed in 12 C+ 12 C scattering is discussed.

The results of a study of neutron transfer reactions at energies below the Coulomb barrier using a recoil separator are reported. Excitation functions for single-neutron pick-up at an angle of 180° in the center-of-mass have been measured for the systems 58 Ni+ 116,118,120,122,124 Sn over an energy range of 40 MeV from near to well below the Coulomb barrier. The data are well described in terms of both DWBA and semi-classical models of the transfer process. The relevance of the direct nucleon transfer cross sections to the sub-barrier fusion of these systems is discussed.