The inclusive breakup for the 11 Li þ 208 Pb reaction at energies around the Coulomb barrier has been measured for the first time. A sizable yield of 9 Li following the 11 Li dissociation has been observed, even at energies well below the Coulomb barrier. Using the first-order semiclassical perturbation theory of Coulomb excitation it is shown that the breakup probability data measured at small angles can be used to extract effective breakup energy as well as the slope of BðE1Þ distribution close to the threshold. Fourbody continuum-discretized coupled-channels calculations, including both nuclear and Coulomb couplings between the target and projectile to all orders, reproduce the measured inclusive breakup cross sections and support the presence of a dipole resonance in the 11 Li continuum at low excitation energy.

The elastic-scattering, neutron transfer and projectile break-up channels have been studied for the reaction 6 He + 64 Zn at energies around the Coulomb barrier. The results show a very large break-up and transfer cross-section corresponding to the largest fraction of the total reaction cross-section. No evidence of threshold anomaly emerged from the elasticscattering optical-model analysis.

No abstract

We have extended the experiment reported in Bradfield-Smith et al. ͓Phys. Rev. C 59, 3402 ͑1999͔͒ concerning the 18 Ne(␣,p) 21 Na reaction, which is of importance to nuclear astrophysics. This study covered an energy region ϳ1.7-2.9 MeV in the center of mass frame of the 18 Neϩ␣ system. A change in the detector geometry resulted in an increase in the detection efficiency and significantly reduced the proton background that hindered the previous measurement. A direct measurement of the energy loss of the 18 Ne beam, as it passed through He gas, was undertaken to reduce a major source of uncertainty in the determination of the stellar reaction rate. Eight states have been identified in the compound nucleus, 22 Mg. These resonances were used to calculate an enhanced stellar reaction rate which shows good agreement with theoretical predictions ͓Görres, Wiescher, and Thielemann, Phys. Rev. C 51, 392 ͑1995͔͒ at and above a temperature of 1.5 GK. The impact of this enhanced stellar reaction rate upon the nucleosynthesis that occurs during the peak phase of an x-ray burst has been investigated.

Yields of neutron-rich projectile fragments have been measured at 0° for the reaction of 212-MeV/amu 48 Ca ions on an 890-mg-cnT 2 beryllium target. Fourteen nuclides have been observed for the first time. The systematics of production cross sections are discussed.The limits of stability for nuclei have been established up to sodium and beryllium for protonrich and neutron-rich nuclides, respectively. Recently, the techniques of relativistic heavy-ion fragmentation, 1 deeply inelastic scattering, 2 and spallation induced by high-energy protons 3 have been used to produce neutron-rich nuclei near the limit of particle stability. In this Letter, we present the first experimental evidence for the particle stability of fourteen nuclides, 22 N, 26 F, 33,34 Mg> 36,37 A1> 38,39^ 41,42 p> 43,44^ and 44,45 Cl, produced in the fragmentation of 212-MeV/amu 48 Ca. In addition, the recent observation 2 of 37 Si, 40 P, and 41 ' 42 s is confirmed. Predictions for the masses of neutron-rich light nuclei have been made based on several methods, including iterative techniques such as the modified GarveyKelson relations, 4,5 the liquid-droplet model, 6,7 and large-basis shell-model calculations. 8 The energy levels of such nuclei have also been predicted using the same shell-model calculations. 8 ' 9 From the present experiment it appears that the production cross sections for very neutron-rich light nuclei may be quite sensitive to their detailed nuclear structure.The experimental arrangement used for the present work was similar to that described in Ref. 1. The fragments, which emerge from the reaction at nearly the beam velocity, were detected in a zero-degree magnetic spectrometer with an acceptance of 0.94 msr. A detector telescope consisting of twelve Si(Li) detectors, two position-sensitive Si(Li) detectors (PSD), and a veto scintillator was placed in the focal plane of the spectrometer. Each of the twelve Si(Li) detectors was 5 mm thick and 5 cm in diameter while the PSD's were 500 /xm thick and 6 cm in diameter. The PSD's were arranged to measure horizontal and vertical position with a resolution of ~ 1 mm. The beam current of 48 Ca ions from the Bevalac was ~10 7 particles/sec and was monitored directly with plastic scintillators, an ion chamber, and a scintillator telescope that monitored particles scattered from the target. The target consisted of 890 mg cm" 2 of beryllium and the beam lost approximately 35 MeV/amu passing through it.Combining the spectrometry with the energyloss measurements in the Si(Li) detectors made it possible to measure M and Z unambiguously as described in Ref. 1. The mass resolution obtained was 0.3 amu. The mass-and atomic-number scales were calibrated by use of the direct 48 Ca beam and also beams of 20 Ne and ^Ar of high energy that were progressively degraded to provide a continuous spectrum of 20 Ne and 40 Ar ions stopping in each detector. Since the detector thicknesses were precisely known, it was then possible to use a range-energy table to make an accurate channel-to-energy calibratio...

The direct breakup of 70-MeV 7 Li scattered from a l20 Sn target is investigated at forward angles. Inside the grazing angle, it is found that the breakup is dominated by the Coulomb interaction between projectile and target.PACS numbers: 25.70.NpThe study of the breakup of light-ion projectiles such as 6 Li and 7 Li is of special interest since the simple cluster nature of these nuclei considerably simplifies calculations concerning the breakup process. Thus using the a-t cluster description for 7 Li in an adiabatic calculation, Thompson and Nagarajan 1 concluded that the direct breakup of 70-MeV 7 Li into the a + t channel was mainly due to the differential nuclear force between the 208 Pb target and the projectile fragments. However, a subsequent study of inelastic scattering of 68-MeV 7 Li from 208 Pb, where a similar cluster-adiabatic calculation was used, showed that the Coulomb interaction becomes increasingly important for smaller angles. 2 This therefore raises the question as to the importance of the Coulomb interaction for projectile breakup at forward scattering angles. In this Letter we present new evidence that, at forward angles, the direct breakup of 70-MeV 7 Li on 120 Sn is primarily due to the Coloumb interaction between projectile and target.The experiment was undertaken by use of the 20-MV NSF tandem accelerator at Daresbury. Since we specifically wished to study small relative energies between the emitted a and t fragments, the two solid-state detector telescopes were placed in close vertical geometry. 3 The collimators were 10 mm x 8 mm and the vertical separation between their centers was 15 mm. The collimators were placed at 115 mm from the target, except at the most forward angle of 11.5°, where they were at 150 mm. The target was isotopically pure 120 Sn of 4 mg/cm 2 thickness.The energy spectra of a particles for events where the total energy of the coincident a and t particles corresponded to the target being left in its ground state are shown in Figs. Kb)-1(d). The spectra for the more backward angles are dominated by a pair of peaks associated with the kinematic solutions for the reaction 120 Sn( 7 Li, 7 Li4. 63 -• a + /) 120 Sn gs .. The center-of-mass (cm.) energy of the a-rpair, e r , for a given a energy, is shown on the top axis. 500 400 ^300 ^200 100 0 400 ^300 D O ^200 100 0 80 £60 D O ^40 20 0 20 £15 D O <-> 10 e (MeV)2. 16 2. 16 310 ITO 0129 f. 0 3T6 a) Monte-Carlo S i mu Lat i on 120c ,7. 7. * s 120c bn ( L i . Li, ,,->a + t) bn ' 4, 63 gs E, =70MeV lab 8 =22.0° ,, 120c 7 , 7 , * . 120c b) Sn (Li. LI -»ot + t) bn E, =70MeV 6, =22. 0° c)6lab=:15. 0° 20. 0 30. 0 40. 0 50. 0 E (MeV) 60.0 FIG. 1. (a) a-energy spectrum for sequential breakup of 7 Li using a Monte Carlo simulation, (b)-(d) Experimental a-energy spectra of the reaction 120 Sn( 7 Li, 7 Li* -a + r) 120 Sn g . s . at 22°, 15°, and 11.5°.

No abstract

No abstract