S. M. Brown

Towards 26Na via (d,p) with SHARC and TIGRESS and a novel zero-degree detector

Nucleon transfer experiments have in recent years begun to be exploited in the study of nuclei far from stability, using radioactive beams in inverse kinematics. New techniques are still being developed in order to perform these experiments. The present experiment is designed to study the odd-odd nucleus 26Na which has a high density of states and therefore requires gamma-ray detection to distinguish between them. The experiment employed an intense beam of up to 3×107 pps of 25Na at 5.0 MeV/nucleon from the ISAC-II facility at triumf. The new silicon array SHARC was used for the first time and was coupled to the segmented clover gamma-ray array TIGRESS. A novel thin plastic scintillator detector was employed at zero degrees to identify and reject reactions occurring on the carbon component of the (CD)2 target. The efficiency of the background rejection using this detector is described with respect to the proton and gamma-ray spectra from the (d,p) reaction.

Search for the alpha + (6)He decay of (10)Be via the (16)O((18)O, (10)Be*)(24)Mg reaction

A search for the a + He decay of Be has been performed using the Li 2 O( 18 O , α 6 He) reaction at 80 and 100 MeV. An array of two Si-Si-CsI telescopes was used for the coincident detection of the breakup fragments. No evidence for the 16 O( 18 O,α 6 He) 24 Mg reaction was obtained, the cross-section being determined as a < 1.9 μb and <3.9 μb at 80 and 100 MeV, respectively. The α + 15 N decay of 19 F was observed via the 7 Li( 18 O,α 15 N) 6 He reaction. For the 19 F excitation energy and centre-of-mass scattering angle ranges covered, the cross-sections are a = (31.7 ± 6.6) μb at 80 MeV and (31.8 ± 6.6) μb at 100 MeV.

Search for the α + 6He decay of 10Be via the 16O(18O, 10Be*)24Mg reaction

A search for the a + He decay of Be has been performed using the Li 2 O( 18 O , α 6 He) reaction at 80 and 100 MeV. An array of two Si-Si-CsI telescopes was used for the coincident detection of the breakup fragments. No evidence for the 16 O( 18 O,α 6 He) 24 Mg reaction was obtained, the cross-section being determined as a < 1.9 μb and <3.9 μb at 80 and 100 MeV, respectively. The α + 15 N decay of 19 F was observed via the 7 Li( 18 O,α 15 N) 6 He reaction. For the 19 F excitation energy and centre-of-mass scattering angle ranges covered, the cross-sections are a = (31.7 ± 6.6) μb at 80 MeV and (31.8 ± 6.6) μb at 100 MeV.

STUDY OF THE 20O(d,t) REACTION WITH THE TIARA-MUST2-VAMOS-EXOGAM SETUP

The reaction 20O(d,t) has been studied in inverse kinematics using a secondary radioactive beam produced with the SPIRAL facility at GANIL. Fragments, light charged particles and gamma rays were measured with the TIARA, MUST2, VAMOS and EXOGAM detectors and preliminary results are reported. The level scheme of 19O is built and the spin and parity of one state is tentatively assigned using the one-neutron transfer angular distribution.

Shell evolution approaching the N=20 island of inversion: Structure of 26Na

The levels in 26Na with single particle character have been observed for the first time using the d(25Na, pγ ) reaction at 5 MeV/nucleon. The measured excitation energies and the deduced spectroscopic factors are in good overall agreement with (0+1)ħω shell model calculations performed in a complete spsdfp basis and incorporating a reduction in the N=20 gap. Notably, the 1p3/2 neutron configuration was found to play an enhanced role in the structure of the low-lying negative parity states in 26Na, compared to the isotone 28Al. Thus, the lowering of the 1p3/2 orbital relative to the 0f7/2 occurring in the neighbouring Z=10 and 12 nuclei – 25,27Ne and 27,29Mg – is seen also to occur at Z=11 and further strengthens the constraints on the modelling of the transition into the island of inversion.

Study of states in 14C via the 10Be(4He,4He)10Be reaction

A study of the 10Be(4He,4He)10Be reaction has been performed at 10Be beam energies of 25.0, 27.0, 29.0, 32.0, 34.0, 38.0, 40.0, 42.0, 44.0 and 46.0 MeV. The measurements were to explore possible molecular rotational bands in 14C. Three states at excitation energies of Ex = 18.8, 19.76 and 20.66 MeV have been measured and their spins have been determined to be 5−, 5− and 6+, respectively.

CLUSTER STATES IN 12C AND 14C

The cluster structure of 12C is explored and recent measurements of proton inelastic scattering, suggesting a 2+ state close to 9.6 MeV are presented. Resonant scattering studies of 10Be + 4He used to populate resonances in 14C are briefly discussed.

Cluster states in C-12 and C-14

The cluster structure of 12C is explored and recent measurements of proton inelastic scattering, suggesting a 2+ state close to 9.6 MeV are presented. Resonant scattering studies of 10Be + 4He used to populate resonances in 14C are briefly discussed.

Excited states of 8Be populated via the p(7Li, 4He)4He and p(7Li, 4He*)4He resonant reactions

A measurement of the p(7Li, 4He)4He resonant reaction on a thick mylar target was used to probe resonances in 8Be in the excitation energy range 20–25 MeV. The 7Li beams, of energies 25.8 and 58 MeV, were stopped in the target and the resulting α-particles were detected at zero degrees. Evidence was found for resonances at ~20 and ~25 MeV with Jπ = 0+ and 2+ character, respectively. A simultaneous measurement of the p(7Li, 4He* → p + t)4He reaction was performed, in which one of the two final-state α-particles was produced in the 20.2 MeV excited state. These events were observed to arise from an excitation energy region 23–25 MeV and have been associated with the decay of the 25.2 MeV 2+ 8Be resonance. The 25.2 MeV resonance is found to have a dominant 4He + 4He* reduced width.

Excited states of 8 Be populated via the p( 7 Li, 4 He) 4 He and p( 7 Li, 4 He * ) 4 He resonant reactions

A measurement of the p(7Li, 4He)4He resonant reaction on a thick mylar target was used to probe resonances in 8Be in the excitation energy range 20–25 MeV. The 7Li beams, of energies 25.8 and 58 MeV, were stopped in the target and the resulting α-particles were detected at zero degrees. Evidence was found for resonances at ~20 and ~25 MeV with Jπ = 0+ and 2+ character, respectively. A simultaneous measurement of the p(7Li, 4He* → p + t)4He reaction was performed, in which one of the two final-state α-particles was produced in the 20.2 MeV excited state. These events were observed to arise from an excitation energy region 23–25 MeV and have been associated with the decay of the 25.2 MeV 2+ 8Be resonance. The 25.2 MeV resonance is found to have a dominant 4He + 4He* reduced width.