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5. Recent HRIBF Research - Measurement of Levels in the Halo Nucleus 11Be via 10Be(d,p) in Inverse Kinematics
[K. Schmitt & K.L. Jones (Univ. of Tennessee), spokespersons]

Phenomena such as neutron halos and level inversion make the light neutron-rich nuclei fascinating test cases to study the evolution of nuclear structure away from stability. 11Be is an archetypal example of both of these effects, and is one of the heaviest nuclei for which ab-initio theory is presently practical. Although 11Be has been studied thoroughly via (d,p) in normal kinematics [1], β-decay[2], breakup[3,4], and (p,d)[5] experiments, there still remains a paucity of knowledge about the bound first-excited state, for which spectroscopic factors are disputed, and the resonances.

We have performed a 10Be(d,p)11Be experiment in inverse kinematics using a new batch-mode 10Be beam at the energies of 60 and 107 MeV and deuterated polyethylene targets. The angular distribution of protons ejected in the population of bound states and low-lying resonances in 11Be will be used to extract spectroscopic factors for those states. The Oak Ridge Rutgers University Barrel Array (ORRUBA) was used in conjunction with the Silicon Detector Array (SIDAR) for a large solid angle coverage and nearly continuous coverage in polar angle from 45 to 165 in the laboratory reference frame. The new QQQ array and Dual MCP detectors were placed at forward angles to detect recoils and to help discriminate between (d,p) and fusion-evaporation events. A schematic view of the silicon detector setup is shown in Fig. 5-1. The angular coverage is shown with expected angular distributions in Fig. 5-2.

Figure 5-1: Silicon detector setup. The ORRUBA and SIDAR arrays were used for detection of protons from (d,p) and elastically scattered deuterons.

Figure 5-2: Angular coverage with expected angular distribution. Coverage in polar angle was nearly continuous from 45 to 165 degrees in the lab frame, with only a small gap due to target frame shadowing.

Preliminary analysis of the proton data in SIDAR yields excellent statistics for the bound states and first resonance, as shown in an ungated spectrum in Fig.5-3. The first excited state at 320 keV is clearly separated from the ground state (two groups to the right of the figure). Other low-lying resonances have been observed in our preliminary analysis of the proton energy spectra from SIDAR.

On completion of calibrations both for SIDAR and ORRUBA, the full data analysis is expected to yield angular distributions with very low statistical uncertainties.

Figure 5-3: Energy distribution of protons at back angles. Protons from the population of the ground state and 0.320 MeV first-excited state are well resolved, and tremendous statistics were recorded for the wider first resonance.

Special thanks are due to the staff at HRIBF for a very successful run, especially Dan Stracener.

References:

[1] D.L. Auton, Nucl. Phys. A 157, 305-322 (1970).
[2] D.E. Alburger and D.H. Wilkinson, Phys. Rev. C 3, 1492 (1971).
[3] B. Zwieglinski, et al. Nucl. Phys. A 315, 124-132 (1979).
[4] V. Lima, et al. Nucl. Phys. A 795, 1-18 (2007).
[5] S. Fortier, et al. Phys. Lett. B 461, 22 (1999).




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