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Phys. Rev. C 62, 064311 (2000) [10 pages]

Dissociation of 8He

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Y. Iwata * and K. Ieki
Department of Physics, Rikkyo University, 3 Nishi-Ikebukuro, Toshima, Tokyo 171-8501, Japan

A. Galonsky, J. J. Kruse †, J. Wang ‡, R. H. White-Stevens §, E. Tryggestad, and P. D. Zecher **
National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321

F. Deák, Á. Horváth, and Á. Kiss
Department of Atomic Physics, Eötvös Loránd University, Pázmány P. sétány 1/A, H-1117 Budapest, Hungary

Z. Seres
KFKI Research Institute for Particle and Nuclear Physics, Konkoly-Thege út 29-33, P.O. Box 49, H-1525 Budapest 114, Hungary

J. J. Kolata and J. von Schwarzenberg
Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556

R. E. Warner
Department of Physics, Oberlin College, Oberlin, Ohio 44074

H. Schelin
CEFET, Av. Sete de Setembro 3165 80230-901, Curitiba, Pr, Brazil

Received 16 June 2000; published 15 November 2000

We have performed kinematically complete measurements of dissociation of 8He into 6He and two neutrons at E/A=24 MeV. The targets were Sn and Pb. A prominent peak around 0.4 MeV in the relative energy distribution of the 6He+n system is consistent with the ground state of 7He, suggesting sequential decay via 7He in 8He dissociation. Further evidence of the sequential decay was found in neutron momentum distributions. The excitation energy distributions of 8He were reconstructed. For the Sn target, it shows a peak which is suggestive of the first excited state of 8He (Ex=3.6 MeV, Γ=0.5 MeV, and Jπ=2+). The distribution for the Pb target was found to have a broad structure, indicating the E1 continuum, as observed in measurements of other halo nuclei. The photonuclear cross section σE1(Ex) and the dipole strength function dB(E1)/dEd were deduced for the first time. The integrated dipole strength up to 3 MeV decay energy is 0.091±0.026 e2fm2. Insignificant energy-weighted strength, compared to the cluster sum rule, indicates that 8He does not have the 6He+2n structure. Agreement of the measured neutron momentum distributions with the COSMA model is in favor of the 4He+4n structure.


©2000 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevC.62.064311
DOI: 10.1103/PhysRevC.62.064311
PACS: 25.70.De, 21.10.Gv, 25.60.Gc, 27.20.+n

* Present address: National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan. Electronic address: y_iwata@nirs.go.jp
† Present address: Radiation Oncology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905.
‡ Present address: American Express Co., 3WFC, 4712B, 200 Vesey Street, New York, NY 10285.
§ Present address: Department of Physics, University of Notre Dame, Notre Dame, IN 46556.
** Present address: Investor Analytics LLC, 630 Fifth Avenue Suite 1919, New York, NY 10111.

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