Dissociation of 8He

Y. Iwata, K. Ieki, A. Galonsky, J. J. Kruse, J. Wang, R. H. White-Stevens, E. Tryggestad, P. D. Zecher, F. Deák, Á Horváth, Á Kiss, Z. Seres, J. J. Kolata, J. Von Schwarzenberg, R. E. Warner, H. Schelin

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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.

Original languageEnglish
Article number064311
Pages (from-to)643111-6431110
Number of pages5788000
JournalPhysical Review C - Nuclear Physics
Issue number6
Publication statusPublished - Dec 2000

ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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    Iwata, Y., Ieki, K., Galonsky, A., Kruse, J. J., Wang, J., White-Stevens, R. H., Tryggestad, E., Zecher, P. D., Deák, F., Horváth, Á., Kiss, Á., Seres, Z., Kolata, J. J., Von Schwarzenberg, J., Warner, R. E., & Schelin, H. (2000). Dissociation of 8He. Physical Review C - Nuclear Physics, 62(6), 643111-6431110. [064311].