The positron peak puzzle - Recent results from APEX

Journal Article · Mon Jan 01 00:00:00 EST 1996 · Acta Physica Polonica. Series B

OSTI ID:1407011

Ahmad, I; Austin, SM; Back, BB; Betts, RR; Calaprice, FP; Chan, KC; Chishti, A; Chowdhury, P; Conner, C; Dunford, RW; Fox, JD; Freedman, SJ; Freer, M; Gazes, S; Hallin, AL; Happ, T; Kaloskamis, N; Kashy, E; Kutschera, W; Last, J ; Lister, CJ; Liu, M; Maier, MR; Mercer, DJ; Mikolas, D; Perera, A; Rhein, MD; Roa, E; Schiffer, JP; Trainor, T; Wilt, P; Winfield, JS; Wolanski, M; Wolfs, FLH; Wuosmaa, AH; Young, A; Yurkon, JE

Results are presented from a new experiment, APEX, designed to study the previously reported sharp lines in sum-energy spectra of positrons and electrons produced in collisions of very heavy ions. Data have been collected for ²³⁸U + ¹⁸¹Ta and ²³⁸U + ²³²Th. No evidence is found for narrow structures similar to those previously reported. For the specific case of the isolated decay of a neutral particle of mass 1.4–2.1 MeV/c², the upper limits on cross sections obtained are significantly less than previously reported. Data are also presented for internal pair conversion in ²⁰⁶Pb. These results are used to set limits for the possible contribution to the pair yield of a 1780 keV transition in ²³⁸U observed in heavy-ion gamma-ray coincidence measurements.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
• Contributing Organization: APEX Collaboration
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1407011
• Journal Information: Acta Physica Polonica. Series B, Journal Name: Acta Physica Polonica. Series B Vol. 27; ISSN 0587-4254
• Publisher: Jagiellonian University
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS