Measurement of internal pairs from {sup 206}Pb

Technical Report · Tue Aug 01 04:00:00 EDT 1995

DOI:https://doi.org/10.2172/166358· OSTI ID:166358

Ahmad, I.; Back, B. B.; Betts, R. R. ^[1]

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1. and others

The failure to observe sharp sum-energy lines in measurements of {sup 238}U + {sup 181}Ta and {sup 238}U + {sup 232}Th raises the issue of the correct functioning of APEX under in-beam conditions. Extensive measurements with electron and pair emitting sources were used to demonstrate the resolution and acceptance of APEX, but the possibility remains that some unforeseen background or other effects might compromise the ability to see peaks in-beam. In order to test the functioning of APEX under the most stringent conditions, we also performed a measurement of internal pairs produced in the decay of the 2.648-MeV 3{sup -} state in {sup 206}Pb to the 2{sup +} state at 0.803 MeV. The 3{sup -} state was excited in the {sup 206}Pb + {sup 206}Pb reaction at 5.9 MeV/u with a cross section of roughly 40 mb, resulting in an expected pair cross section of approximately 16 {mu}b. It should be emphasized that this measurement represents a much stricter test of the functioning of the apparatus than the observation of sum-energy lines would represent, as the internal pair measurement requires a Doppler shift correction before the transition can be seen. These data were analyzed and clearly show the expected peak. A Doppler-corrected sum-energy spectrum showing the expected IPC line at 823 keV. At present we are evaluating the acceptance of APEX for events of this type but it is clear that the observed yield is close to expectations.

• Research Organization: Argonne National Lab., IL (United States)
• OSTI ID: 166358
• Report Number(s): ANL--95/14; ON: DE96000985
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
INTERNAL PAIR PRODUCTION
LEAD 206
LEAD 206 REACTIONS
LEAD 206 TARGET
PROGRESS REPORT