Cosmic-Ray Half-Life of ^144Pm

Details Cosmic-Ray Half-Life of ^144Pm Cosmic-Ray Half-Life of ^144Pm

Oct 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aps..dnp..cd02n&link_type=abstract

American Physical Society, Division of Nuclear Physics Meeting, October 5-8, 1997, abstract #CD.02

Physics

Nuclear Physics

Scientific paper

The galactic confinement time of cosmic rays can be determined by comparing the cosmic-ray abundances of long-lived isotopes to those of their stable neighbors. In the case of Pm, ^143,144,145Pm have sufficiently long half-lives to be present in the cosmic rays. Due to their interactions with the interstellar medium, these isotopes are fully stripped of their atomic electrons. While EC decay thus cannot occur, it is possible for ^143Pm and ^144Pm to decay via β^+ emission which determines the cosmic ray half-lives of these isotopes. We counted a highly purified 1.4 μCi source of ^144Pm in GAMMASPHERE and searched for positron-annihilation gamma-rays in coincidence with the characteristic 697-keV gamma-ray. Analysis of 57 hours of source counting and 15 hours of background measurements, shows a net signal of 2.5±2.3 511-511-697 keV coincident events. This leads to a 1-σ upper limit on the branch for this decay mode to be 1.0x10-5%. The implications of this result for the ^144Pm cosmic-ray chronometer problem will be discussed.

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