Radioactive decay properties of 238Am, 239Am, 240Am, 240Cm and 241Cm

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Abstract

Some electron-capture and α-decay properties of neutron-deficient americium and curium isotopes have been investigated using 2π proportional counting, scintillation spectrometry, and α-pulse analysis. The results for 238Am include a new half-life of 1·86 hr and identification of γ-rays of ∼370 keV (∼12%), 580 keV (∼29%), ∼950 keV (∼2%), 980 keV (∼76%), and ∼1350 keV (∼17%). The data on 239Am (half-life 12·1 hr) indicate γ-rays of 225 keV (∼30%) and 275 keV (∼20%) with a new α-particle energy of 5·77 MeV and abundance of 5·0 × 10−3 per cent. For 240Am (half-life 51·0 hr) γ-rays of 900 keV (∼23%) and 1000 keV (∼77)% and a negatron branching limit of ≤ 6 × 10−6 per cent were established. For 240Cm a new α-particle energy of 6·26 MeV was established. For 241Cm a new alpha particle energy of 5·95 MeV and abundance of 0·96 per cent and a γ-ray of 478 keV (97%) were established. Counting efficiencies for the 2π-geometry methane-flow proportional counter are 60, 90 and 82 per cent for the electron-capture decay of 239Am, 240Am and 241Cm, respectively. These are in the range of values found for other β-unstable isotopes of heavy elements.

The data on 238Am and 240Am are consistent with a rule that only levels ∼1000 keV and higher in even-even plutonium isotopes are populated by relatively fast β-transitions (log ft 5–8) in the decay of odd-odd americium and neptunium isotopes.

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    This work was performed under the auspices of the U.S. Atomic Energy Commission. It is based in part on the Ph.D. theses of R. A. Glass, University of California, June 1954; R. J. Carr, University of California, June 1956; and W. M. Gibson, University of California, June 1957. One of us (W. M. G) wishes to acknowledge the support of the United States Air Force Institute of Technology during this research.

    Present address: Stanford Research Institute, Menlo Park, California.

    §

    Present address: Bell Telephone Laboratories, Murray Hill, New Jersey.

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