Discovery of /sup 260/Md and the decay properties of /sup 258/Fm, /sup 258m,g/Md, and /sup 259/Md

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We have discovered a new neutron-rich isotope, /sup 260/Md, from /sup 18/O and /sup 22/Ne bombardments of /sup 254/Es. We observed a spontaneous-fission (SF) activity with a 32-day half-life in electromagnetically separated mass-260 fractions from these bombardments and we have measured the mass and kinetic energy distributions of this SF activity. The mass distribution was symmetric with the principal energy peak at 234-MeV total kinetic energy (TKE), similar to previous observations for heavy Fm isotopes. Surprisingly, we also observed a smaller symmetric component with 195-MeV TKE. We interpret these two peaks in the TKE distribution as arising from two types ... continued below

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Pages: 15

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Lougheed, R.W.; Hulet, E.K.; Dougan, R.J.; Wild, J.F.; Dupzyk, R.J.; Henderson, C.M. et al. August 1, 1985.

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We have discovered a new neutron-rich isotope, /sup 260/Md, from /sup 18/O and /sup 22/Ne bombardments of /sup 254/Es. We observed a spontaneous-fission (SF) activity with a 32-day half-life in electromagnetically separated mass-260 fractions from these bombardments and we have measured the mass and kinetic energy distributions of this SF activity. The mass distribution was symmetric with the principal energy peak at 234-MeV total kinetic energy (TKE), similar to previous observations for heavy Fm isotopes. Surprisingly, we also observed a smaller symmetric component with 195-MeV TKE. We interpret these two peaks in the TKE distribution as arising from two types of fission in the same nucleus, or bimodal fission. The observed fission activity may be either from the SF decay of /sup 260/Md or /sup 260/Fm which would arise from electron capture (EC) decay of /sup 260/Md. We have eliminated the possible ..beta../sup -/ decay of /sup 260/Md by measuring ..beta../sup -/-SF time correlations for the decay of /sup 260/Md and we plan to determine if /sup 260/Md decays by EC by measuring time correlations between Fm x-rays and SF events. We also measured properties for heavy Fm and Md isotopes which include: (1) more accurate cross sections for the neutron-rich Md isotopes which we use to predict the production rates of yet undiscovered nuclides; (2) improved half-live measurements for /sup 258m,g/Md and /sup 259/Md; (3) confirmation of the EC decay of /sup 258m/Md by measuring Fm x-rays preceding the SF decay of /sup 258/Fm; and (4) very substantially improved mass and TKE distributions for the SF decay of /sup 258/Fm and /sup 259/Md.

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Pages: 15

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NTIS, PC A02/MF A01.

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  • ACTINIDES '85, Aix-en-Provence, France, 1 Sep 1985

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  • Other: DE85017835
  • Report No.: UCRL-93260
  • Report No.: CONF-8509147-5
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 5309390
  • Archival Resource Key: ark:/67531/metadc1064743

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  • August 1, 1985

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  • Feb. 4, 2018, 10:51 a.m.

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Lougheed, R.W.; Hulet, E.K.; Dougan, R.J.; Wild, J.F.; Dupzyk, R.J.; Henderson, C.M. et al. Discovery of /sup 260/Md and the decay properties of /sup 258/Fm, /sup 258m,g/Md, and /sup 259/Md, article, August 1, 1985; United States. (digital.library.unt.edu/ark:/67531/metadc1064743/: accessed June 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.