\ensuremath{\alpha}-decay of the new isotope $^{187}\mathrm{Po}$: Probing prolate structures beyond the neutron mid-shell at N = 104

α-decay of the new isotope ${}^{187}{Po}$ : Probing prolate structures beyond the neutron mid-shell at N = 104

A. N. Andreyev, S. Antalic, D. Ackermann, S. Franchoo, F. P. Heßberger, S. Hofmann, M. Huyse, I. Kojouharov, B. Kindler, P. Kuusiniemi, S. R. Lesher, B. Lommel, R. Mann, G. Münzenberg, K. Nishio, R. D. Page, J. J. Ressler, B. Streicher, S. Saro, B. Sulignano, P. Van Duppen, D. Wiseman, and R. Wyss

Phys. Rev. C 73, 044324 – Published 25 April 2006

Abstract

The new neutron-deficient isotope ${}^{187}{Po}$ has been identified in the complete fusion reaction ${}^{46}{Ti}$ + ${}^{144}{Sm}$ → ${}^{187}{Po}$ + $3 n$ at the velocity filter SHIP. Striking features of the ${}^{187}{Po}$ α decay are the strongly-hindered decay to the spherical ground state and unhindered decay to a surprisingly low-lying deformed excited state at 286 keV in the daughter nucleus ${}^{183}{Pb}$ . Based on the potential energy surface calculations, the ${}^{187}{Po}$ ground state and the 286 keV excited state in ${}^{183}{Pb}$ were interpreted as being of prolate origin. The systematic deviation of the α-decay properties in the lightest odd-A Po isotopes relative to the smooth behavior in the even-A neighbors is discussed. Improved data for the decay of $^{187} {Bi}^{m, g}$ were also obtained.

Received 7 February 2006

DOI:https://doi.org/10.1103/PhysRevC.73.044324

Authors & Affiliations

A. N. Andreyev^1,7, S. Antalic², D. Ackermann^3,8, S. Franchoo⁴, F. P. Heßberger³, S. Hofmann^3,9, M. Huyse⁵, I. Kojouharov³, B. Kindler³, P. Kuusiniemi³, S. R. Lesher⁵, B. Lommel³, R. Mann³, G. Münzenberg^3,8, K. Nishio^3,10, R. D. Page⁶, J. J. Ressler⁷, B. Streicher², S. Saro², B. Sulignano³, P. Van Duppen⁵, D. Wiseman⁶, and R. Wyss¹¹

¹TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, Canada V6T 2A3
²Department of Nuclear Physics and Biophysics, Comenius University, Bratislava SK-84248, Slovakia
³Gesellschaft für Schwerionenforschung, Planckstrasse 1, D-64291 Darmstadt, Germany
⁴IPN Orsay, F-91406 Orsay Cedex, France
⁵Instituut voor Kern- en Stralingsfysica, K.U. Leuven, University of Leuven, B-3001 Leuven, Belgium
⁶Department of Physics, Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United Kingdom
⁷Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A-1S6
⁸Institut fur Physik, Johannes Gutenberg-University, D-55099 Mainz, Germany
⁹Physikalisches Institut, J.W. Goethe-Universität, D-60054 Frankfurt, Germany
¹⁰Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
¹¹Department of Physics, Royal Institute of Technology, 104 05 Stockholm, Sweden

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Vol. 73, Iss. 4 — April 2006

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Figure 1
(a) A part of the $α_{1}$ -energy spectrum from the reaction ${}^{46}{Ti}$ (224 MeV)+ ${}^{144}{Sm}$ → ${}^{190}{Po}$ $^{*}$ registered in the whole PSSD. (b) The same spectrum as in (a), but registered within the time interval $Δ T$ (recoil- $α_{1}$ ) ≤ 7 ms after the recoil implantation; (c) the two-dimensional $E_{α 1} − E_{α 2}$ plot for ΔT(recoil- $α_{1}$ ) ≤ 7 ms and ΔT( $α_{1} − α_{2}$ ) ≤ 3 s. The open rectangle is explained in the text; (d) $E_{α 1} − E_{γ}$ spectrum for $α_{1}$ events in coincidence with γ rays, ΔT(recoil- $α_{1}$ ) ≤ 100 ms and ΔT( $α_{1} − γ$ ) ≤ 5 μs. α- and γ-decay energies are given in keV.Reuse & Permissions
Figure 2
Decay scheme of ${}^{187}{Po}$ deduced in this work. Shown are α-decay energies $E_{α}$ , intensities $I_{α}$ , reduced α widths $δ_{α}^{2}$ and hindrance factor values HF. The tentative 7808 keV decay is shown by the dashed line. The $I^{π}$ assignments in ${}^{187}{Po}$ and of the 286 keV state in ${}^{183}{Pb}$ are tentative and based on a combination of the PES/PPR calculations and α decay hindrance factors, see text for details. Note that both $I^{π} = 1 / 2^{-}$ or $5 / 2^{-}$ are possible for ${}^{187}{Po}$ and for the 286 keV state in ${}^{183}{Pb}$ , but the $I^{π}$ assignments must be the same for both states. The $I^{π}$ values for both α-decaying states in ${}^{183}{Pb}$ were deduced in [17]. The decay scheme of ${}^{183}{Pb}$ was taken from [28].Reuse & Permissions
Figure 3
Decay scheme of ${}^{187}{Bi}$ deduced in this work. Shown are α-decay energies $E_{α}$ , relative intensities $I_{α}$ , reduced α widths $δ_{α}^{2}$ and hindrance factor values HF. The HF values were calculated relative to the unhindered 7000 keV decay of $^{187} {Bi}^{g}$ , for which HF = 1 was assumed. All $I^{π}$ assignments are tentative and shown in brackets. The data for ${}^{183}{Tl}$ are taken from Refs. 29, 30, except for the α-branching ratio of $b_{α}$ ( $^{183} {Tl}^{m}$ ) = 1.5(3)% and position of the excited state at $E^{*} = 273 (1)$ keV measured in our study.Reuse & Permissions
Figure 4
(Color online) Potential energy surfaces for the negative parity states in ${}^{187}{Po}$ (a) and in ${}^{183}{Pb}$ (b). Spherical and prolate minima are indicated by respective shapes and solid circle and triangles, respectively. The solid arrow indicates the observed unhindered decay between two prolate configurations, while the dashed line corresponds to strongly hindered tentative decay to the spherical ground state of ${}^{183}{Pb}$ . The energy separation between the contour lines is 100 keV.Reuse & Permissions
Figure 5
(Color online) α-decay systematics in Po isotopes: (a) α-decay energies. The largest-energy α decays are shown. For ${}^{187}{Po}$ the energy of the tentatively observed 7808 keV crossover decay is given; (b) Partial $T_{1 / 2, α}$ values. For ${}^{187, 189}{Po}$ the partial half-life values are shown both for the largest-energy (hindered) 7808 and 7532 keV decays and for the strongest (unhindered) fine structure 7528 ${}^{187}{Po}$ , and 7529 keV ${}^{189}{Po}$ decays. The data for ${}^{186}{Po}$ are taken from Ref. 21.Reuse & Permissions

Physical Review C

covering nuclear physics

α-decay of the new isotope ${}^{187}{Po}$ : Probing prolate structures beyond the neutron mid-shell at N = 104

A. N. Andreyev, S. Antalic, D. Ackermann, S. Franchoo, F. P. Heßberger, S. Hofmann, M. Huyse, I. Kojouharov, B. Kindler, P. Kuusiniemi, S. R. Lesher, B. Lommel, R. Mann, G. Münzenberg, K. Nishio, R. D. Page, J. J. Ressler, B. Streicher, S. Saro, B. Sulignano, P. Van Duppen, D. Wiseman, and R. Wyss

Phys. Rev. C 73, 044324 – Published 25 April 2006

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Physical Review C

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α-decay of the new isotope Po187: Probing prolate structures beyond the neutron mid-shell at N = 104

Phys. Rev. C 73, 044324 – Published 25 April 2006

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α-decay of the new isotope ${}^{187}{Po}$ : Probing prolate structures beyond the neutron mid-shell at N = 104