Cross sections of the (HI, αn) channel in the cold-fusion-type reactions 209Bi+40Ar and 208Pb+37Cl

doi:10.1016/0375-9474(94)90818-4

Nuclear Physics A

Volume 580, Issue 1, 7 November 1994, Pages 113-132

https://doi.org/10.1016/0375-9474(94)90818-4 Get rights and content

Abstract

By applying an off-line radiochemistry technique, cross sections for the production of the isotope $^{240} Cm (T_{12} =27 d)$ in the cold-fusion-type reactions ²⁰⁹Bi+⁴⁰Ar and ²⁰⁸Pb+³⁷Cl at the bombarding energy E_lab⩽230 MeV were determined to be 0.5±0.2 nb and 0.6±0.3 nb, respectively. The production of ²⁴⁰Cm was attributed to the 1n-deexcitation channel of the composite systems ²⁴⁹Md and ²⁴⁵Es. At the same time, the measured ²⁴⁰Cm production cross sections represent upper cross-section limits for the (HI, αn) channel of the reactions under study. These upper limits are about 100 times lower than the cross-section values reported recently by Nomura et al. for the $(^{40} Ar, αx n)$ channels with x=1,2 of the ²⁰⁹Bi+⁴⁰Ar reaction at E_lab=208 MeV. In the context of the above measurements, presented and discussed is the up-to-date summary of the available evidence on cross sections of the (HI, αxn) channels in the cold-fusion-type reactions induced by projectiles ranging from ³⁷Cl to ⁵⁰Ti on targets of ^203,205Tl, ²⁰⁸Pb, and ²⁰⁹Bi nuclei.

Appreciable EC(β⁺)-delayed or/and spontaneous fission effects were detected in the ²⁰⁹Bi+⁴⁰Ar, ²⁰⁸Pb+³⁷Cl, and ²⁰⁶Pb+³⁷Cl reactions. The obtained data point, in particular, to the EC(β⁺)-delayed fission occuring in the decay chains

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Detailed level schemes, decay schemes, band structure, and the experimental data on which they are based are presented for all nuclei with mass number A=242. The experimental data are evaluated and adopted values are given for level and radiation properties. For references on theory refer to the NSR file at the web site given below under Cutoff Date:. This evaluation replaces the A=242 publication by Y. A. Akovali in Nuclear Data Sheets 96, 177 (2002) (2002Ak06).
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Citation Excerpt :
In the following, the discovery of each einsteinium isotope is discussed in detail and a summary is presented in Table 1. The discovery of 242Es was reported in 1994 by Lazarev et al. in “Cross sections of the (HI, αn) channel in the cold-fusion-type reactions 209Bi + 40Ar and 208Pb + 37Cl” [106]. The isotope was identified using the catcher technique with off-line chemical separation following the irradiation of the targets with beams from the U400 cyclotron of the JINR Laboratory of Nuclear Reactions at Dubna.
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Detailed level and decay schemes, along with the experimental reaction and decay data on which they are based, are presented for nuclei with mass number A=238. Based on evaluation of all available data, adopted values for level properties and for energies and intensities of α and γ radiations are given. This evaluation replaces the 1988 version of data for A=238. Data available prior to September, 2002 have been included.
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Information pertaining to the nuclear structure of all nuclei with mass number A=242 is presented. Various decay and reaction data are evaluated and compared. Adopted data, levels, spin, parity and configuration assignments are given. When there are insufficient data, expectations from systematics of nuclear properties or/and calculations are quoted. Theoretical investigations concerning nuclear structure and properties of A=242 nuclei, are briefly mentioned.
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In bombardments of ^206,207,208Pb with ³⁴S and ²⁰⁶Pb with ³⁶S, we identified a new spontaneously fissioning isotope ²³⁸Cf with $T_{sf} ≈ T_{12} = 21 ± 2 ms$ and obtained evidence of the production of a new isotope ²³⁷Cf with $T_{12} = 2.1 ± 0.3 s$ . The spontaneous-fission (SF) decay mode was established for ²⁴⁰Cf; its SF branch was estimated to be b_sf ∼ 2 × 10⁻². We measured also b_sf ⩽ 1.4 × 10⁻⁴ for ²⁴²Cf and estimated b_sf ∼ 10⁻¹ for ²³⁷Cf. The production cross sections of ²³⁸Cf in the $^{206,207,208} Pb +^{34} S$ reactions were measured to be in the range of 0.3 to 1.1 nb. Finally, we probed the influence of the neutron excess in the N = 20 projectile ³⁶S on cross sections of fusion-evaporation reactions occurring on lead targets.

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Nuclear Physics A

Abstract

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Radiochim. Acta

At. Data Nucl. Data Tables

GSI Scientific report GSI-85-1

Z. Phys. A

Nucl. Phys. A

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Rep. Prog. Phys.

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Nuclear Data Sheets for A=242

Nuclear Data Sheets for A = 238

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Nuclear data sheets for A = 238

Nuclear data sheets for A = 242

Spontaneous fission of light californium isotopes produced in <sup>206,207,208</sup>Pb + <sup>34,36</sup>S reactions; new nuclide <sup>238</sup>Cf