Resonance effects in near-barrier fission observed in (d, pf) reactions

doi:10.1016/0370-2693(69)90012-4

Physics Letters B

Volume 29, Issue 3, 28 April 1969, Pages 176-178

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Abstract

The fission probability as a function of the excitation energy of the fissioning nucleus has been measured for the reactions ²³³U(d,p)²³⁴U, ²³⁵U(d,p)²³⁶U, ²³⁹Pu(d,p)²⁴⁰Pu and ²⁴¹Pu(d,p)²⁴²Pu. In all these cases, the fission barrier lies below the neutron binding energy so that the only competition to fission is γ-decay which is known to vary smoothly with energy. The fission probability shows resonance structure below and at the fission barrier. One explanation for this resonance structure follows from the double-humped fission barrier.

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Nuclear Data Sheets for A = 240
2008, Nuclear Data Sheets
Evaluated experimental data for radioactive decays and reactions for known nuclides (U, Np, Pu, Am, Cm, Bk, Cf) of A = 240 are presented together with adopted values for level energies, γ-ray energies, relative branching ratios and other nuclear properties.
This revision was primarily motivated by the need for re-evaluation of absolute gamma-ray intensities from the ɛ decay of ²⁴⁰Am to ²⁴⁰Pu. These quantities are essential for determining precise and accurate cross-sections for the ²⁴¹Am(n,2n)²⁴⁰Am reaction using fast neutrons (see e.g. Americium Workshop, Santa Fe, New Mexico, September 2007, 2008To06, 2007Ta01, 2006Pe14) and ²⁴¹Am(γ,n) reaction (see e.g. 2006Ri08). For ²⁴⁰U, the γ-ray data have now become available.
The data sets for ²⁴⁴Pu α decay to ²⁴⁰U; ²⁴⁴Cm α decay to ²⁴⁰Pu and ²⁴⁴Cf α decay to ²⁴⁰Cm have been adapted from evaluations by 1998Ak04 and 2003Ak04. For ²⁴⁴Cm decay, evaluation by 2006BeZL under the Decay Data Evaluation Project (DDEP) is also used. The γ-ray data (energies and intensities) for ²⁴⁰Cm decay are not considered (by the evaluators) as well established.
Most detailed data are available only for ²⁴⁰Pu. Extensive data in the second potential well are available for this nuclide together with fission isomers and several superdeformed (SD) structures. For other nuclides spectroscopic data are rather sparse in the literature; especially for the following radioactive decays: The ɛ decays of ²⁴⁰Cf, ²⁴⁰Bk and ²⁴⁰Cm; multipolarities of γ-ray transitions in ²⁴⁰Np from ²⁴⁰U $β^{-}$ decay; γ-ray transitions from ²⁴⁴Cf α decay and %ɛ branch of ²⁴⁴Cf decay; spins and parities of excited states in ²⁴⁰U and multipolarities of associated γ-ray transitions in ²⁴⁰U.
This work supersedes earlier full evaluations of A = 240 published by 2004Ch64, 1984Sh34, 1977Sc13, 1970Sc39; and an evaluation published in update mode by 1990Sh04.
Nuclear data sheets for A = 240
2004, Nuclear Data Sheets
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2002, Progress in Particle and Nuclear Physics
Progress in our understanding of the nuclear structure in the second and third minimum of the potential energy surface is reported emphasizing recent achievements via complementary experimental approaches.
Detailed spectroscopic results of collective properties are obtained in the second and third minimum as well as for spin dependent fission properties. A novel approach could be established to determine the depth of the potential wells.
Empirical collective level systematics developed for normal deformed nuclei were tested upon their predictive power for extremely deformed configurations. A phenomenological approach based on a valence correlation scheme was applied to the second potential well in order to predict β vibrational phonon energies and magic nucleon numbers.
Perspectives for future experimental efforts will be discussed.
Nuclear data sheets for A = 242
2002, Nuclear Data Sheets
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.
Excited superdeformed Kπ = 0+ rotational bands in β-vibrational fission resonances of 240Pu
2001, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
The intermediate structure of fission resonances of ²⁴⁰Pu was observed with an experimental energy resolution of 7 keV in the excitation energy region of $E^{∗} =3.8$ –5.6 MeV using the ²³⁹Pu(d, pf)²⁴⁰Pu reaction. Two-vibrational resonance groups centered at $E^{∗} =4.6$ MeV and 5.1 MeV, and attributed to the excitation of three and four β-phonons, were resolved into individual substates, which could be assigned to the low-spin members of K^π=0⁺ superdeformed (SD) rotational bands. In the region of the lower $E^{∗} =4.6$ MeV resonance individual moments of inertia of six well separated bands could be extracted for the first time with values of Θ/ℏ² around 157 MeV⁻¹, close to that of the ground state band in the second well. From the level density of these K^π=0⁺ band heads the excitation energy of the SD ground state was determined to (2.25±0.20) MeV, in agreement with earlier estimates from excitation functions.
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1976, Nuclear Physics, Section A
Sub-barrier resonances in the ²³⁹Pu(d, pf) reaction have been investigated with a resolution of 3 keV. Many class II resonance groups with an average spacing of 11 keV have been observed in the region of the 5.0 MeV transmission resonance. The coincident fission fragment angular correlations indicate a spin 2⁺ for all lines resolved. The data are analyzed on the basis of a simple model of intermediate structure which also explains the observed broadening of the class II groups.

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^∗: Present address: Physico-Energetical Institute, Obninski, Kaluga region, USSR.

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Physics Letters B

Abstract

References (13)

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Cited by (30)

Nuclear Data Sheets for A = 240

Nuclear data sheets for A = 240

Spectroscopy in the second and third minimum of actinide nuclei

Nuclear data sheets for A = 242

Excited superdeformed K<sup>π</sup> = 0<sup>+</sup> rotational bands in β-vibrational fission resonances of <sup>240</sup>Pu

Intermediate structure in the <sup>239</sup>Pu(d, pf) reaction