Gamma decay of the 238U shape isomer

Russo, P.A.; Pedersen, Jens Olaf Pepke; Vandenbosch, R.

doi:10.1016/0375-9474(75)90434-0

Cited by 60 publications

(27 citation statements)

References 20 publications

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“…Drexler et al obtained a limit for the branching ratio for the decay of the 23sU shape isomer for one high energy tion used to obtain this ratio. Kantele et al [15] observed an E0 conversion electron transition with a halflife of (130_+ 50)ns and a transition energy consistent with the isomer excitation energy of 2.559 MeV reported by Russo et al [4]. They did not observe the E2 K-conversion line of the 2.514 MeV transition and extracted an upper limit of ai; < 50 gbarn for the partial cross section of this transition, whereas Russo et al reported av~, =(90+25)labarn.…”

Section: Introductionsupporting

confidence: 63%

“…On the other hand already in 1975 Russo and coworkers [4] reported a positive result for the gamma-back decay of 23ainu. The shape isomer was populated in a 238U(d, pn) reaction with a bombarding energy of 18 MeV.…”

Section: Introductionmentioning

confidence: 93%

“…One of the still unsettled problems is the role of alternative decay-modes and their competition with fission. Statistical model arguments yielding higher cross sections for the population of the 236U, 238U, 23VNp shape isomers than experimentally [4][5][6] and estimates based on the systematics of the partial half-lives for spontaneous fission of shape isomers [-7] indicate a rather strong contribution of competing decay modes in 236m, 238m w and 237mNp. Theoretically this can be explained as being due to the relative lowering of the inner barrier with decreasing proton number Z.…”

Section: Introductionmentioning

confidence: 99%

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Fission and gamma-ray decay of the238U shape isomer

Steinmayer

Löbner

Corradi

et al. 1992

Z. Physik A - Hadrons and Nuclei

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The decay of the 238U superdeformed shape isomer has been reinvestigated by detecting for the first time simultaneously the fission and the gamma-back decay. An electrostatic deflection system has been used to transport the 238mu recoils, produced in a 238U(d, pn) reaction with a pulsed beam of 18 MeV deuterons, in front of a detector set-up consisting of three ion-implanted solidstate detectors and a Ge(Li) gamma-detector. The gamma-back decay has been measured in coincidence with conversion electrons of the 2 + ~ 0 + transition deexciting the first rotational state in 238U. Two gamma-transitions of 2.513 MeV and 1.878 MeV have been observed with half-lives consistent with the result obtained for the decay by delayed fission T1;2 =(298 _+ 18) ns. PACS" 23.20.Ck; 23.20.Lv; 25.85.Ge; 27.90. + b

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Section: Introductionsupporting

confidence: 63%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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Fission and gamma-ray decay of the238U shape isomer

Steinmayer

Löbner

Corradi

et al. 1992

Z. Physik A - Hadrons and Nuclei

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“…18,andhwa =.63 (Russo et al , 1975), which gives PA/P B :::::: 5XI0 7 which translates into a gamma~ack-decay partial width 20 times larger than the partial fission…”

Section: Fig 2-12mentioning

confidence: 99%

Search for the gamma-branch of the shape isomers of separated U isotopes using muon for nuclide excitation

Mireshghi¹

1982

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We have searched for back-decay gainmaray~' from the shape isomeric'states in 23SU,' 236U,and 2J8U possibly excited iii muon r~diationiess tr~nsiiion. The energies ilrtd intensities of g~ rays foll~~ng muon atomi~ Ca.pt~re were measured as a function of time after muon stopping. Background was suppressed by requiring that the candidate gamma ray be followed by another gamma ray (It-capture gamma ray). The prompt gamma-ray spectra included the Umuonic x rays. The measured 23SU and 238U x-ray energies were in good agreement with previously reported results. The x-ray spectrum from 236U has not been previously reported. The '-236U spectrum is very similar to that of 238U, except that the K x-rays exhibit an isotope shift of approximately 20 kev, the 236U energies being higher.In the analysis of the delayed spectra of 236U and 238U using the GAMANL peak searching program, and with an effective lower-limit detection efficiency of .15% per stopping muon, no candidate gamma rays for the back decay transitions from the shape isomeric state were observed. However, a more sensitive hand a:nalysis of the "smoothed background-subtracted" spectra resulted in the identification of some delayed ganirriil activities close to or below the 0.15% level. Both nuclei would be produced by muon capture on ~.

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“…They also pointed out that the change in the fission barrier due to the presence of the ls muon will reduce the prorrpt yields. In uranium the fission mode for the isomer is expected to be extremely weak because the inner potential barrier more transparent than the outer one 7 ), especially in the presence of the muon 5 ). The delayed fisson yields have also been calculated from photofission and neutron-induced fission cross sections 8 ).…”

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confidence: 99%

Fission yields and lifetimes for muon induced fission in 235U and 238U

et al. 1980

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1The absolute yields prompt and delayed fission induced by negative muons stopping in 2 3 5u and 2 3 Bu have been rreasured. A coincidence with muonic K a x~rays was used to identify the muon stop in the target. The time distribution of fissions following the muon stopping were also obtained.When a negative muon is captured into the atomic orbit of an actinide nucleus undergoes an atonic cascade, ordinarily reaching the muonic K shell through radiative transitions. The muon then disappears from the K shell at a dlaracteristic rate :A ("' (75 ns) ~l), vihich the sum of leptonic decay rate and nuclear muon capture rate. The rate can be obtained by measuring the time distributions of emitted decay electrons, neutrons, capture y rays, or fission fragments relative to the muon arrival time at the target. Prompt nuclear excitation also occurs, arising from non radiative atomic transitions by some of tr1e cascading muons. A fraction of these excitations wi 11 cause the nucleus to tnn,Dr~n prorrpt fission, leaving the muon attached predominantly to the heavier ' 2 ). The corresponding disappearance rate of the muon attached to the h is observable in all decay channels except that for fission. Another a.ction of the prompt excitations may populate an isomeric state of large deformation 3~5 ), whose decay rate contains components for fission and for y back decay to the less deformed ground state.The prompt fission process was discussed the pioneering work of Zaretski and Novikov 6 ), which related ~~e prompt fission yields to photofission cross sections. They also pointed out that the change in the fission barrier 2 due to the presence of the ls muon will reduce the prorrpt yields. In uranium the fission mode for the isomer is expected to be extremely weak because the inner potential barrier more transparent than the outer one 7 ), especially in the presence of the muon 5 ). The delayed fisson yields have also been calculated from photofission and neutron-induced fission cross sections 8 ).Previous measurernents 9~12) exhibit a large variation in the prompt fission yield 9 y (of up to a factor of five), 'Which indicates large systematic p uncertainties. In fission chamber experiments it is often difficult to estimate the fraction of muons captured onto the thin actinide target, particularly if it is in the form of a compound or mixture. In the present work we identify muon capture onto U by requiring a rnuonic K x ray to precede the fission event.a After applying a correction for the detection efficiency of the fission charrber, the absolute yield for delayed fission is sirrply the ratio of coincidences to total K x rays. In addition, we have observed the time distributions for a fission of rnuonic 2 3 5 ' 2 3 8 u, without coincidence, to determine the mean lifetimesbf,and the prorrpt relative fission yields.In the present measuraments the muon beam from the M9 channel at the TRIUMF meson facility was used. The rnuon~stop signal was obtained from a four~scintillator telescope. In order to reduce the nurrber of false stopp...

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Gamma decay of the 238U shape isomer

Cited by 60 publications

References 20 publications

Fission and gamma-ray decay of the238U shape isomer

Fission and gamma-ray decay of the238U shape isomer

Search for the gamma-branch of the shape isomers of separated U isotopes using muon for nuclide excitation

Fission yields and lifetimes for muon induced fission in 235U and 238U

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