Towards a better understanding of deep subthreshold photofission of238U

Bellia, G.; Zoppo, A. Del; Maiolino, C.; Migneco, E.; Russo, G.

doi:10.1007/bf01411827

Cited by 19 publications

(22 citation statements)

References 20 publications

(35 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The left panel of figure 5 shows the fission yield as obtained from bremsstrahlung experiments with ∆E∼200 keV. However, as outlined by [23], the broad structure of the isomeric shelf is predicted to be intrinsically composed of a multitude of individual sharp resonances, which so far could not be resolved.…”

Section: Exploring the Triple-humped Fission Barrier Via Photofissionmentioning

confidence: 99%

“…It is caused by a competition of prompt and delayed (isomeric) fission in this energy region. Figure 5 displays the isomeric shelf as obtained in theoretical studies [23] for 238 U. According to [23], the isomeric shelf consists of contributions from 2 + (K=0) quadrupole and 1 − (K=0) dipole resonances as gateway states to the second minimum.…”

Section: Exploring the Triple-humped Fission Barrier Via Photofissionmentioning

confidence: 99%

“…a deviation from the exponential decrease of the fission yield with decreasing excitation energy, the so-called 'isomeric shelf' [23,24]. It is caused by a competition of prompt and delayed (isomeric) fission in this energy region.…”

Section: Exploring the Triple-humped Fission Barrier Via Photofissionmentioning

confidence: 99%

See 2 more Smart Citations

Perspectives for photofission studies with highly brilliant, monochromaticγ–ray beams

Thirolf

Csige

Habs

et al. 2012

EPJ Web of Conferences

View full text Add to dashboard Cite

Abstract. New research facilities like MEGa-Ray (Livermore) or ELI-NP (Bucharest) will provide within the next years (2013)(2014)(2015)(2016) photon beams of unprecedented quality with respect to both photon intensity (total flux ∼ 10 13 γ/s) and spectral intensity (∼ (10 4 -10 6 )/eVs), thus exceeding the performance of existing facilities by several orders of magnitude. This tremendous progress will be enabled by Compton-backscattering of an intense laser off a high-quality electron beam, in conjunction with novel refractive bremsstrahlung beams focusing γ optics and efficient monochromatization techniques. We envisage to employ these γ beams for photofission studies on extremely deformed nuclear states of actinides, investigating their multiple-humped potential energy landscape in a highly selective way. Transmission resonances in the prompt fission cross section from the (superdeformed) second and (hyperdeformed) third potential minimum will be studied, where the fission decay channel can be expressed as a tunnelling process of these gateway states through the multiple-humped fission barrier. Novel brilliant γ beams for photonuclear sciencePhotonuclear physics is a well-established field of research since decades [1]. Mostly bremsstrahlung has been used to excite nuclei or to induce fission in the actinides [2]. A significant improvement in narrowing the energy resolution of photon beams from typically 200-300 keV at bremsstrahlung facilities to about 15-25 keV was achieved by introducing the tagged-photon technique [3]. In recent years increasingly also Compton-backscattering of (laser-) photons off an energetic electron beam was used to generate γ beams according to the scheme illustrated by figure 1. Here the Doppler-upshift experienced by the initial pho- Fig. 1. Sketch of the mechanism to produce MeV photon beams (E γ ) by exploiting the Doppler-upshift experienced by a laser photon (energy E 0 ) which is Compton-backscattered off a relativistic electron. ton with energy E 0 is exploited to generate photon beams with high energies E γ via Compton-backscattering from a counter-propagating fast electron beam, characterized by its relativistic factor γ according to a e-mail: Peter.Thirolf@lmu.deThe simplified scaling of the backscattered photon energy with 4γ 2 holds for exactly backscattered photons and takes into account that the recoil term 4γE 0 /mc 2 is negligible for initial photon energies of a few eV. In realistic experiments, the angular spread after Compton scattering, described within the Klein-Nishina formula by the angle θ between the incident laser direction and the direction of the scattered γ beam, will be reduced by appropriate collimation of the back-scattered photons.Presently the world-leading γ-beam facility HIγS (High Intensity Gamma-Ray Source) is operated at Duke University in the US [4]. A free-electron laser (FEL) operated in a 1.2-GeV electron storage ring is used to produce photons (from IR to VUV) that subsequently are Comptonbackscattered off the relativistic electron beam. Cu...

show abstract

Section: Exploring the Triple-humped Fission Barrier Via Photofissionmentioning

confidence: 99%

Section: Exploring the Triple-humped Fission Barrier Via Photofissionmentioning

confidence: 99%

See 1 more Smart Citation

Perspectives for photofission studies with highly brilliant, monochromaticγ–ray beams

Thirolf

Csige

Habs

et al. 2012

EPJ Web of Conferences

View full text Add to dashboard Cite

show abstract

“…On the other hand, a previous 236 U(p, t) measurement [7] showed pronounced resonance structures at E = 5.6-5.8 MeV and at 5.15 MeV, as well as a weaker resonance at 4.9 MeV. A whole sequence of further transmission resonances at lower energies is expected to explain the isomeric shelf [8], but such resonances have never been observed.…”

Section: Photofission Of 238 Umentioning

confidence: 79%

Photofission of 238U Induced by a Quasi-monochromatic, Compton Backscattered γ Beam

Csige¹,

Filipescu

Gulyás

et al. 2013

Acta Phys. Pol. B

View full text Add to dashboard Cite

The photofission cross-section of 238 U was measured in the sub-barrier energy region as a function of the γ energy using, for the first time, a monochromatic, high-brilliance, Compton backscattered γ beam. This prototype experiment was performed at the HIγS gamma beam facility of the Duke University at Durham (North Carolina, US) using the 238 U(γ, f ) reaction at a beam energy varied between E γ = 4.7-6.0 MeV and with an energy resolution of ∆E = 150-200 keV (∆E/E ≈ 3%). The photofission cross-section was determined down to E * = 4.7 MeV. Indications of transmission resonances have been observed at excitation energies of E * = 5.1 and 5.6 MeV with moderate amplitudes.

show abstract

“…So far experimental progress was achieved mainly via light-particle induced nuclear reactions studying transmission resonances, or by performing conversion electron or γ-ray spectroscopy [2]. In sub-barrier photofission experiments the so-called 'isomeric shelf' in the fission cross-section was observed [6,7], resulting from a competition between prompt and delayed photofission. Until now nearly all measurements of subbarrier photofission have been performed with bremsstrahlungs photons, measuring integrated fission yields, where the fission cross-section is folded with the increasing γ-ray spectrum, resulting in a typical effective γ band width of only ∼ 4-6 × 10 −2 (energy resolution 200-300 keV).…”

Section: Introductionmentioning

confidence: 99%

Untitled

et al. 2012

View full text Add to dashboard Cite

Presently two new research facilities are either already under construction ('MEGa-Ray' at Lawrence Livermore National Laboratory/US) or soon ready to start construction (ELI-Nuclear Physics in Bucharest/ Romania), both aiming to provide highly brilliant γ beams with so far unprecedented properties (ca. 10 13 photons/s, energy resolution ≤10 −3 ) via Compton-backscattering of laser photons from a high-quality relativistic electron beam. With these intense, monochromatic γ beams, a new era of photonuclear physics will be enabled. It is envisaged to exploit the novel beams for highly-selective studies of extremely deformed nuclei in the multiple-humped potential energy landscape of the actinides via photofission. We will be able to populate gateway states in the first potential minimum of nuclei, predominantly originating from collective states in the (superdeformed) second or (hyperdeformed) third potential minimum, tunnelling back into the first well. The γ beam energy resolution of 10 −3 will allow to resolve individual resonances due to the lower level density in the higher potential minima. Excited states in these minima can be rather selectively populated with much larger intensities than achieved with former methods based on light-ion induced reactions. Also the large background from prompt fission with σ isomer /σ prompt ≈ 10 −5 is avoided. Hence a detailed γ spectroscopy in the second and third minimum will be enabled.

show abstract

Towards a better understanding of deep subthreshold photofission of238U

Cited by 19 publications

References 20 publications

Perspectives for photofission studies with highly brilliant, monochromaticγ–ray beams

Perspectives for photofission studies with highly brilliant, monochromaticγ–ray beams

Photofission of <sup><span class="cmr-7">238</span></sup>U Induced by a Quasi-monochromatic, Compton Backscattered <span class="cmmi-10">γ</span> Beam

Untitled

Contact Info

Product

Resources

About