Spectroscopy of neutron rich nuclei using cold neutron induced fission of actinide targets at the ILL: the EXILL campaign

Blanc, A.; Drouet, F.; Jentschel, M.; Köster, U.; Mutti, P.; Régis, J.-M.; Simpson, G. S.; Söldner, T.; Stézowski, O.; Ur, C. A.; Urban, W.; Vancrayenest, A.

doi:10.1051/epjconf/20146602010

Cited by 10 publications

(8 citation statements)

References 8 publications

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“…More recently, the EXILL experimental campaign using the EXOGAM spectrometer coupled to thermal neutron beams from the ILL reactor has produced prompt spectroscopic information on lighter fissile systems 235 Uðn th ; fÞ and 241 Puðn th ; fÞ for nuclear structure studies [14,15]. In contrast to fast-neutron-induced fission, the yields of these thermal neutron-induced reactions are well known and have been measured extensively, for example, with the Lohengrin spectrometer [16].…”

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confidence: 99%

Anomalies in the Charge Yields of Fission Fragments from the U(n,f)238 Reaction

Wilson¹,

Lebois²,

Qi³

et al. 2017

Phys. Rev. Lett.

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Fast-neutron-induced fission of 238 U at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency γ-ray spectrometer (MINIBALL) to an inversekinematics neutron source (LICORNE) to extract charge yields of fission fragments via γ-γ coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fastneutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly. DOI: 10.1103/PhysRevLett.118.222501 We report on results which will affect current knowledge at the interface of three separate domains: nuclear fission, nuclear structure, and energy applications. Measurements of fission fragment charge yields have been made using a novel experimental technique of coupling an innovative, inverse-kinematics, fast-neutron source, LICORNE [1,2], to a high-resolution, high-efficiency γ-ray spectrometer, MINIBALL [3]. This has allowed a detailed spectroscopic study of fission fragments produced via fast-neutroninduced fission of 238 Uðn; fÞ for the first time. Nuclear fission is a complex, dynamical nuclear process and there are still a number of unanswered questions which remain, particularly with regards to the evolution of isotopic fragment yields as a function of excitation energy. Experimental data are crucial to fully understand what drives the fragment split in fission and, in particular, the respective role of neutron and proton shells remains an unresolved issue [4].Second, neutron-induced fission is obviously important for energy applications since fragment yields influence reactor function through the total energy release, the synthesis of neutron poisons, the decay heat, and the production of long-lived waste. However, existing data on isotopic and charge yields at energies relevant for future PRL 118, 222501 (2017) P H Y S I C A L

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confidence: 99%

Anomalies in the Charge Yields of Fission Fragments from the U(n,f)238 Reaction

Wilson¹,

Lebois²,

Qi³

et al. 2017

Phys. Rev. Lett.

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“…to extract complete excitation energy and spin distributions in both fragments and their correlations. As a first step in this direction, the recent EXILL campaign combined a well-collimated cold neutron beam, incident on 235 U or 241 Pu targets, with an efficient Ge detector array consisting of EXOGAM clovers from GANIL, LOHEN-GRIN clovers and GASP detectors from Legnaro [183]. Besides a wealth of new nuclear-spectroscopy information, this campaign also provided new data on the population of excited states in the fission fragments [184].…”

Section: 12mentioning

confidence: 99%

Nuclear fission: a review of experimental advances and phenomenology

2017

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In the last two decades, through technological, experimental and theoretical advances, the situation in experimental fission studies has changed dramatically. With the use of advanced production and detection techniques both much more detailed and precise information can now be obtained for the traditional regions of fission research and, crucially, new regions of nuclei have become routinely accessible for fission studies. This work first of all reviews the recent developments in experimental fission techniques, in particular the resurgence of transfer-induced fission reactions with light and heavy ions, the emerging use of inverse-kinematic approaches, both at Coulomb and relativistic energies, and of fission studies with radioactive beams. The emphasis on the fission-fragment mass and charge distributions will be made in this work, though some of the other fission observables, such as prompt neutron and γ-ray emission will also be reviewed. A particular attention will be given to the low-energy fission in the so far scarcely explored nuclei in the very neutron-deficient lead region. They recently became the focus for several complementary experimental studies, such as β-delayed fission with radioactive beams at ISOLDE(CERN), Coulex-induced fission of relativistic secondary beams at FRS(GSI), and several prompt fusion-fission studies. The synergy of these approaches allows a unique insight in the new region of asymmetric fission around [Formula: see text]Hg, recently discovered at ISOLDE. Recent extensive theoretical efforts in this region will also be outlined. The unprecedented high-quality data for fission fragments, completely identified in Z and A, by means of reactions in inverse kinematics at FRS(GSI) and VAMOS(GANIL) will be also reviewed. These experiments explored an extended range of mercury-to-californium elements, spanning from the neutron-deficient to neutron-rich nuclides, and covering both asymmetric, symmetric and transitional fission regions. Some aspects of heavy-ion induced fusion-fission and quasifission reactions will be also discussed, which reveal their dynamical features, such as the fission time scale. The crucial role of the multi-chance fission, probed by means of multinucleon-transfer induced fission reactions, will be highlighted. The review will conclude with the discussion of the new experimental fission facilities which are presently being brought into operation, along with promising 'next-generation' fission approaches, which might become available within the next decade.

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“…In the second setup, the GASP and ILL detectors were replaced by 16 LaBr 3 crystals for lifetime measurements by fast-timing techniques. A digital data acquisition, triggerless, allowed event rates up to 0.84 MHz to be handled and to study coincidences among γ transitions separated in time by several tens of μs [19]. 133 Sb was populated in two long runs of neutron induced fission of 235 U and 241 Pu targets.…”

Section: Sbmentioning

confidence: 99%

Interplay between collective and single particle excitations around neutron-rich doubly-magic nuclei

Leoni

2016

EPJ Web of Conferences

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The excitation spectra of nuclei with one or two particles outside a doubly-magic core are expected to be dominated, at low energy, by the couplings between phonon excitations of the core and valence particles. A survey of the experimental situation is given for some nuclei lying in close proximity of neutron-rich doubly-magic systems, such as 47,49 Ca, 133 Sb and 210 Bi. Data are obtained with various types of reactions (multinucleon transfer with heavy ions, cold neutron capture and neutron induced fission of 235 U and 241 Pu targets), with the employment of complex detection systems based on HPGe arrays. A comparison with theoretical calculations is also presented, in terms of large shell model calculations and of a phenomenological particle-phonon model. In the case of 133 Sb, a new microscopic "hybrid" model is introduced: it is based on the coupling between core excitations (both collective and non-collective) of the doubly-magic core and the valence nucleon, using the Skyrme effective interaction in a consistent way.

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Spectroscopy of neutron rich nuclei using cold neutron induced fission of actinide targets at the ILL: the EXILL campaign

Cited by 10 publications

References 8 publications

Anomalies in the Charge Yields of Fission Fragments from the U(n,f)238 Reaction

Anomalies in the Charge Yields of Fission Fragments from the U(n,f)238 Reaction

Nuclear fission: a review of experimental advances and phenomenology

Interplay between collective and single particle excitations around neutron-rich doubly-magic nuclei

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