Two-mode fission – experimental verification and characterization of two fission-modes

Nagame, Y.; Nakahara, Hiromichi

doi:10.1524/ract.2012.1968

Cited by 6 publications

(5 citation statements)

References 67 publications

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“…Competition between symmetric and asymmetric fission, corresponding to respectively lower and higher TKE and resulting in a triple-humped MD has been reported around 226 Th [16][17][18]. These observations strongly support the hypothesis that nuclei may fission through several independent fission modes corresponding to different pre-scission shapes and fission paths in a multidimensional potential-energy landscape, referred to in literature as multimodal or multichannel fission [4,5,11,[16][17][18][19]. In the pre-actinide region, predominantly symmetric FF mass distributions were measured.…”

supporting

confidence: 72%

“…Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy density functional yields discrepancies. This demonstrates once more the need of dynamical fission calculations, as for both models the potential-energy surfaces lack pronounced structures, in contrast to the actinide region.Nuclear fission, the division of a heavy atomic nucleus into predominantly two parts, continues to provide new and unexpected features in spite of a long history of intensive theoretical and experimental studies [1][2][3][4][5][6][7]. The fission process is not only important for several applications, such as energy production and radiopharmacology, but also has a direct impact on the understanding of the fission recycling process in r -process nucleosynthesis [8,9].…”

mentioning

confidence: 99%

“…Mass distributions (MDs) are usually predominantly symmetric or asymmetric with the yields exhibiting a single peak or two distinct peaks, respectively. However, in several cases a mixture of two modes was observed [5]. Experimental observables characterizing various fission modes are the width of the MD peak(s), the position of these peaks in asymmetric mass division and total kinetic energy (TKE) of the FFs.…”

mentioning

confidence: 99%

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Evolution of fission-fragment mass distributions in the neutron-deficient lead region

Ghys¹,

Andreyev²,

Huyse³

et al. 2014

Phys. Rev. C

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Low-energy β-delayed fission of 194,196 At and 200,202 Fr was studied in detail at the mass separator ISOLDE at CERN. The fission-fragment mass distributions of daughter nuclei 194,196 Po and 202 Rn indicate a triple-humped structure, marking the transition between asymmetric fission of 178,180 Hg and symmetric fission in the light Ra-Rn nuclei. Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy density functional yields discrepancies. This demonstrates once more the need of dynamical fission calculations, as for both models the potential-energy surfaces lack pronounced structures, in contrast to the actinide region.Nuclear fission, the division of a heavy atomic nucleus into predominantly two parts, continues to provide new and unexpected features in spite of a long history of intensive theoretical and experimental studies [1][2][3][4][5][6][7]. The fission process is not only important for several applications, such as energy production and radiopharmacology, but also has a direct impact on the understanding of the fission recycling process in r -process nucleosynthesis [8,9]. Therefore, a description of the fission process with reliable predictive power is needed, in particular for low-energy fission where the fission-fragment (FF) mass distributions are strongly * lars.ghys@fys.kuleuven.be sensitive to microscopic effects [4]. Mass distributions (MDs) are usually predominantly symmetric or asymmetric with the yields exhibiting a single peak or two distinct peaks, respectively. However, in several cases a mixture of two modes was observed [5]. Experimental observables characterizing various fission modes are the width of the MD peak(s), the position of these peaks in asymmetric mass division and total kinetic energy (TKE) of the FFs. The dominance of asymmetric fission in most of the actinide region beyond A = 226 up to about 256 Fm was attributed to strong microscopic effects of the heavier FF, near the doubly-magic 132 Sn [4,10,11]. However, nuclei such as 258 Fm and 259,260 Md exhibit complex MDs, each with a narrow and a broad symmetric component with a higher and lower TKE, respectively. 2This phenomenon is called bimodal fission [12][13][14][15]. Competition between symmetric and asymmetric fission, corresponding to respectively lower and higher TKE and resulting in a triple-humped MD has been reported around 226 Th [16][17][18]. These observations strongly support the hypothesis that nuclei may fission through several independent fission modes corresponding to different pre-scission shapes and fission paths in a multidimensional potential-energy landscape, referred to in literature as multimodal or multichannel fission [4,5,11,[16][17][18][19]. In the pre-actinide region, predominantly symmetric FF mass distributions were measured. A few relevant cases for the present discussion (see also Fig.1) are 195 Au, 198 Hg and 208,210 Po, studied by means of charged-particle induced reactions [20][21][22] and 204,206,...

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supporting

confidence: 72%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Evolution of fission-fragment mass distributions in the neutron-deficient lead region

Ghys¹,

Andreyev²,

Huyse³

et al. 2014

Phys. Rev. C

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“…[12], such a pattern in the PES for 196 Po, without well-defined shell corrections, should lead to several fission paths possibly giving rise to a mixture of symmetric and asymmetric mass distributions, which is in agreement with our experimental data. This work therefore extends the previous studies of the multimodal fission [49] phenomenon in the transactinides to the very neutron-deficient nuclei in the lead region.…”

Section: A Fission-fragment Energy and Mass Spectrasupporting

confidence: 83%

β-delayed fission andαdecay ofAt196

Truesdale¹,

Andreyev²,

Ghys³

et al. 2016

Phys. Rev. C

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A nuclear-decay spectroscopy study of the neutron-deficient isotope 196 At is reported where an isotopically pure beam was produced using the selective Resonance Ionization Laser Ion Source and On-Line Isotope Mass Separator (CERN). The fine-structure α decay of 196 At allowed the low-energy excited states in the daughter nucleus 192 Bi to be investigated. A β-delayed fission study of 196 At was also performed. A mixture of symmetric and asymmetric fission-fragment mass distributions of the daughter isotope 196 Po (populated by β decay of 196 At) was deduced based on the measured fission-fragment energies. A βDF probability P βDF (196 At) = 9(1) × 10 −5 was determined.

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“…This implies that the light mass peak approaches the heavy peak with increasing mass of the fissioning nucleus, until there is a sharp transition to symmetric fission with a narrow mass distribution and high total kinetic energy (TKE) between 256 Fm and 258 Fm. The same feature was also observed for several isotopes of other neighboring elements of similar mass [47,48,32,77]. In fact, already in the earlier fission studies further complex features in the FFMDs, TKE, and promptneutron multiplicity were observed in asymmetric…”

Section: Page 6 Of 77 Author Submitted Manuscript -Ropp-100800r2supporting

confidence: 76%

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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Two-mode fission – experimental verification and characterization of two fission-modes

Cited by 6 publications

References 67 publications

Evolution of fission-fragment mass distributions in the neutron-deficient lead region

Evolution of fission-fragment mass distributions in the neutron-deficient lead region

β-delayed fission andαdecay ofAt196

Nuclear fission: a review of experimental advances and phenomenology

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