Asymmetric Fission Research Articles

Simultaneous description of charge, mass, total kinetic energy, and neutron multiplicity distributions in fission of Th and U isotopes

For fissioning isotopes of thorium and uranium, the simultaneous description of the charge, mass, total kinetic energy, and neutron multiplicity distributions of fission fragments is presented within the improved scission-point model. Correlations between all these observables are analyzed. The influence of the transition from symmetric to asymmetric fission mode on the shape of neutron multiplicity distribution is studied.

Crypts in Asymmetric Fission in Endoscopic Biopsies from Swedish Patients With Inflammatory Bowel Disease

We previously found crypts in symmetric fission (CSF) and in asymmetric fission (CAF) in colectomy-specimens with ulcerative colitis. We now analyzed CSF and CAF (CSAF) in biopsies from 80 patients with inflammatory bowel disease (IBD) without dysplasia or carcinoma. One unselected double-biopsy from affected endoscopic areas was investigated in the 80 cases. A total of 353 crypts in fission were found. The median number of CAF/biopsy was 3.7 and for CSF/biopsy, 0.7 (p<0.00001). CSAF often occur in unselected biopsies from patients with IBD. Whereas the increased frequency of CSF might mirror a compensatory mechanism of crypt production in areas occupied by inflammation, CAF reflects a pathological aberration of cryptogenesis, probably generated by somatic mutations. The biological significance of CAF in IBD without dysplasia or carcinoma, deserves to be further investigated.

Effect of compact and elongated configurations on the spontaneous and induced fission of Fm isotopes

The spontaneous fission (SF) analysis of even mass $^{242\ensuremath{-}260}\mathrm{Fm}$ isotopes is carried out using a preformed cluster model based on quantum mechanical fragmentation theory. The deformation effects are included up to the quadrupole (${\ensuremath{\beta}}_{2}$) deformed nuclei with optimum orientations (${\ensuremath{\theta}}_{i}^{\mathrm{opt}.}$) leading to hot-compact (side-to-side) and cold-elongated (tip-to-tip) configurations. The spherical and hot-compact deformed configurations of decay fragments result in the symmetric fragment mass distributions for Fm isotopes; however, the symmetric peak gets sharper with an increase in the neutron ($N$) number of the parent nucleus. In the case of cold orientations, a transition from two-peaked (asymmetric fission) to three-peaked (multimodal fission) mass distribution is observed with an increase in the mass number of Fm. The SF half-lives (${T}_{1/2}^{\mathrm{SF}}$) are calculated using the neck-length parameter ($\mathrm{\ensuremath{\Delta}}R$) for $^{242\ensuremath{-}260}\mathrm{Fm}$ isotopes and compared with the experimental data. Besides this, the induced fission of Fm isotopes is studied within the dynamical cluster-decay model. The energy dependence of fission fragment mass distributions and the isotopic dependence is analyzed at energy range ${E}^{*}=5$--42 MeV. In addition, the role of temperature-dependent deformations in the fission dynamics is also explored.

Fission fragment mass distribution in the S32+Sm144 reaction

Background: An asymmetric fission was reported by Andreyev et al. in \ensuremath{\beta}-delayed fission of $^{180}\mathrm{Tl}$ [Phys. Rev. Lett. 105, 252502 (2010)]. Subsequent theoretical calculations suggested that the asymmetric nature of the mass distribution is not restricted to the $^{180}\mathrm{Hg}$ only but is also expected for many other nuclei in the mass region $A\ensuremath{\approx}180$. Thus, it is important to investigate fission fragment mass distribution for different fissioning systems over a wide range of excitation energy in the mass region $A\ensuremath{\approx}180$.Purpose: Present measurements have been carried out to study the nature of the fission fragment mass distribution in the $^{32}\mathrm{S}+^{144}\mathrm{Sm}\ensuremath{\rightarrow}^{176}\mathrm{Pt}$ reaction in the compound nucleus excitation energy range of 38.7--47.5 MeV and investigate the role of multimodal fission.Method: Mass distributions have been determined from the time of flight (TOF) of the fission fragments, which was measured with respect to the beam pulse. Two multiwire proportional counters were placed at the folding angle to detect the fission fragments. Measured TOF of the fission fragments was used to obtain their velocities, which were further used to obtain the fission fragment mass distribution.Results: The fission fragment mass distributions at all three beam energies were observed to have flattop natures, which could not be fitted well by a one-Gaussian function. A fit using a two-Gaussian function significantly improved the ${\ensuremath{\chi}}^{2}$ values. The ratio of the most probable heavy to light fragment mass (${A}_{\mathrm{H}}/{A}_{\mathrm{L}}$) was observed as $\ensuremath{\approx}99.4/76.6$. A systematic study of the centroid values of asymmetric peaks in the mass distribution for different fissioning systems around mass region $A\ensuremath{\approx}180$ showed that heavier mass peak is centered around ${A}_{\mathrm{H}}\ensuremath{\approx}100$. Further analysis of ${A}_{\mathrm{H}}$ and ${A}_{\mathrm{L}}$ to obtain the corresponding neutron and proton numbers gave heavy fragment neutron number (${N}_{\mathrm{H}}$) around $\ensuremath{\approx}56$ and light fragment proton number (${Z}_{\mathrm{L}}$) in the range of $\ensuremath{\approx}34--36$.Conclusions: Observation of the flattop nature indicated the contributions from multimodal fission having both symmetric and asymmetric fission components, similar to those reported earlier in the mass region $A\ensuremath{\approx}180$, although it did not show a clear dip in symmetry as observed in some of the studies. The observed values of the neutron number in the heavy fragment (${N}_{\mathrm{H}}$) and proton number in the light fragment (${Z}_{\mathrm{L}}$) are consistent with the values recently proposed in Phys. Rev. C 100, 041602(R) (2019) and arXiv:2007.16184] for fissioning systems in the similar mass range. Comparison of the data on the width of the mass distribution from the present paper with those from similar fissioning systems with different ${Z}_{P}{Z}_{T}$ values suggested that the observed width of the mass distribution has a dependence on the neutron-proton configuration along with the entrance channel dynamics.

Nondysplastic Crypts in Fission in Nonpolypoid Adenomas and in the Adjacent Mucosa Support Field Cancerization in the Colon

We recently noticed in nonpolypoid adenomas (NPA) and the adjacent normal mucosa, nondysplastic crypts in symmetric and asymmetric fission (NDCSAF). All NDCSAF found in 80 small NPA and in the adjacent mucosa were registered. A total of 178 NDCSAF (mean, 2.2) were found: 12 (6.7%) interspersed between adenomatous glands, 36 (20.2%) partially replaced by dysplastic epithelium, and 130 (73%) underneath the adenomatous tissue. Of the 61 cases with normal mucosa adjacent to NPA, 40 (65.6%) disclosed NDCSAF, and the remaining 21 (34.4%) normal crypts, exclusively. The accruing of NDCSAF within NPA and surrounding mucosa, are outstanding findings. Given that colonic crypts may undergo only one fission every 30-40 years, the accruing of NDCSAF in and about small NPA reveals mucosal hubs with pathological aberrations of cryptogenesis, probably conveyed by somatic mutations. The findings support the existence of field cancerization in the colonic mucosa.

Impact of different hydrodynamical mass transfer approaches in the spontaneous fission of Cf isotopes

Theoretical possibilities for the spontaneous emission of fission fragments from [Formula: see text]Cf parents are investigated within the framework of preformed cluster decay model (PCM). The fragmentation potential exhibits a modification from dominated asymmetric fission profile to symmetric splitting with the rise in the N/Z ratio of parent nuclei. The calculated spontaneous fission (SF) half-life times of Cf isotopes find nice agreement with the experimental data, except for [Formula: see text]Cf nucleus. Within the PCM, the hydrodynamical mass transfer among the outgoing binary fragments occurs through a cylindrical vessel connecting them. For the overlapping configuration [Formula: see text]), the two classical models namely Model A and Model B (differ in the way the radius of the connecting cylinder is controlled) are used to estimate mass transfer flow of binary fragmentation. It is observed that with change in the overlapping distance, the radius of the cylindrical vessel changes in Model A, whereas the same remains fixed in Model B. In case of Model B, the effect of cylindrical radii parameter ([Formula: see text]) is also analyzed for [Formula: see text]Cf parents at optimum neck-length ([Formula: see text]R) in view of different observable such as most probable SF fragments, preformation probability, mass transfer, the SF half-lives and the results are compared with Model A calculations. The magnitude of mass transfer, preformation probability, and hence the SF half-lives gets significantly modified on switching from Model A to Model B. Further, a large amount of mass is transferred between the asymmetric fragments as compared to the symmetric ones. The SF half-lives are shown to depend strongly on the choice of classical models as well as on the cylindrical radius parameter, [Formula: see text]. The study infers the importance of classical models to spread further light in the understanding of the dynamical behavior of fragment formation in the fission process.

Asymmetric crypt fission in colectomy specimens in patients with ulcerative colitis

AimsWe previously found colonic crypts with asymmetric fission bordering regenerating ulcers in ulcerative colitis (UC). The present objective was to assess the frequency of asymmetric crypt-fission in colectomy specimens from...

Total kinetic energy release in the fast-neutron-induced fission of Np237

The total kinetic energy (TKE) release in the fast neutron-induced fission of $^{237}\mathrm{Np}$ was measured for neutron energies from ${E}_{n}=2.6--100\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ at the Los Alamos Neutron Science Center at the Weapons Neutron Research facility. The post-TKE release decreases nonlinearly with increasing incident neutron energy and can be represented as $\mathrm{TKE}\phantom{\rule{0.16em}{0ex}}(\mathrm{MeV})=(174.38\ifmmode\pm\else\textpm\fi{}0.72)--(5.11\ifmmode\pm\else\textpm\fi{}0.5821){\mathrm{log}}_{10}{E}_{n}$ for ${E}_{n}&gt;1\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Analysis of the fragment mass distributions indicates that the decrease in TKE with increasing ${E}_{n}$ is a consequence of the fading out of shell effects at high excitation energies (resulting in an increase of symmetric fission) and the decrease of the total kinetic energy associated with asymmetric fission with increasing ${E}_{n}$.

Analysis of various competing binary and ternary decay processes of the Es253 nucleus

The ground state binary and ternary decays of the $^{253}\mathrm{Es}$ radioactive nucleus are investigated using the quantum mechanical fragmentation theory (QMFT) based cluster decay models. First, the relative fragmentation of $^{253}\mathrm{Es}$ is analyzed within the framework of the preformed cluster model (PCM). The PCM-calculated binary fragmentation structure is explored for two types of nuclear potential, i.e., Yukawa plus exponential and proximity potentials. The structure of the fragmentation potential and the location of potential minima are found to be independent of the choice of nuclear potential. It is observed from binary fragmentation structures that $\ensuremath{\alpha}$ $(^{4}\mathrm{He})$ decay, cluster $(^{46}\mathrm{Ar})$ emission, heavy particle $(^{82}\mathrm{Ge})$ radioactivity, and spontaneous fission fragmentation $(^{125}\mathrm{In})$ are the possible ground state decay modes of the $^{253}\mathrm{Es}$ nucleus. The competitive emergence of these decay channels is explored by studying the preformation probability ${P}_{0}$, penetrability $P$, and half-lives ${T}_{1/2}$. The calculated half-lives of $\ensuremath{\alpha}$ and spontaneous fission match nicely with the experimental measurements. Also, the half-lives are predicted for cluster and heavy particle radioactivity, for which experimental verification would be of further interest. Further, an effort is made to explore the possibility of ternary fission (particle accompanied fission) for the decay of the $^{253}\mathrm{Es}$ nucleus using the three-cluster model (TCM), where $^{4}\mathrm{He}$ is observed to be the third fragment along with two binary fission fragments. A comparison of relative yields of binary and ternary fission confirm that the probability of the binary fission decay mode is larger than that of ternary fission. Moreover, closed shell effects play a significant role in the symmetric and asymmetric fission of binary and ternary fission, respectively.

Role of higher order deformations in fission fragment mass distribution of Astatine isotopes within collective clusterization approach

The fission fragment mass distribution is used as an investigation tool which assists to disentangle between different modes of fission (symmetric fission and asymmetric fission). In the present work, the fission dynamics of various ‘At*’ isotopes with mass number A=191 to 220 formed in 19F-induced reactions at common centre-of-mass energy Ec.m .=78.5 MeV is explored. The calculations are made within the dynamical cluster-decay model (DCM) using three type of fragmentation such as spherical, (β 2-deformed and (β 2 – β 2-deformed with hot compact optimized orientations. The structural effects come into picture when deformation effects are included in the fragmentation potential. The mass distributions of ‘At*’ isotopes gets significantly modified after inclusion of deformation effects of decaying fragments. The preformation yield shows a drift from symmetric to asymmetric fission with increase in mass of compound nuclei from ACN =191 to 220. The clear signature of fine-structure effects is evident in view of single humped to double humped preformation structure in the fissioning region. However, the mass division of At isotopes is symmetric for spherical choice of fragments. Finally, the analysis of hot (compact) and cold (elongated) configurations of β 2-deformed and oriented fragments is also carried out.

Alpha and heavy cluster radioactivity of superheavy nuclei 100 ⩽ Z ⩽ 120

Using Cubic plus Yukawa plus Exponential (CYE) model, half lives of alpha decay and heavy cluster radioactivity of Superheavy nuclei have been systematically investigated for even-even, even-odd, odd-even and odd-odd nuclei with 100 ⩽ Z ⩽ 120. We have done our calculations by considering the Coulomb, centrifugal and Yukawa plus exponential potentials as an interacting barrier for separated fragments and the cubic potential for the overlapping region.The predicted half life time values by including deformation effects on parent and parent cluster have been compared with theAnalytical Super Asymmetric Fission (ASAF) model of D.N.Poenaru et.al. In this work, we have compared the half life time values of alpha and heavy cluster radioactivity of Super heavy nuclei leading to 208Pb. This study suggests that heavy-cluster radioactivity may be comparable to or even dominant over a decay for some of the isotopes with Z ⩾ 118. Furthermore, branching ratio calculations have been performed to find out the probable cluster emitters. The predictions for cluster emitters are in agreement with CPPM model by Santhosh et. al.,and Wentzel-Kramers-Brillouin (WKB) method by A.Soylu et. al. We hope that this study will help in future measurements on α-decay and cluster radioactivity half-lives of SHN.

Mass-asymmetric fission of Bi205,207,209 at energies close to the fission barrier using proton bombardment of Pb204,206,208

Background: Recent observation of mass-asymmetric fission in neutron-deficient Hg and Pt nuclei has reignited interest in fission fragment mass distributions close to Pb. Investigations at energies close to the fission barrier, where mass-asymmetric fission is expected to be most obvious and the sensitivity to shell effects is maximized, are limited in this mass region.Purpose: To measure fission mass distributions for $^{205,207,209}\mathrm{Bi}$ nuclei at the lowest possible excitation energies to determine how the mass distributions change with excitation energy and the neutron number of the compound nucleus.Method: Proton beams bombarding targets of $^{204,206,208}\mathrm{Pb}$ were used to study the fission of $^{205,207,209}\mathrm{Bi}$ at energies from just above to 10 MeV above their fission barriers. Fission fragments were measured using the CUBE fission spectrometer. Fission fragment mass distributions were determined using a newly developed time difference analysis method. Mass distributions were characterized by triple-Gaussian fits to determine the systematic trends across each isotope with excitation energy.Results: Measured mass distributions of all three Bi isotopes exhibit a component of mass-asymmetric fission at all energies studied. The probability of mass-asymmetric fission decreases significantly with increasing excitation energy, from $\ensuremath{\approx}70$ to $\ensuremath{\approx}40%$ over a 10-MeV range. Comparisons between the three Bi isotopes hint at an increase in the mass-symmetric fission yield with increasing neutron number, which could be due to a decrease in the difference between the symmetric and asymmetric fission barriers. The centroids of the mass-asymmetric peaks suggest that several deformed shell gaps in the fission fragments could be contributing to the presence of the mass-asymmetric fission mode with ${Z}_{\mathrm{light}}\ensuremath{\simeq}38$, ${Z}_{\mathrm{heavy}}\ensuremath{\simeq}45$, and ${N}_{\mathrm{light}}\ensuremath{\simeq}56$ all present in the fission fragments.Conclusions: Measurements of fission mass distributions at the lowest possible excitation energies above the fission barrier provide an excellent platform to investigate the origins of the mass-asymmetric fission mode. Further systematic measurements at these energies offer an opportunity to rigorously test new models of fission in this mass region.

Measurement of fragment-mass distributions from fission of At214 following the Be9+Tl205 reaction

Background: The recent surprising experimental discovery of asymmetric fission in the nucleus $^{180}\mathrm{Hg}$ at low excitation energy has renewed interest concerning our understanding of the role of nuclear shell effects in the dynamics of the fission process. New theoretical models have been developed that claim to successfully explain the observed asymmetric fission of $^{180}\mathrm{Hg}$ and also predict the nature of mass distributions of several other preactinide nuclei for which experimental data are scarce.Purpose: We investigated fragment-mass distributions in the fission of the preactinide nucleus $^{214}\mathrm{At}$ at different excitation energies near the Coulomb barrier. The present results were compared with the predictions from a recent state-of-the-art theoretical calculation, as well as with our previous measurement for the nearby nucleus $^{210}\mathrm{Po}$.Methods: A pulsed heavy-ion beam was used in the experiment. Fission fragments were detected with two large-area position-sensitive multiwire proportional counters placed at the folding angle. Mass distributions were extracted from time-of-flight differences and position information ($\ensuremath{\theta},\ensuremath{\phi}$) for the fission fragments.Results: An asymmetry in fragment-mass distribution in the fission of $^{214}\mathrm{At}$ was observed at an excitation energy of $\ensuremath{\approx}31$ MeV, where a shell effect is found to influence the potential energy surface. At higher excitation energies, mass distributions are predominantly symmetric indicating the absence of shell effects.Conclusion: This finding is consistent with the prediction of a recent macroscopic-microscopic dynamical model. However, for the preactinides, static models with nascent fragment shell structure are likely to produce similar results.

Asymmetric crypt fission in sessile serrated lesions

ObjectiveSessile serrated lesions without dysplasia (SSL-ND) are epitomised by dilated crypts with epithelial serrations and architectural distortions portraying boot-shapes, L-shapes or inverted-T shapes. Recently, crypts in asymmetric fission were detected...

Clipper, a novel lncRNA regulating cardiomyocyte mitochondrial biogenesis and proliferation

In the adult heart, regeneration after myocardial infarction (MI) is extremely limited. Enhancing cardiomyocyte (CM) proliferation represents a promising approach for inducing regenerative repair in the damaged heart. Long noncoding RNAs (lncRNAs) represent a class of epigenetic regulatory molecules controlling genes expression and thereby crucial regulators of cell identity and behavior. Identification and characterization of lncRNAs inducing proliferation in cardiomyocytes in order to promote heart regeneration following myocardial infarction. Three hundred and fifty antisense oligonucleotide were selected to knockdown (KD) individually 350 heart-enriched LncRNAs in a high-throughput screening assay in vitro using neonatal CMs. Mitochondrial dynamics and respiration were evaluated via Seahorse XF Analyzers and SIM microscopy respectively. The effect of Clipper KD on CM proliferation and heart function in vivo was investigated in a mouse model of MI. We identified Clipper, a nuclear CM-enriched enhancer-associated lncRNA, located in the Lipin1 locus. Clipper KD induced significant CM proliferation in vitro, associated with a reduction of Lipin1 expression, indicating that Clipper could work via regulating Lpin1. Lpin1 encodes a transcriptional regulator involved in mitochondrial biogenesis. Upon Clipper KD, mitochondrial dynamics and function were decreased. In particular, mitochondrial asymmetric fission was reduced. Asymmetric fission is a response to oxidative stress and mitochondrial turnover under stress conditions. ROS, a major determinant of CM cell cycle arrest, are therefore reduced following Clipper KD in CMs. In vivo, CM proliferation is also observed after Clipper KD following MI. However, function is not restored, likely because energy metabolism is simultaneously affected. This study suggests the existence of coordinated regulation of CM mitochondrial function and proliferation, in part through the Clipper/Lipin1 axis.

Macroscopic–microscopic calculations of fission potential surface of uranium isotopes in the three quadratic surfaces parametrization

Five-dimensional (5D) fission potential energy surfaces (PES) for uranium nuclei are investigated based on the macroscopic–microscopic Lublin–Strasbourg drop model in the three-quadratic-surface parametrization, and the heights of static fission barriers are obtained. Asymmetric and symmetric fission paths are presented on the 5D PES of 236U for different nuclear shapes. The calculated barrier heights, EA and EB, are quite consistent with the experimental data for all even–even nuclei of uranium isotopes, from 230U to 244U.

Two histologic compartments in nonpolypoid conventional colon adenomas.

Two intertwined compartments coexisting in nonpolypoid conventional (i.e. tubular or villous) adenomas are highlighted in this review: one built of dysplastic tissue on top and the other portraying crypts with irregular, corrupted shapes, albeit lined with normal epithelium, below. The latter compartment has remained unattended in the literature. Recently, however, the histologic characteristics of the nondysplastic compartment in nonpolypoid conventional adenomas were closely examined, and some of its biological attributes were unveiled. Studies with the proliferation marker ki67 showed that the crypts with irregular, corrupted shapes in the nondysplastic compartment displayed haphazardly distributed proliferating cell-domains. Given that the proliferating cells are generated by stem cells, the relocation of proliferating cell-domains in those crypts seems to be the result of a reorganization of the stem cells within the crypts. The abnormal distribution of proliferating cells, the finding of p53-upregulated cells, and of crypts in asymmetric fission suggest that the crypts in that compartment are histo-biologically altered, probably somatically mutated. This new information might contribute to unravel the riddle of crypto-histogenesis of nonpolypoid conventional adenomas of the colon. More research along these lines is necessary, before the biology of the crypts in the nondysplastic compartment can be fully translated into molecular terms.

Fission partition a reflection of shell closures: Decay of 220,224U⁎ at eight excitation energies

Decay modes of the compound systems formed in 86Kr + 134,138Ba → 220,224U⁎ reactions at eight excitation energies have been compared to explore the influence of shell closures and excitation energy. The mass distributions of the cross-sections have been calculated for the two compound systems by keeping their excitation energies the same. The production cross-section for the light particles, intermediate mass fragments, symmetric and asymmetric fission fragments, total fission fragments, percentage of the cross-section for symmetric and asymmetric fission fragments, the ratio of the cross-sections of the symmetric and asymmetric fission fragments and fission barrier as a function of the incident energy have been compared. The range of the incident energy which corresponds to the high probability of the compound nucleus process has been obtained. Three angular momentum windows have been realized from the variation of the production cross-section for the light particles, intermediate mass fragments, fission fragments and the total fragments as a function of the angular momentum which correspond to the dominance of a reaction mechanism in that window. The shell closures have been reflected in the fission partition and weaken with the increase of the incident energy along with the loss of odd-even effects. The mode of the reaction depends upon the excitation energy and angular momentum of the compound system.

Study of Mass-Asymmetric Fission of 180,190Hg Formed in the 36Ar + 144,154Sm Reactions

t—The mass–energy distributions of fission fragments of excited 180,190Hg nuclei formed in 36Ar + 144,154Sm reactions are measured at incident 36Ar energies of 158, 181, and 222 MeV using the double-arm time-of-flight spectrometer CORSET. The asymmetric fission of 180,190Hg with the most probable masses of light and heavy fragments of 79 and 101 amu, and 84 and 106 amu, respectively, is observed in mass distributions of 180,190Hg at energies of excitation of up to 75 MeV. Two components manifesting the symmetric and asymmetric fission modes are observed in the kinetic energy distributions.

Evidence for a New Compact Symmetric Fission Mode in Light Thorium Isotopes.

Taking benefit of the R3B/SOFIA setup to measure the mass and the nuclear charge of both fission fragments in coincidence with the total prompt-neutron multiplicity, the scission configurations are inferred along the thorium chain, from the asymmetric fission in the heavier isotopes to the symmetric fission in the neutron-deficient thorium. Against all expectations, the symmetric scission in the light thorium isotopes shows a compact configuration, which is in total contrast to what is known in the fission of the heavier thorium isotopes and heavier actinides. This new main symmetric scission mode is characterized by a significant drop in deformation energy of the fission fragments of about 19MeV, compared to the well-known symmetric scission in the uranium-plutonium region.