Fission Fragment Mass Distributions Research Articles

The FFIS spectrometer for determination of fission fragment mass distribution with the energy–velocity method

The FFIS spectrometer (Fission Fragment Identification Spectrometer) for determining independent fission yields has been developed based on the E–v method. By directly measuring the time-of-flight (TOF) and kinetic energy of fission fragments on their flight path, the post-neutron-emission mass yield distributions can be obtained. With the aim of getting the highest possible mass resolution, an axial grid ionization chamber and a TOF measurement system based on microchannel plate (MCP) detectors were designed. The ionization chamber with a silicon nitride entrance window of 100 nm thickness was tested and calibrated with a 252Cf spontaneous fission source. The intrinsic energy resolution for 1.27 MeV/u 63Cu particles is measured to be 450 keV (FWHM). The time resolution was determined with two MCP timing detectors to be 157 ps (FWHM) for 241Am radiation source, implying that the intrinsic time resolution is about 110 ps (FWHM) for a single timing detector. Thermal-neutron-induced fission of 235U was studied at the In-hospital Neutron Irradiator (IHNI). An event-by-event energy loss addback technique was developed based on Geant4 calculation to minimize the correction error. The first results of mass yield distributions from 235U(nth,f) are reported.

Measurement of mass and total kinetic energy distributions for the C12+Lu175 system

Fission fragment mass and total kinetic energy (TKE) distributions were measured for $^{12}\mathrm{C}+^{175}\mathrm{Lu}$ system at excitation energies down to 16.7 MeV above the saddle point. The overall mass and TKE distributions could be fitted with single Gaussian functions. The observed width of the mass and TKE distributions agree well with the systematics based on liquid drop (LD) behavior. The average TKE also shows parabolic dependence on fragment mass, as expected from LD behavior. Small contributions due to microscopic corrections from $Z\ensuremath{\approx}38$ and 45 shells can be extracted, if the widths of the LD component are fixed from systematics. Contrary to the theoretical predictions of substantial contributions from microscopic corrections, dominance of liquid drop behavior was observed.

Impact of nuclear dissipation on the fission dynamics within the Langevin approach

The impact of nuclear dissipation on the dynamics of nuclear fission at low excitation energy is studied with a three-dimensional Langevin approach in which the two-center shell model is adopted to describe the nuclear shape and the single-particle potential. With three types of formulas for the friction tensor, such as the wall formula, the wall-and-window formula with and without the term related to the mass asymmetry change, the fragment mass and the total kinetic energy (TKE) distributions in low-energy fission are calculated. The calculated fragment mass distributions are almost identical for both with the wall formula and with the wall-and-window model without the term related to the mass asymmetry change, and both the results are consistent with the evaluated mass yields and the calculated results with the GEF model. Our study found that the term related to the mass asymmetry change in the window formula leads to an unreasonable shift of the peak position of the mass distribution. The TKE values calculated with the wall model are slightly larger than those with the wall-and-window model due to the more compact configuration obtained with the pure wall model. Moreover, the influences of the strength of friction tensor on the fragment distribution, the scission configuration, and the fission time distribution are investigated. With the present model the fission fragment mass distributions of U, Np, Pu, and Am isotopes are well reproduced and the systematic dependence of the averaged TKE on the Coulomb parameter is also well reproduced.

Fission mechanism inferred from nuclear shape fluctuation by the Langevin equation

One of the dynamical investigations foran understanding of the fission process is the analysis through Langevin trajectories in the nuclear deformation space. The main motivation of this analysis is to elucidate the characteristic nuclear-shape oscillation induced by a random force in the Langevin equation and its impact on the fission process. The characteristic random oscillation originates from the requirement of an overdamped condition. The properties of the friction tensor in the equation reveal that the directional nuclear shape fluctuations originate in the subspace of nuclear deformation. Our calculations exhibit a good agreement with the fission data for fermium isotopes, where the fission-fragment mass distribution changes dramatically from the asymmetric shape to the sharp symmetric shape as the masses of the fissioning Fm isotopes increase.

Characterize the grid inefficiency correction of Frisch grid ionization chamber with Garfield and SRIM

Grid inefficiency (GI) correction is critically important to accurately determine the energy and emission angle of charged particles in Frisch grid ionization chambers (FGIC). Presently, three correction methods have been proposed in the literature. All these three methods rely strongly on the accurate and stable calibration between two different electrical chain gains in experiments. To avoid these challenges, they are firstly investigated with Monte Carlo method by using Garfield and SRIM toolkit. Two types of grid wire (diameter 90 and 180 μm) were simulated to investigate the impacts of GI correction on energy correction, and ten different emission angles were adopted to estimate the effects of these correction methods on the angle reconstruction. The simulation results clearly distinguished the differences among these correction methods in energy determination. The correlation analysis (R = 0.99) among these different correction methods indicated that the impact of either correction approach is small on the determination of emission angle. The present work firstly investigates the effects of GI correction on emission angle with Monte Carlo methods, which is the basis of future work to measure the total kinetic energy and mass distribution of Fission Fragment (FF).

Experimental study of fast fission and quasifission in the Ca40+Pb208 reaction leading to the formation of the transfermium nucleus No248

Background: The stability of the transfermium nucleus against fission is mainly determined by the shell correction depending on its angular momentum and excitation energy.Purpose: The study of the fast fission process of the transfermium nucleus $^{248}\mathrm{No}$ and its dependence on the interaction energy and introduced angular momentum.Methods: Mass-energy distributions of the $^{248}\mathrm{No}$ fission fragments formed in the $^{40}\mathrm{Ca}$ + $^{208}\mathrm{Pb}$ reaction at energies above the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the $^{40}\mathrm{Ca}$-beam energies of 223, 250, and 284 MeV.Results: The contribution of the fast fission process is determined from the calculations of the driving potential, taking into account shell effects and rotational energy and amounts to 39% and 61% at 250 and 284 MeV, respectively. The mass-energy distributions of the quasifission and fast fission fragments have been extracted by subtracting the mass-energy matrices associated with compound nucleus fission from those of all measured fissionlike events. The asymmetric fragments with masses 97 and 151 u were found to be the most probable in the fast fission of $^{248}\mathrm{No}$. With increasing $^{40}\mathrm{Ca}$ energy from 250 to 284 MeV the mass distributions of the fast fission fragments change slightly.Conclusions: Contrary to quasifission in which the fragments are focused mainly around the closed neutron or proton shells, the influence of known proton or neutron shells on the asymmetric mass distribution in the fast fission process was not observed.

Reaction dynamics of the C12+Ta181 system near the Coulomb barrier: Evidence of fusion-fission events

Background: Interaction of a heavy projectile with a heavy target produces a massive compound nucleus (CN), which deexcites through two possible modes: evaporation of light particles and fission. In order to develop a clear understanding of fusion-fission (FF) dynamics, it is important to explore the preactinide region at energies around and above the Coulomb barrier.Purpose: The objective is to study the dynamics involved in the fusion of $^{12}\mathrm{C}$, a cluster structured projectile, with $^{181}\mathrm{Ta}$ target, at energies within 4.3--6.0 MeV/nucleon, by measuring the production cross sections of the radionuclides formed through complete/incomplete fusion (CF/ICF) and fission processes. In addition, the mass distribution of fission fragments, which is an important fission observable, is probed for a better understanding of dynamics.Method: Tantalum foil, backed by the aluminum catcher, arranged in a stack, was bombarded by $^{12}\mathrm{C}$ ions of 52--73 MeV energy. The off-beam $\ensuremath{\gamma}$-ray spectrometry method was adopted to measure the activity of the residues produced in each Ta target after the end of bombardment (EOB), and cross sections were calculated. To analyze the experimental cross sections, PACE4 and EMPIRE3.2.2 reaction model codes were employed. Further, the mass distribution of fission fragments was explored to obtain mass variance information.Results: In general, measured excitation functions of the residues produced through the evaporation of particles in $^{12}\mathrm{C}+^{181}\mathrm{Ta}$ reaction showed good agreement with the predictions of PACE4. ICF of $^{12}\mathrm{C}$ in $^{181}\mathrm{Ta}$ target with strength up to $7.7%$ has been observed and compared with the strength deduced from previously reported data for the same system. However, no signature of precompound processes has been observed in this study. A total of 12 fission fragments within $71\ensuremath{\le}A\ensuremath{\le}135$ mass range have been identified. Further, mass variance is rising with increasing mass asymmetry, which hints at the importance of entrance-channel parameters' role in deciding the spread of the mass distribution.Conclusions: Good agreement of PACE4 with the excitation functions of $xn$ channel evaporation residues confirms their production through the CF mechanism. Enhancement of cross sections in the $\ensuremath{\alpha}xn$ channel is attributed to the ICF process. Further, evidence of the production of fission fragments through a compound nuclear mechanism is indicated as a broad and symmetric mass distribution, observed through the Gaussian fitting. The trend of mass variance with rising excitation energy and mass asymmetry is found to be growing.

Construction of high-resolution energy—time-of-flight spectrometer for determination of fission fragment mass distributions

Construction of high-resolution energy—time-of-flight spectrometer for determination of fission fragment mass distributions

Potential energy surfaces and fission fragment mass yields of even-even superheavy nuclei * *Supported by the Polish National Science Center (2018/30/Q/ST2/00185) and the National Natural Science Foundation of China (11961131010, 11790325)

Potential energy surfaces and fission barriers of superheavy nuclei are analyzed in a macroscopic-microscopic model. The Lublin-Strasbourg Drop (LSD) model is used to obtain the macroscopic part of the energy, whereas the shell and pairing energy corrections are evaluated using the Yukawa-folded potential; a standard flooding technique is utilized to determine barrier heights. A Fourier shape parametrization containing only three deformation parameters is shown to effectively reproduce the nuclear shapes of nuclei approaching fission. In addition, a non-axial degree of freedom is taken into account to better describe the structure of nuclei around the ground state and in the saddle region. In addition to the symmetric fission valley, a new highly asymmetric fission mode is predicted in most superheavy nuclei. The fission fragment mass distributions of the considered nuclei are obtained by solving 3D Langevin equations.

Evaluation of pre-neutron-emission mass distributions of neutron-induced typical actinide fission using scission point model * *Supported by the NSFC-Nuclear Technology Innovation Joint Fund (U1867213), the NSAF (U1830102), the National Natural Science Foundations of China (12075105, 11705071, 11875155) and the Fundamental Research Funds for the Central Universities (lzujbky-2021-kb09)

The scission point model is improved by considering the excitation-dependent liquid drop model to calculate mass distributions for neutron-induced actinide nuclei fission. Excitation energy effects influence the deformations of light and heavy fragments. The improved scission point model shows a significant advance with regard to accuracy for calculating pre-neutron-emission mass distributions of neutron-induced typical actinide fission with incident-neutron-energies up to 99.5 MeV. The theoretical frame assures that the improved scission point model is suitable for evaluating the fission fragment mass distributions, which will provide guidance for studying fission physics and designing nuclear fission engineering and nuclear transmutation systems.

ИССЛЕДОВАНИЯ ВРЕМЕННОЙ ЗАВИСИМОСТИ СПАДА ИНТЕНСИВНОСТИ ЗАПАЗДЫВАЮЩИХ НЕЙТРОНОВ ПРИ ДЕЛЕНИИ ЯДЕР 237Np С РАЗЛИЧНОЙ ЭНЕРГИЕЙ ВОЗБУЖДЕНИЯ

Development of the technologies of nuclear energy utilization, particularly involving of the minor actinides nuclides in the fuel cycle, due to the differences of time characteristics of the fissioning systems and the number of neutrons emitted by nuclides in the fission process, including its growth with the growth of primary neutron energy require the increase of accuracy and the volume of nuclear data. In the present work the behavior of the time dependence of delayed neutron intensity is studied for the neutron induced fission of the 237Np with the growth of the excitation energy. In the process of the comparative analysis there have been used the data calculated using GEF code and experimental data. Comparative analysis of the mass distributions of fission fragments for the fission of 237Np by neutrons with energies 1 and 18 MeV shows the difference in the magnitude of the separate masses from 15 times in the region of the asymmetric fission to 100 times in the region of the symmetric fission, that is the evidence of the differences in the time behavior of the decay curves of delayed neutron intensity. Using the set-up, that allows registering the delayed neutrons, installed of the neutron-physical research channel of Tandem-3M accelerator there have been made the measurement of the decay curves of delayed neutron intensity using the primary neutrons with different energy.

Observation of a fission mode with very short elongation for the neutron-rich Md257 nucleus at high excitation energy

Mass and total kinetic-energy (TKE) distributions of fission fragments from $^{257}\mathrm{Md}$ nucleus populated by complete fusion of $^{19}\mathrm{F}$ with $^{238}\mathrm{U}$ have been measured in the range of excitation energy ${E}^{*}\ensuremath{\approx}37\text{\ensuremath{-}}48\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Due to the skewness of the measured TKE distributions, two Gaussian distributions were required to explain the data. The events with high TKE must originate from the supershort mode of fission, the presence of which has been confirmed by measuring two additional reactions: $^{19}\mathrm{F}+^{232}\mathrm{Th}$ and $^{18}\mathrm{O}+^{238}\mathrm{U}$ involving first a different target and then a different projectile leading to compound nuclei $^{251}\mathrm{Es}$ and $^{256}\mathrm{Fm}$, respectively, at similar excitation energies and comparing their mass-TKE correlation plots. The existence of considerable supershort mode of fission for the $^{257}\mathrm{Md}$ nucleus up to ${E}^{*}\ensuremath{\approx}48$ MeV, observed for the first time, reveals that such rare fission modes for neutron-rich exotic nuclei are far off from the liquid drop model predictions, even at high excitation energies.

Examination of different features of fission fragments of the excited compound nucleus Np236 produced in the p+U235 reaction at 10.3≤Ep≤30.0MeV within a stochastic approach

A stochastic approach based on four-dimensional Langevin equations has been used to estimate the mass distributions of fission fragments, the average masses of heavy fragments, the average total kinetic energies of fragments, and the average number of neutrons emitted per fission of $^{236}\mathrm{Np}$ produced in the $p+^{235}\mathrm{U}$ reaction at $10.3\ensuremath{\le}{E}_{p}\ensuremath{\le}30.0\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Three collective shape coordinates plus the projection of total spin of the compound nucleus to the symmetry axis $K$ were considered in the four-dimensional dynamical model. The effects of shell corrections and dissipation coefficient of $K {\ensuremath{\gamma}}_{K}$ were considered in the dynamical calculations. Comparison of the theoretical results for the mass distributions of fission fragments, the average masses of heavy fragments, and the average number of neutrons emitted per fission with the experimental data showed that the results of calculations were in good agreement with the experimental data, although the results of calculations for the average total kinetic energies of fission fragments were slightly higher than the experimental data. It was also shown that the number of fission events increased with time, and almost all of the fission events occurred dynamically until $t=4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ and that the number of fission events became saturated. Furthermore, it was also shown that the average masses of heavy fragments and the average total kinetic energies of fission fragments of $^{236}\mathrm{Np}$ decreased with increasing projectile energy.

Mass Distribution of Fission Fragments and Abundances of Heavy Nuclei Produced in the r-Process

Mass Distribution of Fission Fragments and Abundances of Heavy Nuclei Produced in the r-Process

Fission fragment mass and folding angle distributions in the reaction Be9+U238

Background: The excitation energy dependence of the fission fragment mass and folding angle distributions for reactions with loosely bound projectiles are reported to be significantly different compared to the reactions with tightly bound nuclei. Extensive study to understand the reaction mechanism of weakly bound projectiles is required as it can simulate the mechanism of fission induced with radioactive ion beams.Purpose: The effect of loosely bound nuclei on fission fragment folding angle and mass distributions in the $^{9}\mathrm{Be}+^{238}\mathrm{U}$ reaction near the Coulomb barrier energies is investigated and the contributions of incomplete fusion fission in the total fission cross section are studied.Methods: Mass and folding angle distributions of the fission fragments have been measured near the Coulomb barrier energies using two large area multiwire proportional counters. Fragment masses were determined from the time-of-flight difference method. To understand the effect of breakup of loosely bound nuclei, the results are compared with tightly bound proton-, $\ensuremath{\alpha}$-particle-, and carbon-induced reactions, as well as with the predictions from semiempirical calculations.Results: The width of folding angle distributions is found to increase with lowering excitation energy in the $^{9}\mathrm{Be}+^{238}\mathrm{U}$ reaction. This is in contrast to the reaction $^{12}\mathrm{C}+^{232}\mathrm{Th}$ involving tightly bound projectiles, populating similar compound nuclei. The peak-to-valley ratios of the fission fragment mass distributions for all events are found to sharply increase with lowering excitation energy in the $^{9}\mathrm{Be}+^{238}\mathrm{U}$ reaction. The possible contribution of incomplete fusion into the total fission cross section could be extracted. The measured mass distributions were found to be consistent with the semiempirical calculation gef and macro-microscopic two-center shell model calculations considering the admixture of incomplete fusion fission.Conclusion: For actinide targets, mass distributions of inclusive fission are influenced by the breakup/transfer channels of the weakly bound projectiles. At the above-barrier energies, the contribution of incomplete fusion is found to be $\ensuremath{\approx}25\ifmmode\pm\else\textpm\fi{}4%$ which is similar to the reported value of the complete fusion suppression factor in reactions involving nuclei with low binding energies. The increase in the peak-to-valley ratio with lowering excitation energy in the fission fragment mass distribution could be explained by the combined analysis of folding angle and mass distributions.

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.

Development of a time of flight spectrometer based on position sensitive multi-wire proportional counters for fission fragment mass distribution studies.

Characteristics and performance of a time of flight (TOF) spectrometer developed for performing fission mass distribution studies are presented. The spectrometer contains two TOF arms based on multi-wire proportional counters (MWPCs). Each arm has two MWPCs to form a start-stop detection system for TOF measurements. The start detector has an active area of 4 × 4cm2. The stop detector is a two-dimensional position sensitive MWPC with an active area of 16 × 11cm2. Salient features of the MWPCs are the use of reduced sub-millimeter wire pitches of 0.635 and 0.317mm in the electrodes along with the use of gold plated tungsten wires of diameters 10 and 20 µm. A delay line for position electrodes is prepared using chip inductors and capacitors. Ten different configurations of MWPC were investigated for the start detector, which involved the use of three and four electrode geometries, use of different wire pitches, and use of aluminized mylar for timing electrodes. Performance results close to micro-channel plate detectors have been observed with some designs of MWPC, displaying rise times better than 2ns with an estimated inherent time resolution of ∼100ps FWHM. A position resolution of ∼1mm (FWHM) has been observed. Design features of the MWPCs and their test performance results are described in this article.

Fission studies using multinucleon transfer reactions

It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions (FFMDs) are measured for each transfer channel, in selected bins of excitation energy. It was found that the mass distributions for all the studied nuclides maintain a double-humped shape up to the high energies that the shell effects are expected to smear out. From a comparison with the dynamical calculation based on the fluctuation-dissipation model, this behavior of the mass distributions was unambiguously attributed to the effect of multichance fission.

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.