Spontaneous Fission Properties Research Articles

The SFiNx Detector System

A new detector system for investigating the properties of spontaneous fission of short-lived transuranium nuclei has been created. This system consists of an assembly of double-sided silicon strip detectors surrounded by 116 proportional neutrons counters filled with 3He. The neutron registration efficiency is 54.7 ± 0.1%. The detector system is tested in an experiment investigating the characteristics of spontaneous fission of the 252No isotope. The experimental data on neutron yields are compared with previously published results. The average number of neutrons per fission act ( $$\bar {\nu }$$ = 4.25 $$ \pm $$ 0.09) and the multiplicity distribution of prompt neutrons are obtained. The true form of the neutron distribution is reconstructed via a statistical regularization.

K isomerism in Rf255 and total kinetic energy measurements for spontaneous fission of Rf255,256,258

Spontaneous fission properties of the isotopes $^{255}\mathrm{Rf}$, $^{256}\mathrm{Rf}$, and $^{258}\mathrm{Rf}$ produced in the reactions $^{50}\mathrm{Ti}+^{207}\mathrm{Pb}$, $^{50}\mathrm{Ti}+^{208}\mathrm{Pb}$, and $^{50}\mathrm{Ti}+^{209}\mathrm{Bi}$ were studied. The method of time and position correlations was used to identify spontaneous fission events. The correction to the energy deficit in measured total kinetic energy (TKE) determined on the basis of a study of $^{252}\mathrm{No}$ was applied to evaluate the $\overline{\mathrm{TKE}}$ of investigated rutherfordium isotopes. A signature which we assigned tentatively to bimodal fission was observed in TKE distributions of $^{255}\mathrm{Rf}$ and $^{256}\mathrm{Rf}$. Two new high-K isomeric states in $^{255}\mathrm{Rf}$ were identified by ER-CE-(CE)-$\ensuremath{\alpha}$/SF correlation search, with half-lives of ${38}_{\ensuremath{-}7}^{+12}$ and ${15}_{\ensuremath{-}4}^{+6}$ $\ensuremath{\mu}\mathrm{s}$ at excitation energies 1150--1450 and 900--1200 keV, respectively. Including those metastable states a tentative partial level scheme was proposed.

Determining spontaneous fission properties by direct mass measurements with the FRS Ion Catcher

We present a direct method to measure fission product yield distributions (FPY) and isomeric yield ratios (IYR) for spontaneous fission (SF) fragments. These physical properties are of utmost importance to the understanding of basic nuclear physics, the astrophysical rapid neutron capture process ('r process') of nucleosynthesis, neutron star composition, and nuclear reactor safety. With this method, fission fragments are produced by spontaneous fission from a source that is mounted in a cryogenic stopping cell (CSC), thermalized and stopped within it, and then extracted and transported to a multiple-reflection time-of-flight mass-spectrometer (MR-TOF-MS). We will implement the method at the FRS Ion Catcher (FRS-IC) at GSI (Germany), whose MR-TOF-MS relative mass accuracy (~ 10-7) and resolving power (~ 600,000 FWHM) are sufficient to separate all isobars and numerous isomers in the fission fragment realm. The system's essential element independence and its fast simultaneous mass measurement provide a new direct way to measure isotopic FPY distributions, which is complementary to existing methods. It will enable nuclide FPY measurements in the high fission peak, which is hardly accessible by current techniques. The extraction time of the CSC, tens of milliseconds, enables a direct measurement of independent fission yields, and a first study of the temporal dependence of FPY distributions in this duration range. The ability to resolve isomers will further enable direct extraction of numerous IYRs while performing the FPY measurements. The method has been recently demonstrated at the FRS-ICr for SF with a 37 kBq 252Cf fission source, where about 70 different fission fragments have been identified and counted. In the near future, it will be used for systematic studies of SF with a higher-activity 252Cf source and a 248Cm source. The method can be implemented also for neutron induced fission at appropriate facilities.

Characteristics of spontaneous fission of 250No

This study describes an experiment on investigating the properties of spontaneous fission of shortlived neutron-deficient nuclei synthesized in the reaction of complete fusion 48Ca + 204Pb = 252No*. The experiment is performed using the SHELS separator and the beam of multicharged ions at U-400 accelerator (LNR, JINR). Two activities undergoing spontaneous fission, which can be related to the ground and isomeric states of 250No nucleus, are registered. The half-lives, total kinetic energies of fission fragments, and neutron multiplicities are measured for the short-lived nuclei. The average number of neutrons per fission for the activity with t 1/2 = 5.1 ± 0.3 μs is = 4.38 ± 0.13 μs, and for nuclei with the half-life t 1/2 = 36 ± 3 μs it is xxxxx.

Spontaneous fission properties of superheavy elements

Spontaneous fission properties of transuranium isotopes are reviewed. Specific emphasis was laid on brief historical overviews of theoretical descriptions and experimental determination of basic properties as spontaneous fission half-lives, fission barriers, or total kinetic energy release in fission. Experimental spontaneous fission half-lives are compared with the results of recent theoretical predictions. Hindrance factors for spontaneous fission of odd-mass nuclei are discussed in context with the configuration (spin, parity) of the fissioning states and the change in energy of single particle levels at deformation. Kinetic energy release and mass distributions are discussed in the context of different fission modes, as symmetric and asymmetric or fission from elongated or compact shapes of the nascent fission fragments. An overview of recent fission barrier calculations of superheavy elements on the basis of macroscopic-microscopic models or self-consistent calculations is given, and the results are compared for selected examples.

Spontaneous fission of 256Rf, new data

Spontaneous fission properties of the short-lived neutron-deficient 256Rf nucleus produced in the complete fusion reaction with a beam of multiply charged heavy 50Ti ions from the U-400 cyclotron (FLNR, JINR) are experimentally investigated. Its half-life and decay branching ratio are measured. The average number of neutrons per spontaneous fission of 256Rf (\(\bar v = \;4.47 \pm \;0.09\)) is determined for the first time.

Superheavy nuclei from 48Ca-induced reactions

The discovery and investigation of the new region of superheavy nuclei at the DGFRS separator based on fusion reactions of 48Ca with 238U–249Cf target nuclei are reviewed. The production cross sections and summaries of the decay properties, including the results of the posterior experiments performed at the SHIP, BGS, and TASCA separators, as well as at the chemistry setups, are discussed and compared with the theoretical calculations and the systematic trends in the α-decay and spontaneous fission properties. The properties of the new nuclei, isotopes of elements 112–118, and their decay products demonstrate significant increases in the stability of the heaviest nuclei with increasing neutron number and closer approach to magic number N=184.

Nuclear Structure of the Heaviest Elements – Investigated at SHIP-GSI

The quest for the heaviest nuclei that can exist is a basic topic in natural science as their stability is characterized by a delicate interplay of short range nuclear forces acting between the nucleons (protons and neutrons) and long-range Coulomb forces acting solely between charged particles, i.e. the protons. As the stability of a nucleus is strongly correlated to its structure, understanding the nuclear structure of heaviest nuclei is presently a main challenge of experimental and theoretical investigations concerning the field of Superheavy Elements. At the velocity filter SHIP at GSI Darmstadt an extensive program on nuclear structure investigations has been started about a decade ago. The project covered both as well systematic investigations of single particle levels in odd-mass isotopes populated by α-decay as investigation of two- or fourquasi-particle states forming K isomers and was supplemented by direct mass measurements at SHIPTRAP and investigation of spontaneous fission properties. Recent experimental studies allowed to extend the systematics of low lying levels in N = 151 and N = 153 up to 255Rf and 259Sg, investigation of possible relations between nuclear structure and fission properties of odd-mass nuclei and investigation of shell strengths at N = 152 and towards N = 162.

FISSION PROPERTIES OF ODD-A NUCLEI IN A MEAN FIELD FRAMEWORK

Theoretical tools at the level of the mean field approximation are used to explore the spontaneous fission properties of odd-A nuclei. The tools rely on the equal (or uniform) filling approximation to deal with the unpaired nucleon in a time-reversal preserving manner. Realistic calculations have been carried out with the finite range Gogny force D1S, which was tailored to reasonably reproduce fission properties in the actinides. The preliminary results obtained for the nucleus 235 U are analyzed and the physical origin for the hindrance factor for the spontaneous fission half life is discussed.

Fission modes ofFm256andFm258in a microscopic approach

A static microscopic study of potential-energy surfaces within the Skyrme-Hartree-Fock-plus-BCS model is carried out for the $^{256}\mathrm{Fm}$ and $^{258}\mathrm{Fm}$ isotopes with the goal of deducing some properties of spontaneous fission. The calculated fission modes are found to be in agreement with the experimentally observed asymmetric-to-symmetric transition in the fragment-mass distributions and with the high- and low-total-kinetic-energy modes experimentally observed in $^{258}\mathrm{Fm}$. Most of the results are similar to those obtained in macroscopic-microscopic models as well as in recent Hartree-Fock-Bogolyubov calculations with the Gogny interaction, with a few differences in their interpretations. In particular an alternative explanation is proposed for the low-energy fission mode of $^{258}\mathrm{Fm}$.

Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactionsU233,238,Pu242, andCm248+Ca48

We have studied the dependence of the production cross sections of the isotopes 112282,283 and 114286,287 on the excitation energy of the compound nuclei 112286 and 114290. The maximum cross section values of the xn-evaporation channels for the reaction U238(Ca48,xn)112286−x were measured to be σ3n=2.5−1.1+1.8pb and σ4n=0.6−0.5+1.6pb; for the reaction Pu242(Ca48,xn)114290−x: σ2n∼0.5pb, σ3n=3.6−1.7+3.4pb, and σ4n=4.5−1.9+3.6pb. In the reaction U233(Ca48,2–4n)112277–279 at E*=34.9±2.2MeV we measured an upper cross section limit of σxn⩽0.6pb. The observed shift of the excitation energy associated with the maximum sum evaporation residue cross section σER(E*) to values significantly higher than that associated with the calculated Coulomb barrier can be caused by the orientation of the deformed target nucleus in the entrance channel of the reaction. An increase of σER in the reactions of actinide targets with Ca48 is consistent with the expected increase of the survivability of the excited compound nucleus upon closer approach to the closed neutron shell N=184. In the present work we detected 33 decay chains arising in the decay of the known nuclei 112282, 112283, 114286, 114287, and 114288. In the decay of 114287(α)→112283(α)→110279(SF), in two cases out of 22, we observed decay chains of four and five sequential α transitions that end in spontaneous fission of Sg271(Tα∕SF=2.4−1.0+4.3min) and Rf267(TSF∼2.3h), longer decay chains than reported previously. We observed the new nuclide 116292(Tα=18−6+16ms,Eα=10.66±0.07MeV) in the irradiation of the Cm248 target at a higher energy than in previous experiments. The observed nuclear decay properties of the nuclides with Z=104–118 are compared with theoretical nuclear mass calculations and the systematic trends of spontaneous fission properties. As a whole, they give a consistent pattern of decay of the 18 even-Z neutron-rich nuclides with Z=104–118 and N=163–177. The experiments were performed with the heavy-ion beam delivered by the U400 cyclotron of the FLNR (JINR, Dubna) employing the Dubna gas-filled recoil separator.Received 9 August 2004Corrected 28 January 2005DOI:https://doi.org/10.1103/PhysRevC.70.064609©2004 American Physical Society

Degrees of deformation at scission and correlated fission properties of atomic nuclei

The degrees of the deformation of atomic nuclei at scission configurations of the mass-symmetric and mass-asymmetric fission modes are studied. The \ensuremath{\beta} shape elongation of the fissioning nucleus, associated with the asymmetric fission is found to be constant for ${A}_{f}=213\char21{}260,$ while that associated with the symmetric fission is larger but also constant for a wide range of fissioning nuclei ${(A}_{f}=205\char21{}260)$ except for the low-energy induced and spontaneous fission of heavy nuclei with ${A}_{f}=245\char21{}262$ where a change of the nucleon number by one unit is found to cause a very rapid change in \ensuremath{\beta}. A systematic correlation between the scission deformation and the fission properties such as the mass-yield distribution and the TKE are found. The constancy of the \ensuremath{\beta} gives rise to new formulas of ${\mathrm{TKE}}_{\mathrm{sym}}=0.1173\ifmmode\times\else\texttimes\fi{}{(Z}_{f}^{2}{/A}_{f}^{1/3})+7.5\mathrm{MeV}$ for symmetric fission, and of ${\mathrm{TKE}}_{\mathrm{asym}}=0.1217\ifmmode\times\else\texttimes\fi{}{(Z}_{f}^{2}{/A}_{f}^{1/3})+3.5\mathrm{MeV}$ for asymmetric fission. The physical origin of the well-known simple linear function for the TKE released in the fission process is found to be the invariance of the degrees of the elongation of scissioning nuclei. The mass dispersion of fission products was found to have a direct correlation with the \ensuremath{\beta} value; as \ensuremath{\beta} becomes larger, the width of the mass yield distribution becomes wider. Our understanding of the spontaneous fission properties of heavy nuclides in the ${}^{258}\mathrm{Fm}$ region is presented. In this region, two different scission configurations, one giving $\ensuremath{\beta}\ensuremath{\sim}1.53$ which is the characteristic value for the asymmetric deformation and the other giving $\ensuremath{\beta}\ensuremath{\sim}1.33$ which is for the symmetric deformation, are found.

Spontaneous fission

The spontaneous fission (SF) of the heaviest actinides and the transactinides is of particular interest, because of the dramatic changes in properties observed in the region of the heavy fermium isotopes and for still heavier elements. The existing experimental information on SF properties, including half-life systematics, fragment kinetic energy and mass yield distributions, prompt neutron emission and gamma emission, will be reviewed. Possibilities for extending studies of SF properties to other regions are considered, and the potential for obtaining additional information about low-energy fission properties is discussed.

Spontaneous fission properties of 252,254No and 256,258[104] and the disappearance of the outer fission barrier

We have measured the mass and total kinetic energy distributions from the spontaneous fission of 252No, 254No, 256[104] and 258[104]. The results, in combination with earlier measurements for 256No, 258No and 262No, show a sharp transition from asymmetrical mass division in 256No to symmetrical division for 258No and 262No. However, all isotopes of element 104, including 260[104], appear to yield broadly symmetrical mass distributions. The total kinetic energies around 200 MeV for the element 104 isotopes indicate that they fission by the low-energy mode of bimodal fission. Recent calculations of static potential energy surfaces including higher-order asymmetric deformations suggest that the outer fission barrier is well below the ground state in energy, which accounts for the observance of the symmetric mass division.

Spontaneous fission in the heavy elements

Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results have been surprising in that spontaneous fission half-lives have turned out to be much longer than expected and mass and kinetic-energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments have caused a re-evaluation of our understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties.

Spontaneous-fission properties and production of heavy-element isotopes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSpontaneous-fission properties and production of heavy-element isotopesDarleane C. HoffmanCite this: Acc. Chem. Res. 1984, 17, 7, 235–242Publication Date (Print):July 1, 1984Publication History Published online1 May 2002Published inissue 1 July 1984https://doi.org/10.1021/ar00103a003RIGHTS & PERMISSIONSArticle Views172Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

12.3-minCf256and 43-minMd258and systematics of the spontaneous fission properties of heavy nuclides

The new isotope 12.3-min $^{256}\mathrm{Cf}$ was produced via the $^{254}\mathrm{Cf}$($t$,$p$) reaction, and a new 43-min isomer of $^{258}\mathrm{Md}$ was produced via the $^{255}\mathrm{Es}$($\ensuremath{\alpha}$,$n$) reaction. The fragment mass and kinetic energy distributions from the spontaneous fission of $^{256}\mathrm{Cf}$ were found to be very similar to those from the spontaneous fission of lighter Cf isotopes. The mass division is primarily asymmetric, and the average total kinetic energy is 189.8\ifmmode\pm\else\textpm\fi{}0.9 MeV. The 43-min $^{258}\mathrm{Md}$ presumably decays by electron capture and provides an opportunity to study the mass and kinetic energy distributions from the spontaneous fission of the 380-\ensuremath{\mu}s $^{258}\mathrm{Fm}$ daughter. The observed narrow, symmetric mass distribution and the most probable total kinetic energy of 238\ifmmode\pm\else\textpm\fi{}3 MeV are similar to those reported for the spontaneous fission of $^{259}\mathrm{Fm}$ but show a sharp increase in symmetric mass division and total kinetic energy compared to $^{257}\mathrm{Fm}$ and the lighter Fm isotopes. No such abrupt change in properties was observed for $^{256}\mathrm{Cf}$, which, like $^{258}\mathrm{Fm}$, has 158 neutrons. The marked difference between the spontaneous fission properties of the heavier Fm isotopes and those of other spontaneously fissioning nuclides is compared to some theoretical predictions.RADIOACTIVITY, FISSION $^{256}\mathrm{Cf}$ (SF); measured ${T}_{\frac{1}{2}}$, fragment-fragment coin; deduced TKE, mass distribution. $^{258}\mathrm{Md}$; Measured ${T}_{\frac{1}{2}}$; EC decay to $^{258}\mathrm{Fm}$ (SF); measured fragment-fragment coin; deduced TKE, mass distribution.