Spontaneous Fission Branching Research Articles

Prediction of half-lives of even–even superheavy nuclei

α-decay half-lives (-values) of even–even and superheavy nuclei (SHN) are determined employing interaction potential involving Coulomb and proximity potentials. The obtained results are compared with the experimental ones and to assess the precision of the present model in reproducing the experimental half-lives, a comparison is drawn with the other methods as well. We require disintegration energy (Q α -values) as an input in order to predict the (-values) of an experimentally unknown SHN. So, utilizing periodic-orbit theory within microscopic-macroscopic formalism, we have calculated the binding energies and thereafter, Q α -values of known SHN. The results are found to be in good agreement with the experimental ones. Subsequently, we predict the logarithmic values of ’s for even–even unknown SHN whose atomic numbers lie in 118 ⩽ Z ⩽ 126 regime and compare our results with those calculated employing other theoretical methods. Also, the study of spontaneous fission half-lives and branching ratios leads us to predict the SHN which can be identified through α-decay chains in the laboratories. We believe that this work can play a significant role in the experiments leading to the synthesis and identification of new superheavy elements.

High-precision spontaneous fission branching-ratio measurements for Pu240,242 and Cf252 isotopes

We report here very precise measurements of the spontaneous fission branching ratio for the $^{240,242}\mathrm{Pu}$ and $^{252}\mathrm{Cf}$ isotopes, performed with a new kind of active scintillating target. It is shown that the method itself leads to unprecedentedly small uncertainties, and that these uncertainties are negligible compared to uncertainties on the isotopic content of the sample. Besides this capability we discuss the possibility to use this kind of detector for the systematic study of charged particle radioactivity, i.e., spontaneous fission, \ensuremath{\alpha} decay, and heavy-ion radioactivity.

Calculation of Neutron Production Rates and Spectra from Compounds of Actinides and Light Elements

The code NEDIS allows the calculation of neutron production rate and continuous energy spectra due to (α,n) reaction on Li, Be, B, C, O, F, Ne, Na Mg, Al, Si, P, S, Cl, Ar, K, and Ca. It accounts for anisotropic angular distribution of neutrons of (α,n) reaction in centre-of- mass system and dimensions of alpha emitting source material particles. Spontaneous fission spectra are calculated with evaluated half-life, spontaneous fission branching, ν- averaged per fission, and Watt spectrum parameters. The results of calculations by NEDIS can be used as input for Monte Carlo simulation for materials that will be used in radiation shielding and for underground neutron experiments

Measuring the α/SF Branching Ratio of 252Cf with the NIFFTE TPC

A fission TPC is being developed to measure the energy-dependent neutron induced fission cross sections of the major and minor actinides to an accuracy of better than 1%. Achieving such an accuracy will depend in part, on the ability of the TPC to provide precise tracking and identification of charged particles. A measurement of the α-decay to spontaneous fission branching ratio of 252Cf used to benchmark the performance of the TPC will be discussed.

Decay study of 246Fm at SHIP

The decay chain of 246Fm has been investigated employing the SHIP separator at GSI Darmstadt. The 246Fm nuclei were produced via the 40Ar(208Pb, 2n)246Fm fusion-evaporation reaction. Improved values of the half-life, T 1/2 = 1.54(4) s, and of the spontaneous fission branching ratio, b SF = 0.068(6) , of 246Fm were obtained. The $ \beta^{+}_{}$ /electron capture branching ratio, b EC = 0.39(3) , of 242Cf was deduced. Possible structures of high-K states in 246Fm are discussed within the framework of a model calculation based on the Woods-Saxon potential.

The new isotope 236Cm and new data on 233Cm and 237, 238, 240Cf

The isotopes 237, 238, 240Cf were produced in irradiations of 204, 206, 207Pb targets with 36S ions. At bombarding energies close to the Coulomb barrier two or three neutrons were evaporated from the compound nuclei 240, 242, 243Cf . Cross-sections were on the order of a few hundred nanobarns. For the isotope 240Cf a spontaneous fission branching of 0.015±0.002 was determined. The new isotope 236Cm was produced by \( \alpha\) decay of 240Cf and identified by \( \alpha\) -\( \alpha\) correlations. It decays with an \( \alpha\) -decay energy of (6954± 20)keV and a half-life of (410±50 s. For the first time, the \( \alpha\) decay of 237Cf was observed having an energy of (8081±20 keV. For the isotope 233Cm a half-life of ( 23+13-6 s was measured for first time. Spontaneous fission of 237, 238Cf was confirmed and mass-excess values of the nuclei 236Cm and 237, 240Cf were determined.

Alpha-decay properties of 261Bh

The isotope 261Bh was produced in the reaction 209Bi(54Cr, 2n)261Bh and its \( \alpha\) decay has been remeasured. It was found that it populates by an unhindered transition of \( \approx\) 10 MeV an excited level at E * > 350 keV in the daughter nucleus 257Db . The latter decays by internal transitions either into the isomeric state or the ground state. A somewhat improved half-life value of T1/2 = 11.8+3.9-2.4 ms was obtained for 261Bh . The data support the previous assignment of the \( \alpha\) activities 257Db (1) and 257Db (2) to the isomer and to the ground state, respectively. No evidence for an isomeric state in 261Bh decaying by \( \alpha\) emission was found. Based on the experimental results and theoretical calculations a partial decay scheme of 261Bh including spin and parity assignments of the ground-state and excited levels in the daughter nucleus 257Db populated by the \( \alpha\) decay and succeeding internal transitions have been suggested. 261Bh represents so far the heaviest nucleus for which such an attempt has been made. No spontaneous fission (SF) events that could be attributed to 261Bh were observed, resulting in an SF branching bSF < 0.05 . The measured production cross-section is (64±15) pb at E * = 22 MeV.

Sources: A code for calculating (alpha, n), spontaneous fission, and delayed neutron sources and spectra

SOURCES is a computer code that determines neutron production rates and spectra from (alpha, n) reactions, spontaneous fission, and delayed neutron emission due to the decay of radionuclides in homogeneous media, interface problems, and three-region interface problems. The code is also capable of calculating the neutron production rates due to (alpha, n) reactions induced by a monoenergetic beam of alpha particles incident on a slab of target material. The (alpha, n) spectra are calculated using an assumed isotropic angular distribution in the center-of-mass system with a library of 107 nuclide decay alpha-particle spectra, 24 sets of measured and/or evaluated (alpha, n) cross sections and product nuclide level branching fractions, and functional alpha particle stopping cross sections for Z < 106. Spontaneous fission sources and spectra are calculated with evaluated half-life, spontaneous fission branching, and Watt spectrum parameters for 44 actinides. The delayed neutron spectra are taken from an evaluated library of 105 precursors. The code outputs the magnitude and spectra of the resultant neutron sources. It also provides an analysis of the contributions to that source by each nuclide in the problem.

The Systematic Behavior of the Spontaneous Fission Branching Ratios of Even-Z Isotopes

The spontaneous fission branching ratios (B) of even-Z, 90 ≤ Z ≤ 100, nuclei were found to be correlated to log B = 1.6247 × Z – 1.0361(2Z – N) – 114.66. Based on this correlation, it is predicted that the isotopes 226Ra and 228Th are spontaneous fission isotopes.

SOURCES: a code for calculating (α,n), spontaneous fission, and delayed neutron sources and spectra

SOURCES is a computer code that determines neutron production rates and spectra from (alpha,n) reactions, spontaneous fission and delayed neutron emission owing to the decay of radionuclides in homogeneous media, interface problems and three-region interface problems. The code is also capable of calculating the neutron production rates due to (alpha,n) reactions induced by a monoenergetic beam of alpha particles incident on a slab of target material. The (alpha,n) spectra are calculated using an assumed isotropic angular distribution in the centre-of-mass system with a library of 107 nuclide decay alpha-particle spectra, 24 sets of measured and/or evaluated (alpha,n) cross sections and product nuclide level branching fractions, and functional alpha particle stopping cross sections for Z < 106. Spontaneous fission sources and spectra are calculated with evaluated half-life, spontaneous fission branching and Watt spectrum parameters for 44 actinides. The delayed neutron spectra are taken from an evaluated library of 105 precursors. The code outputs the magnitude and spectra of the resultant neutron sources. It also provides an analysis of the contributions to that source by each nuclide in the problem.

Measurement of alpha-decay constant to fission cross section ratio for 237Np, 241Am and alpha to spontaneous fission branching ratio for 243Am using solid state nuclear track detectors

The alpha-decay constant to fission cross section ratio for epi-cadmium neutron induced fission of 237Np, 241Am have been measured using solid state nuclear track detectors (SSNTDs). The measured values were (0.63±0.14).109 s-1.cm-2, (2.31±0.46).1012 s-1.cm-2 for 237Np and 241Am, respectively. The alpha to spontaneous fission branching ratio for 243Am was also measured to be (2.66±0.50).1010 using SSNTDs. These ratios are useful as signatures for the trace level identification of these actinides.

Measurement of alpha to spontaneous fission branching ratios of238Pu and240Pu by solid state nuclear track detectors

Alpha to spontaneous fission branching ratios of heavy actinides such as238Pu and240Pu in solution have been determined by solid state nuclear track detectors (SSNTDs). The detectors used in the present studies are LR-115, CR-39 (DOP), Lexan polycarbonate and Tuffak polycarbonate. Before using Tuffak polycarbonate, a detailed and systematic study on the registration and chemical etching characteristics of fission fragment tracks in this detector was also carried out. The experimentally measured values of alpha to spontaneous fission ratios by this method are found to agree well with the expected values.

Half-life ofPu242from precise low-temperature heat capacity measurements

Heat capacity measurements on three pure compounds, PuF/sub 3/, PuF/sub 4/, and PuO/sub 2/, made from 99.91 at.% /sup 242/Pu, have been used to evaluate the power produced by radioactive decay. The mean specific power was found to be (0.12099 +- 0.00024) mW per gram of plutonium in the samples. The contribution of nuclides other than /sup 242/Pu to the power was calculated to be (5.15 +- 0.11) ..mu..W per gram of plutonium, and so the specific power of pure /sup 242/Pu is (0.115 94 +- 0.000 26) mW g/sup -1/. A correction for the (5.50 x 10/sup -4/) % spontaneous fission branching reduces the specific power due to ..cap alpha.. decay to (0.11591 +- 0.00026) mW g/sup -1/. Combining this value of the specific power with the total disintegration energy of (4.9823 +- 0.0012) MeV, we obtain (3.763 +- 0.009) x 10/sup 5/ years as the ..cap alpha.. half-life of pure /sup 242/Pu. (AIP)