Fission Of 239Pu Research Articles

Noble gases and nitrogen in natural gases from Gujarat, India

Isotopic and elemental ratios have been measured in three natural gas samples from Gujarat, India. The 3He/ 4He ratio is radiogenic for Kalol- 166 and Kalol- 183, while a mantle component is clearly indicated for Motwan- 2. Although Ne is atmospheric in these Kalol gases, for Motwan- 2, a clear excess 21Ne due to 18O(α,n) 21Ne is present. All three gases have radiogenic 40Ar and air values for 36Ar/ 36Ar. Krypton is atmospheric in composition for all three gases. Xenon in Kalol- 183 is purely atmospheric, but for Kalol- 166 a pure fission Xe from 238U is also present. Xenon from Motwan- 2, on the other hand, shows excess 129Xe, 131Xe, 132Xe, 134Xe and 136Xe which do not match either 238U or 244Pu fission yields. The higher yields of 131Xe and 132Xe are most likely a result of preferential migration or leaching of their radioactive precursors from their host rock. But the 129Xe excess could not be due to such preferential effects, and represents a mantle component. Both 3He and 129Xe excesses can be accounted for by the presence of ∼20% mantle component. The δ 15N-values for the three gases Kalol- 166, Kalol- 183, and Motwan-2 are (in ‰) +9.27, −12.56 and −11.48, respectively. They indicate a sedimentary source combined with effects due to migration.

Noble gases and nitrogen in natural gases from Gujarat, India

Isotopic and elemental ratios have been measured in three natural gas samples from Gujarat, India. The 3He/ 4He ratio is radiogenic for Kalol- 166 and Kalol- 183, while a mantle component is clearly indicated for Motwan-2. Although Ne is atmospheric in these Kalol gases, for Motwan-2, a clear excess 21Ne due to 18O(α,n) 21Ne is present. All three gases have radiogenic 40Ar and air values for 38Ar/ 36Ar. Krypton is atmospheric in composition for all three gases. Xenon in Kalol- 183 is purely atmospheric, but for Kalol- 166 a pure fission Xe from 238U is also present. Xenon from Motwan-2, on the other hand, shows excess 129Xe, 131Xe, 132Xe, 134Xe and 136Xe which do not match either 238U or 244Pu fission yields. The higher yields of 131Xe and 132Xe are most likely a result of preferential migration or leaching of their radioactive precursors from their host rock. But the 129Xe excess could not be due to such preferential effects, and represents a mantle component. Both 3He and 129Xe excesses can be accounted for by the presence of20% mantle component. The δ 15N-values for the three gases Kalol- 166, Kalol- 183 and Motwan- 2 are (in ‰) +9.27, −12.56 and −11.48, respectively. They indicate a sedimentary source combined with effects due to migration.

Study of the surface-barrier semiconductor detector response to the fission fragments in the channeling mode

This study of the silicon semiconductor surface-barrier detector response to 239Pu(n th, f) fission fragments separated according to mass, charge and energy shows that, in the axial channeling mode, the energy resolution is two times better than in the ordinary mode. The achieved resolution is about 1.0 MeV (1.5%) for fission fragments of mass 137 amu and energy 67.3 MeV. The estimated energy value for channeled ions derived by the extrapolation of the pulse height to the infinite electric field strength in the detector and an alpha-particle calibration is in good agreement with the true energy. This fact may be the basis of a new calibration procedure.

Calculation of Beta-Ray Spectra from Individual and Aggregate Fission Products.

The β-ray spectra of individual fission products were calculated by using the β-decay data assuming every β-decay to be allowed transition. For the nuclides without measured decay data the β-feeding function was evaluated with the gross theory of β-decay and the β-ray spectrum was calculated from the function. The measured decay data were also supplemented with the data calculated by the gross theory for the excitation energy range above the highest measured excitation energy level. The β-ray spectra from aggregate fission products after a burst fission were calculated by using the β-ray spectrum and the atom number of each fission product nuclide and they were compared with the ones measured for thermal neutron induced fission of 235U, 239Pu and 241Pu at Oak Ridge National Laboratory. The spectrum calculations showed excellent agreement with the measured data at shorter cooling times than 10s when many short-lived nuclides without measured decay data contributed considerably to the spectrum.

Analysis of Uncertainties in Summation Calculations of Decay Heat Using JNDC FP Nuclear Data Library

Uncertainties of decay heat summation calculations are derived for the thermal fission of 235U and 239Pu and the fast fission of 238U through sensitivity analyses using data given in the JNDC FP nuclear data library. The uncertainties analyzed are those relevant to decay energies, fission yields and decay constants among the nuclear data contained in the summation calculation. For nuclides lacking complete experimental data, the uncertainties of the decay energies are theoretically calculated. Thus analyzed, the maximum uncertainties of burst fission are 2.8 % for 235U, 3.2%” for 239Pu and 4.2% for 238U in the range of cooling time between 1 and 109s, and in the case of infinite irradiation, the corresponding level of maximum uncertainty is below 1.6% for all three fissioning nuclides.

Analysis of Uncertainties in Summation Calculations of Decay Heat Using JNDC FP Nuclear Data Library.

Uncertainties of decay heat summation calculations are derived for the thermal fission of 235U and 239Pu and the fast fission of 238U through sensitivity analyses using data given in the JNDC FP nuclear data library. The uncertainties analyzed are those relevant to decay energies, fission yields and decay constants among the nuclear data contained in the summation calculation. For nuclides lacking complete experimental data, the uncertainties of the decay energies are theoretically calculated. Thus analyzed, the maximum uncertainties of burst fission are 2.8 % for 235U, 3.2%” for 239Pu and 4.2% for 238U in the range of cooling time between 1 and 109s, and in the case of infinite irradiation, the corresponding level of maximum uncertainty is below 1.6% for all three fissioning nuclides.

Prediction Uncertainty Analysis of Neutronic Properties of Fast Breeder Reactor by Use of Sensitivity-Based Methodology.

The prediction accuracies of key neutronic characteristics including burnup properties evaluated with use of the sensitivity-based methodology have been reviewed for a fast breeder reactor. The bias factor method, the cross section adjustment method and the combined method are used to evaluate the prediction accuracies. The calculation method of sensitivity coefficients used in the uncertainty analysis is discussed. The three methods are compared from the theoretical and numerical points. For the numerical comparison, they are applied to a 1,000 MWe fast breeder reactor. The prediction uncertainties are within the range of 0.7~1.0% for keff , 3~5% for control rod worth, 1~2% for 239Pu fission rate distribution, 12% for burnup reactivity loss and 1.5% for breeding ratio. These values are much smaller than those predicted without any integral data.

244Pu-Xe formation and gas retention age, exposure history, and terrestrial age of angrites LEW86010 and LEW87051: Comparison with Angra dos Reis

We have studied noble gas isotopic abundances in the two angrites LEW86010 and LEW87051. Many characteristics of LEW86010 are similar to those observed for the basaltic achondrite Angra dos Reis, until recently the only known angrite. Fission Xe in LEW86010 originates almost entirely from 244Pu fission. We calculate an atomic ratio 244Pu 150Nd = 1.36 × 10 −3 that corresponds to a fission Xe retention age 19 ± 40 Ma younger than that of Angra dos Reis. Thus, LEW86010 formed contemporaneously with Angra dos Reis for which previous analyses yielded a formation age of 4550 Ma. The U/ Th- 4He age (3700 Ma) of LEW86010 is higher than the K- 40Ar gas retention age, a feature observed earlier for Angra dos Reis. LEW87051 shows the lowest nominal U/Th- 4He gas retention age (4 Ma) ever observed for a stone meteorite. The cosmic-ray exposure histories are very different for the three angrites: for LEW86010 and LEW87051 we calculate 17.6 ± 1.0 Ma and ≧ 0.2 Ma, respectively, compared to a previously reported exposure age of 55.5 Ma for Angra dos Reis. For the radionuclide 81Kr we measured an activity of 0.012 dpm/kg in LEW86010 and derive a terrestrial age of 420 000 ± 100 000 years.

Fission following complete or incomplete fusion of 135 MeV16O and238U

From measurements of the laboratory angular distribution and the projected range distribution for each of 26 individual radioactive fission products from the interaction of 135 MeV16O on238U, we have determined for each product quantities including the average velocity,ν, of the parent fissioning system and the anisotropy,ω, of the fission angular distribution. We have interpreted the results in terms of two competing mechanisms: complete fusion and a process involving transfer of anα-particle from projectile to target followed by fission of242Pu. The values ofν lie betweenνcn, the complete fusion value, and 0.3νcn, and can be taken as a measure of the relative importance of the two processes competing in populating each observed product. These two contributions to each measured product yield can then be separated, and understood using a simple model of the fission process. The data suggest that approximately 24% of the overall fission yield is due to incomplete fusion processes. The anisotropy,ω, is strongly correlated with the value ofν, indicating anisotropies of 1.4 and 2.8 for the two individual processes.

Plutonium-244 dating

Re-examination of all known xenon isotope data for the carbonaceous chondrites Murray and Murchison reveals that these meteorites contain (25±1)•10 12 and (23±1)•10 −12 ccSTP 136f Xe/g of 244 Pu fission xenon, respectively, and they started to retain their xenon at about the same time the Allende meteorite started to retain its xenon more than 4800 million years ago. Some of the mineral inclusions isolated from these meteorites contain xenon and barium isotopes which had been exposed to very high fluences of thermal neutrons

Plutonium-244 dating

Re-examination of xenon isotope data for lunar fines, breccia and rocks reveals that in situ decay product of the spontaneous fission of 244 Pu is widely distributed in the lunar samples and some of the lunar samples contain in excess of 1000 0 10 −12 ccSTP 136f Xe/g of 244 Pu fission xenon. The 244 Pu ages calculated from the ratios of 136f Xe to 238 U in these samples vary from 3965 to 4909 million years

Actinide abundances in ordinary chondrites

Measurements of 244Pu fission Xe, U, Th, and light REE (LREE) abundances, along with modal petrographic determinations of phosphate abundances, were carried out on equilibrated ordinary chondrites in order to define better the solar system Pu abundance and to determine the degree of variation of actinide and LREE abundances. Our data permit comparison of the directly measured Pu/ U ratio with that determined indirectly as ( Pu/ Nd) × ( Nd/ U) assuming that Pu behaves chemically as a LREE. Except for Guareña, and perhaps H chondrites in general, Pu concentrations are similar to that determined previously for St. Séverin, although less precise because of higher trapped Xe contents. Trapped 130Xe 136Xe ratios appear to vary from meteorite to meteorite, but, relative to AVCC, all are similar in the sense of having less of the interstellar heavy Xe found in carbonaceous chondrite acid residues. The Pu/U and Pu/Nd ratios are consistent with previous data for St. Séverin, but both tend to be slightly higher than those inferred from previous data on Angra dos Reis. Although significant variations exist, the distribution of our Th/U ratios, along with other precise isotope dilution data for ordinary chondrites, is rather symmetric about the CI chondrite value; however, actinide/(LREE) ratios are systematically lower than the CI value. Variations in actinide or LREE absolute and relative abundances are interpreted as reflecting differences in the proportions and/or compositions of more primitive components (chondrules and CAI materials?) incorporated into different regions of the ordinary chondrite parent bodies. The observed variations of Th/U, Nd/U, or Ce/U suggest that measurements of Pu/U on any single equilibrated ordinary chondrite specimen, such as St. Séverin, should statistically be within ±20–30% of the average solar system value, although it is also clear that anomalous samples exist.

Coordinate-Dependent Mass and the Validity of the WKB Approximation in Fission Barrier Penetration Calculations

It is shown that the quasi-classical condition for the validity of the WKB approximation is satisfied although the mass associated with the spontaneous fission of 240pu varies by a factor of 12. It has been known for quite some time that the mass (or mass parameter) associated with collective nuclear motion may vary substantially with the collective coordinates. For instance, the microscopically calculated l ) diagonal matrix elements of the five-dimensional mass-matrix of 152Sm vary by as much as a factor of 7 as the qu'adrupole deformation /3 varies from 0.0 to 0.5 and as the axial asymmetry variable r varies from 0 to 60'. In a recent calculation 2) of the fission lifetimes of transuranic and of superheavy nuclei, even larger variations (by factors of about 12) have been found. Such large variations are not very model-dependent. They arise from the general variation of Nilsson-type single-particle levels 3 ),4) some of which go up as deformation increases while the others go down. Consequently, the energy denomi­ nator appearing in the cranking-type expression for the mass parameter varies rapidly with deformation, especially near level crossings. Such variations of the collective mass by factors of 12, as the nucleus fissions, seem rather large from the point of view of using the WKB approximation to the barrier penetration probability. Hence, the quasi-classical condition necessary for the validity of the WKB approximation is examined below. The WKB approximation is expected to be valid when the quasi-classical condi­ tion is satisfied. This condition is given by5) IdJ'/drl~l , (1)

Beta decay energies and nuclear masses of148Ba,148La and151Pr

Theβ-decay energy of the neutron-rich isotopes148Ba,148La and151Pr has been measured at the Institute Laue-Langevin (ILL). The148Ba- and148La-nuclei were produced using a high-temperature ion source at the OSTIS separator of this institute, whereas samples of151Pr were obtained from the thermal fission of239Pu, used as a target in the mass separator LOHENGRIN. At both instruments,βγ-coincidences were measured with a plastic scintillator telescope and a Ge(I)-detector, together withβ-singles andγ-singles spectra. Theβ-spectra emitted in coincidence with 44γ-lines in the decay of these nuclei have been evaluated. From their endpoint energies, the followingQβ-values have been obtained:Qβ(148Ba)=5115±60keV;Qβ(148La)=7255±55 keV;Qβ(151Pr)=4170±75 keV. Using these results, the nuclear massesA of these nuclei can be calculated with a relative error ΔA/A≃5·10−7. In addition, the two-neutron separation energies and the mass excesses have been derived; the results are compared with recent predictions of theoretical mass calculations.

Measurement and evaluation of some low-energy fission yield

Methods of independent fission yield measurement are briefly reviewed and compared one to another, experimental yield data are compiled for some low-energy fissioning systems. Example of predicting fission yields in thermal-neutron induced fission of239Pu is evaluated with even-odd effect presented. Future directions of experiments and evaluations are discussed.

39Ar- 40Ar dating of mesosiderites: Evidence for major parent body disruption < 4 Ga ago

39Ar- 40Ar ages were measured on 17 samples of 14 different mesosiderites and indicate major degassing of Ar by one or more thermal events less than 4.0 Ga ago. Three samples gave release patterns of constant age, whereas the other samples typically showed 200–400 Ma increases in 39Ar- 40Ar age with increasing gas extraction temperature. These stepwise releases indicate ages of ~3.4–3.8 Ga (1 Ga = 10 9 a); averaged ages for individual meteorites are 3.45–3.82 Ga. No substantial evidence exists in the temperature releases for 39Ar- 40Ar ages older than 4.0 Ga and the Ar ages appear to be in contradiction to 244Pu fission track ages previously reported for a few mesosiderites. The Ar ages probably date the event that caused disturbance in previously reported Rb-Sr, Sm-Nd, and Pb-Pb ages of Estherville and other mesosiderites. Data on release of Ar as a function of extraction temperature were used in Arrhenius plots to estimate activation energies for Ar diffusion of 18–52 kcal/mol. These values were then used to calculate closure temperatures against Ar loss of 2–340°C and 180–600°C for assumed cooling rates of 1°C/Ma and 1°C/a, respectively. The Ar data suggest that, for certain assumed models of mesosiderite formation, the 39Ar- 40Ar ages may date the time of formation of those metal textures in mesosiderites which have led others to calculate cooling rates of ~1°C/ Ma. Models which call for metal-silicate mixing ~4.5 Ga ago, followed by cooling at 1°C/Ma from temperatures >1150°C, seem unlikely. Single-event models which produce the silicate-metal mixture at high temperatures, rapidly cool the objects to temperatures of ~500°C, followed by cooling of ~1°C/Ma and are not consistent with the Ar data unless the thermal event occurred <4 Ga ago. Collisional break-up of the mesosiderite parent object < 3.9 Ga ago, followed by gravitational reassembly, is consistent with the Ar ages and metal textures. We suggest that metal-silicate mixing occurred ~4.4 Ga ago, but that a major collisional event disrupted the mesosiderite parent planet < 3.9 Ga ago, heated mesosiderites to >500°C, and left them deeply buried to undergo slow cooling.

Spin-Dependent Calculation of Fission Neutron Spectra and Fission Spectrum Integrals for Six Fissioning Systems

Calculations of fission neutron spectra and fission spectrum integrals for six fissioning systems are reported. The systems studied are thermal-neutron-induced fission of 233U, 235U, and 239Pu; 2-MeV neutron fission of 232Th and 238U; and spontaneous fission of 252Cf The Madland-Nix formalism is used, but is extended to take account of the spin of the fission fragment. Also, more recent values for the average energy release in fission are used. The results of the fission neutron spectrum calculations are given in tabular and graphical form for applied purposes and are compared with experimental data. Similar deviations from a Maxwellian spectrum are seen for each system. The effect on the fission neutron spectra of 233U, 235U, and 239Pu from inclusion of alternative values for the average total fragment kinetic energy is shown.

Antineutrino spectra from 241Pu and 239Pu thermal neutron fission products

The antineutrino spectrum of fission products from thermal neutron induced fission of 241Pu was derived from a measurement of the correlated beta spectrum. The energy range 1.5 MeV to 9 MeV was covered and a precision of 4% was achieved at 4 MeV. A revised version of the antineutrino spectrum from 239Pu fission is also presented.

Fitting and optimal grouping on gamma reliability data : Duan Wei and C. K. Shau. IEEE Trans. Reliab.R-36, 595 (1987)

Exsting experimental thermal, fast, and 14-MeV neutron-induced fission-product cumulative and independent yieds have been compiled, corrected to common reference values, and listed in tabular form for the following fissile nuclides:Thermal-neutron fission: cumulative yields for 227Th, 229Th, 233U, 235U, 239Pu, 241Pu, 241Am, 242Am, 245Cm, 249Cf, 251Cf, 254Es, and 255Fm; independent yieds for 233U, 235U, 237Np, 238U, and 239Pu.Fast-neutron fission: cumulativ yields for 227Ac, 231Pa, 232Th, 233U, 235U, 237Np, 238U, and 239Pu; independent yields for 235U and 238U.14-MeV-neutron fission: cumulative yields for 231Pa, 232Th, 233U, 235U, 237Np, 238U, and 239Pu; independent yields for 232Th, 233U, 235U, 238U, and 239Pu.11-MeV-neutron fission: cumulative yields for 232Th.3-MeV-neutron fission: cumulative yields for 231Pa, 232Th, and 238U.1.1-MeV-neutron fission: cumulative yields for 237Np.From these experimental values the unknown independent yields are deduced empirically for thermal-neutron fission of 233U, 235U, 239Pu, and 241Pu; the fast fission of 232Th, 233U, 235U, 238U, 239Pu, 240Pu, and 241Pu (the chain yields for 240Pu and 241Pu used at this energy being predictions); and the 14-MeV-neutron fission of 232Th, 233U, 235U, and 238U.Finally, by the fitting of the preceding information to condition equations derived from the conservation laws, adjusted sets of chain and independent yields are calculated for thermal fission of 233U, 235U, 239Pu, and 241Pu; fast fission of 232Th, 233U, 235U, 238U, 239Pu, and 241Pu; and 14-MeV fission of 232Th, 233U, 235U, and 238U. The literature search is probably complete to the end of 1975; some 1976 results are included.This paper replaces and makes obsolete the following UKAEA reports: AERE-R7209, AERE-R7394, AERE-R7680, and AERE-R8152.

System reliability using binomial failure rate : Kyung C. Chae. Proc. a. Reliab. Maintainab. Symp., 136 (1988)

Exsting experimental thermal, fast, and 14-MeV neutron-induced fission-product cumulative and independent yieds have been compiled, corrected to common reference values, and listed in tabular form for the following fissile nuclides:Thermal-neutron fission: cumulative yields for 227Th, 229Th, 233U, 235U, 239Pu, 241Pu, 241Am, 242Am, 245Cm, 249Cf, 251Cf, 254Es, and 255Fm; independent yieds for 233U, 235U, 237Np, 238U, and 239Pu.Fast-neutron fission: cumulativ yields for 227Ac, 231Pa, 232Th, 233U, 235U, 237Np, 238U, and 239Pu; independent yields for 235U and 238U.14-MeV-neutron fission: cumulative yields for 231Pa, 232Th, 233U, 235U, 237Np, 238U, and 239Pu; independent yields for 232Th, 233U, 235U, 238U, and 239Pu.11-MeV-neutron fission: cumulative yields for 232Th.3-MeV-neutron fission: cumulative yields for 231Pa, 232Th, and 238U.1.1-MeV-neutron fission: cumulative yields for 237Np.From these experimental values the unknown independent yields are deduced empirically for thermal-neutron fission of 233U, 235U, 239Pu, and 241Pu; the fast fission of 232Th, 233U, 235U, 238U, 239Pu, 240Pu, and 241Pu (the chain yields for 240Pu and 241Pu used at this energy being predictions); and the 14-MeV-neutron fission of 232Th, 233U, 235U, and 238U.Finally, by the fitting of the preceding information to condition equations derived from the conservation laws, adjusted sets of chain and independent yields are calculated for thermal fission of 233U, 235U, 239Pu, and 241Pu; fast fission of 232Th, 233U, 235U, 238U, 239Pu, and 241Pu; and 14-MeV fission of 232Th, 233U, 235U, and 238U. The literature search is probably complete to the end of 1975; some 1976 results are included.This paper replaces and makes obsolete the following UKAEA reports: AERE-R7209, AERE-R7394, AERE-R7680, and AERE-R8152.