Fission Of 239Pu Research Articles

A General Correlation for Independent Fission Product Yield Uncertainties

Measurements of independent fission product yields from thermal-neutron fission of 235U, 239Pu, 233U, and 241Pu have been compared with expected yields from a semiempirical analytical model. A general correlation between the experimental/theoretical ratio and the distance of the nuclide from Zp, the most probable charge in a fission product mass chain, has been constructed. This correlation can serve as a basis for assigning uncertainties to theoretical yield estimates.

Application of Sensitivity and Uncertainty Methodology to Fast Reactor Integral Experiment Analysis

This paper presents the first results of a comprehensive application of the sensitivity theory developed for the FORSS code system to the analysis of fast reactor integral experiments. A variety of assemblies and performance parameters were studied to determine the nuclear data sensitivity as a function of nuclide, reaction type, and energy. Comprehensive libraries of energy-dependent sensitivity coefficients were developed in a computer retrievable format for several critical assemblies. Uncertainties induced by nuclear data were quantified using preliminary energy-dependent relative covariance matrices evaluated with ENDF/B-IV cross sections and processed for 238U(n,f), 238U(n,γ), 239Pu(n,f), 239Pu(n,γ), and . Calculational results, cross-section covariances, and integral results and their covariances were used in a consistent fashion to improve uncertainty estimates of fast reactor core performance. A first attempt was made to quantify specifications for new cross-section measurements required to satisfy specific design goals at minimum experimental cost.An analysis of several critical experiments indicated that design accuracy goals of 0.5% in k and 2% in the central 238U capture: 239Pu fission ratio (28c/49f) ratio in mixed oxide liquid-metal fast breeder reactor cores are unlikely to be attained in the near future. This assumes that the nuclear data are based only on microscopic measurements, and the current cross-section measurement program is not changed dramatically. Current estimates are 2.3% in k and 7.3% in central reaction ratio using only differential covariance information. Using the measurements in ZPR-6/7 for k and central 28c/49f in a cross-section adjustment scheme with assigned uncorrected standard deviations of 1 and 2%, respectively, standard deviations of the same parameters were computed to be 0.7 and 1.8%. Results of integral experiments, therefore, are needed to improve uncertainty estimates of reactor performance for current fast reactor design work.

Independent yields of 96Nb and 51 min 98Nb in the thermal neutron-induced fission of 233U, 235U and 239Pu

Abstract The independent yields of 96 Nb and 51 min 98 Nb were determined in the thermal neutron-induced fission of 233 U, 235 U and 239 Pu using radiochemical techniques. The results for these fissionable nuclides are as follows for 96 Nb: (5.3±0.3) × 10 −3 %, (5.2±0.2) × 10 −4 % and (3.6±0.1) × 10 −3 %, respectively, and for 51 min 98 Nb: (0.13± 0.03)%, (0.034±0.015)% and (0.16±0.03)%, respectively.

Identification of short-lived ruthenium and rhodium isotopes in fission by rapid chemical separations

Short-lived ruthenium and rhodium isotopes were produced via thermal neutron induced fission of 235U, 239Pu and 249Cf and via fast neutron induced fission of 238U. The ruthenium isotopes and their descendants were isolated from the fission product mixtures by means of a rapid chemical separation procedure. Typically 7.6 sec were required from the end of irradiation to the start of counting. The γ-ray singles spectra as well as the γ-γ-coincidences were recorded with Ge(Li)-detectors. New short-lived nuclides were identified on the basis of their decay characteristics, and existing data of the longer lived isotopes were confirmed. Results are presented for the ruthenium isotopes 3.75 min 107Ru, 4.55 min 108Ru, 34.5 sec 109Ru, 12.9 sec 109Ru (isomer), 12.6 sec 110Ru, 3 sec 111Ru, 3.6 sec 112Ru, 3 sec 113Ru, and the rhodium isotopes 17 sec 108Rh, 79.8 sec 109Rh, 3.3 sec 110Rh, 11 sec 111Rh.

Evidence on the influence of fission channels on fission phenomena

Partial fission channel widths can be extracted from fission cross-section analysis only up to a rotation in the space of fission vectors. We propose to obtain a physically significant basis for fission vectors taking into account information from other fission characteristics such as the valley-to-peak ratio of the mass distribution and the number of prompt neutrons emitted per fission event. Fission widths and other channel characteristics are calculated for 0 + resonances in low energy neutron induced fission of 239Pu.

The decay of 79.8 sec 109Rh into levels of 109Pd

The β −-decay of 79.8 sec 109Rh into levels of 109Pd has been investigated by γ-ray spectroscopy and γ-γ-coincidence measurements. The activities have been produced by thermal-neutron induced fission of 239Pu and subsequent chemical separation of the rhodium fraction from the fission product mixture. A total of 31 γ-rays have been assigned to the decay of 109Rh, and a level scheme of 109Pd is proposed and briefly discussed within the framework of different nuclear models. From beta branching ratios a groundstate spin and parity of 5 2 + can be deduced for 109Rh.

Determination of Fallout Nuclides by the 19th Chinese Nuclear Explosion Test

This paper describes analysis of the fallout from the 19th Chinese nuclear explosion test. 1. The analysis identified the following 16 nuclides using the radioactive decay method: 95Zr, 95Nb, 97Zr, 97Nb, 99Mo, 99mTc, 131I, 132Te, 1321, 133I, 137Cs, 140La, 143Ce, 147Nd, 237U and 239Np.2. Assessment of a baby's thyroid dose by radioiodine based on this nuclear explosion test was carried out. Culculated dose is 4.5 mrem/yr which is nearly one-third of radioiodine release guideline for a light-water-cooled nuclear power station.3. Nuclide concentration, (number of nuclides)/(nuclear fission yield), going back to predicted fission time was calculated. Assuming the fast fission of 239Pu, the concentration curves of each nuclide crossed at approximately the same point.The reported fission time by ERDA of U.S.A. fell into the authors' speculated fission time region which was calculated from the time dependent nuclide concentration curves mentioned above.4. The 237U was identified from the decay curves of 239Np photopeak (278 keV) and of multiplet of 239Np and 237U (207 keV). The estimated atomic ratio of 239Np: 237U at fission time was 28: 1.

Absolute measurements of 235U and 239Pu fission cross-sections with photoneutron sources

the fission cross-sections of 235U and 239Pu for NaBe, LaBe, NaD and GaD photoneutrons have been measured absolutely. The neutron source strength was measured using a manganese bath to compare the photoneutron yield from the sources with the standard source NBS-II. Fission counts were accumulated with the source positioned symmetrically between two identical fission foils in an experiment package suspended in a low-albedo laboratory. Fission fragments passing through limited solid angle apertures were recorded on polyester track-etch films. The masses of the foil deposits were determined by microbalance weighings and confirmed by thermal neutron fission and alpha counting. After making a correction for the calculated energy distribution of the source neutrons, values of 1.471 ± 0.029, 1.274 ± 0.026, 1.162 ± 0.025 and 1.195 ± 0.026 barns were obtained for the 235U fission cross-section at the source median energies of 140, 265, 770 and 964 keV, respectively. Corresponding values of 1.469 ± 0.045, 1.515 ± 0.038, 1.670 ± 0.039 and 1.643 ± 0.038 barns were determined for 239Pu.

HIAWATHA, a fission-fragment recoil mass spectrometer

A new fission-fragment recoil mass spectrometer, called HIAWATHA, has been designed, constructed, and tested. Working on a unique principle, HIAWATHA has achieved better than 0.5 amu mass resolution measuring fragments directly from fission. The good mass resolution obtained by HIAWATHA permitted us to make a direct physical measurement of the mass yields in thermal-neutron fission of 235U. The results of this measurement are in good agreement in general with evaluated mass yields. Future experiments planned for HIAWATHA include measuremes of the mass yields for thermal-neutron fission of 233U and 239Pu, measurements of the nuclide yields for all three of the fissile isotopes by incorporating a fragment energy-loss detector for atomic-number identification, and various studies of heavy-ion transport in matter.

Uncertainties in Fission Product Decay-Heat Calculations

Based on a sensitivity analysis of decay-heat summation calculations, uncertainties are obtained for the calculated decay heat associated with the thermal fission of 235U and the fast fission of 238U and 239Pu. For typical reactor irradiation times and cooling times >100 s, these uncertainties are <3.5% for 235U, 4% for 238U, and 5% for 239Pu. All calculations are based on ENDF/B-IV data.

Distributions isotopiques des gaz rares et de leurs précurseurs dans la fission thermique de 239, 241Pu: Etude de l'effet “pair-impair”

The independent and cumulative fission yields of rare gas and halogen isotopes produced from the fission of 239Pu and 241Pu by thermal neutrons have been measured by means of on-line isotopic separation. Mass and charge distributions have been studied. Elemental yields can be deduced for the two fissioning systems. A comparison with 233U and 235U fission is made for the proton odd-even effect.

Fission of 232Th, 238U, 244Pu, 248Cm induced by Xe and Kr ions at coulomb barrier energies

Excitation functions and angular distributions have been measured for the fission of 232Th, 238U, 244Pu and 248Cm induced by 86Kr and 136Xe ions at energies in the vicinity of the Coulomb barrier. No large differences as a function of either target or projectile were found. These results suggest that the main process occuring is not Coulomb fission.

239Pu Fission Isomer in the Reaction with 3–5 Mev Neutrons

The 239 Pu fission isomer with T 1/2 =8 µs has been produced in the ( n , n ') reactions with 3–5 MeV pulsed neutrons from the D + d reaction ( E d =1.8 MeV), and the ratio (σ i /σ f ) of cross section (σ i ) for the formation of fission isomer to that (σ f ) for prompt fission was obtained from the time distribution of fission fragments. Thus the value of σ i and the isomer ratio (σ i /σ ground state ) were derived.

Evaluated Delayed Neutron Spectra and Their Importance in Reactor Calculations

Delayed neutron emission spectra from thermal-neutron fission of 233U, 235U, 239Pu, and 241Pu, from fast-neutron fission of 232Th, 235U, 238U, and 239Pu and from high-energy neutron (14.7-MeV) fiss...

Haloes from plutonium minerals and fission alphas?

The normal alpha decay of naturally occurring 244Pu can be expected to have produced pleochroic haloes detectable in existing rocks. Several methods of identifying such haloes are described here. Giant haloes might also be produced by the α particles that occasionally accompany the spontaneous fission of 244Pu. It is plausible to speculate that in ideal circumstances such gaint haloes might be as large as 100 µm, and that the X rays recently induced from central inclusions of giant haloes and identified as L rays of Z = 126 might instead have been K X rays from Te fission fragments.

Absolute yields in the fission of 239Pu by mono-energetic neutrons of energy 130–1700 keV

Absolute fission yields of 99Mo, 111Ag, 140Ba, 147Nd and 153Sm have been measured for fission of 239Py by neutrons of energies 130, 300, 700, 900, 1300 and 1700 keV. While yields of 99Mo and 140Ba are constant, those of the other three nuclides increase with energy. This result has implications both for fission theory and for practical applications of fission yields in fast reactors.

Vibrational resonances below 5 MeV in the fission of 240Pu

Using the 239Pu(d, pf) reaction, the next lower K π = 0 + vibrational resonance below 5 MeV in the deformed potential of 240Pu was located at 4.55 MeV. The resultant spacing of fission vibrations near 5 MeV in the second minimum is 500 keV. A resonance at 4.70 MeV is interpreted as the K π = 0 − vibration coupled to the 4.55 MeV K π = 0 + state, which yields E( K π = 0 −) = 150 keV relative to the ground state of the second minimum.

Independent yields of 150Pm in the thermal neutron-induced fission of 233U, 235U, 239Pu and 249Cf and cross-section for the 149Pm( n, γ) 150Pm reaction

Independent yields for the shielded nuclide 150Pm were determined in the thermal neutron-induced fission of 233U, 235U, 239Pu and 249Cf using radiochemical techniques. They were found to be (2·6±0·2)×10 −4%, (3±1)×10 −5%, (1·15±0·07)×10 −3% and (1·9±0·2)×10 −2%, respectively; these values correspond to empirical Zp values of 58·66, 58·31, 58·79 and 59·18, respectively, if a Gaussian charge dispersion function with a σ of 0·56 is used. A comparison of the Zp values for 150Pm with Zp values for other nuclides in the thermal neutron-induced fission of several actinide isotopes is given. The cross-section for 149Pm( n, γ) 150Pm in a swimming pool reactor neutron spectrum was found to be (1630±160) barn.

Xenon isotope anomalies and extinct superheavy elements in carbonaceous chondrites.

And in this also (pursues Eleutherius) methinks both you and the chymists may easily agree, that the surest way is to learn by particular experiments, what differing parts particular bodies do consist of, and by what wayes (either actual or potential fire) they may best and most conveniently be separated, as without relying too much upon the fire alone, for the resolving of bodies, so without fruitlessly contending to force them into more elements than nature made them up of, or strip the severed principles so naked, as by making them exquisitely elementary to make them almost useless. ROBERT BOYLE (1661) The Sceptical Chymist Carbonaceous chondrites contain approximately 10-11cc per gram of excess fission xenon, most of which is released from the meteorites at temperatures 1, 200 to 1, 400°C. It appears to be the xenon from the decay of 244Pu, but its concentration is at least several times the amount calculated from the uranium content of the meteorites. The so-called Renazzo-type fission xenon, which is released at temperatures 600 to 1, 000°C, can be shown to be non-fissiogenic. While the Renazzo-type fission xenon can be enriched by treating the meteorites with acids, the 244Pu fission xenon component becomes depleted in the residual mineral fractions.

Mass Yields in the Fission of Uranium-235 and Plutonium-239 in the Neutron Spectrum of a Gas-Cooled Fast Reactor

The yields of 27 mass chains in the fission of 235U and the ratio of fast-neutron to thermal-neutron fission yields (the “R” value) of 21 mass chains in the fission of 239Pu induced by fast neutron...