Fission product yields in the fast-neutron fission of238U

The fission yields of 38 fission products in the fast-neutron induced fission of²³⁸U have been determined using a rapid, multiscaling gamma-ray spectroscopic method. To obtain absolute yields for fission products having half-lives ranging from 32 s to 40 d, a total of 56 multi-scaling gamma-ray spectra were collected using various irradiation and cooling periods. Gamma-rays and photopeak areas of interest were assigned to the fission products by their energies and half-lives. Fission product activities were evaluated from spectral data using growth and decay calculations and fission yields were determined by normalizing the¹⁴⁰Ba yield to the average value from reported data. The depleted uranium target, covered with a boron-cadmium thermal neutron shield, was used to keep interference from the fission of²³⁵U minimal. Results for the cumulative fission yields, including 17 mostly short-lived fission products measured for the first time, are compared with previous measurements and with the recommended yields in recent evaluations. The agreement, and some discrepancies, in the comparisons are discussed. No explicit even-odd pairing effects are observed in the fission yield data for fast-neutron induced fission of²³⁸U.     

Determination de l'enrichissement de l'uranium par comptage du rayonnement Cerenkov

A method for the measurement of²³⁵U in dilute uranium solutions based on Cerenkov radiation is described. It is applicable to solutions treated in fuel element production where the enrichment factor of the uranium solution is to be known, thus to solutions of uranyl nitrate not containing other fission products.      

Fine structure of mass and charge distribution in low energy fission

Studies of finer details in mass and charge distribution fission leads to a better understanding of the fission process. Experimental determination of independent and cumulative yields using radiochemical techniques as well as mass spectrometers and fission product recoil separators form the basis of such studies. It has been established that closed shells as well as an even number of nucleons influence both mass and charge distributions. The magnitudes of these effects may be estimated from existing experimental yield data and various fission models. Using our measurements of several fission yields and those existing in the literature we have calculated even-odd proton and neutron effects for various low energy fissioning systems. Where enough data existed, direct calculations were made, whereas for other cases the Z_p-model of WAHL has been used. It is found that the even-odd proton effect is well established and pronounced in thermal neutron fission of²³⁵U and²³³U. Lesser effects were found for reactor neutron induced fission of²³²Th, thermal neutron fission of²³⁹Pu and spontaneous fission of²⁴⁵Cm and²⁴⁹Cf. No effect seems to exist in the thermal neutron fission of²⁴¹Pu and the spontaneous fission of²⁵²Cf. The even-odd neutron effect is found to be much lower than the corresponding proton effect in²³⁵U and²³³U fissions and is nonexistent in the rest of the fissioning systems.     

Non-destructive determination of spontaneously fissioning nuclides by neutron coincidence counting using multichannel time spectroscopy

A non-destructive method for determining the amount of actinoids has been developed. The method is based on thermal neutron coincidence counting and employs a selective detection of neutrons resulting from the spontaneous fission of actinoids. The detection system is described in detail and the measurement results of²⁴⁴Cm as an example are presented. The results show that the measured fission rate of²⁴⁴Cm is consistent with the fission rate calculated from ENDF/B-V data and that the amount of²⁴⁴Cm can be determined within about 5% accuracy even in the presence of a large amount of actinoids, for example, up to 2.6·10⁶, 3.6·10⁴, or 1.6·10³ times in the mass ratio of²³⁹Pu,²⁴¹Am, or²⁴⁰Pu to²⁴⁴Cm, respectively.     

Determination of the fast fission yield of141Pr using neutron activation analysis

A method is described for the determination of the fission yield of¹⁴¹Pr. This method was developed to determine the fast fission yield of¹⁴¹Pr in the Mark III loading (enriched uranium with about 2% zirconium) of the fast fission breeder reactor, EBR-1. The burnup of the fuel sample was determined using the previously reported fission yield of¹³⁷Cs. Praseodymium was separated from uranium, plutonium and other fission products by a combination of precipitation and ion exchange stages. Thereafter,⁵⁵Mn was added to serve as an internal flux monitor and praseodymium determined by neutron activation analysis. A precision of ±2% was obtained. Presented at the 15th Annual Meeting of the American Chemical Society, Miami Beach, Florida (USA), April 1967.     

Computerized on-line measurement the yield of short-lived bromine and iodine isotopes from thermal neutron fission of235U

The short-lived bromine and iodine isotopes from thermal neutron fission of²³⁵U have been separated from fission products by one step solvent extraction combined with an ion exchange fast chemistry system. The measured gamma spectra have been acquisited by an automatic computer on-line system. The results include experimental independent fission yields of⁸⁶Br,^134mI,^134gI,^136mI, and^136gI, the cumulative yields of⁸⁷Br,⁸⁸Br,¹³⁷I,¹³⁸I. The isomeric yield ratio of¹³⁴I and¹³⁶I has been determined and the iodine isotopic distribution curve has been constructed and analyzed.     

Rendements de fission cumulatifs du252Cf

The cumulative yields of 28 isotopes have been measured in the spontaneous fission of²⁵²Cf. Measurements were made by Ge(Li) gamma-spectrometry. An average number of neutrons per fission \(\bar V:3.71\) was derived from the mass distribution. Using Terrell's method, and with the mass distribution before neutron emission, measured in an other laboratory and with our results, the mass-dependent variation of \(\bar V\) was also deduced.     

Yields of rare earth fission products in the spontaneous fission of californium-252

Cumulative fission yields of rare earth isotopes have been determined in the spontaneous fission of²⁵²Cf by fast radiochemical separation and gamma-ray spectrometry. The determined yield values are compared with the available literature data. The yield values for¹⁴⁷Nd,¹⁵¹Nd and¹⁵¹Pm differ from the reported values. The yield for¹⁴⁵Ce is determined for the first time.     

Nuclear charge distribution in the spontaneous fission of252Cf: Determination of fractional cumulative yields of133mTe and133gTe

The fractional cumulative yields (FCY) of^133mTe and^133gTe in the spontaneous fission of²⁵²Cf were measured for the first time by a radiochemical method. The values ofFCY are 0.533±0.014 and 0.291±0.042 for^133mTe and^133gTe, respectively. The isomeric state to ground state fractional independent yield (FIY) ratio of¹³³Te,R, was found to be 3.5. The root-mean-square angular momentum of the primary fragment corresponding to the fission product¹³³Te, Jr.m.s.=8.8h, was estimated according to a simple one-parameter statistical model. The fractional cumulative yields from this work together with other literature data in the mass region A=131–141 are compared with the normal yields given by the empiricalZ _p model by Whhl. It suggests that both theN=82 neutrons shell and nucleus pairing effects are not apparent for the spontaneous fission of²⁵²Cf.     

Plutonium-244 fission xenon and primordial xenon in the Allende meteorite

The carbonaceous chondrite Allende contains (22±1)·10⁻¹² cm³STP/g of²⁴⁴Pu fission xenon and two kinds of primordial xenon: Type I and Type II. The former represents the isotopic composition of a primordial xenon, which resided in the vicinity of a supernova shortly before it exploded, while the latter represents that of the xenon, which resided in the supernova. The isotopic composition of xenon found in the pink inclusion of the Allende meteorite, corrected for the presence of very large excesses of²⁴⁴Pu fission xenon,¹²⁹Xe from the decay of¹²⁹I, and of¹²⁸Xe from the neutron-capture reactions on¹²⁷I, resembles that of Type-I primordial xenon. The isotopic composition of xenon found in the diamond inclusions of the Allende meteorite, on the other hand, represents that of Type-II primordial xenon and it resembles that of a mixture of Type-I primordial xenon whose isotopic composition is severely altered by a combined effect of (a) mass-fractionation, (b) spallation, (c) stellar-temperature neutron-capture reactions, and (d) the presence of a large excess of²⁴⁴Pu fission xenon.     

Production of99Mo and its application in nuclear medicine

Molybdenum-99 is produced in large quantities as the parent radioisotopes of^99mTc, which has been used recently in nuclear medicine. The neutron capture reaction on molybdenum and the nuclear fission of uranium are used for the large scale production of⁹⁹Mo. The products by these methods are used properly according to the objects of diagnosis. In this paper, the production of⁹⁹Mo is reviewed and the development of the production in JAERI is outlined.     

Isomeric yield ratios of fission products in proton-induced fission of232Th

Isomeric yield ratios of 11 fission products were measured in the system of 13 MeV proton-induced fission of²³²Th by an on-line ion-guide isotope separator. It was found that the closed shell structures of primary fragments and their complementary fragments affect the isomeric yield ratios. Isomeric yield ratios of¹²¹Cd (11/2⁻, 3/2⁺) and¹³⁵Xe (11/2⁻, 3/2⁺) were measured precisely in the proton energy range of 13 to 26 MeV to investigate their energy dependence. It was found that the isomeric yield ratios increased slightly with proton energy. The results were discussed in connection with the deformation of fission fragments and fission modes.     

Charge degree of freedom as a sensitive probe for fission mechanism

The role of the charge degree of freedom in the heavy-ion-induced fission was investigated by carrying out a systematic analysis of radiochemically observed charge distribution in the fission of²³⁸U with¹²C ions of the incident energy between 85 and 140 MeV, particularly in connection with the energy given to the compound system. The charge distribution was found to follow essentially identical systematics as those which govern the light-ion fission except for the extremely weak energy dependence of the most probable chargeZ _p. That is, values of the derivative ofZ _p with respect to the energy were found to be quite small, or nearly zero, in the heavy-ion fission as compared to those of the light-ion fission. According to an analysis combining the derivatives ofZ _p and fission neutron data, it was deduced that the excess energy given to the fused system was spent completely in the form of pre-scission neutrons and hence the number of post-scission neutrons remained constant as in the case of light-ion fission. The observed charge distribution was reproduced under the conditions that the relaxation of the charge degree of freedom be very fast and that the separation between the two potential fragments at the moment when the charge degree of freedom has been frozen is determined by usingViola's systematics on the fragment kinetic energy.     

Static aspects of the fission and fusion of3He drops

Using an effective³He-³He interaction, we have investigated the fission and fusion of³He drops from a static point of view. Our calculations show that a fission barrier develops for these neutral systems, and that their saddle configurations are rather elongate. The transition from oblate to prolate shapes as a function of the angular momentumL, as well as critical values for fission and fusion are discussed for some selected cases. We show that a kind of proximity potential can be extracted from the drop-drop interaction potentials.     

Radiochemische Untersuchungen zur Verteilung von129J und3H in Bestrahltem Kernbrennstoff aus Leistungsreaktoren

The working techniques used for the investigation of¹²⁹I and³H sectional distribution in highly irradiated UO₂ pellets are described. The analytical samples are taken by a micro drilling technique. For the determination of¹²⁹I concentration in the UO₂ samples neutron activation analysis following iodine separation from uranium and bulk fission products is used.³H is measured by liquid scintillation counting after distillation. Reliability of the analytical results is discussed as well as possible interferences.     

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.     

A rapid separation of radioactive cesium by nitrobenzene extraction using the chromium complex [Cr(aniline)2(NCS)4]−

A rapid separation of radioactive cesium by the solvent extraction method was investigated. Cesium ions are quantitatively extracted with [Cr(NH₂C₆H₅)₂(NCS)₄]⁻ into nitrobenzene. EDTA is an effective masking agent for other polyvalent cations. The extracted cesium can be back-extracted into the aqueous phase by shaking with 6N HCl. The method was applied to samples of a natural mixture of fission products and a reactor coolant. The decontamination factors for other predominant isotopes in fission products were 10²∼10⁴. The separation of^137m Ba from a mixture of¹³⁷Cs and^137m Ba is also described.     

Production of87Br for studying neutron decay

An improved gas flow system is described for the production of⁸⁷Br through a fast radiochemical separation of fission products from a solution of²³⁵U irradiated with thermal neutrons. It can produce⁸⁷Br with a higher yield relative to⁸⁸Br than was previously possible for measurement of neutron energy distribution. Contrary to previous indication, large amounts of iodine fission products have been found to come out of the irradiation cell in the gas stream necessitating their isolation.     

Yields of fission products with masses A=131 to 135 for the fast neutron induced fission of U-238

Yields of eleven fission products with masses A=131 to 135 have been determined for the reactor neutron induced fission of²³⁸U by means of radiochemical separation combined with high-precision Ge(Li) -ray spectrometry. The charge distribution in the isobaric chains 131 to 134 and the isotopic distribution of₅₂Te have been studied.     

INAA of Zr,La, Ce and Nd in geological samples in the presence of different uranium concentratios

Rock samples which contain relatively high concentrations of uranium may create problems of interference produced by fission products, when instrumental neutron activation analysis is used. The isotopes⁹⁵Zr,¹⁴⁰La,¹⁴¹Ce, 143Ce and 147Nd, which are commonly used in the neutron activation analysis of the corresponding elements, are also produced as fission products of²³⁵U. For each of these radioisotopes, a contribution factor is calculated theoretically and meaured experimentally using geological samples with different uranium contents.