Particle Fission Research Articles

Surface Charge Density Determination of Micaceous Minerals by 235U Fission Particle Track Method

AbstractThe surface charge density of mica (001) cleavages was determined by counting the number of fission particle tracks in a given area of a 6-mm muscovite disc replica with optical and scanning electron microscopy after saturation of the layer charge by washing with 0.5 M UO2(NO3)2 solution, dilution of the excess salt by washing with 0.01 M UO2(NO3)2 in 0.005 M HNO3 (pH 2.4), blotting off the excess liquid, thermal neutron activation in contact with the muscovite disc, etching the muscovite, and counting the 235U fission tracks/cm2. In initial studies, the uranyl cations were found to hydrolyze from the cleavage surface continuously during the washings with water, ethanol or acetone to remove excess salts, but the uranyl cations in the interlayers near broken edges and crystallographical steps were strongly retained even against washings with 0.5 M CaCl2 solution. The hydrolysis of UO22 + from the smooth portions of the flake surfaces was avoided by the use of three 1-hr final washings with the 0.01 M UO2(NO3)2 in 0.005 M HNO3 solution. Each flake was pressed between filter papers three times to remove the excess solution. A negligible amount of excess salt remained on the cover glass controls. The UO22 + cations retained (mean, 3.6 ± 0.2 × 10−7 mequiv./cm2) on the cleavage surfaces of various micas were nearly equivalent to the theoretical surface charge (cation exchange capacity, 3.5 × 10−7 mequiv./cm2), showing that hydrolysis was prevented. The uranium on the unblemished mica planar surfaces increased with increasing uranyl concentrations in the final washing solution, indicating that the excess salt remaining on the surfaces had become significant. With a given UO22 + salt concentration, the uranium on the surface increased on increasing the solution pH from 2.5 to 3.5, attributable to the formation of polymeric ions such as U2O52 + and U3O82 + with higher uranium retention per unit positive charge equivalent to the fixed negative charge of the mineral surface. Uranyl cations replaced much of the interlayer cations from vermiculites even after K, Rb and Cs presaturation and drying from 110°C were employed. Strong adsorption of uranyl cations (in a form not replaced by washings with a neutral salt solution), which occurred in the defects of micaceous minerals, is important in the interpretation of actinide element retention in soils and sediments wherein these minerals are abundant.

AGE AND URANIUM CONTENT OF SOIL MICAS FROM ANTARCTICA BY THE FISSION PARTICLE TRACK REPLICA METHOD

A replica method was developed for fission particle track age dating and determination of uranium content of micas in a Wright Valley, Antarctica, soil and parent rock. The mica particles in the soil were relatively small, fragile, and easily dissolved by chemical etchings. Muscovite mica flakes were therefore used as a replicating substrate to register induced fission tracks of the soil mica. The micas from three soil horizons (0–10, 10–30, and 30–50 cm depths) and parent rock, in four size fractions (100–500,2–5, 0.2–2, and < 0.2μm) were examined to illustrate use of the method. The fission track age of the soil mica particles was 4.1±0.2 million years (MY), slightly older than the minimum landscape (glacial bench) age of 3.7 ± 0.2 MY obtained previously by K-Ar dating of a volcanic cone formed after the glacial valley was formed. The ages of the 2–5,0.2–2, and < 0.2μm fractions were the same as for the 100–500 μm flakes, when the spontaneous track density was calculated from that of the latter, in proportion to the U content. The fission track age of parent rock mica was 151 million years. The U content of the soil mica was 0.5 to 1.6 ppm which is 20 to 50 times higher than that of mica from the parent rock (0.03 ppm). The mica in the soil appears from age and petrographie thin-section results to be of pedogenic origin, formed by replacement in feldspars after the bench was carved. The fission particle track replica method is useful for age-dating of micas in soils, for determining trace amounts of uranium in micas, and for study of soil genesis in the Antarctic cold desert.

Nuclear charge distribution of fission products fromU235(nth),fof the masses 79 to 100

Passing mass separated recoil fission particles through a $\ensuremath{\Delta}E \mathrm{Si}$-surface barrier detector the nuclear charge distributions of fission products were measured in the mass chains 79 to 100. The average nuclear charge as well as the second, third, and fourth moment of the nuclear charge distribution reveal odd-even and shell effects.NUCLEAR REACTION, FISSION $^{235}\mathrm{U}({n}_{\mathrm{th}},f)$, measured nuclear charge distribution of $A=79$ to $A=100$, deduced element and isotone yields, proton and neutron odd-even effect.

Fission Particle Tracks in Micas and Micaceous Vermiculites as Related to Chemical Weathering and Cation Exchange Properties

AbstractFission particle tracks from 238U impurities in natural micas and micaceous vermiculites were observed by scanning electron microscopy after hydrofluoric acid etching. Track frequency was increased by neutron activation in a thermal nuclear reactor. Without HF etching, the average rate of interlayer K+ released from micas saturated with UO22+ and activated, during 6 days depletion in 0.5N Mg(OAc)2 solutions at pH 7 renewed every few min, were 40 to 50% higher than that from nonactivated samples. Activated UO22+ saturated micaceous vermiculites from Colorado (CO) and Wisconsin (WI) liberated more K, Fe, and Si(OH)4 compared to that from the controls, in 0.5N Mg(OAc)2 at pH 4, renewed frequently. Weathering of micaceous minerals in nature would thus be accelerated by the additional diffusion of interlayer and structural cations through the natural fission particle tracks. The cation exchange capacity (CEC) of the activated micaceous vermiculites after UO22+ saturation increased from 16 to 25 meq/100g (CO) and from 6 to 12 meq/100g (WI) after the extensive salt treatments involved in CEC measurement, while negligible change in CEC occurred in the CO Na controls and one‐third as much change occurred in the WI Na control. The observed higher K+ selectivity (relative to Ca2+) of the activated samples (0.86 for CO and 1.39 for WI), compared to the controls (0.43 and 1.21, respectively), indicates that activation provided an increase in edge wedge sites for the selective adsorption of fixing cations including the fission product 137Cs+.

28.—Simultaneous Emission of two Light Charged Particles in Fission

SynopsisThe suggestion is made that in certain cases the light particles emitted in ternary fission may be released otherwise than in the ground state—and, in particular, that low-lying particle-unstable states may be involved. This suggestion is examined quantitatively in respect of the release of 8Be in the first excited short-lived state of 2·9 MeV excitation, and is shown to provide a satisfactory interpretation of the observation of quaternary fission in the α,α mode recently reported by Kataria et al. (1973). It appears probable that the other modes of quaternary fission observed by these authors should be similarly interpreted.

A “Dust Curtain” in Gaseous Core Nuclear Reactors for Rockets

THE use of nuclear, rather than chemical, energy for the propulsion of space vehicles would greatly extend the possibilities of space travel, and in recent years much progress has been made towards the realization of nuclear propulsion devices. The principle of rocket propulsion rests on the production of a highly heated working fluid, called the propellant gas, which is expanded and ejected through a nozzle, thereby converting its thermal energy to directed kinetic energy. The heating of the propellant can be derived from the reaction of combustibles with a chemical system, or, in the nuclear system, from the nuclear reaction of fissile materials. In the nuclear reactor the fissile material is the fuel, and the thermal energy released by fission is transferred to the propellant, usually hydrogen. This energy transfer can be achieved by the use of a solid core which serves as an intermediate medium for the energy delivery to the propellant. Although the solid core reactor has reached a prototype engine demonstration after a decade of development1, it does not, however, make the optimum use of the nuclear energy in a rocket engine. This stems from the fact that fission energy is released at very high level (106 eV or 1010 K) which has been degraded in a solid core reactor to 3,000 K, the limit of the operational temperature of a solid core heat exchanger. It is therefore desirable to use a gaseous core in which the fuel, namely the highly energetic fission particles, and the propellant are intimately mixed, thus transferring energy directly via collisions and radiation.

Etching of Submicron Pores in Irradiated Mica

As discovered by Price and Walker, small uniform pores may be created in muscovite by etching in HF thin samples that have been subjected to fission particle irradiation. The process of pore growth is followed by monitoring the conductance across a thin sample as the etching proceeds. For irradiation with 252Cf the tracks quickly etch to a radius of 33 Å-the region of primary damage. Further radial etching in the undamaged material is slow but increases to a fixed rate as the radius increases. This radius dependence of etching is interpreted by a kinetic analog of the Kelvin equation for vapor pressure over curved surfaces. With suitable assumptions on the mechanism of attack, the surface energy of the muscovite-solution interface is calculated to be about 300 ergs/cm2.

Fission fragment tracks in semiconducting layer structures

Abstract Fission fragment irradiation of a number of semiconducting materials establishes that permanent tracks are formed only when the conductivity is ≲2 × 103 (ohm-cm)−1. The intermittent nature of particle tracks is a characteristic of layer structures and further analysis confirms that there is one ‘defect’ per sandwich plane crossed by the fission particle. The intermittency is ascribed to the reduced energy loss of the fission fragment when it travels in the interplanar channel.

Die automatische auswertung von kernspur- und festkörperdetektorplatten

An “orthogonal mechanical scanner“ is described here which makes the time consuming and tedious task of visual scanning of nuclear emulsions and solid detector plates in special cases obsolete. With this instrument in about 120 min a plate of 2.5×7.5 cm 2 can be scanned completely in 10μm wide stripes with a velocity of 2.8 cm/sec. The advantage of this instrument is the electronic pulse-length-discrimination which makes it unnecessary to use several photomultipliers and several channels of discriminators. The handling of the instrument as well as the particle identification thus is very much simplified. The instrument is used to scan the mass spectrum of fission particle tracks in nuclear emulsions as well as in solid detectors.

Response of semiconductor surface barrier detectors to fission fragments

The pulse height defect for fission fragments of surface barrier detectors from the firms ORTEC, Oak Ridge and NUCLETRON, Munich has been investigated dependent on mass and kinetic energy of the fission particles. An exact determination of these quantities was possible by means of the Mattauch-Herzog-type fission particle mass spectrometer at FRM, Munich. For constant kinetic energy of the detected particles the variation of pulse height with mass proved to be about 100 keV/amu. Losses in the dead layer measured by tilting the detector respective to the direction of the particle beam proved to be somewhat larger for fission fragments compared with those calculated from α-particle losses. For fission particles these losses increase considerably when bias is decreased and therefore very probably are caused by recombination effects. Furthermore energy resolution respective to fission fragments is given for several detectors. Unexpectedly some counters showed a very poor resolution though possessing the same resistivity and even better α-resolution than others showing good resolution, what suggests that the region very close to the surface layer plays an important role for forming the fission fragment response pulses.

The kinetic energy of fragments and alpha particles in the ternary fission of U235

We measured the energy distributions of ternary fission fragments corresponding to different energy intervals in the spectrum of long-range alpha particles with average energies of 10.6, 16.4, 20.3, and 24.0 MeV. It was found that for Eα>15 MeV the most probable total energy of ternary fission fragments, within the limits of experimental error, was independent of the energy of the alpha particles and that for Eα=10.6 MeV it was about 4 MeV higher.

Long-Range Particle Emission in Coincidence with Fission at Moderate Excitation Energies

The production rate of long-range particles in coincidence with fission was studied in bombardments of Th/sup 232/ and U/sup 238/ with 10.5-Mev protons and with helium ions of 29.5 and 42.0 Mev. The number of coincident charged particles per fission observed in the proton bombardment is consistent with the numbers of such particles observed in earlier measurements (spontaneous fission, neutron-induced fission). These results indicate that the production rate of charged particles in fission decreases smoothly with increasing excitation energy of the fissioning compound nucleus. For a nucleus excited to 15 Mev, the rate is about half that for a nucleus in its ground state. The charged particle yields obtained in thc helium ion bombardments are, however, much larger than one would expect on the basis of the excitation energy dependence indicated by the other (lower energy) measurements. Some possible explanations for these observations are briefly and quantatively considered. (auth)

Heavy Ion Energy Accumulation in the Tandem Van de Graaff Accelerator

A new energy-accumulation method has been found for accelerating very small but usable beams of artificial fission fragments such as bromine and iodine ions to energies three times higher than those previously available from tandem Van de Graaff accelerators. Energies up to 120 MeV now available cover completely the energy range found for the fission particles from uranium. The ions have been used to study the behavior of silicon solid-state fission-particle detectors of many types. For the first time direct calibration methods are available to aid in experimental studies of the fission process. Further work will be directed toward an experimental study of the stopping power of various elements for heavy ions.

Процессы фрагментации и деления при взаимодействии частиц высоких энергий с ядрами

A review is presented of available data on the formation of multi- charged particles in nuclear fission and on the mecharism of nuclear fission at high excitation energies, a phenomena of special interest among the processes eccurring during high-energy particle interactions with nuclei. (R.V.J.)

Emission of Long-Range Particles in the Fast Neutron Ternary Fission of U-238 and Th-232

Emission of Long-Range Particles in the Fast Neutron Ternary Fission of U-238 and Th-232

The emission of light charged particles in the slow neutron fission of uranium

This paper describes the extension of the photographic plate technique to the recording of fission fragment tracks and the application of this method to the study of rare modes of fission in the case of the slow neutron fission of uranium. The emission of a short-range group of light particles in the fission of U 235 , reported by Cassels, Dainty, Feather &amp; Green, is confirmed and the angular and range distributions of these particles described. In addition, the emission of long-range light particles with ranges up to 45 cm. of air is described. The abundance of this mode of fission is 1 in 340 + 40 fission events. The angular and range distributions of these long-range particles are given.

Emission of Secondary Charged Particles in Fission

IT now seems fairly well established that in roughly 1 per cent of all fissions an I±-particle is liberated at the moment of fission1,2. These secondary A particles are mostly of small energy (< 2 MeV.), but some are found having energies greater than 20 MeV. It is obviously of interest to discuss the conditions in which such 'secondary'emission may occur.

Possible Delay in the Emission of Neutrons from Uranium

ROBERTS1 and others have reported the emission of delayed neutrons with a period of 12 sec. from uranium under neutron bombardment, but the effect seems to be a small one2, the main body of neutrons being produced in a much shorter period. Green and Alvarez have Shown that there is no delay exceeding 3 × 10–3 sec. in the actual production of fission, but it seemed possible that the neutrons might not be produced at the moment of fission but rather as the products of rapid disintegration of the primary fission particles.