Fission Of Heavy Elements Research Articles

A dynamical-statistical model of nuclear fission of heavy elements

A dynamical-statistical approach to the description of induced fission of heavy nuclei allowing for the nuclear dissipation phenomenon is proposed. The potential of the approach is demonstrated in processing experimental data on the fission probabilities for Pu isotopes, yields of shape isomers, and total fission time for the α + 238U reaction at Eα = 20–32 MeV.

Hazards of Managing and Disposing of Nuclear Waste

Although it is arguably for the benefit of society, the translation of basic nuclear processes into technological achievements produces nuclear wastes that can become environmental hazards if they are not properly cared for. Light-element fusion, heavy-element fission and radioactive decay have provided us with nuclear weapons, nuclear power plants and nuclear medicine. But they all produce radioactive materials that are unusable, no longer needed, or unwanted. Ultimately, these materials require long-term isolation from the biosphere.

Radiostrontium-90 (90Sr) Ultra-Traces Measurements by Coupling Ionic Chromatography (HPIC) and on Line Liquid Scintillation Counting (OLLSC)

The important role of the beta emitter Strontium-90 in our environmental has been studied since the nuclear age. This long half-life isotope (28.1 years) is produced in a relatively high yield (5.8 % from Uranium-235) during the fission of heavy elements. It has been reported to be the major artificial source of internal irradiation of the human body. Its valence shell electron configuration is the same as Calcium and so this isotope is easily fixed in the bones. The classical analysis of this particular isotope requires several weeks since it produces Yttrium-90 which is also a beta emitter. We developed a new trace analysis method by coupling High Performance Ionic Chromatography (HPIC), to separate Strontium-90 from natural or power plant reactor water, and on-line liquid scintillation counting detector, measuring the beta emission of low concentration Strontium-90 before Yttrium-90 is formed in a significant amount. We report here some analysis parameters : HPIC setup, scintillation cocktail, window, counting efficiency, linearity, pre-concentration and detection limits. We were able to determine very low concentrations of Strontium-90. The minimum concentration detected without a pre-concentration system was 0.5 ppt from a 200 µL sample (6.3×10-12 mole/L). The analysis only requires a few hours.

Studies on the separation of cesium-137 from the acidic fission product waste solutions on a new complex inorganic exchanger (Zr−P-APW)

A new inorganic exchanger zirconiumphosphate-ammonium phosphotungstate (Zr-P-APW) has been synthesized in granular form suitable for column work. The K dvalues for different metal ions were determined and the affinity order was found to be Cs >> Rb > Zr > Ce > rare earths. Sodium exchange capacity, pH-titration curve, breakthrough capacities for cesium (both in pure HNO 3 and in different types of simulated nuclear wastes) and elution of cesium from the Zr-P-APW column have been studied. A selective method for the removal of cesium from other radioactive fission products has been developed. The exchanger was found to be stable to a '/-radiation dose of 108 rads in presence and absence of 2M nitric acid. Radioisotopes of long half-life like 137Cs, which is obtained from nuclear fission of heavy elements like U, Pu, etc., find a wide variety of applications as radiation sources in medical and industrial uses. 1-3 The safe disposal of nuclear fuel reprocessing waste is of great importance and the removal of long-lived fission products like 137Cs from the bulk of these wastes will considerably reduce the controlled storage time. Inorganic exchangers were increasingly used during the last three decades for such separations from fission product waste solutions 4-8 because of their stability towards high doses of radiation and elevated temperatures. 9-11 The inorganic exchangers that are specific for cesium removal from salt loaded acidic solutions 12-~6 include heteropolyacid and acid salts of tungsten and molybdenum as well as the zirconium, titanium and tin salts of condensed phosphates. KRTIL 17 separated cesium from rubidium on a column of APW with asbestos as inert binder, MURTHY et al.18 have investigated extensively the removal of cesium from gross fission products solutions on this exchanger. This paper describes the method of preparation of Zr-P-APW, a new complex inorganic exchanger, which is granular and suitable for column operation. The studies and the results pertaining to the separation of 137Cs from gross fission products waste solution are reported.

Energy of 242Am and 242mAm fission fragments

The energy spectra of single fragments from spontaneous fission of the 14 msec 242mAm isomer and from prompt fission of 242Am were measured. The isomer was produced by the 242Pu(d, 2n) 242mAm reaction, and the prompt fissions were produced by the 240Pu(d, f) reaction. The fragments from delayed fission were observed by semiconductor detectors after the compound nucleus had recoiled to a rotating catcher wheel. The usual doubly peaked spectra of fragment energies from heavy element fission were observed in both cases. The valley of the spectrum from spontaneous fission of the isomer is equally deep as the valley of the spectrum from prompt fission induced by 12 MeV deuterons. Energies of the peaks were the same for prompt fission and for spontaneous fission of the isomer. The former energies were constant over the 7.6 to 14 MeV span of incident deuteron energy. Comparisons of these fragment energies with those from 252Cf spontaneous fission and from deuteron-induced fission of other heavy elements agree with Z 2 A 1 3 systematics.

Ambient Xenon : A Key to the History of Meteorites

Xenon exhibits a special anomaly in many meteorites in which Xe/sup 129/ is greatly enhanced with respect to terrestrial Xe. Smaller general anomalies also affect the remainder of the Xe isotopes. It is postulated that the xenon special anomalies are a result of the meteorite parent bodies having formed quickly enough after the last synthesis of I/sup 129/ to permit an excess of the radiogenic daughter Xe/sup 129/ to accumulate in the iodine-bearing minerals. Since it is not certain which processes contributed to the nucleosynthesis of iodine, relative rather than absolute decay intervals can be derived. It is suggested that radiogenic Xe/sup 129/, from I/sup 129/, and Xe/sup 131/ to Xe/sup 136/, from fission of heavy elements, was produced in those regions of the parent body that were at relatively high temperatures and mixed freely with the ambient xenon, so that the isotopic abundance in ambient xenon of Xe/sup 129/ and Xe/sup 131/ to Xe/sup 136/ increased with time. Applications of xenon chronometry in studies on the interiors of meteorite parent bodies are discussed. Data on the xenon content of the Sardis iron troilite and of Abee are compared. An ideal model is presented and theoretical measurements of xenon isotopicmore » abundance are compared with measurements on Abee. Equations are presented for the correlation of Xe/sup 129//Xe/sup 132/ and Xe/sup 128//Xe/sup 132/, in w hich consideration is given to the effects of temperature on the release of xenon from iodine-bearing minerals. It is suggested that the method may be applied in studies on environmental parameters of meteorites of different types and should give new insight into the significance of the high- and low-iron groups of chrondrites, the galliumgermanium group of meteorites, and the clusters of cosmic ray ages. (C.H.)« less

Kinetic Energy Distributions of Fragments from the Fission of Au, Tl, Pb, and Bi

Single fragment and total kinetic energy distributions have been measured for fission induced by helium ions and deuterons in Au, Tl, Pb, and Bi targets. The average total kinetic energy release has the same proportionality with $\frac{{Z}^{2}}{{A}^{\frac{1}{3}}}$ found for fission of heavier elements. The widths for the total kinetic energy distributions are comparable to those observed for fission of heavy elements. A preliminary mass distribution curve has been obtained by measuring the energies of coincident fragments.

Angular correlations in high energy fission

The existence of an angular correlation between the incident beam of nucleons and the fission fragments in high energy fission of heavy elements leads to the conclusion that the number of neutrons evaporated before fission is probably zero or very small.