Temperature nuclide transport

IMPACT OF TEMPERATURE INCREASE ON NUCLIDE TRANSPORT IN CRYSTALLINE ROCK ON THE NEAR FIELD SCALE... 

A selective separation of fission technetium induced by fission of can be performed by stopping the speed of the Tc nuclides in solid KCl and SrClj catchers. At temperatures of 300 to 750 °C, 30% to 85% of Tc is selectively released. Purified nitrogen is used for the transportation of the nuclides from the target to the detector. The release is accelerated by increasing the temperature and adding ZrCl as a carrier. 

We report on a number of on-line chemical procedures which were developed for the study of short-lived fission products and products from heavy-ion interactions. These techniques combine gas-jet recoil-transport systems with I) multistage solvent extraction methods using high-speed centrifuges for rapid phase separation and II) thermochromatographic columns. The formation of volatile species between recoil atoms and reactive gases is another alternative. We have also coupled a gas-jet transport system to a mass separator equipped with a hollow cathode- or a high temperature ion source. Typical applications of these methods for studies of short-lived nuclides are described. 

A first attempt to chemically identify one of the recently found long-lived isotope of element 112, namely 283112 (SF, Tm 3 m), in the elemental state was made by A. Yakushev et al. [109] in Dubna. The nuclide was produced by bombarding a nat U target with 48Ca ions. Simultaneously, short-lived Hg isotopes were produced from a small admixture of Nd to the target material. In test experiments short-lived Hg isotopes could be isolated in the elemental form from other reaction products and were transported in He quantitatively through a 30 m long Teflon capillary at room temperature. 

Direct searches for superheavy elements in the U+ U reaction were undertaken at the unilac by several groups. All these efforts remained without positive evidence. The data are summarized in Figure 13. The curve labeled chem [106] was obtained with off-line chemical separations [107] and an assay for a-and spontaneous fission activities here, the 10 picobam level was reached for half-lives between several days and years. Attempts to detect short-lived nuclides were less sensitive. The curve labeled gas holds for an on-line search [108] for components volatile at room temperature. wheel [106] refers to fission track detection in the unseparated product mixture deposited on a rotating catcher, rec [109] to implantation of recoil atoms in a surface barrier detector, and JET to on-line transport from target to detector with a gas jet [91,110],... 

Most models assessing the long-term behaviour of Cs and Sr from fallout include processes relevant to LMM ionic species only. However, radionuclides may be associated with particles due to (a) release of fuel matrix or clusters, (b) condensation of volatiles on available particle surfaces after the release of (c) interactions with aerosol particulates during atmospheric transport. For volatile radionuclides (e.g., Cs, °Sr), all three mechanisms may be equally relevant, while the deposition of nuclides of refractory elements (e.g., " Ce, Nb, Zr) indicates the release of fuel particles. For fuel particles, depletion of volatiles relative to refractory elements would be expected to depend on the temperature reached during the releases, whereas the activity ratios for refractory elements should reflect the reactor fuel bum-up. 

The coupled system of equations includes equation of continuity, Darcy s law for nonconstant density of fluid, balance of thermal energy equation, transport and mass balance equations for TDS and nuclides and closure equations for density and viscosity of fluid (Pruess, 1991). It is supposed that thermal properties do not depend on temperature. 

A similar experiment was reported by Dougan et al. [1(X)]. A setup called Online Separation and Condensation AppaRatus (OSCAR) was installed at the LBNL 88-Inch Cyclotron. Nuclear reaction products were collected with a KCl aerosol gas-jet and were transported from the target chamber to the OSCAR set-up where O2 was added. The aerosol particles were destroyed on a hot quartz wool plug and ffie formation of tetroxides occurred at a temperature of 650 °C. Nonvolatile reaction products were retained on the quartz wool plug, whereas the volatile tetroxides were swept by the carrier gas flow to a condensation chamber. Here, ffiey were deposited on a Ag disk, which was cooled with liquid N2. An annular Si surface barrier detector registered a particles and SF decays of nuclides adsorbed... 

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