Akibumi Danno

Gamma‐Ray Induced Conductivity in Polyethylene and Teflon under Radiation at High Dose Rate

The conductivity induced by gamma radiation from Co60 has been measured for polyethylene and Teflon as functions of temperature, dose rate, and applied voltage. The range of dose rates was from about 103 to 105 R/h and of the temperature from 190° to 300°K. The value of Δ, which shows the dependence of the induced current i on the dose rate R, i.e., i ∝ RΔ, varies from 1 (characteristic of the monomolecular recombination) to ½ (characteristic of the bimolecular recombination) with decreasing temperature. In both polymers, below about 240°K the induced current at a thermal equilibrium was independent of temperature, although it was slightly increased with decreasing temperature. From the investigation of temperature and dose‐rate dependences, it is considered that the thermal electrons are dominant as charge carriers above 230°K, but fast electrons at below that temperature.

Design and operational features of the low temperature fissiochemical loop

A low temperature in-pile loop for the irradiation of chemical reactants, especially by fission fragments, has been designed, constructed and operated successfully. The main features of the loop are briefly described: the capsule for sample irradiation, the design and performance of the helium cooling system and safety considerations. Gaseous chemical reactants charged in an instrumented double capsule at pressures up to 20 kg/cm2, can be irradiated in a nuclear reactor at any temperature between + 20° and – 190°C, for periods up to 5hr. The thermal performance of the helium cooling system was in good agreement with the design calculations. Irradiations of ethylene and other gases could be conducted at an absorbed fission fragment dose rate of about 20 Mrad/hr, which is several times larger than the background reactor radiation. Thus, chemical reaction studies by fission fragments can be safely conducted at. ambient to low temperatures in this loop.

Chemical Dosimeters for Mixed Radiations in a Nuclear Reactor

The dose rates due to mixed reactor radiations were measured by five gaseous chemical dosimeters – nitrous oxide (natural), 15N-enriched nitrous oxide, ethylene, ethane and carbon dioxide. The observed dose rates for these gases at the same irradiation position in a nuclear reactor were, 1.8×108, 1.5×l08, 1.9×108, 2.5×l08 and 1.0×108 rad/hr, respectively. These values were compared with those calculated from the mass stopping power of the gases for secondary electrons produced by γ-rays and those from thermal and fast neutron fluxes. No contradiction was found among them. A method of analysis of the reactor radiation dose rates into γ, thermal and fast neutron components is proposed, which is based solely on chemical dosimetry.

GAMMA-RAY INDUCED CONDUCTIVITY IN POLYETHYLENE COAXIAL CABLE

The electrical conductivity changes in a 3C-2V-type polyethylene high- frequency coaxial cable are reported for conditions of high dose rates of gamma radiation. The dose rates ranged from 4.2 x 10/sup 3/ to 1 x 10/sup 6/ r/hr and potentials of 0 to 1000 v at currents of 10/sup -11/ to 10/sup -9/ amp. Relations between the induced currents and dose rates give straight lines of slope 0.68 except for zero voltage. The direction of the current for V = 0 is reversed to that for the voltage supply, resulting in a greater value for the slope. (B.O.G.)

Measurement of Absorbed Dose and Flux in a Reactor by Chemical Dosimetry

Nitrous oxide, carbon dioxide and ethylene were utilized as gaseous chemical dosimeters, and measurements were made of the doses absorbed by these substances in a nuclear reactor. The neutron and photon fluxes as well as their contributions to the absorbed doses were determined by analyzing the data obtained from the chemical dosimetry, with particular consideration given to the fast neutron energy spectrum. The values of the photon, thermal neutron and fast neutron fluxes thus determined were 2. 6×1013 γ/cm2·sec, 3. 5 × 1013 n/cm2·sec and 7.0×1013 exp(- E)sinh√2E n/cm2·sec. These values were compared with the results from calorimetrie and activation methods, and were found to be in fair agreement with each other. From the above results, it was confirmed that the above combination of chemical dosimeters are serviceable for the measurement of both absorbed dose and fluxes in a nuclear reactor.

Reaction of Recoil Tritium Atoms in a Mixture of Carbon Tetrachloride and Aliphatic Acids

Yields of products from neutron irradiation of a mixture of carbon tetrachloride as additive and aliphatic acids containing lithium chloride have been investigated. In each system, the major products were HT, T-labeled aliphatic acid and T-labeled hydrocarbons. The yield resulting from the abstraction reaction of hydrogen atoms bonded to carbon atoms was affected by the concentration of the additive and depended on the C-H bond strength. On the other hand, the substitution reaction of recoil tritium was not influenced by the concentration of additive. The yield of degradated products from the mixture was smaller than from the irradiation of pure acid. This may be interpreted to be the result of dimer formation in a non-polar solvent.