INDUCED CONDUCTIVITIES IN IRRADIATED POLYETHYLENE

Journal Article · Tue Jan 01 00:00:00 EST 1963 · Proc. Japan Conf. Radioisotopes

OSTI ID:4708935

Yahagi, K; Shinohara, K; Mori, K; Fukada, E

Induced conductivities in irradiated polyethylene were observed as functions of dose rate and applied voltage. Irradiated polyethylenes were prepared with electron beams from a Van de Graaff Generator. The total doses of radiation were from about 10/sup 7/ rad to 10/sup 8/ rad. The experiments on induced conductivities were carried out under gamma irradiation from Co/sup 60/. The gamma dose rates were from about 162 r/hr. The samples were circular films of Marlex and Arathene 90 mm in diameter and 0.076 mm thick. Each sample was coated with silver paste and then irradiated with the electron beams. The irradiated samples were set in a vacuum vessel to minimize the effects of ionization and oxidation. The induced current of irradiated samples was not dependent on the gamma dose rate, but the samples quenched from about 160 deg C were dependent on the dose rates. The dark currents of the irradiated samples were slightly less than the induced currents in the irradiated samples. The absorbed currents were observed by the application of d-c voltage. These results suggest that the large number of trapped electrons in the irradiated samples liberated thermally are moved in the sample. The appreciable flows of absorbed currents in irradiated samples are due to the space charge effects of these trapped electrons in the samples. (JAIF) In order to investigate the physical situations of the free radicals trapped in irradiated polymers, the saturation phenomena of the electron spin resonance are examined on the radicals in polyethylene (polyphenyl type radical and alky type radical) and polymethylmethacrylate irradiated with 1.5-Mev electrons in vacuo at liquid nitrogen temperature. For compariaon with these radicals, the stable free radical, DPPH, dispersed in polymethylmethacrylate is also examined, From the saturation curves, namely, the relations between the strength of the microwave magnetic field in the sample cavity and the resonance signal intensity, the spin-lattice relaxation time, T/sub 1/, and the spin-spin relaxation time, T/ sub 2/, are calculated, and the paramagnetic relaxation mechanism of the free radicals is discussed. The dependences of T/sub 1/ and T/sub 2/ upon the temperature and the radical concentration are also observed in most cases. The DPPH case, in which DPPH molecules are homogeneously distributed, was used as an example to test the relaxation mechanism. It is concluded from this example that the relaxation mechanism of the radicals trapped in polymers is due to the dipolar interaction between radicals influenced by the internal motion of polymers. The relaxation mechanism is, therefore, analyzed at least qualitatively with the well-known Kubo-Tomita's theory, wlth the assumption that the internal motion is ascribed to be the single thermal-activation process. The relaxation mechanism of the radicals in irradiated polymers is observed to act also on the theory. The internal motion of polymer around the trapped radicals is not considerably different from that of ordinary undamaged region. Although the macroscopic concentration of the radicals measured from resonance signal intensity varies, the saturation behaviors are independent of the concentration in the case of the polyphenyl type radical in irradiated polyethylene and of irradiated polymethylmethacrylate. Therefore, the microscopic distribution of the radicals does not change within the range of irradiation dose. This result suggests that the radicals in irradiated polymers are trapped in radiation- induced spurs, and that the amount of the spurs increases with the irradiation dose but the radical concentration in the spurs remains unchanged. (JAIP)

• Research Organization: Wasede Univ.
• NSA Number: NSA-17-030130
• OSTI ID: 4708935
• Journal Information: Proc. Japan Conf. Radioisotopes, Vol. Vol: 5th, No. 3; Other Information: Orig. Receipt Date: 31-DEC-63
• Country of Publication: Country unknown/Code not available
• Language: Japanese

Related Subjects

GENERAL AND MISCELLANEOUS
ABSORPTION
COATING
COBALT 60
ELECTRIC CHARGES
ELECTRIC CONDUCTIVITY
ELECTRIC POTENTIAL
ELECTRON BEAMS
ELECTRONS
FILMS
GAMMA RADIATION
IONIZATION
IRRADIATION
OXIDATION
POLYETHYLENES
PREPARATION
RADIATION DOSES
SILVER
SPACE CHARGE
TEMPERATURE
THICKNESS
TRAPS
VACUUM
VAN DE GRAAFF ACCELERATORS
VESSELS