Influence of radiation environments on space charge formation in gamma-irradiated LDPE

In the present paper the formation of space charge in irradiated low-densit y polyethylene (LDPE) was investigated using the pulsed electroacoustic (PE A) technique. Specimens of LDPE, similar to 100 mu mm thick, were irradiate d to various doses at room temperature in a Co-60 gamma source in one of th ree different environments: ambient room air, oxygen-free nitrogen and vacu um. The results obtained indicate that the space charge distribution is dep endent on the irradiation environment. There is a large concentration of po sitive charge evident in the sample irradiated in air compared to very litt le for material irradiated in either vacuum or nitrogen under similar condi tions. This indicates that the presence of oxygen during irradiation, and t hereby oxidation itself, has a major influence on the mechanism by which sp ace charge evolves. Thus the monitoring of space charge may in itself be an indicator of the degree of oxidation and of aging in a material. The evolu tion of space charge and its decay are discussed.