title: Dynamic nuclear polarization of electron-beam irradiated polyethylene by pairs of alkyl free radicals.
abstract: We compared dynamic nuclear polarization (DNP) behavior of electron-beam irradiated polyethylene (e-PE) with that of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-doped polystyrene (T-PS). Growth and decay rates of nuclear polarization P(n) of e-PE increased linearly with increasing concentration C(e) of free radicals, whereas those of T-PS increased with square of C(e). From these results, we suggest that the pair of alkyl radicals produced by the radiolysis, -CH(2)-CH(2)-CH(2)-→-CH(2)-CH()-CH(2)-+H(), and the subsequent hydrogen abstraction reaction, H()+-CH(2)-CH(2)-CH(2)-→H(2)+-CH(2)-CH()-CH(2)- in e-PE plays an important role on DNP by the cross effect, whereas T-PS is polarized by a pair of unspecified TEMPO radicals accidentally located nearby. We propose that higher P(n) would be expected by optimizing the inter-radical distance within the pair in e-PE and other irradiated samples.
authors.affiliation: Quantum Beam Science Directorate, Kansai Photon Science Institute, Japan Atomic Energy Agency, Umemidai, Kizugawa, Kyoto 619-0215, Japan. kumada.takayuki@jaea.go.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kumada
authors.forename: Yohei
authors.initials: Y
authors.lastname: Noda
authors.forename: Norito
authors.initials: N
authors.lastname: Ishikawa