Γ-irradiated 3-methylpentane Research Articles

Trapped Electrons in γ-Irradiated 3-Methylpentane at −196°

The yield of solvent-trapped electrons in γ-irradiated 3-methylpentane at −196° was 0.75 per 100 eV when measured within a few seconds, and diminished to ∼0.6 after 3 min. The quantum yield for bleaching at 950 mμ decreased from 0.8 toward zero with progressive bleaching. Addition of 0.05% biphenyl maintained the quantum yield at >0.8 until more than 90% of the solvent trapped electrons had bleached. The initial quantum yield at λ>1.7μ was ∼0.01, both with and without added biphenyl. There is qualitative correlation between photobleaching and the rate of spontaneous decay.

Ionic Processes in γ-Irradiated Organic Solids: Electrons in 3-Methyl Pentane

γ-irradiated 3-methylpentane (3MP) and solutions of biphenyl (φ) have been examined at −196° at doses of 1 to 26×1018 eV ml−1. The half-life for decay of the trapped electron (e−) in 3MP is independent of dose for t<1 h and the rate is approximately second order for t>1 h. This behavior, as well as very efficient formation of φ− at small % φ, requires electron track lengths of ∼10−4 cm. The 100 eV yield of (e−) shortly after γ irradiation is ∼0.9, in terms of the measured extinction coefficient ε(e−)≅3.0×104 liter mole−1·cm−1 at 2.3×1018 eV ml−1, but only 60% as great at 10-fold greater dose. At 0.04% φ, the rate of (e−) decay is much faster and approximates first order. The ratio of reaction cross sections of (e−) with positive holes and φ is ∼120. Addition of 2% 2-methylpentene−1 as positive hole trap increases the yield of (e−) and decreases the rate of decay, which becomes second order throughout. Recombination luminescence intensity from TMPD at t>1 h decays at the same rate following uv and γ excitation. The evidence for randomization of relatively large yields of ion pairs and very long track lengths, as well as trapping and escape, may require a new theoretical framework.