Radical Electron Spin Resonance Research Articles

The demagnetizing field on the surface of disc-shaped ferromagnetic samples

The local demagnetizing fields on the surface of flat cylindrical samples (disc) are measured by means of the free radical electron paramagnetic resonance for several thickness-to-diameter ratios from 0·01 to 0·15 and at two values of the external magnetic field (around 4 and 14 kOe). An empirical expression for the demagnetizing field intensity is found and anisotropy of the demagnetizing field is detected in the sample plane. The experimental results are compared with the conclusions of the theory of Joseph and Schlomann.

Electron spin resonance evaluation of pigment accumulation during asexual sporulation in Aspergillus flavus

The association between pigment accumulation and a free radical electron spin resonance (ESR) signal produced during sporulation in Aspergillus flavus was investigated. In wild-type cultures, the onset of the ESR signal coincided with the onset of both pigmentation and sporulation. Mutant colonies, affected in their pigmentation and/or their ability to produce conidia, failed to give a free radical signal. However, pigmentation apparently was not essential for either sporulation or spore germination in A. flavus. Pigmentless conidia were obtained which germinated as well as wild-type conidia. There did appear, though, to be some form of association between pigment accumulation and sporulation, since all the asporogenous mutants which were isolated also were non-pigmented.

Electron Paramagnetic Resonance of Radicals Formed during Milling

Abstract It is well known that during the mechanical degradation of polymers there takes place scission of molecular chains and the formation of macroradicals. It is of considerable interest to study the electron paramagnetic resonance (EPR) spectra of the macroradicals produced by milling, and to compare them with the spectra of the macroradicals formed in the process of polymerization, and also during the irradiation of polymers by gamma rays and neutrons. We may endeavor to compare the amount of macroradicals formed with the extent of mechanical destruction (for instance with the area of the new interface which is formed). In addition, as was found by experience, the macroradicals formed by mechanical scission are good models for the investigation of reactivity since practically all of them are in the newly formed surface layers and are therefore very accessible to various chemical influences. They enter easily into reaction with various agents present in the medium since in this process diffusion from the surface is found in practice not to be a predominating factor. In the present communication we give the first EPR results obtained on mechanically degraded polymers.