A Combined Atomic and Molecular Probe Characterization of Aromatic Hydrocarbons via PALS and ESR: Methylbenzene

A combined study of one of the simplest aromatic hydrocarbons, i.e., methylbenzene (toluene) (TOL), via the annihilation of an ortho-positronium (o-Ps) probe via positron annihilation lifetime spectroscopy (PALS) and the rotation dynamics of nitroxide spin probe 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) using electron spin resonance (ESR) over a wide temperature range, 10–300 K, is reported. The o-Ps lifetime, τ3, and the relative o-Ps intensity, I3, as a function of temperature exhibit changes defining several characteristic PALS temperatures in the slowly and rapidly cooled samples. Similarly, the spectral parameter of TEMPO mobility in TOL, 2Azz‘, and its correlation time, τc, reveal several effects at a set of the characteristic ESR temperatures, which were determined and compared with the PALS results. Finally, the physical origins of the changes in free volume expansion and spin probe mobility are revealed. They are reflected in a series of the mutual coincidences between the characteristic PALS and ESR temperatures and appropriate complementary thermodynamic and dynamic techniques.

Using X-Ray As An Irradiation Source For Direct ESR Dating of Fossil Teeth

In this paper we have tested the potential application of X-rays as an irradiation source in Electron Spin Resonance dating of tooth enamel. Both modern and fossil samples were used to assess the feasibility of dose estimations using this alternative irradiator. Equivalent doses obtained with gamma-rays on fossil powder enamel was frequently less than the doses obtained on fragments using only X-rays. It is believed that a combination of NOCORs (non-orientated CO2- radicals) and local internal dose discrepancy may be the origin of the difference. Here, we show that testing penetration attenuation for each individual irradiation source is required to accurately estimate the maximum enamel thickness and produce reliable protocols. The use of a known laboratory additive dose allows the calculation of an absorption equivalent coefficient between gamma-rays and X-rays. We conclude that X-rays are an alternative irradiation source for ESR dating protocols, however, limitations remain in particular with alpha efficiency.