Product numbers that include "PQ" belong to our Precision Tube Family. Those with "SQ" are our Economy brand tubes. Precision brand EPR tubes hold 10-15 times tighter tolerance on the inner diameter, and >5 times smaller camber and concentricity over Economy Brand tube. Precision tubes are recommended for cw-experiments that require a constant filling factor or reproducibility on sample volume in the cavity.
Clear Fused Quartz (CFQ) is purified from naturally occurring quartz so the existence of certain material radicals from mining is inevitable. Due to technological advancements the sensitivity of EPR has gradually increased. The direct result is that certain high Q cavities will pick up the signal from these impurities, especially in tubes of over 4 mm OD. In this case we recommend switching to Suprasil EPR products which are made of synthetic material and suppress major impurity contents shown in Table 1 by the average of 2 orders of magnitude. Impurity analysis test results for Suprasil are shown below:Chemical impurity analysis results for CFQ are shown below:
Table 1: Impurity Analysis for Clear Fused Quartz (unit: ppm in weight)