Analysis of cadmium in food by multiple prompt gamma-ray spectroscopy

Effect of sample density in prompt γ-ray analysis

A high-accuracy analytical method is broadly required to obtain reliable research results. Thus, prompt γ-ray analysis (PGA), one of the most accurate non-destructive analytical methods, has been employed in various fields. However, the measurement accuracy of PGA is also known to degrade in hydrogenous samples. The degradation is caused by variation in the measurement sensitivity (counts per milligram) following the change in neutron energy due to scattering with hydrogen nucleus. Number of scatterings is well known to depend on the hydrogen content in a sample. However, considering multiple scatterings, hydrogen density, which has not been taken into account as yet, may also lead to the accuracy degradation. Here, we show the effect of the hydrogen density in PGA by evaluating the measurement sensitivity of samples with the same hydrogen content and different densities. We find that the measurement sensitivity varies by more than 30% depending on the hydrogen density even at the same hydrogen content. The variation is a particularly serious problem for PGA requiring a few percent accuracy in most cases. Additionally, although the variation is apparently observed in hydrogenous samples, the similar phenomenon can occur in other nuclides with a large scattering cross section; it may affect nuclear cross-section measurements using neutrons in such fields as astrophysics and nuclear energy.

Design of a laser-induced breakdown spectroscopy system for on-line quality analysis of pulverized coal in power plants

It is vitally important for a power plant to determine the chemical composition of coal prior to combustion in order to obtain optimal boiler control. In this work, a fully software-controlled laser-induced breakdown spectroscopy (LIBS) system comprising a LIBS apparatus and sampling equipment has been designed for possible application to power plants for on-line quality analysis of pulverized coal. Special attention was given to the LIBS system, the data processing methods (especially the normalization with Bode Rule/DC Level) and the specific settings (the software-controlled triggering source, high-pressure gas cleaning device, sample-preparation module, sampling module, etc.), which gave the best direct measurement for C, H, Si, Na, Mg, Fe, Al, and Ti with measurement errors less than 10% for pulverized coal. Therefore, the apparatus is accurate enough to be applied to industries for on-line monitoring of pulverized coal. The method of proximate analysis was also introduced and the experimental error of A(ad) (Ash, 'ad' is an abbreviation for 'air dried') was shown in the range of 2.29 to 13.47%. The programmable logic controller (PLC) controlled on-line coal sampling equipment, which is designed based upon aerodynamics, and is capable of performing multipoint sampling and sample-preparation operation.