Radioactivity calculations using spectrum windows were widely used in the LSC technique since the beginning especially for measuring low levels of 3H, 14C and Cherenkov counting. Thus for standardization of spectra were used one of the methods based on external standard.
For a precise standardization of the spectra we use sets of calibration spectra measured under different quenching conditions, count the sample for a long time, we introduce a controlled shifting of sample spectra for processing and we apply multi-window calculation of high energy part of the spectra. Our approach to the processing of the spectra we use both for the old and the new LS spec-trometers Quantulus 1220TM when measuring 14C using two types of 7 ml and 0.8 ml Teflon vials. To prove the method we analyzed results given by our approach when measuring samples prepared from the one quenched sample of benzene by various dilutions. We used six high energy windows that partially overlap. Sample spectra were controlled shifted until coincidence of spectra end-point. Visu-al comparison of spectra was performed using automatic selection of scale for each spectrum. Con-trolled sample spectra shift and a common visualization of set of spectra: calibration, sample and background allow achieving an acceptable coincidence of spectra end-point. Another way of optimi-zation is to perform set of calculation for each of several shifts of sample spectrum and chose an op-timal based on standard deviation.
Spectra processing program Easy View enables in one-step loading of calibration and back-ground spectra and choose pre-set of windows and then save the processing parameters of the spec-trum of the sample in a spreadsheet format for subsequent calculations. During the processing of all spectra we apply one step smoothing. However, it is not applicable in Easy View to make spectra shift by channel after applying several smoothing steps that hinder achievement matches end-points of spectra. The use of specially developed software code which compares net spectra: sample-background to calibration-background provides a much better coincidence for spectra end-point, which is only attainable that way for low active samples. Performing calculations in multiple win-dows for shifted spectra allows obtaining optimal result and simultaneous assessing its uncertainty (discrepancy).