This is a sample page from the help file for LSCAnalysis, a software application that analyzed data from a liquid scintillation counter. This material is reprinted here with the client's permission. This material is ©2005 by Andy Humphrey and may not be reprinted without permission.
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Interface
The main interface is where you will do most of your interaction with LSC Analysis. Each control is explained below.
Machine
The machine dropdown allows you to select which machine generated the files to be analyzed. This is important because the databases of pure radionuclide spectra are kept separate for each machine in order to compensate for measurement differences between them.
tSIE Range
This allows you to restrict the range of tSIE values analyzed to increase accuracy. For example, if you are analyzing three unknowns with tSIEs of 472, 462, and 461, you'll get more accurate results by limiting the tSIE range to 430-500 rather than analyzing across the entire range of 0 to 1000. The application will use only those pure data files that fall within that range in its analysis.
Radionuclide (#)
The three radionuclide dropdowns allow you to select which radionuclides you expect to find in the sample. In order for a radionuclide to be on the list, you must have previously set up a database for it on the particular machine selected. When analyzing fewer than four radionuclides, select "<NOTHING>" for the remaining dropdowns.
Estimate Unquenched Values
If this box is checked, it will extrapolate the counts of each radionuclide for an unquenched sample (tSIE of 1000). This extrapolation is done by means of a polynomial regressing tSIE against counts measured in pure samples at varying quench levels.
# Windows
Here you can indicate the number of sets of window definitions to use, from 1 to 4. If more than 1 window definition is used, the results table will calculate the mean and standard deviation of the CPMs for each radionuclide in order to illustrate the system's sensitivity to the given window definitions.
Window Definitions
Here you can adjust the limits of the three detection windows. The parameters are given in KeV (thousands of electron volts). The allowable range is from 0.0-2000.0 KeV, in increments of 0.5 KeV. If more than one window definition is to be entered, each column is a different set of window parameters. You will be able to define only as many windows as there are radionuclides. So if you are analyzing three radionuclides, you will define windows A, B, and C, while window D will be left undefined and unused in the calculations.
Analyze button
Once you have set all parameters and loaded the files to be examined, the Analyze button will be activated. Pressing it will begin the analysis process. Each file will be compared against data for pure radionuclides and the amounts (in counts per minute) will be calculated for each radionuclide. A running total below the button show you the progress of the current analysis.
Fraction Poly Order
Sets the order of the polynomial used when regressing the fraction of counts in each window against tSIE. It defaults to a 1st order polynomial. No matter how high you set it, the order of the polynomial used will be no higer than the number of pure samples available within the tSIE range minus two. So if you specify a tSIE range that encompasses three samples in the pure radionuclide database, then this polynomial will be no higher than 1st order.
Efficiency Poly Order
Sets the order of the polynomial used when regressing efficiency factor against tSIE. It defaults to a 2nd order polynomial and has the same limit on maximum order as Fraction Poly Order described above.
Reference tSIE
This is provided by the application for the user's reference. Once analysis begins, it chooses a reference tSIE to use the correct the measurement efficiency of each sample. This value is set to the lowest value of the set of the highest values of tSIE for each radionuclide within the tSIE range specified. For example, let's say you are analyzing for 3H, 90SR, and 239 Pu in the tSIE range of 430-500. And let's say that the samples of the pure radionuclides that fall into this tSIE range themselves have the tSIE ranges of 454-481, 458-475, and 431-490 respectively. The highest tSIE sample for each radionuclide would be 481, 475, and 490. The lowest of these maximum values would be 461, so the reference tSIE would be set to 475.
Results Table
Once LSC data files have been loaded they will be listed here by batch (which is the name of the directory that contains the file) and file name. Once the analysis begins, this table will be cleared and repopulated as each file is analyzed. For each file the table will list the mass, the measured counts per minute per gram (CPM/g) in each window (averaged across multiple scans), the tSIE, and the estimated total CPM/g of each radionuclide. For multiple window definitions, this data will be displayed for each set of window parameters plus the mean CPM/g and standard deviation will be displayed for each radionuclide. Any time it shows "NaN" (not a number) for counts or tSIE it indicates that there are multiple data files for that sample and when it attempted to average the counts or tSIE among the multiple files, the standard deviation was so high that this data point is being thrown out. The standard deviation threshold is 25% of the average value; this can be changed in the file "LSC Analysis.ini"