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2.5.4  Import Procedure Blank Toolbox

This special toolbox is provided to help you analyze the Evolution of your Procedure Blanks over a single day or a range of days. To use this toolbox, first activate the blanks table via the Edit # Procedure Blanks menu item. Now select one or more analyses and click the Import Procedure Blanks button on the ArArCALC Toolbar. Since the blank measurements are all saved in text files organized by measurement date, this tool allows you to import multiple blank measurements for a range of days, by opening more than one of these text files. Hold down the control key when selecting more than one file.

 

The Advanced Blank Calculations dialogbox is now shown, in which you can select/deselect blanks and go through the Ar36, Ar37 ... Ar40 isotopes to calculate either a Linear, Parabolic, Polynomial or Average Fit (pink dashed line). These calculations also return Confidence Envelopes (grey dashed lines) at three different kinds of confidence levels. When you are finished calculating your blank evolutions, click the OK button and ArArCALC will replace your blanks and uncertainties with the newly calculated values. If the predicted error envelop gives an uncertainty that is smaller than the average error bars on the measured blanks, then the larger of the two error estimates is used by default.

Selecting Isotopes and Regression Types
To select different argon isotopes, click on the radio buttons labeled Ar36, Ar37 ... Ar40. To select and show a particular regression, click on any of the check boxes in the upperleft table. This will select the blank data for a particular argon isotope, while calculating the chosen regression line and its uncertainties. The resulting r2 and SEyx (in %) statistics are immediately updated, as are the regression lines and error envelopes in the plot.

Selecting and Deselecting Blanks Files
To deselect blank files from the calculations, click on their file name in the Select Blank Files list box. You can also use the button beneath this list box to Deselect All or Select All. When you deselect blanks, the horizontal scale will be adjusted to closely fit the data points in the plotting window. Deselected files are indicated by red squares (see below).

Note   For a Polynomial Fit this toolbox requires at least 5 data points, whereas for a Parabolic Fit it requires at least 4 data points and for a Linear Fit at least 3 data points. The calculation scheme for a Polynomial Fit is a little bit more involved, where a 3rd degree polynomial is calculated when 5 data points are available, and a 4th degree polynomial when more points are available. This allows you to follow the blank evolution more closely. The Selected Analyses or Unknowns are shown by gray circles at the bottom of the diagram

Calculation Mode
In this toolbox you can calculate the blank evolutions with respect to either Time for laser runs or Temperature for furnace runs. You can only check one of these checkboxes at a time.

Air Normalization
This option allows you to subtract a presumed Atmospheric Component from your blank measurements (see also: Blank Corrections) before it is used in the age calculations. You should give in the 40Ar/36Ar Ratio most recently measured for your air shots and you should provide an intensity for the Default 40Ar Blank that is close to what you measured for the particular blanks during your experiment. As a result, the blank evolutions for 38Ar and 36Ar may become more "flat" while the 40Ar remains constant. Check the Normalize 38Ar-36Ar to 40Ar checkbox to activate this option.

Options
Your calculated blank uncertainties also can be replaced with a default set of percentual uncertainties. Click the Default Blank Errors checkbox to activate this option and click on the Change button to edit these percentages, which should be given at the 1σ Confidence Level.