10Be - 26Al exposure age calculator


For determining reference production rates from a calibration data set.

Version 2.3. June, 2016. Written by Greg Balco, balcs@bgc.org

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Name for this calibration data set (text only):
Enter calibration measurement data block here.See below for formatting instructions.


How does this work?

This page allows you to enter a set of Be-10 production rate calibration data and find the value of the reference Be-10 production rate that best fits those data. You can then use that best-fitting reference production rate to compute exposure ages from Be-10 and Al-26 measurements at unknown-age sites. Here is how it works:

1. Get some calibration data. Up-to-date calibration data, in the correct format for entering in this page, can be obtained from the ICE-D calibration database here. Select a 'site' and then copy and paste the version 2 text input from the site page into the box on this page above. Give the calibration data set a name in the other box.

2. Press 'calculate now.' Wait; the calculation may take a few minutes. If it takes more than 10 minutes, you can probably assume it has crashed. The result of the calculation will be a new page that resembles the normal exposure-age data input form here , but contains additional information about the results of the production rate calibration calculations.

3. Save that page to your local machine, either as just the page source or as a 'web archive' (available in some browsers).

4. You can then open the local copy of the page and send data for exposure age calculations to use the results of the production rate calibration that you just did without having to re-do the calibration.

There are several potential sources of difficulty here. One is just getting the input data correct. The ICE-D database interface should do pretty well, but in some cases you may have to remove stray lines with missing data. See the format definition below. The other is that some calibration data sets are poorly behaved in a numerical sense -- for example, if they are multimodal around two different implied production rates, then the calibration code will have difficulty choosing the correct one. In this case some sort of an error message should appear. If you have problems with this issue, try increasing the measurement uncertainty in either the true ages or the nuclide concentrations. Finally, this is just slow. If you send a huge pile of data it may take a while and create server/browser timeout problems as discussed below.

Some other notes. First, the minimization scheme that chooses the best-fitting production rate is somewhat restricted in order to keep the computation time to reasonable levels. The main restriction here is that the best-fitting reference Be-10 production rate must be between 3 and 5; if it's not, the algorithm will fail, hopefully with an error message explaining why. A secondary issue is that the misfit statistic that is being minimized is expected to fall within a reasonable range, the definition of which is based on typical measurement uncertainties expected for Be-10 data. If you enter data with uncertainties that are much smaller than expected, difficulties may result. As noted above, that can be dealt with by increasing the uncertainties.

Note changes in Version 2.3:
Version 2.3 has updated muon interaction cross-sections and minor bug fixes.
Notes on current limitations
First, this only uses Be-10 measurements to determine the Be-10 production rate, and then multiplies by the production ratio to obtain an Al-26 production rate. Al-26 measurements are ignored. Second, this uses an extremely simplified optimization scheme to obtain the best-fitting production rate. This is designed to minimize calls to the time-consuming parts of the exposure age calculation, but it can break if the calibration data set is particularly badly behaved. Third, at present there is no way to deal with artificial target experiments, i.e. zero-age measurements.
Is your browser timing out before receiving the results?
It can take a long time to do the production rate calibration, because each measurement has to be pushed through all of the exposure-age calculation code many times. If the timeout setting on your browser is too short, it will stop waiting for the page before the calculations are done. You can set the wait time to a longer value on some browsers. If that's not true of yours (Safari, for example), you may be out of luck.
Formatting instructions:
This form is designed to have text pasted into it from a text editor or an Excel spreadsheet. The formatting requirements are unforgiving, but easy to follow once you have a spreadsheet set up appropriately. An example spreadsheet of calibration data is here. The rules are as follows:
  1. Enter plain ASCII text only.
  2. Each sample should occupy its own line.
  3. Each line should have seventeen elements, as described below.
  4. Elements should be separated from each other by white space (spaces or tabs).
  5. Something other than white space must be entered for each element. For example, if you have no Al measurements for a sample, you must enter "0" in the Al concentration and Al uncertainty positions.
The seventeen elements are as follows:

  1. Sample name. Any text string not exceeding 24 characters. Sample names may not contain white space or any characters that could be interpreted as delimiters or escape characters, e.g., slashes of both directions, commas, quotes, colons, etc. Stick to letters, numbers, and dashes.
  2. Latitude. Decimal degrees. North latitudes are positive. South latitudes are negative.
  3. Longitude. Decimal degrees. East longitudes are positive. West longitudes are negative.
  4. Elevation/pressure. Meters or hPa, respectively, depending on selection below.
  5. Elevation/pressure flag. Specifies how to treat the elevation/pressure value. This is a three-letter text string. If you have supplied elevations in meters and the standard atmosphere is applicable at your site (locations outside Antarctica), enter "std" here. If you have supplied elevations in meters and your site is in Antarctica, enter "ant" here. If you have entered pressure in hPa, enter "pre" here. Any text other than these three options will be rejected.
  6. Sample thickness. Centimeters.
  7. Sample density. g cm-3.
  8. Shielding correction. Samples with no topographic shielding, enter 1. For shielded sites, enter a number between 0 and 1.
  9. Erosion rate inferred from independent evidence. cm yr-1.
  10. 10Be concentration. Atoms g-1. Standard or scientific notation.
  11. Uncertainty in 10Be concentration. Atoms g-1. Standard or scientific notation.
  12. Name of Be-10 measurement standard. Text. Acceptable values for this parameter are given on this page.
  13. 26Al concentration. Atoms g-1. Standard or scientific notation. Note: at present this does not determine Al-26 production rates. This is here as a placeholder.
  14. Uncertainty in 26Al concentration. Atoms g-1. Standard or scientific notation. Note: as above, this is a placeholder.
  15. Name of Al-26 measurement standard. Text. Acceptable values for this parameter are given on this page. Note: as above, this is a placeholder, but you still have to enter something.
  16. Independently measured exposure age for the site. Years. Note: the code is not yet set up to deal with artificial target measurements, so '0' is not an acceptable input value.
  17. Uncertainty in independently measured exposure age. Years.
Note: Nuclide concentrations should already take account of carrier and process blanks.