Luminescence (version 1.0.0)

calc_FastRatio: Calculate the Fast Ratio for CW-OSL curves

Description

Function to calculate the fast ratio of quartz CW-OSL single grain or single aliquot curves after Durcan & Duller (2011).

This function follows the equations of Durcan & Duller (2011). The energy required to reduce the fast and medium quartz OSL components to x and x2 % respectively using eq. 3 to determine channels L2 and L3 (start and end). The fast ratio is then calculated from: \((L1-L3)/(L2-L3)\).

Usage

calc_FastRatio(
  object,
  stimulation.power = 30.6,
  wavelength = 470,
  sigmaF = 2.6e-17,
  sigmaM = 4.28e-18,
  Ch_L1 = 1,
  Ch_L2 = NULL,
  Ch_L3 = NULL,
  x = 1,
  x2 = 0.1,
  dead.channels = c(0, 0),
  fitCW.sigma = FALSE,
  fitCW.curve = FALSE,
  plot = TRUE,
  ...
)

Value

Returns a plot (optional) and an S4 object of type RLum.Results. The slot data contains a list with the following elements:

summary

data.frame summary of all relevant results

data

the original input data

fit

RLum.Results object if either fitCW.sigma or fitCW.curve is TRUE

args

list of used arguments

call

call the function call

Arguments

object

RLum.Analysis, RLum.Data.Curve or data.frame (required): x, y data of measured values (time and counts).

stimulation.power

numeric (with default): Stimulation power in mW/cm²

wavelength

numeric (with default): Stimulation wavelength in nm

sigmaF

numeric (with default): Photoionisation cross-section (cm²) of the fast component. Default value after Durcan & Duller (2011).

sigmaM

numeric (with default): Photoionisation cross-section (cm²) of the medium component. Default value after Durcan & Duller (2011).

Ch_L1

numeric (with default): An integer specifying the channel for L1.

Ch_L2

numeric (optional): An integer specifying the channel for L2.

Ch_L3

numeric (optional): A vector of length 2 with integer values specifying the start and end channels for L3 (e.g., c(40, 50)), with the second component greater than or equal to the first.

x

numeric (with default): Percentage of signal remaining from the fast component. Used to define the location of L2 and L3 (start).

x2

numeric (with default): Percentage of signal remaining from the medium component. Used to define the location of L3 (end).

dead.channels

numeric (with default): Vector of length 2 in the form of c(x, y). Channels that do not contain OSL data, i.e. at the start or end of measurement.

fitCW.sigma

logical (optional): fit CW-OSL curve using fit_CWCurve to calculate sigmaF and sigmaM (experimental).

fitCW.curve

logical (optional): fit CW-OSL curve using fit_CWCurve and derive the counts of L2 and L3 from the fitted OSL curve (experimental).

plot

logical (with default): enable/disable the plot output.

...

available options: verbose (logical). Further arguments passed to fit_CWCurve.

Function version

0.1.1

How to cite

King, G.E., Durcan, J., Burow, C., 2025. calc_FastRatio(): Calculate the Fast Ratio for CW-OSL curves. Function version 0.1.1. In: Kreutzer, S., Burow, C., Dietze, M., Fuchs, M.C., Schmidt, C., Fischer, M., Friedrich, J., Mercier, N., Philippe, A., Riedesel, S., Autzen, M., Mittelstrass, D., Gray, H.J., Galharret, J., Colombo, M., Steinbuch, L., Boer, A.d., 2025. Luminescence: Comprehensive Luminescence Dating Data Analysis. R package version 1.0.0. https://r-lum.github.io/Luminescence/

Author

Georgina E. King, University of Bern (Switzerland)
Julie A. Durcan, University of Oxford (United Kingdom)
Christoph Burow, University of Cologne (Germany) , RLum Developer Team

References

Durcan, J.A. & Duller, G.A.T., 2011. The fast ratio: A rapid measure for testing the dominance of the fast component in the initial OSL signal from quartz. Radiation Measurements 46, 1065-1072.

Madsen, A.T., Duller, G.A.T., Donnelly, J.P., Roberts, H.M. & Wintle, A.G., 2009. A chronology of hurricane landfalls at Little Sippewissett Marsh, Massachusetts, USA, using optical dating. Geomorphology 109, 36-45.

Further reading

Steffen, D., Preusser, F. & Schlunegger, 2009. OSL quartz age underestimation due to unstable signal components. Quaternary Geochronology 4, 353-362.

See Also

fit_CWCurve, get_RLum, RLum.Analysis, RLum.Results, RLum.Data.Curve

Examples

# load example CW-OSL curve
data("ExampleData.CW_OSL_Curve")

# calculate the fast ratio w/o further adjustments
res <- calc_FastRatio(ExampleData.CW_OSL_Curve)

# show the summary table
get_RLum(res)