Calculate the Fast Ratio for CW-OSL curves

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,
  ...
)

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.

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

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/

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.

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

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)
#> 
#> [calc_FastRatio()]
#> 
#>  -------------------------------
#>  Fast Ratio		: 405.12
#>   ˪ Absolute error	: 119.74
#>   ˪ Relative error (%)	: 29.56
#>  Channels		: 1000
#>  Channel width (s)	: 0.04
#>  Dead channels start	: 0
#>  Dead channels end	: 0
#>  Sigma Fast		: 2.6e-17
#>  Sigma Medium		: 4.3e-18
#>  I0			: 7.2e+16
#>  Stim. power (mW/cm^2)	: 30.60
#>  Wavelength (nm)	: 470.00
#>  -
#>  Time L1 (s)		: 0.00
#>  Time L2 (s)		: 2.45
#>  Time L3 start (s)	: 14.86
#>  Time L3 end (s)	: 22.29
#>  -
#>  Channel L1		: 1
#>  Channel L2		: 62
#>  Channel L3 start	: 373
#>  Channel L3 end		: 558
#>  -
#>  Counts L1		: 11111
#>  Counts L2		: 65
#>  Counts L3		: 37.67
#>  -------------------------------
#> 


# show the summary table
get_RLum(res)
#>   fast.ratio fast.ratio.se fast.ratio.rse channels channel.width
#> 1    405.122      119.7442       29.55756     1000          0.04
#>   dead.channels.start dead.channels.end  sigmaF   sigmaM           I0
#> 1                   0                 0 2.6e-17 4.28e-18 7.240067e+16
#>   stimulation.power wavelength t_L1     t_L2 t_L3_start t_L3_end Ch_L1 Ch_L2
#> 1              30.6        470    0 2.446413   14.86139 22.29208     1    62
#>   Ch_L3_start Ch_L3_end Cts_L1 Cts_L2   Cts_L3
#> 1         373       558  11111     65 37.66667