Radiocarbon dates - from the horses mouth

[Jack]

Found this in the 'notes for contributors' for RADIOCARBON

Calibrated Ages: cal BC, cal AD, cal BP

The symbol cal is used to express calibrated radiocarbon ages. Note that ?cal? should be understood as ?calibrated?, not ?calendar?. A ?calendar age? is an absolute date, whether known or guessed; a ?calibrated date? is an estimate based on statistical probability, and is therefore properly expressed as one or more ranges of calendar years, accompanied by the appropriate confidence level.
Wrong: The linen sample dated to 780 ? 40 BP, or cal AD 1263
Correct: The linen sample dated to 780 ? 40 BP, or cal AD 1220?1281 (1[FONT=&quot]σ[/FONT])
Correct: The linen sample dated to 780 ? 40 BP, or cal AD 1220 (1263) 1281 (1[FONT=&quot]σ[/FONT])
In this example, AD 1263 is the intercept of 780 BP on the dendrochronological calibration curve; it is nota calendar equivalent of a conventional 14C age. The first correct form expresses a calibrated date range at the 1-sigma confidence level; the second form gives the end points of the 1-sigma range with the intercept year in parentheses.
There are several valid ways to express calibrated dates; see Stuiver and Pearson (1993, p 5?6) and Stuiver and Reimer (1998, Section 4) for technical details. The method(s) chosen to represent cal dates should always be explicitly mentioned when the dates are presented.
RADIOCARBON Instructions for Authors 7 22 August 2005

Some in the radiocarbon community object to the term cal BP because they feel that BP is properly reserved for conventional radiocarbon ages, which yield BC/AD date ranges when calibrated. However, cal BP is widely used in the literature and has the advantage of providing a scale that does not break at AD 1 / 1 BC. A date expressed as ?N cal BP? is equivalent to the date (AD 1950 ? N years).


Seems both BP or BC/AD are technically correct

[GnomeKing]

useful stuff that every professional should be thoroughly versed in (hmmm)

- now all we need to worry about is 'legacey' C14 from decades past, C14 from uncalibrated sources, and doubtless there is much still to discover about the mechanisms of C-isotope production, accumulation, distribution from cosmic source to muddy archaeological lump, and so on.....

[moreno]

Thank frick for that! I had visions of having to revise all publications. Although in saying that, it would have been fun to wind up my colleagues!

It's prudent to use BP and AD/BC where appropriate. Due to the nature of the archaeology (Near East Prehistory), my 14C dates have always come back Cal BP (ORAU and Beta Analytic). Using 1950 as the bench mark is based on the assumption of radiocarbon half life and atmospheric radiocarbon constant. I'm no expert but if it's good enough for the lab rats it's good enough for me.

Good info and very useful!

[Dinosaur]

The book I'm wading my way through at the moment gives uncalibrated dates BP, 2 sigma ranges BP and also BC/AD in date-tables for their own sites (although annoyingly without the calibration graphs and individual range probabilities etc.), but then wierdly in the main text just gives single dates BP (presumably calibrated, although I haven't yet found the bit where they explain themselves) for other sites without any explanation of the confidence/date-ranges - confusing....

[Jack, don''t lose that bit of text, not connected to a printer here]

[moreno]

Took me a fair bit of time to sort through uncalibrated, calibrated, sigma'd and 14C conversions. It's always been an issue. Spent quite a bit of time discussing these things with a considerable number of people. For my purposes, I did get it sorted and published the results. Hopefully down the line it will help someone make sense of the confusion, then again....

[moreno]

Oh and good thread btw.

[P Prentice]

there is no point calibrating to BP if you work in archaeology and as far as i know only palaeontologists who work with quarternary scientists and geologist do so. if you get a date from a proper lab they will calibrate using oxcal 4 to give you a range BC or AD at 95% and 62%

the majority of dates in older publications are pretty much useless because they were taken from dumps of burnt looking 'stuff' which may have been from a multiple burning episode and when calibrated now usually produce a date range often over half a millennium or more. some people used to be able to guess the real date from the uncalibrated BP date but nowadays it is better to use the most uptodate calibration programme

[moreno]

there is no point calibrating to BP if you work in archaeology and as far as i know only palaeontologists who work with quarternary scientists and geologist do so.

Calibrated BP is the standard for Near Eastern Prehistory where many of us work with Quaternary scientists.

...the majority of dates in older publications are pretty much useless because they were taken from dumps of burnt looking 'stuff' which may have been from a multiple burning episode and when calibrated now usually produce a date range often over half a millennium or more. some people used to be able to guess the real date from the uncalibrated BP date but nowadays it is better to use the most uptodate calibration programme

Again, as mentioned in several threads, using Cal BP is relative. What you're suggesting may apply here in the UK, but it is simply not the case for the Near East.

[Dinosaur]

.....the majority of dates in older publications are pretty much useless because they were taken from dumps of burnt looking 'stuff' which may have been from a multiple burning episode and when calibrated now usually produce a date range often over half a millennium or more. some people used to be able to guess the real date from the uncalibrated BP date but nowadays it is better to use the most uptodate calibration programme

There are plenty of single-object old dates floating around though? [or are you suggesting starting again on all the dating and forget what's gone before?]- they just need running through modern calibration, the basic science of counting from the sample hasn't changed much, merely what's then done with the data

[BAJR]

Been very useful this thread... learned quite a bit. Just goes to show how something that sounds so simple is quite complicated, but when explained it becomes simple again.

Thanks