But wouldn't you agree that it's one of the simplist, and if a hobiest were to attempt any radiometric dating experiments, it would be the ideal one? I'm open to suggestions to a better one.
Counting beta decay in theory is very simple. In practice, getting accurate radiocarbon dates from archaeological materials is much more difficult.
As an archaeologist I send a lot of samples off for dating,
Cool! I always wanted to meet a real life scientist! Can you tell me more? What lab to you usually send them to, and what does it cost? Also, what particular type of archaeology do you work in, and where? Very cool!
I use Beta Analytic in Coral Gables, Florida. They charge $375 for a standard sample, and $595 for an AMS sample. Standard samples need to be quite large (for example 15 grams of clean shell) while AMS samples can be very small (a few milligrams of shell will work). I do prehistoric archaeology in the western US.
and most of the tricky parts are in sample selection and interpretation of the results.
Could you clarify selection and interpretation, here? As an archaeologist, do you do this selection and interpretation?
Yes. The lab does the sample processing, which includes decontamination and determination of C13 and C14. They will provide a calibration using the latest calibration curve.
But there is much more to it than that. The samples I send in need to be representative of something. If I send in a sample consisting of hundreds of pieces of shell or bulk soil, the resulting date may be of little use because it mixes multiple events. I prefer a single piece of bone, shell, or charcoal because that represents a single event. And a single piece of charcoal might represent a forest fire, so you need to use charcoal from a reliable provenience, such as a fire pit or hearth. A single piece of shell is almost always good as shellfish don't walk up and out of the ocean.
To further complicate matters, that piece of wood might have been from the center of a 500 year old oak. Whoops! Your date is off by 500 years and you don't know it. (A shellfish is usually much shorter-lived, so that won't be much of a problem.)
For this and other reasons it is extremely dangerous to rely on a single sample. If you have a dozen dates you can see trends and spot outliers. When working a major site, I usually send in a few samples and evaluate the results before sending in the next batch. It is not unusual to send the samples off in four or five batches, using subsequent batches to expand or clarify the results of earlier batches. Some sites I have worked have required over 30 samples to provide good estimates of the ages of the different cultural layers.
When the results come back from the lab you have to know what to make of them. If you sent off a sea mammal bone you need to make sure it is calibrated using a marine dataset, rather than a terrestrial dataset. Same for shell. The C13/C12 ratio can also provide useful information on the nature of the sample, and that figure is used in calculating the "conventional" age from the "measured" age. Human bone can provide erroneous answers if you calibrate using a terrestrial dataset while the people were eating a heavily marine diet. The (N15 and C13 readings can help determine the percent of marine organisms in the diet.)
Radiocarbon dates often come back calibrated with a range, calculated at one and two sigmas. Some labs also provide an intercept. It is much safer to use the range at two sigmas as your date (that might be expressed as Cal AD 250 to 420 (Cal BP 1700 to 1520). This represents a statistical reliability of about 95%.
It wouldn't hurt to clarify that since the suggestion has been made in this thread that scientists select just the evidence that supports their belief. Also, what do you mean by interpretation? I think radiocarbon dating is pretty well defined -- it should be a matter of science, I'm not sure why different people would interpret it in different ways.
The interpretation comes in when you are trying to figure out what your dates mean in terms of the people who lived at a site. If you have six dates between 500 and 1000 years ago and six more dates between 1500 and 2000 years ago, does that 500 year gap represent an abandonment of the site, or is it an artifact of the number of samples you submitted. Was there some bias in your sample selection that created the gap? Did you select six samples from the top of the site and six from the bottom, neglecting to date the middle of the site? That is what I mean by interpretation. (And it is often a lot more complex than this.)
I must tease you a little here for refering me to a religious website about a scientific matter and in response to a scientific question. Radiometric Dating: A Christian Perspective by Dr. Roger C. Wiens.
Many of the people I discuss C14 dating with are anti-science because of their religious beliefs, so I find that this source can help. Besides, it is the best summary article I have found.
Could you please be so kind as to point out where on this extensive site I would most likely find the information that would be most helpful in teaching me how to perform the excercise of carbon dating?
Beats me. Archaeologists don't tend to do the dating themselves. It is much easier to let a good lab do that. You could try the earliest issues of Radiocarbon and see what you can find. I tend to ignore those articles in favor of those dealing with calibration and interpretation.
Thanks very much for the information. Incidentally, most of it was geared towards proving that radiocarbon dating works and is accurate. But my question wasn't whether it was accurate, but "How do I do it."
But I think I did gleam some clues -- C14 comes at about 1part per trillion as compared to non-radioactive carbons. Now I just need to find out how many beta decays there are per million C14 per second, or however it's done.
You also need to separate the sample's beta decay from the background. The labs I have been in have used extensive shielding of their counters to reduce the background. One lab was in a second sub-basement, and had piles of lead bricks all around the counters. I believe they also recorded the ambient background as a control against which to compare the sample count.
Hope this helps.
You also need to separate the sample's beta decay from the background.
Yes, this is true. My counter picks up around 12 counts per minute background around here, if I recall correctly. I've heard before that lead plates were used, and I noted when I was at the dentists they put a blanket filled with lead bbs on me when they xrayed my teeth. But one would want to make sure that their lead plates weren't themselves radioactive!
Thanks again,
-Jesse