Radioactive dating unreliable - Radiometric Dating - Tulane University


Iodine-131 can be "seen" by nuclear medicine imaging techniques (., gamma cameras ) whenever it is given for therapeutic use, since about 10% of its energy and radiation dose is via gamma radiation. However, since the other 90% of radiation (beta radiation) causes tissue damage without contributing to any ability to see or "image" the isotope, other less-damaging radioisotopes of iodine such as iodine-123 (see isotopes of iodine ) are preferred in situations when only nuclear imaging is required. The isotope I-131 is still occasionally used for purely diagnostic (., imaging) work, due to its low expense compared to other iodine radioisotopes. Very small medical imaging doses of I-131 have not shown any increase in thyroid cancer. The low-cost availability of I-131, in turn, is due to the relative ease of creating I-131 by neutron bombardment of natural tellurium in a nuclear reactor, then separating I-131 out by various simple methods (., heating to drive off the volatile iodine). By contrast, other iodine radioisotopes are usually created by far more expensive techniques, starting with reactor radiation of expensive capsules of pressurized xenon gas.

The story of this great change in the conception of the history of Earth is not a simple one. The chronicle of this great change can be broken into five periods;

Love-hungry teenagers and archaeologists agree: dating is hard. But while the difficulties of single life may be intractable, the challenge of determining the age of prehistoric artifacts and fossils is greatly aided by measuring certain radioactive isotopes.

Until this century, relative dating was the only technique for identifying the age of a truly ancient object. By examining the object's relation to layers of deposits in the area, and by comparing the object to others found at the site, archaeologists can estimate when the object arrived at the site. Though still heavily used, relative dating is now augmented by several modern dating techniques.

Radiocarbon dating involves determining the age of an ancient fossil or specimen by measuring its carbon-14 content. Carbon-14, or radiocarbon, is a naturally occurring radioactive isotope that forms when cosmic rays in the upper atmosphere strike nitrogen molecules, which then oxidize to become carbon dioxide. Green plants absorb the carbon dioxide, so the population of carbon-14 molecules is continually replenished until the plant dies. Carbon-14 is also passed onto the animals that eat those plants. After death the amount of carbon-14 in the organic specimen decreases very regularly as the molecules decay. Carbon-14 has a half-life of 5,730 ± 40 years, meaning that every 5,700 years or so the object loses half its carbon-14.

Samples from the past 70,000 years made of wood, charcoal, peat, bone, antler or one of many other carbonates may be dated using this technique.


Radioactive dating unreliable

Radioactive dating unreliable