# Dating based on radioactive decay table

Play a game that tests your ability to match the percentage of the dating element that remains to the age of the object. There are two types of half-life problems we will perform.

One format involves calculating a mass amount of the original isotope. Using the equation below, we can determine how much of the original isotope remains after a certain interval of time. The half-life of this isotope is 10 days. Solution To determine the number of half-lives nboth time units must be the same.

For example, carbon has a half-life of 5, years and is used to measure the age of organic material. The ratio of carbon to carbon in living things remains constant while the organism is alive because fresh carbon is entering the organism whenever it consumes nutrients.

When the organism dies, this consumption stops, and no new carbon is added to the organism. As time goes by, the ratio of carbon to carbon in the organism gradually declines, because carbon radioactively decays while carbon is stable. Analysis of this ratio allows archaeologists to estimate the age of organisms that were alive many thousands of years ago. Along with stable carbon, radioactive carbon is taken in by plants and animals, and remains at a constant level within them while they are alive.

After death, the C decays and the C C ratio in the remains decreases. Comparing this ratio to the C C ratio in living organisms allows us to determine how long ago the organism lived and died.

Image used with permission CC-BY 4. C dating does have limitations. It may include tools, clothing, or sludges.

## 5.7: Calculating Half-Life

These are buried like low-level waste from hospitals and universities at federal or commercial disposal sites. In the s, nine sites in three rock types were selected as potentially acceptable ones for development of a high-level waste disposal site Table 3. Low-level commercial wastes are currently being stored at Hanford, Yucca Mountain and at a site in South Carolina.

Others promoted disposal of radioactive wastes by jettisoning them into space, but this proposal has not been seriously considered because of cost, the difficulty of recovery, and the potential for them to fall back to Earth. Many countries in Europe, limited by the availability of geologically reasonable disposal areas and their relatively small areas, do currently dispose of nuclear wastes on the seabed.

Measurements of Radioactivity and Hazard Assessment There are several ways in which measures of radiation are presented. Some of these rely on direct measurements of disintegrations over time, and others are used to determine radiation hazard to living tissue Table 4.

The Systeme International SI units of measurement for radioactivity are Becquerels, which are defined in disintegrations per second. A Becquerel is equivalent to 2.

• 5.4: Rates of Radioactive Decay

Energy emitted during radioactive processes can be measured in joules J. The absorbed dose of radiation is considered in terms of grays Gywhere 1 Gy is equivalent to absorption of 1 joule J of radiation by 1 kg of material for example, a human body. However, the situation is complicated for living matter because certain types of radiation energy do more damage to living tissue than others.

The radiation dose equivalent, which takes such differences into account, is the sievert Svalso with dimensions of joules per kilogram. For neutrons and alpha particles, however, a multiplication factor is required.

For neutrons, 1 Gy is considered equivalent to 10 Sv; for alpha particles, 1 Gy is considered equivalent to 20 Sv.