Chapter 20, Problem 105RQ

Interpretation Introduction

Interpretation:

The percentage of tritium in a given sample of ‘young’ groundwater is to be determined and the quantity that is represented by sum of moles of tritium and ${}^3\text{He}$ is to be determined.

Concept Introduction:

The age of groundwater in terms of being old or young depends on the time elapsed since the rain water first entered the respective aquifer. This groundwater may be days to thousands of years old. Different methods have been devised to measure the age of groundwater. The use of isotopes $\text{tritium}-3$ and $\text{helium-3}$ is one such method.

Tritium $-3$ $\left({}^{3}H\right)$ has a half-life of $12.26\text{ years}$ and is an excellent tracer for young waters. It is a radioactive element and emits into $\text{helium}-3$ $\left({}^3\text{He}\right)$ on its radioactive decay. The ${}^{\text{3}}{\text{H / }}^{\text{3}}\text{He}$ dating can be applied to a wide range of hydrologic investigations of the ‘young’ ground water, such as, uses of chlorofluorocarbons and sulfur hexafluoride.