The rate of decay for a radioactive substance is dependent upon its half-life, which is the time required for half of the radioactive atoms in a sample to decay. Each radioactive isotope has a unique half-life, ranging from fractions of a second to billions of years, influencing how quickly it decays. Environmental conditions, such as temperature and pressure, do not affect this rate. Understanding half-lives is crucial for applications like radiometric dating, nuclear medicine, and managing nuclear waste. The predictable nature of decay allows scientists to estimate the age of materials and assess safety in handling radioactive substances.