The time needed for half of a radioactive sample to decay is called its __ period transmutation time decay period half-life

## Step 1<br />The problem is asking for the term that describes the time it takes for half of a radioactive sample to decay. This is a concept in nuclear physics, specifically in the study of radioactivity.<br /><br />## Step 2<br />The term "half-life" is used to describe this phenomenon. It is the time required for a quantity to reduce to half of its initial value. In the context of radioactive decay, it is the time it takes for half of the atoms in a sample to decay.<br /><br />## Step 3<br />The other options provided, "period", "transmutation time", and "decay period", are not the correct terms for this concept. The term "period" is a general term that can refer to any recurring event, not specifically to radioactive decay. "Transmutation time" and "decay period" are not standard terms used in the context of radioactive decay.