ASNT Industrial Radiography Radiation Safety Practice Test

If a radiographer has 98 Ci of Ir-192, how many curies would be left after 148 days?

1. 15.5 Ci

2. 24.5 Ci

3. 40.5 Ci

4. 60.5 Ci

The correct answer is: 24.5 Ci

To determine how many curies would be left after a specified period, we need to consider the half-life of the radioactive material in question. Iridium-192 (Ir-192) has a half-life of approximately 74 days. This means that every 74 days, the amount of Ir-192 will reduce to half of its previous amount. In the scenario provided, the initial amount of Ir-192 is 98 Ci, and we want to find out how much remains after 148 days. Since 148 days is exactly two half-lives (74 days × 2 = 148 days), we can find the remaining amount by calculating half of the amount twice: 1. After the first 74 days (one half-life), the amount would be: 98 Ci ÷ 2 = 49 Ci. 2. After the next 74 days (another half-life), the amount would be: 49 Ci ÷ 2 = 24.5 Ci. Therefore, after 148 days, the quantity of Ir-192 remaining is indeed 24.5 Ci. This calculation confirms that selecting 24.5 Ci is accurate based on the half-life decay process of Ir-192.