Measuring Radioactivity: Study with Video Lessons, Practice Problems & Examples

Radioactivity is measured using various units, including the Curie (Ci), which equals 3.7 × 10¹⁰ disintegrations per second, and the SI unit, Bq, where 1 Bq equals 1 disintegration per second. Other units include the Roentgen (R) for ionizing radiation exposure, Rad for energy absorbed by tissue, and Rem, which accounts for biological effects. The Sievert (Sv) is another unit, equal to 100 Rem. Understanding these units is crucial for assessing radiation's impact on health and safety.

Measuring Radioactivity Concept 1

Now, when it comes to measuring radioactivity, we're going to say that radiation can be measured in several different ways depending on which property is being measured. Now, here we're going to have some units of radiation measurement. So the first one we're going to look at is the common unit of the Curie after Madame Curie. So here it is abbreviated as Ci. We're going to say here that 1 Curie is equal to 3.7×1010 disintegrations per second. And we're going to say the SI unit is Becquerel, Bq. So for those French speakers, I know I kind of butchered the name a little bit. But here, we're going to say that 1 Bq equals 1 disintegration per second. And the property being measured here is basically the activity or decay events that occur. Next, we have Rontgen which is R, capital R. We're going to say one of these is equal to 2.1×109 charges per cubic centimeter. Here, it does not have an applicable SI unit involved. We're going to say here this deals with the exposure of ionizing intensity of gamma and x-rays. Remember these are high energy states when we look at the electromagnetic spectrum. Next, we have Rad. We're going to say here that 1 Rad is equal to 1×10-5, which is Joules per gram. 1 Rad equals 1 capital R here, and this argon is the Rontgen. Next, we have Gray which is Gy. One Gray is equal to 1 Joule over kilograms, or we can say that 1 Gray is equal to 100 rads. Here, we're looking at the energy absorbed by tissue. Alright. Next, we're going to say here we have REM. REMS equals rads times RBE. What is an RBE? Well, an RBE is your relative biological effectiveness. This factor accounts for both of our ionizing intensity as well as biological effect. And we're going to say here that X-rays, gamma rays, and beta particles, 1 RBE equals 1. And then for alpha particles, since they're larger, they are equal to 20. Now coming up here, we have a Sievert which is Sv. One of these is equal to 100 rems and then here this looks at tissue damage. So these are the most common types of units of radiation measurements that you're going to encounter when dealing with conversions between them.

Measuring Radioactivity Example 1

The initial responders of the Chernobyl nuclear disaster were exposed to 23sv of radiation. Convert this value to REM. Alright. So, all we have to do here is use the conversion factor, and realize 23 sv, the conversion factor is that for every one sv we have 100rem. So when we do that, svs cancel out and we will go off with rem at the end. This comes out to 2300rem as the new units for our radiation.

Two technicians in a nuclear laboratory were accidentally exposed to radiation. If one was exposed to 5 mGy and the other to 9 rad, which technician received more radiation?

• A. The one exposed to 5 mGy
• B. The one exposed to 9 rad
• C. The two technicians were exposed to the same amount of radiation

A solution of iodine-131, a radioisotope used in the diagnosis and treatment of thyroid disease, is found just prior to administration to have an activity of 1.08 x 10⁶ Bq/mL. If 2.57 mL were delivered intravenously to the patient, what dose of I-131 ( in µCi) did the patient receive?

• A. 7.50×10^–5 µCi
• B. 75.0 µCi
• C. 29.2 µCi
• D. 0.075 µCi
• E. 0.029 µCi

Here’s what students ask on this topic:

What is the difference between Curie (Ci) and Becquerel (Bq) in measuring radioactivity?

The Curie (Ci) and Becquerel (Bq) are both units used to measure radioactivity, but they differ in scale and origin. The Curie, named after Marie Curie, is a traditional unit where 1 Ci equals 3.7 × 10¹⁰ disintegrations per second. In contrast, the Becquerel is the SI unit for radioactivity, defined as 1 disintegration per second. Therefore, 1 Ci is equivalent to 3.7 × 10¹⁰ Bq. The Curie is often used in contexts where large amounts of radioactivity are present, while the Becquerel is more commonly used in scientific and medical settings due to its alignment with the International System of Units (SI).

How is the Roentgen (R) used to measure ionizing radiation exposure?

The Roentgen (R) is a unit used to measure the exposure of ionizing radiation, specifically gamma and X-rays. It quantifies the amount of ionization produced in air by these high-energy photons. One Roentgen is defined as producing 2.1 × 10⁹ ion pairs per cubic centimeter of air. Unlike other units, the Roentgen does not have a direct SI equivalent. It is primarily used in radiology and radiation protection to assess the intensity of radiation fields and ensure safety standards are met.

What is the relationship between Rad and Gray (Gy) in measuring absorbed radiation dose?

The Rad and Gray (Gy) are units used to measure the absorbed dose of radiation by tissue. One Rad is defined as the absorption of 0.01 joules of radiation energy per kilogram of tissue. The Gray, an SI unit, is defined as the absorption of 1 joule of radiation energy per kilogram of tissue. Therefore, 1 Gy is equivalent to 100 Rads. The Gray is more commonly used in scientific and medical contexts due to its alignment with the International System of Units (SI).

How does the Sievert (Sv) account for biological effects of radiation?

The Sievert (Sv) is a unit that measures the biological effects of ionizing radiation. It accounts for both the type of radiation and its impact on different tissues. The Sievert is calculated by multiplying the absorbed dose (in Grays) by a quality factor known as the Relative Biological Effectiveness (RBE). For example, X-rays, gamma rays, and beta particles have an RBE of 1, while alpha particles have an RBE of 20. This means that 1 Sv of alpha radiation causes the same biological effect as 20 Sv of X-rays or gamma rays. This unit is crucial for assessing radiation exposure risks and ensuring safety in medical and occupational settings.

What is the significance of REM in measuring radiation exposure?

REM (Roentgen Equivalent Man) is a unit used to measure the biological effect of ionizing radiation on human tissue. It is calculated by multiplying the absorbed dose (in Rads) by the Relative Biological Effectiveness (RBE) of the radiation type. For example, X-rays, gamma rays, and beta particles have an RBE of 1, while alpha particles have an RBE of 20. This means that 1 REM of alpha radiation has the same biological effect as 20 REM of X-rays or gamma rays. The REM is essential for evaluating radiation exposure in medical, industrial, and environmental contexts, helping to ensure safety and compliance with regulatory standards.