Measuring Radioactivity - Online Tutor, Practice Problems & Exam Prep

Radiation measurement involves various units, including curies (Ci), roentgens (R), rads, and rems. One curie equals 3.7 × 10¹⁰ disintegrations per second, while 1 roentgen measures ionizing intensity. Rads quantify energy absorbed by tissue, with 1 rad equal to 1 × 10^-5 joules per gram, and the SI equivalent is gray (Gy). Rems measure tissue damage, with 1 rem equal to rad times relative biological effectiveness (RBE). X-rays and gamma rays have an RBE of 1, while alpha particles have an RBE of 20, highlighting their differing biological impacts.

Measuring Radioactivity Concept 1

Here we're going to say that radiation can be measured in several different ways depending on which property is being measured. So here we're going to have units of radiation measurement, and what we need to realize is that there are a lot of common units used for radiation. We have curie, we have Roentgen, we have rads, and we have REM. Alright. So let's start out with our curies. We're going to say here that 1 curie is equal to 3.7×1010 disintegrations per second. And we're going to say that the SI unit is 1 becquerel, which is Bq. So I'm going to butcher some of these because the names are a little bit different than what we're used to seeing. So we're going to say that 1 Bq is equal to 1 disintegration per second. And we're going to say here, what property it is measuring? We're going to say that it's measuring decay events.

Next, we have one Roentgen, which is R. We're going to say that 1 Roentgen is equal to 2.1×109 charges per cubic centimeters. Here we don't have an SI unit equivalent to it, and we need to realize here it deals with the exposure in terms of ionizing intensity of gamma and x-rays.

Next, we're going to say we have rads. So we're going to say here 1 rad is equal to 1×10-5 joules per gram, and that 1 rad is equal to 1 Roentgen. Alright. Next, we're going to say the SI unit equivalent of that is gray or Gy. We're going to say here that 1 gray is equal to 1 joule per kilogram, and it's also equal to 1 rad. So you can start seeing that some of these units are connected to one another. This will allow us later on to convert from one radiation unit to another. Now here, this deals with energy absorbed by tissue.

Then we have REM, rem. REMs equal rad times RBE. RBE is your relative biological effectiveness. We're going to say the SI unit of that is sievert or Sv. One sievert is equal to 100 REM. And then we're going to say what exactly is the property measuring? It's measuring tissue damage.

Now finally coming back to RBE, which is your relative biological effectiveness, it factors account for both your ionizing intensity and biological effect. And we're going to say here that x-rays, we're going to say here gamma rays, we're going to say here beta particles, their RBE is equal to 1. And when it comes to alpha particles which are larger, their RBE is equal to 20. So here these are the most important types of radiation units that you should keep in mind. Realize only the ones that are in purple, remember our purple boxes, are the ones that are important in terms of memorization. The others would be given to you in some way either in a formula sheet or within the question itself.

Measuring Radioactivity Example 1

The initial responders of the Chernobyl nuclear disaster were exposed to 23 Sv 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 100 REMs. So when we do that, Svs cancel out, and we'll end up with REM at the end. This comes out to 2300 REM 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 are the different units used to measure radioactivity?

Radioactivity can be measured using several units, each focusing on different properties. The common units include curies (Ci), roentgens (R), rads, and rems. One curie equals 3.7 × 10¹⁰ disintegrations per second, measuring decay events. Roentgens measure ionizing intensity, particularly for gamma and X-rays. Rads quantify the energy absorbed by tissue, with 1 rad equal to 1 × 10^-5 joules per gram. The SI equivalent of rad is gray (Gy), where 1 Gy equals 1 joule per kilogram. Rems measure tissue damage and are calculated as rad times the relative biological effectiveness (RBE). The SI unit for rem is the sievert (Sv), where 1 Sv equals 100 rems.

How is the curie unit defined in terms of disintegrations per second?

The curie (Ci) is a unit of radioactivity that measures the number of disintegrations per second. Specifically, 1 curie is defined as 3.7 × 10¹⁰ disintegrations per second. This unit is used to quantify the rate at which a radioactive substance undergoes decay. The SI unit equivalent to the curie is the becquerel (Bq), where 1 Bq equals 1 disintegration per second.

What is the difference between rads and rems in measuring radiation?

Rads and rems are both units used to measure radiation, but they focus on different aspects. Rads measure the energy absorbed by tissue, with 1 rad equal to 1 × 10^-5 joules per gram. The SI equivalent is the gray (Gy), where 1 Gy equals 1 joule per kilogram. Rems, on the other hand, measure the biological effect of the absorbed radiation. Rems are calculated as rad times the relative biological effectiveness (RBE). The SI unit for rem is the sievert (Sv), where 1 Sv equals 100 rems. Essentially, rads quantify energy absorption, while rems assess biological damage.

What is the relative biological effectiveness (RBE) and how does it vary for different types of radiation?

Relative biological effectiveness (RBE) is a factor used to compare the biological damage caused by different types of radiation. It accounts for both ionizing intensity and biological effect. For example, X-rays and gamma rays have an RBE of 1, meaning they have a standard level of biological impact. In contrast, alpha particles, which are larger and more ionizing, have an RBE of 20, indicating they cause significantly more biological damage. RBE is crucial for calculating rems, as rems equal rads times RBE.

How do you convert between different units of radiation measurement?

Converting between different units of radiation measurement involves understanding their relationships. For example, 1 curie (Ci) equals 3.7 × 10¹⁰ disintegrations per second, and the SI unit is the becquerel (Bq), where 1 Bq equals 1 disintegration per second. For absorbed dose, 1 rad equals 1 × 10^-5 joules per gram, and the SI unit is the gray (Gy), where 1 Gy equals 1 joule per kilogram. To convert rems to sieverts (Sv), use the relationship 1 Sv equals 100 rems. Understanding these equivalences allows for accurate conversions between units.