Measuring Radioactivity: Videos & Practice Problems

Radiation measurement is crucial in understanding the intensity and impact of radioactive decay. The unit curie (Ci) quantifies radiation as 3.7×10¹⁰ disintegrations per second, while the SI unit becquerel (Bq) represents one disintegration per second. The roentgen (R) measures ionizing intensity of gamma and X-rays without an SI equivalent. The rad, equal to 1×10^-5 joules/gram, and its SI counterpart, the gray (Gy), indicate energy absorbed by tissue. Furthermore, the rem (radiation equivalent man) and sievert (Sv) assess tissue damage, with 1 Sv equating to 100 rem. The relative biological effectiveness (RBE) factor, which is 1 for X-rays, gamma rays, and beta particles, and 20 for alpha particles, accounts for ionizing intensity and biological effect, emphasizing the varying impacts of different types of radiation on biological tissues. Understanding these units and their interrelations is essential for accurately assessing radiation exposure and its potential biological effects.

Units of Radiation Measurement

Radiation can be quantified using various units, each measuring different properties. Key units include the curie, roentgen, rad, and rem, each serving distinct purposes in radiation measurement.

The curie (Ci) is a unit that quantifies radioactive decay, defined as 1 \text{ Ci} = 3.7 \times 10^{10} \text{ disintegrations per second}. The SI equivalent is the becquerel (Bq), where 1 \text{ Bq} = 1 \text{ disintegration per second}.

Next, the roentgen (R) measures exposure to ionizing radiation, particularly gamma and X-rays. It is defined as 1 \text{ R} = 2.1 \times 10^{9} \text{ charges per cm}^3, and it does not have a direct SI equivalent.

The rad is a unit that measures the energy absorbed by tissue, defined as 1 \text{ rad} = 1 \times 10^{-5} \text{ joules per gram}. The SI equivalent is the gray (Gy), where 1 \text{ Gy} = 1 \text{ joule per kg} = 100 \text{ rad}.

The rem (roentgen equivalent man) is used to measure biological effects of radiation, calculated as \text{rem} = \text{rad} \times \text{RBE}, where RBE is the relative biological effectiveness. The SI unit for rem is the sievert (Sv), with 1 \text{ Sv} = 100 \text{ rem}. This unit specifically measures tissue damage.

Relative biological effectiveness (RBE) accounts for the type of radiation and its biological impact. For example, X-rays, gamma rays, and beta particles have an RBE of 1, while alpha particles, being larger and more damaging, have an RBE of 20. Understanding these units and their relationships is crucial for converting between them and assessing radiation exposure and effects on biological tissues.

Radiation Measurement Units Conversion Example

The Chernobyl nuclear disaster exposed initial responders to a radiation level of 23 sieverts (Sv). To convert this measurement into rem, a common unit for radiation exposure, we can utilize the conversion factor where 1 Sv is equivalent to 100 rem. By applying this conversion, we can calculate the exposure in rem as follows:

Given:

Exposure in Sv = 23 Sv

Conversion factor: 1 Sv = 100 rem

To perform the conversion:

Exposure in rem = 23 Sv × 100 rem/Sv = 2300 rem

Thus, the radiation exposure of the initial responders at Chernobyl was 2300 rem. This conversion highlights the significant levels of radiation they encountered during the disaster response.

A typical chest X-ray exposes a patient to an effective dose of 0.09 mSv. How many Rad is this?

• A. 25 rad
• B. 0.125 rad
• C. 0.009 rad
• D. 37 rad

Answer: (C)

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

Answer: (B)

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

Answer: (B)

Here’s what students ask on this topic:

What is the unit of measurement for radioactivity?

The unit of measurement for radioactivity is the becquerel (Bq) in the International System of Units (SI). One becquerel is defined as one disintegration or nuclear transformation per second. It indicates the activity of a quantity of radioactive material in which one nucleus decays per second. This unit is named after Henri Becquerel, who shared a Nobel Prize with Pierre and Marie Curie for their work in the discovery of radioactivity.

Another older unit that is still used, particularly in the United States, is the curie (Ci), which is defined as 3.7 × 10¹⁰ disintegrations per second. The curie is a much larger unit than the becquerel and was originally based on the activity of one gram of radium-226. For practical purposes, such as medical treatments and radiation safety, you may encounter submultiples like millicuries (mCi) or microcuries (µCi).

What is the SI unit in the measurement of radioactivity?

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The SI unit used to measure radioactivity is the becquerel (Bq). One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. This unit is named after Henri Becquerel, who was one of the discoverers of radioactivity. It's important to note that the becquerel is a very small unit, so in practical situations, you'll often encounter larger multiples like kilobecquerels (kBq), megabecquerels (MBq), gigabecquerels (GBq), and so on, where each step up represents a thousand-fold increase in activity. Another older unit of radioactivity that is still used in some contexts is the curie (Ci), which is equivalent to 3.7 × 10<sup>10</sup> becquerels.

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What is the unit for becquerel?

The becquerel (symbol: Bq) is the SI (International System of Units) derived unit for radioactivity. One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. It is a measure of the rate at which a given radioactive substance is undergoing radioactive decay. The becquerel is a relatively small unit, and often larger multiples such as kilobecquerels (kBq), megabecquerels (MBq), gigabecquerels (GBq), terabecquerels (TBq), and so on are used when dealing with significant quantities of radioactive substances. The unit is named after Henri Becquerel, one of the discoverers of radioactivity.

What unit is used to measure radioactivity?

Radioactivity is measured in a unit called the becquerel (Bq). One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. It's a measure of the rate at which a sample of radioactive material is undergoing nuclear decay. Another older unit of radioactivity is the curie (Ci), which was originally based on the radioactivity of one gram of radium-226. The curie is a much larger unit than the becquerel, with one curie equal to 3.7 × 10¹⁰ becquerels. For measuring radiation dose absorbed by biological tissue, the gray (Gy) is used, and for the risk of radiation exposure, the sievert (Sv) is the unit of choice. Both of these units take into account the biological effects of radiation, not just the activity.