Question

What units, SI and common, are used to describe each of the following? (a) the activity of a radioactive sample (b) the energy of a particle or of a photon of radiation given off by a nucleus (c) the amount of energy absorbed by a given mass by a dose of radiation (d) dose equivalents for comparing biological effects

Short answer

The SI units are (a) becquerel (Bq), (b) joule (J), (c) gray (Gy), and (d) sievert (Sv). The common units are (a) curie (Ci), (b) electronvolt (eV) and its multiples, (c) rad, and (d) rem.

Step-by-step solution

Identify the SI unit for the activity of a radioactive sample

The activity of a radioactive sample, which is a measure of the number of decays per second, is measured in becquerels (Bq) in the SI system. One becquerel is defined as one transformation (or decay) per second.

Identify common unit for the activity of a radioactive sample

A commonly used non-SI unit is the curie (Ci), which was originally defined as the activity of 1 gram of radium-226. The relation is 1 Ci = 3.7 x 10^10 Bq.

Identify the SI unit for the energy of a particle or photon of radiation

The energy of a particle or a photon of radiation is measured in joules (J) in the SI system. For photons, specifically in the context of radiation, electronvolts (eV) are also commonly used.

Identify common unit for the energy of a particle or photon of radiation

In the field of nuclear physics, the energy of particles or radiation photons is often described in electronvolts (eV) and its multiples like kiloelectronvolts (keV), megaelectronvolts (MeV), and gigaelectronvolts (GeV).

Identify the SI unit for the amount of energy absorbed by a given mass

The amount of energy absorbed by a given mass from radiation is measured in grays (Gy) in the SI system. One gray is defined as the absorption of one joule of radiation energy by one kilogram of matter.

Identify common unit for the amount of energy absorbed by a given mass

The rad is a non-SI unit still used in the United States. The conversion is 1 Gy = 100 rads.

Identify the SI unit for dose equivalents

For dose equivalents, which compare the biological effects of radiation, the SI unit used is the sievert (Sv).

Identify common unit for dose equivalents

A non-SI unit that is sometimes used is the rem. The relationship is 1 Sv = 100 rems. The rem is the traditional unit still being used in the United States in some contexts.

Key concepts

Becquerel (Bq)

The measurement of radioactivity in a sample is expressed in becquerels (Bq), which is the SI unit. A single becquerel represents one atomic decay per second, showing how often unstable atoms are losing energy by emitting radiation.

This unit is particularly useful when discussing small amounts of radioactive substances. For instance, when considering the contamination of food or environmental samples, measuring the activity in becquerels provides a clear idea of the potential radioactive exposure.

Gray (Gy)

When focusing on the amount of energy that a radiation dose imparts on matter, we use the gray (Gy). Essentially, a dose of one gray is the absorption of one joule of radiation energy by one kilogram of matter. The gray is crucial in various fields, such as medicine, where it helps to ensure that the correct dose of radiation is administered for cancer treatments.

Understanding grays helps to evaluate risks of radiation exposure and is vital for radiation protection purposes.

Sievert (Sv)

The sievert (Sv) measures the biological effects of radiation, with a focus on the risk it poses to human tissue. It takes into account not just the energy but also the type of radiation and its potential for causing harm.

Thus, sieverts are essential in radiation safety to estimate the risk of cancer or other health problems after exposure to ionizing radiation. Occupational exposure limits for workers in nuclear industries and radiology departments are often expressed in sieverts.

Curie (Ci)

The curie (Ci) is a traditional unit that was previously used to express the activity of radioactive substances. It links back to the early days of radioactive research, defined as the activity of 1 gram of radium-226. Although primarily replaced by the becquerel in the SI units system, one curie is noteworthy as it equals 3.7 x 10^10 becquerels.

Its common use in historical contexts and older literature makes an understanding of the curie valuable for students and professionals when dealing with legacy systems or documents.

Electronvolt (eV)

The electronvolt (eV) is a unit of energy most commonly used when discussing the microscopic scale of particles and photons, especially within the fields of atomic, nuclear, and particle physics. An electronvolt equals the amount of kinetic energy gained by a single electron when it is accelerated through an electric potential difference of one volt.

In practice, the electronvolt and its multiples, like the megaelectronvolt (MeV), provide a convenient way of describing the energies involved in nuclear reactions and decay processes, including the energies of emitted particles and radiation.

Rad

The rad, short for radiation absorbed dose, is a non-SI unit that still finds use, particularly in the United States. It quantifies the energy of ionizing radiation absorbed by a mass of tissue, with one rad equaling 0.01 joules absorbed per kilogram of tissue.

This unit, while less common now, can be found in older literature and is sometimes used in medical contexts where legacy equipment or protocols are in place. For conversion purposes, it's essential to remember that 1 gray is equivalent to 100 rads.

Rem

Lastly, the rem, which stands for roentgen equivalent man, is a non-SI unit used to express dose equivalents. It assesses the biological effect of ionizing radiation on human tissue. Like the rad, it's not commonly used internationally but persists in certain regulatory frameworks, especially in the U.S.

The rem is valuable for dose calculations and risk assessment in health physics, factoring the different biological impacts of various types of ionizing radiation. The relationship between sieverts and rems is important to note, with 1 sievert being equal to 100 rems.