By Arif Subhan, MS, CCE, FACCE

Arif SubhanThis article will review radiation safety. The discovery of x-rays in 1895 opened the door for using radiation in medicine. Not long after, in the early 1900s, the dangers of x-rays became well known. The first organized effort at radiation safety was undertaken in 1915 by the British Roentgen Society, which adopted a resolution to protect people from overexposure to x-rays.1,2 The knowledge and understanding of radiation safety is very important for BMETs and clinical engineers.

Radiation safety is one of 18 topics found in the section “Risk Management/Safety,” which constitutes 10% of the Certification in Clinical Engineering (CCE) examination. (Find a listing of all 18 topics at the end of this column.3,4)

Electromagnetic Spectrum

The electromagnetic spectrum is shown in Figure 1. The energy of the radiation increases from left (non-ionizing) to right (ionizing) as the frequency increases.2

Figure 1: Different types of electromagnetic radiation.

Figure 1: Different types of electromagnetic radiation.

The electromagnetic spectrum consists of all frequencies and wavelengths of electromagnetic waves. The spectrum is classified into two categories of radiation: non-ionizing and ionizing.2

Non-Ionizing Radiation. Non-ionizing radiation does not have enough energy to remove electrons from the atom. Examples of non-ionizing radiation include visible light, infrared rays, radio waves, and microwaves. Microwaves are used in telecommunications and heating food, and radio waves are used in broadcasting.

Ionizing Radiation. Ionizing radiation has higher frequency and enough energy to break chemical bonds. Examples of ionization radiation include x-rays, gamma rays, and alpha and beta particles. Alpha particles (also known as alpha rays) consist of two protons and two neutrons. Beta particles (also known as beta rays) are essentially high-speed electrons.

Basics of Radiation Protection

There are three basic principles of radiation protection: Time, distance, and shielding.2,6

Time. The quantity of radiation a person receives is directly proportional to the length of time that person spends near the source of radiation. If the radioactive material is inside a patient’s body, they can’t move away from it. The patient has to wait until it decays or until the body can remove it. In this case, the biological half-life of the radionuclide controls the time of exposure.

Distance. The patient or personnel will receive less exposure if they are farther away from the radiation source. Distance is a main concern when dealing with gamma rays, as they can travel long distances. Alpha and beta particles can’t travel far, because they don’t have sufficient energy.

The inverse square law governs the relationship between distance and intensity of radiation received. If the distance is doubled, the exposure is reduced by a factor of four. If the distance is reduced to half, the exposure is increased by a factor of four.

Shielding. Shielding (with appropriate thickness) between the radiation source and the subject can provide protection from radiation. The shielding materials commonly used for structural barriers are lead and concrete. The effectiveness of a material in attenuating radiation depends on its atomic number, density, and thickness. The amount of shielding required depends on the energy of the different kinds of radiation. Gamma rays and x-rays are more penetrating radiation compared to alpha and beta rays.7

Review Questions

1. The dangers of x-rays have been known since _____________.

a) 1895
b) 1939
c) The early 1900s
d) 1830

2. Which of the following statements about ionizing radiation is not true?

a) They are higher energy
b) They are high frequency
c) They can damage DNA
d) They are low energy

3. Which of the following types of radiation is not considered ionizing radiation?

a) X-rays
b) Gamma rays
c) Alpha rays
d) Microwaves

4. Which of the following statements about nonionizing radiation is not true?

a) They are higher energy
b) They are low frequency
c) They cannot damage DNA
d) They are low energy

5. Which of the following types of radiation is not considered non-ionizing?

a) Gamma rays
b) Infrared rays
c) Radio waves
d) Microwaves

6. Which of the following is not a basic principle of radiation protection?

a) Time
b) Distance
c) Shielding
d) Weight

See answers below.

Arif Subhan, MS, CCE, FACCE, is the chief biomedical engineer at VA Greater Los Angeles Healthcare System and a member of 24×7’s editorial advisory board. The suggestions and views expressed in this article are of the author. They do not represent the views of the Department of Veterans Affairs. For more information, contact [email protected]

Risk Management/Safety Topics

1) Patient Safety
2) Product Safety / Hazard Alerts / Recalls
3) Incident / Untoward Event Investigation
4) Engineering Assessment of Medical Device Failures
5) Risk Management
6) Root Cause Analysis
7) Medical Device Incident Reporting (SMDA)
8) Infection Control
9) Failure Mode and Effect Analysis
10) Workplace Safety Practices (OSHA)
11) Fire Protection/Safety (Life Safety Code)
12) Radiation Safety
13) Hazardous Materials
14) Industrial Hygiene
15) Other Risk Management / Safety Responsibilities
16) Expert Witness
17) Investigational Research (Human Use)
18) Forensic Investigations


1. US Environmental Protection Agency, History of Radiation Protection. Available at: Accessed August 12, 2014.

2. Haynes K, Statkiewicz Sherer MA, Visconti PJ, Ritenour ER. Radiation Protection in Medical Radiography. 7th ed. Elsevier Health, 2013.

3. Healthcare Technology Certification Commission (HTCC). 2014 Candidate Handbook for Certification in Clinical Engineering by the HTCC. Available at: August 9, 2014.

4. American College of Clinical Engineering (ACCE). Clinical Engineering Certification Study Guide, V4.0, available in pdf format only online through ACCE.5. US Environmental Protection Agency, Radiation: Non-Ionizing and Ionizing. Available at: Accessed August 12, 2014.

6. US Environmental Protection Agency, Radiation Protection Basics. Available at: Accessed August 12, 2014.

7. Health Physics Society, What Types of Radiation Are There? Available at: Accessed August 12, 2014.


1—C; 2—D; 3—D; 4—A; 5—A; 6—D