About Radiation

Understanding Radiation

Understanding Radiation

There are two types of radiation, ionizing and non-ionizing radiation. Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing the atom to become ionized. Non-ionizing radiation is type of radiation that does not have enough energy to cause ionization. The ionization ability is not determined by the amount of radiation but the energy level of the radiation.

Ionizing radiation has high energy and is powerful enough to break molecular bonds to create charged ions. This process can result in DNA damage, thus the risk of exposing oneself to ionizing radiation.

Non-ionizing radiation has a longer wavelength compared to ionizing radiation like X-ray. Since it has less energy, it cannot cause ionization.

Non-ionizing radiation Ionizing radiation
Cell phones X-rays
Microwave Ovens
Radiofrequency waves in TV & Radios Radioactive substance
e.g. technetium-99m
Low-frequency UV

Types of Radiation

  • Ionizing
  • Non-Ionizing Radiation

Measuring Radiation

  • The scientific unit of measurement for radiation dose is the milliSievert (mSv).
  • Other units used for measuring radiation dose include Gray, Sievert, Rad, Rem and Roentgen.
  • Different tissues and organs have varying sensitivity to radiation exposure, the actual radiation risk to different parts of the body from an x-ray procedure varies.

Effective Dose

  • The term effective dose is used when referring to the radiation risk averaged over the entire body.
  • The effective dose accounts for the relative sensitivities of the different tissues exposed.
  • It allows for quantification of risk and comparison to more familiar sources of exposure that range from natural background radiation to radiographic medical procedures.
  • The average dose per person from all sources is about 6.2 mSv per year but is variable.
  • In HK, the annual natural background radiation is 2.4 mSv.
  • International Standards allow exposure to as much as 50 mSv a year for those who work with and around radioactive material.