Radiation: introduction

Ionising radiation and the substances that emit it are naturally present in the environment. They may also be made, concentrated, or actually spread by humans. Increased exposure to radiation heightens the probability of damage to health, for example in the form of cancer.

The type of exposure (distance, duration and frequency) and the characteristics of the source (amount and type of radiation emitted) ultimately determine the risk. The various concepts relating to radiation are explained in the glossary at the bottom of this introduction.

Policy

The environment policy relating to radiation focuses on:

• artificial sources, such as nuclear power plants or radioactive substances in consumer goods;
• natural sources which can be influenced by human activities, such as radioactivity in ore handling and radon in the indoor environment.

The law imposes limits on both the use and discharge of a radioactive substance and on the radiation load. For instance, the maximum permissible load per capita is 0.1 mSv per radiation source and 1mSv for all combined sources. These limits do not apply to natural or medical exposure.
For exposure to radon, a separate policy is being developed in the Netherlands that focuses on limiting the radiation load generated by radon in building materials. This is known as the Radiation Performance Standard (SPN).

Definitions

Ionising radiation	The nuclei in the atoms of radioactive substances are unstable. As a result, these substances decay. The radiation emitted by radionuclides during this process of decay is known as ionising radiation. This is an umbrella term for ?-, ?-, and ?- radiation.
Radioactivity	The amount of radioactivity is expressed in becquerels (Bq). One becquerel corresponds to one decaying nucleus per second. The radioactivity of a substance depends on the amount of radionuclides present and the half-life of those radionuclides. The half-life is the time it takes for half of the original nuclei to decay.
Radiation dose and radiation load	The radiation dose (in sieverts (Sv)) is a measure for the dose absorbed by organs and is also a measure for the probability of biological effects caused by exposure to ionising radiation. The dose for all organs can be used to establish, by using weightings for the organs, a representative picture of the total radiation load (also known as the effective dose) for an individual. This dose (that is also expressed in Sv) is used in this document. For practical reasons, millisieverts (mSv) or microsieverts (?Sv) are often used.

Relevant sections and indicators in the Environmental Data Compendium

• Radiation level by source, 2000
• Radon concentrations in housing, 1930-2000
• Radiation dose from artificial radioactive substances, 1960-2000
• Radiation dose from emissions of radioactive substances to air by Dutch industry, 2000
• Radioactivity in surface water, 1980-2000
• Radioactivity in consumer goods