Becquerel (Bq)

Radioactivity is measured in units called becquerels (Bq).  One becquerel corresponds to one radioactive disintegration per second.

Becquerels per cubic metre (Bq/m³) define the concentration of radioactive gases, such as radon, in the air.

Becquerels per kilogram (Bq/kg) define the concentration of radioactivity in a kilogram of material.

Becquerels per litre (Bq/l) define the concentration of radioactivity in a litre of liquid.

Collimator

A collimator is a device that filters radiation so that it travels in a specific direction. Collimators are used in neutron, X-ray, and gamma-ray applications.

Controlled area

This is any area to which access is restricted for the purpose of limiting the exposure of individuals to radiation. Any person who enters or works in a controlled area is required to follow safety instructions.

 A controlled area is normally a permanently designated area.  If a worker is liable to receive a radiation dose greater than 6 mSv over a 12-month period, or three tenths of any relevant dose limit specified in paragraph 1(2) of Schedule 2 of S.I. No 125 of 2000, then this work area is defined as a 'controlled area'.

A controlled area can also be established in the event of a radiological accident such as a spillage.

Dose limits for exposed workers

The dose limit for workers is 20 mSv in any 12 month period.

Additional limits apply to exposure to specific parts of the body:

(a) The dose limit for the lens of the eye is 150 mSv in any period of 12 months

(b) The dose limit for the skin is 500 mSv in any period of 12 months; this limit applies to the dose averaged over any area of 1 cm², regardless of the area exposed

(c) The dose limit for the hands, forearms, feet and ankles is 500 mSv in any period of 12 months. 

In the case of female workers, once pregnancy is declared the dose to the unborn child is limited to 1 mSv for the remainder of the pregnancy.

Dose limits for members of the public

The dose limit for a member of the public is 1 mSv in any period of 12 months

Additional limits apply to exposure of specific parts of the body:

(a) The dose limit for the lens of the eye is 15 mSv in any period of 12 months

(b) The dose limit  for the skin is 50 mSv in any period of 12 months; this limit applies to the dose averaged over any 1 cm² of skin, regardless of the area exposed.

Early radiation effect

 A radiation induced health effect that occurs within months of the exposure that caused it. Generally, a threshold level of dose exists below which the effect is not observed.  Above the threshold, the severity of the effect increases with dose. Examples of early effects include erythema (burning of the skin) and acute radiation syndrome (radiation sickness with vomiting and diarrhoea).

Effective dose

This is the sum of doses in all the tissues and organs of the body from both internal and external radiation. Specific details can be found in Schedule 6 of S.I. No 125 of 2000.

Emergency plan

A description of the structure, authorities and responsibilities in place for response to an emergency. An emergency plan serves as the basis for the development of other plans, procedures and checklists. For example there can be International Emergency Plans, National Emergency Plans or Local Emergency Plans (such as those operated by the RPII's licensees).

Emergency preparedness

The capability to take actions that will minimise the consequences of an emergency. It refers to the actions (e.g. training, documentation, preparation of procedures) taken in anticipation of potential emergencies.

Emergency procedure

A set of instructions describing in detail the actions to be taken in response to an emergency.

Emergency response

 Actions taken in response to an actual emergency to lessen the impact of the emergency.

Equivalent dose

This is the radiation dose in any tissue or organ, weighted to take into account different types of radiation and their effect.

Exposed worker

Any person, either self-employed or an employee, who receives a radiation dose at work in excess of the limits set for a member of the public from practices or work activities to which S.I. No 125 of 2000 applies.

First responders

The first members of an emergency service to respond at the scene of an emergency e.g An Garda Síochána, the Ambulance Service and the Fire Service.

Gray

The gray (symbol: Gy) is the SI unit of absorbed radiation dose of ionizing radiation, and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter (usually human tissue).

For X-rays and gamma rays, these are the same units as the sievert (Sv). To avoid any risk of confusion between the absorbed dose (by matter) and the equivalent dose (by biological tissues), one must use the corresponding special units, gray is used instead of the joule per kilogram for absorbed dose and the sievert instead of the joule per kilogram for the dose equivalent.

High Radon Area

A High Radon Area is an area where, on the basis of the National Radon Survey, it is predicted that 10% or more of homes have radon concentrations above the national Reference Level of 200 Bq/m³.

Intervention plan

Similar to an emergency plan, but only required where a licensed practice could give rise to a significant risk to a member of the public.

Ionising radiation

The transfer of energy in the form of particles or electromagnetic waves of a wavelength of 100 nanometers or less, or a frequency of 3 x 10¹⁵ Hertz or more, capable of producing ions directly or indirectly.

Radioactivity produces ionising radiation.  Microwaves, mobile telephones and overhead power lines do not produce ionising radiation.

Irradiating apparatus

Apparatus capable of producing ionising radiation and containing components operating at potential difference of more than 5 kiloVolts (kV).

Late radiation effects

A radiation induced health effect that occurs years after the exposure that caused it. Generally, there is no dose threshold for late effects and the probability of occurrence increases with increasing dose. The most common late radiation effects are leukaemia and solid cancers.

Major emergency

An incident which, usually with little or no warning, causes or threatens death or injury, serious disruption of essential services or damage to property, the environment or infrastructure beyond the normal capabilities of the principal emergency services (An Garda Síochána, the Ambulance Service and the Fire Service) in the area in which the event occurs. In relation to radiation, major emergencies include hazardous material incidents (e.g. a serious spill or fire involving a radioactive source) and terrorist incidents (e.g. a ‘dirty bomb’).

Major Emergency Framework

Each Local Authority has a Major Emergency Plan that sets out the specific arrangements for that authority in the event of a major emergency. Similar plans are in place in An Garda Síochána and the Health Service Executive.

National Emergency Plan for Nuclear Accidents

The national emergency plan that co-ordinates the emergency response to an incident leading to widespread radioactive contamination in Ireland. It includes the following types of incidents

• Accident at a nuclear plant abroad
• A terrorist attack on a nuclear plant abroad
• A nuclear explosion abroad
• Marine incidents close to the coast involving nuclear-powered ships or submarines or vessels carrying radioactive materials.

It could also be invoked for incidents in Ireland (e.g. serious spillages or fires) but these would be normally dealt with by licensee’s emergency plan or the local authority’s Major Emergency Plan.

National Reference Level

The national Reference Level is a radon concentration above which action should be taken to reduce exposure. It is measured in units of becquerels per cubic metre (Bq/m³). In Ireland, the national Reference Level for radon in homes is 200 Bq/m³. This value was adopted by Government in 1991.  The national Reference Level for radon in workplaces, which is legally enforceable, is 400 Bq/m³.

Schools are workplaces for teachers but not for students.  The RPII has advised that children should expect the same level of radiation protection at school as at home.  Consequently, the Department of Education and Science applies a Reference level of 200 Bq/m³ to radon exposure in schools.

Nuclear device

Any equipment, the operation of which involves the use of a radioactive substance, or any irradiating apparatus.  Under S.I. No. 125 of 2000, a nuclear reactor is also defined as a nuclear device.

Practice

A human activity that can increase the exposure of individuals to radiation from an artificial source, or from a natural radiation source where materials are processed for their radioactive, fissile or fertile properties. The term 'practice' refers to a deliberate activity, such as the use of radiation in a medical or industrial application, rather than an activity that accidentally results in an exposure.

Principal emergency services

In Ireland, this term refers to the Fire Brigade, Ambulance Service, An Garda Síochána and the Coastguard.

Radiation emergency

A radiation accident or incident which has the potential to result in a worker or member of the public being exposed to elevated levels of ionising radiation.

Radioactive substance

Any substance, either naturally occurring or artificial, capable of emitting ionising radiation.

Radionuclide

An unstable form of an element that decays or disintegrates spontaneously, emitting radiation. There are naturally occurring radionuclides (e.g. potassium-40, thorium-232, uranium-235, uranium-238) and man-made radionuclides (e.g. strontium-90, technetium-99, caesium-137, plutonium).

Sealed source

A radioactive source whose structure is such as to prevent, under normal conditions of use, any dispersion of the radioactivity into the environment.

Sievert (Sv)

When radiation interacts with body tissues and organs, the radiation dose received is a function of factors such as the type of radiation, the part of the body affected, the exposure pathway, etc. This means that one becquerel of radioactivity will not always deliver the same radiation dose. A unit called ‘effective dose’ has been developed to take account of the differences between different types of radiation so that their biological impact can be compared directly. Effective dose is measured in units called sieverts (Sv).

The sievert is a large unit, and in practice it is more usual to measure radiation doses received by individuals in terms of fractions of a sievert.

1 sievert = 1000 millisievert (mSv)
                = 1,000,000 microsievert (μSv)
                = 1,000,000,000 nanosievert (nSv)
 

Throughout this website and in RPII reports the term ‘effective dose’ is often referred to as ‘radiation dose’ or simply ‘dose’.

Source

An apparatus, a radioactive substance or an installation capable of emitting ionising radiation or radioactive substances.

Supervised area

Any area, not classified as a controlled area, in which it is necessary to keep the conditions of the area under review to determine whether the area should be designated as a controlled area.

It can also refer to an area in which any person working is liable to receive a dose greater than 1 mSv in any period of 12 months, or a dose greater than one tenth of any relevant dose limit specified in paragraph 1(2) of Schedule 2 of S.I. No 125 of 2000 in respect of a member of the public.
 

Undertaking

Any natural or legal person who, as a self employed person or employer, carries on or intends to carry on any practice or work activity to which S.I. No 125 of 2000 applies. 

Unsealed Radioactive Substance

A radioactive substance that cannot be classified as a sealed source.