ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

Get our Baseline Environmental Radiation Study information sheet (PDF 59kb)

Background Radiation

The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has an on-going interest in assessing radiation exposure in the environment and in the workplace. The Agency maintains radiation measurement systems for the determination of radioactivity in soil, water, air, food and other materials, as well as within the body. Presently the Agency is studying the variability of the natural radiation background across Australia and is determining the baseline background levels at selected locations, including the suburbs around Lucas Heights, in the immediate area around the ports that host visits by nuclear powered warships and in regions with high levels of natural radiation. ARPANSA field teams are involved in two types of measurements for this survey.

Get a background radiation information sheet (PDF 182kb)
or an ARPANSA - Environmental Radioactivity Section information sheet (PDF 16kb)

Mapping of Background Gamma-ray Radiation

The Health Physics Section from ARPANSA will use a vehicle mounted gamma-ray spectroscopy system to measure the natural radiation in the suburbs within a 5 km radius of Lucas Heights. The measurement system can identify and quantify levels of naturally occurring and artificial gamma-ray emitting radioactivity within a 100 metre radius of the vehicle. The data will be analysed to produce maps showing the variation of background radiation dose rate and the concentration of selected naturally occurring radionuclides (such as uranium, thorium and potassium).

Gamma mapping with the vehicle mounted system was carried out on 15 October 2002 in the Sydney suburbs of Engadine and Woronora Heights. Three preliminary maps of the variation of the gamma dose rate from the background radiation were produced using Mapinfo thematic mapping of the recorded data.

Woronora Heights gridded dose rate map 15 Oct 2002
Engadine gridded dose rate map 15 Oct 2002
Engadine dose map 15 Oct 2002
Engadine Menai Barden Ridge gamma dose rate map 30 Oct 2002
Engadine gridded dose map 16 Oct 2002

The measured dose rates are in the range 30 nanogray (nGy) per hour to 60 nGy per hour, compared with an average value for background radiation dose rate of about 50 to 60 nGy per hour. That is, the values measured to date range from close to the Australian average value to about one half. The lower values possibly reflect the predominance of sandstone rock in the area. Sandstone has lower levels of uranium and thorium than other rock types such as granites and produce lower levels of background gamma radiation.

Analysis of Environmental Samples - Preliminary Results

Water samples:

Read the Radioactivity Analysis Report for water samples (PDF 86kb)

The Australian Drinking Water Guidelines recommends screening value of 0.5 Bq/L for gross alpha and 0.5 Bq/L for gross beta (after subtraction of the contribution from potassium-40). The guideline values for Radium-228 and Radium-226 are both 0.5 Bq/L.

All results from the analysis of the river water samples were below the recommended drinking water guideline values.

The sample collected below the causeway on the Woronora River was in a location that has some tidal influence and therefore the water was saline. The high salt content limits the detection of alpha particles by the gross alpha screening procedure. The gross beta in this sample is high due to the high level of the naturally occurring beta emitter, potassium-40, in the salt.

The values for tritium were below the detection limit of 20 Bq/L

Definitions: Bq/L becquerel per litre

Analysis of data is continuing ...

Units Used

Grays (Gy) are the unit of Absorbed Dose (abbreviation Gy). One gray corresponds to one joule of radiation energy deposited in one kilogram of matter. This is a large unit and for environmental levels of radiation the nanogray (nGy) is more appropriate. One nanogray is one thousand millionth of a gray ( 1/ 1,000,000,000).

When radiation interacts with living tissue the effect it has varies with the type of radiation. To allow for this, the dose in grays is multiplied by an effectiveness factor and the new units are called sieverts (abbreviation Sv) and the dose is called the effective dose.

A one milligray dose of gamma rays is equal to 1 mSv effective dose because the effectiveness factor is 1 for gamma rays.

Exposure to 50 nGy per hour for one year would give an effective dose of 0.44 millisieverts (mSv)

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