The Radiation Protection Service (RPS) department of the South African Bureau of Standards (SABS) provides the national dosimetry service for most radiation workers in South Africa and some neighbouring countries (i.e., external ionising radiation monitoring service to radiation workers, and retention of dose records of radiation workers’ accumulated life doses to external ionising radiation). All radiation workers are legally required to be monitored.
RPS is purely a dose monitoring service provider – the regulating bodies are:
South African Health Products Regulatory Authority (SAHPRA-Directorate: Radiation Control – www.sahpra.org.za) National Nuclear Regulator (NNR – www.nnr.co.za)
The dosimetry service entails issuing and dispatching dosimeters to radiation workers for monitoring radiation exposure. A dosimeter is issued to the radiation worker for a specific period. Before the end of the wearing period (WP), a replacement dosimeter is sent to the radiation workers so that they can return the used dosimeter for processing. The returned dosimeter is processed and the doses received are reported to the client. Monitoring provides the means to determine the effectiveness of Radiation Protection (RP) measures. It also helps determine the need for corrective/preventive measures in the radiation working environment. Low/zero doses indicate a good working practice or equipment and thus an effective RP programme.
The primary objective of dosimetry is the monitoring of radiation dose delivered to personnel during routine occupational exposure. By monitoring personnel, it is hoped that their exposure will be kept to within the prescribed safety limits. The limits as prescribed by the International Commission on Radiological Protection (ICRP) and recommended by the regulatory authorities as follows:
Extremity Dosimetry:
The determination of the maximum dose equivalent to any part of the hands, arms or feet.
Limit of 500 mSv (millisievert) per year.
Whole-body Dosimetry:
Equivalent dose absorbed at a depth of 1000 mg.cm-2 (1.0 cm deep) in human tissue below the surface of the body, and dose equivalent in critical organs. The interest here is in penetrating radiation, i.e. -, X-rays (>15 keV) and neutrons
Limit of 20 mSv effective dose per annum - averaged over 5 years
(and a maximum of 50 mSv accumulated in one year).
Tissue Dosimetry (i.e. skin dose):
Dose equivalent absorbed at a depth of 5 – 10 mg.cm-2. Here one is interested in non-penetrating radiation [e.g. gamma-particles and X-rays (<15 keV)].
Limit of 500 mSv per year.
The increasing concern in environmental dosimetry is with regard to the potential environmental impact of ‘man-made’ radiation release. Escape of radionuclides from nuclear power stations, low-level waste disposal, nuclear fuel reprocessing, nuclear power stations accidents, etc. have led to widespread of public concern about possible detrimental effects upon the environment. Dosimeter use in environmental monitoring requires long exposure times, since exposure levels are low. gamma-rays’ emitters are the main radiation sources of interest.
Two areas of use for clinical radiation exposure of humans are diagnostic radiology (e.g. X-ray exposure in mammography, dentistry and general health scanning) and radiotherapy (primarily cancer therapy of various types).
The use of dosimeters in monitoring high dose concentration (e.g. from 102 Grey (Gy) up to 106 Gy) is a further example of one of the mainstream uses of the technology. Such high doses may be found inside nuclear reactors, or during food sterilisation and materials testing.
TYPES OF SERVICES ARE AVAILABLE (LANDAUER DOSIEMTRY SYSTEM)
Personnel Dosimetry
InLight dosimeter badge provides X, gamma and beta radiation monitoring with Landauer Optically Stimulated Luminescence (OSL) technology. The Detector is a GA or GN new detector. The OSL material used across the majority of LANDAUER dosimetry products is aluminium oxide (Al2O3) that has been doped with carbon (Al2O3:C) to create electron vacancies (traps) in the oxygen atoms located within the crystal matrix.
Aluminium oxide doped with carbon (Al2O3:C). Monitoring for X-ray, gamma and beta radiation is done with the Landauer OSLR readers designed for use with HYPERLINK "https://www.landauer.eu/produit/dosimetre-inlight-ga/" InLight® dosimeters. OSL dosimeters are worn in a sealed plastic bag from which it must never be removed. No calibration is required, sensitivity is engraved on detectors.
Neutron Dosimetry – Landauer Albedo Neutron (OSLN) Detector
The InLight® Albedo neutron dosimeter is capable of measuring radiation doses received from beta, photon and neutron radiation fields. It is specifically designed to be used in neutron dosimetry and is capable of detecting mixed radiation fields. The OSLN material is made up of Al2O3:C coated with 6Li2 CO3 to make the Al2O3:C sensitive to neutrons. The OSLN element is located in read position 2 (E2).
People monitored for neutron radiation must also wear InLight dosimeter
Extremity Dosimetry
A ring (wrist) dosimeter providing optimum wearing comfort. Finger rings are used for monitoring. They are made of shape memory polyethylene; it fits perfectly to the shape of a finger. It is thin and lightweight with rounded edges enabling the use of gloves without the risk of tearing them. To ensure easy cleaning and disinfection, the ring is one-piece, with no corner or gap. It is used to measure Hp(0.07) photon and beta doses to extremities from 0.1 mSv. Moreover, its high measuring dynamic and extreme accuracy allow dose measurement up to 10 Sv with a standard deviation greater than 7%.
Eye Dosimetry This lens of the eye dosimeter uses a novel tissue equivalent MP7 OSL sensor. The OSL material is made from Aluminium oxide doped with Carbon (Al2O3:C).
The most accurate method for monitoring the equivalent dose to the lens of the eye is to measure the personal dose equivalent at 3 mm depth, Hp(3), with a dosimeter worn as close as possible to the eye and calibrated on a phantom representative of the head. In certain circumstances the measurement of Hp(0.07) or sometimes Hp(10) can provide a suff ciently accurate estimate of Hp(3).
Environmental Dosimetry
The InLight Environmental dosimeter is specifically designed to be used for monitoring Area/ Environmental radiation exposure.
REMEMBER: A DOSIMETER DOES NOT PROTECT YOU FROM RADIATION; IT MERELY PROVIDES A MEANS OF MONITORING THE AMOUNT OF RADIATION THAT YOU HAVE RECEIVED! THE DOSIMETER SHOULD BE WORN ON TOP OF A LEAD APRON IF A LEAD APRON IS USED WITHOUT THYROID AND EYE SHIELDING. IF THE THYROID AND EYES ARE SHIELDED, THE PRIMARY DOSIMETER MUST BE WORN UNDER THE LEAD APRON!
MUST BE WORN ON THE TORSO OR IN THE PELVIC REGION!
South African Health Products Regulatory Authority (SAHPRA-Directorate: Radiation Control – www.sahpra.org.za)
