Procedures

Personal Radiation Monitoring - Procedures

Printer-friendly version
Body

1. Purpose and Objectives

This procedure is intended to provide appropriate technical information to the local organisation unit Radiation Safety Officer (RSO) and persons who work with ionizing radiation to understand and employ appropriate personal radiation monitoring as required by the Radiation Safety Regulation 2010, and associated requirements.

2. Definitions, Terms, Acronyms

ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

ARS - Australian Radiation Services Pty Ltd

eV - SI Unit electron volt (eV) a unit of energy equal to the energy acquired by an electron in being accelerated through a potential difference of 1 volt; equal to 1.602 × 10−19 joule

GMS - Global Medical Solutions

keV - kiloelectron volt (keV) one thousand electron volts (103 eV)

OSL - Optically Stimulated Luminescence

RPA - OHS Division Radiation Protection Advisor

RSO - Radiation Safety Officer

RSPP - Radiation Safety and Protection Plan

TLD - Thermoluminescent dosimetry

XRD - X-Ray Diffraction

XRF - X-Ray Fluorescence

3. Procedures Scope/Coverage

This procedure explains the requirements for personal radiation monitoring for UQ researchers working with radiation sources.

4. Procedures Statement

Personal Radiation Monitoring is referred to under Section 38 of the Radiation Safety Act 1999. Persons who use radiation sources may require personal monitoring as a requirement of a specific licence condition or by a provision in the Radiation Safety and Protection Plan (RSPP) approved for their school, institute or centre.

This procedure outlines the various personal radiation monitoring that is available for different radioactive activities. The preferred monitoring techniques for various types of ionizing radiation are outlined below. This procedure does not recommend any particular monitoring method or supplier.

5. Types of Radiation Monitors

5.1 Photon radiation: X-rays and gamma rays

5.1.1 Thermoluminescent dosimetry (TLD)

Thermoluminescent dosimetry (TLD) dosemeters have been the most common means of monitoring the radiation exposure of users of gamma emitters - including unsealed sources of 125I and 51Cr and sealed sources such as 137Cs and 60Co. They are also suitable for persons working with diagnostic X-rays, including those used in this University’s veterinary and dental practices. TLD personal dosemeters are available from the personal radiation monitoring services such as ARPANSA, ARS and GMS.

5.1.2 Optically stimulated luminescence (OSL)

Optically stimulated luminescence (OSL) dosemeters are available from Landauer Australasia Pty Ltd and are equally suited to measuring X and gamma ray doses as are TLDs. They are increasingly becoming the most popular personal dosemeter for Photon radation.

5.1.3 Personal alarming dosemeters (PADs)

Personal alarming dosemeters (PADs) may also be used to record X and gamma ray doses. However, the RSO is required to make a record of any doses recorded by them and to furnish these to the Chief Executive of Queensland Health as soon as practicable. In most research applications PADs are not regarded as practical, mainly because of the difficulties of recording doses.

5.2 Neutron radiation

Users of neutron sources, which are incorporated in soil density or moisture gauges, are required to use specialised neutron dosemeters which are only available from ARPANSA, Landauer Australasia or GMS. Neutrons monitoring is generally more expensive than X-ray or gamma ray monitoring as it requires manual assessment of counting neutron tracks in the surface of polymers.

5.3 Beta radiation

5.3.1 Thermoluminescent dosimetry (TLD)

Beta radiation with average energies greater than 70 keV can be monitored using the standard TLD dosemeters supplied by ARPANSA. The energy limitation means that only 32P and some of the less common high energy beta (or beta and gamma) emitters (e.g. 36Cl, 46Sc, 82Br and 103Ru) can be satisfactorily monitored with these personal dosemeters.

5.3.2 Optically stimulated luminescence (OSL)

The Luxel® OSL dosemeters supplied by Landauer Australasia are also sensitive to beta radiation, although the lower energy limit for useful results is 150 keV which, like the Teledyne units, effectively restricts their beta monitoring capability to 32P (and other high energy beta emitters listed above) and not for monitoring users of tritium, 14C, 35S or 33P.

5.3.3 Finger/extremity dosemeters

Users of 32P may also wish to use TLD or OSL finger or extremity dosemeters, particularly where pipetting high specific activity stock solutions is a common practice. These are available from ARPANSA, Landauer Australasia or Global Medical Supplies.

5.3.4 Low energy beta emitters

Tritium, 14C, 35S and 33P have relatively low average beta energies and external monitoring is of little value (none in the case of tritium) when the relatively small amounts typically handled in university laboratories are considered. In any case, the principal hazard of these substances is linked to inhalation or ingestion rather than external exposure. The control measures are therefore directed at entirely preventing the exposure rather than at monitoring.

5.4 Analytical X-rays: XRF and XRD

In the majority of cases, personal monitoring with conventional TLD or OSL is not required for users of XRF and XRD units. Such equipment has either a totally enclosed target chamber or, where external beams are available, sophisticated interlock systems are fitted to prevent access to the direct beam. The very small diameter of the beam also means that any exposure that did occur would be only of a very restricted area and so would be unlikely to be detected by a conventional dosemeter worn on the chest or waist.

Note: With XRD units capable of producing external beams without interlocked enclosures, extremity dosemeters (e.g. finger rings/dosemeters) are indicated - particularly where manual sample changing or beam alignment is required.

6. Using Dosemeters

The instructions provided by the issuing service for each type of dosemeter should be followed closely, however there are some procedures common to all personal monitoring practices, these are:

  • Dosemeters should only be worn in the workplace and should be returned to a designated location at the end of the work period;
  • All dosemeters should be stored in the same location when not in use, together with any control dosemeter issued. The area chosen for dosemeter storage must be located away from sources of radiation;
  • Dosemeters are issued to a particular person. They should not be worn by any other person or used for any purpose other than the monitoring of that person’s exposure to radiation. The use of dosemeters as area monitors or for other radiation dosimetry activities can only be undertaken by arrangement with the issuing service and with the approval of the statutory authority, the Radiation Health section of Queensland Health.

6.1 Wearing periods

For University practices the following monitoring periods are recommended:

Practice category

Dosemeter wearing period

Unsealed sources research laboratories (beta or beta and gamma emitters)

3 months

Veterinary X-ray

3 months

Dental X-ray

3 months

Analytical X-ray

3 months

Soil moisture gauging

1 month

Fixed radiation gauges

(service and installation only)

3 months

These monitoring periods are for whole body dosemeters only. Extremity dosemeters are generally changed monthly or according to the advice of the supplier.

6.2 Ordering dosemeters

It is the responsibility of the Faculty, Institute, School or Centre to order and maintain their radiation dosimetry. Where radiation sources are to be used for the first time, or work is beginning with a new isotope or type of X-ray unit, it is recommended your organisational area RSO or contact the OHS Division Radiation Protection Advisor (RPA) regarding personal monitoring requirements.

The cost of personal monitoring is the responsibility of the Faculty, Institute, School or Centre in which the radiation sources are used.

6.3 Reporting of radiation doses

Section 38(2) of the Act requires that the results of the assessment of dosemeters must be provided to the Chief Executive of Queensland Health as soon as practicable. To allow this to be done, possession licensees may approve the direct transfer of radiation monitoring results from the relevant monitoring service to the Radiation Health section. Faculty, Institute, School or Centre Radiation Safety Officers need to ensure that these arrangements are in place.

7. Record Keeping

Licensees who are required to provide personal monitoring are obliged under Section 38(4) of the Radiation Safety Act 1999 to keep up-to-date records of doses as assessed by the monitoring service. Personal monitoring records are to be kept for the duration of the wearer’s working life. The records are to be keep for not less than 30 years after the last exposure assessment, and at least until the person has reached the age of 75 years.

In practice, radiation monitoring records will continue to be kept by Faculty, Institute, School or Centre RSOs for the possession licensee.

8. Contact for Further Information

Contact your local Radiation Safety Officer, or

OHS Division Radiation Protection Advisor ohs@uq.edu.au

Custodians
Director, Occupational Health and Safety
Mr Jim Carmichael
Custodians
Director, Occupational Health and Safety
Mr Jim Carmichael