passive ionising radiation monitoring report - former...

PASSIVE IONISING RADIATION MONITORING REPORT -

FORMER ABC TV NEWS BUILDING, TOOWONG, QUEENSLAND

Rick Tinker Tracy Wright Technical Report (Version 1) October 2008

619 Lower Plenty Road Yallambie Vic 3085 Telephone: +61 3 9433 2211 Fax: +61 3 9432 1835

Background The purpose of this investigation was to gain further information about the ionising radiation levels at the former ABC TV News building in Toowong, Queensland. It is supplementary to ARPANSA’s initial report “Ionizing Radiation Survey of the ABC TV News Building – Toowong Queensland”, dated March 2007. Scope This report is based on passive measurements of the radon concentration in air and the environmental gamma radiation level in the building. Monitoring Equipment Radon concentrations in air were measured using passive CR-39 track-etch detectors. These monitors consist of a CR-39 detector and a thermoluminescent dosimeter (TLD) detector for measuring the environmental gamma level. The components measure the average radon concentration and gamma level respectively over the exposure period. The radon monitors used were the same type as those used in the previous assessment (Wilson, 2007). The calibration of radon monitors is provided as an in-house service. A second measurement of the environmental gamma level was made using TLD area monitors sealed in PVC envelopes. These are the same type of monitor used in the previous assessment, however they were assessed differently. The natural background radiation was only subtracted for the time the monitors were in transit, so the monitors indicate the radiation levels at the measurement site including the contribution by natural background radiation. The TLD area monitor results are provided by a NATA accredited laboratory and are traceable to national standards of measurement. An effective dose rate was estimated for all environmental gamma levels by assuming a dose conversion factor of 1 (worst case scenario based on ICRP 74) over a measurement period of 8 weeks. Radiological Investigation Methods Eight passive radon monitors, eight TLD area monitors and one TLD control monitor were sent by courier to Mr. Clyde Riches at ABC Brisbane. The TLD control monitor was stored on Level 1 of 57 Coronation Dr, Brisbane. The remaining monitors were paired so that each measurement location had a radon and TLD measurement. Two pairs were positioned in the ABC News Room at the Mt. Coot-tha Channel 10 Studios to be used as blank monitors for comparison. The other six

Passive Ionising Radiation Monitoring Report – Former ABC TV News Building, Toowong Page No. 2

pairs were placed in various locations at the Toowong site. Table 1 gives descriptions of the monitor locations and the Appendix includes a monitor location summary provided by Mr. Riches at the ABC. All monitors were collected after eight weeks and returned to ARPANSA by courier for assessment. Table 1: Locations of radon and TLD area monitors

TLD monitor number

Radon monitor number

Location description

M0831-09390 8314850 Toowong office Level 1, middle of old On-Line News office area M0831-09391 8314853 Toowong office Level 1, old studio Control Room area M0831-09392 8314849 Toowong office Level 1, shelf outside Meeting Room M0831-09393 8314846 Toowong office Ground Floor, middle of News Room M0831-09394 8314848 Toowong office Ground Floor, old news paper reading stand M0831-09395 8314852 Toowong office Ground Floor, near old chief of staff desk area M0831-09396 8314847 Mt. Coot-tha News Room, outside news editor’s office M0831-09397 8314851 Mt. Coot-tha News Room, News Exchange room

Radiological Survey Results The results of the radiological survey are shown in Table 2. Radon concentrations varied from 61 to 89 Bq/m3 at the Ground Floor and Level 1 of the Toowong office. There is no statistical difference in radon levels between the Ground Floor and Level 1 given an uncertainty of measurement of 20%. The radon levels at the Mt. Coot-tha News Room (control site) were 52 and 39 Bq/m3, slightly lower than the levels measured at the Toowong office. These two monitors had sticky tape wrapped around the lid of the monitor. The radon gas diffuses into the monitor through the gap between the lid and the container so it can be measured by the CR-39 track detector inside the container. The rate of diffusion of radon through sticky tape is unknown, however it is expected that the tape would reduce the amount of radon that diffuses into the container. As a result, it is expected that the measured radon concentration will be lower than if there was no tape around the lid. Previous measurements of radon concentration in the Toowong building ranged from 21 to 37 Bq/m3 (Wilson, 2007). These lower concentrations may be due to seasonal changes or variations in local conditions. For example, lack of ventilation or air exchange in a building is likely to result in radon build-up inside the structure. It is likely that during this survey there was less opportunity for natural venting of radon by opening and closing doors when compared to the previous survey (Wilson, 2007).


All measured radon concentrations are below the recommended action level for workplaces of 1000 Bq/m3, and are below the recommended action level for dwellings of 200 Bq/m3 (ARPANSA, RPS 1). Table 2: Measurements from radon monitors and TLD area monitors Radon monitor

number

Measured radon concentration

(Bq/m3)a,b

Environmental gamma level

(nSv/h)c

Corresponding TLD number

TLD area monitor (nSv/h)d

8314850 64 89 M0831-09390 112 8314853 77 119 M0831-09391 112 8314849 89 126 M0831-09392 97 8314846 61 119 M0831-09393 104 8314848 61 112 M0831-09394 112 8314852 68 119 M0831-09395 89 8314847 52e 60 M0831-09396 82 8314851 39e 89 M0831-09397 74

a Measured radon concentration is calculated based on a 5 day transit time and monitoring period of 8 weeks. b Radon concentration measurements accurate to within ± 20% c Environmental gamma level measurements accurate to within ± 20% d Expanded uncertainty (k=2): ± 15% e Radon concentration may be in error due to the application of sticky tape around the lid of the monitor. The environmental gamma level measured by the TLD disc in the radon monitor and the TLD area monitor are in good agreement. They range from 60 to 89 nSv/h at the Mt. Coot-tha site and 89 to 126 nSv/h at the Toowong site. These values tend to be slightly lower than the range of 116 to 151 nSv/h measured by Wilson in 20071. There was no evidence of beta radiation on the TLD area monitors. The PVC envelopes would have caused some attenuation, however some beta radiation would have penetrated if there was plate out of radon daughters as was seen on the personal TLD monitors in the 2007 survey. The results from this survey can be compared to the nationwide survey of environmental gamma levels in Australian homes (Langroo et al, 1990). Gamma dose rate levels from this survey fall in the 5th and 95th percentile distribution range of that measured in the 1990 Australian home survey of 60 and 165 nSv/h with a mean of 100 nSv/h.

1 Converted from μGy/y to Sv/h using a worst case scenario dose conversion factor of 1 based on ICRP 74 and an exposure period of 8 weeks.


Conclusion The low radon-222 levels measured during this investigation indicate that ventilation in both sites is adequate to maintain levels below the action levels for the public. The recommended action level for radon concentration in dwellings for members of the public is 200 Bq/m3 (ARPANSA, RPS 1). The annual public limit is 1 mSv (APRANSA, RPS 1). Given a typical 2000 hour working year at the maximum dose rate of 89 nSv/h measured at the Mt. Coot-tha site, the annual dose received would be 0.18 mSv. For the same conditions at the Toowong site where there was a maximum dose rate of 126 nSv/h, the annual dose received would be 0.25 mSv. Under these circumstances, the pubic dose limit will not be exceeded in either location. The radon-222 levels and gamma dose rates are below Australian action limits and present no radiation hazard. Limitations of this Report This report has been prepared in accordance with the scope and services described, in consultation with the ABC and subject to any limitations expressed within it (the Scope of Works). To the best of our knowledge the information contained in this report is accurate at the date of issue. It is not intended to be used by third parties. ARPANSA will not be liable to the ABC for any indirect or consequential loss or damage (including without limitation, loss of profits or revenue) arising out of its performance or non-performance of its obligations under the Scope of Works. REFERENCES ARPANSA, Radiation Protection Series No. 1 (RPS 1), Recommendations for Limiting Exposure to Ionizing Radiation (Printed 1995 - Republished 2002) and National Standard for Limiting Occupational Exposure to Ionizing Radiation (Printed 1995 - Republished 2002) International Commission on Radiological Protection, Conversion Coefficients for use in Radiological Protection against External Radiation., Pergamon Press, ICRP Publication 74 (1995). Langroo, M. K., Wise K. N., Duggleby, J. C. and Kotler, L. H., “A nationwide survey of Radon-222 and gamma radiation levels in Australian homes”, Health Physics (1991), 61, 753-761. Wilson, O., Ionizing Radiation Survey of the ABC TV News Building – Toowong Queensland, March 2007.


APPENDIX

Monitor location summary provided by the ABC


Placement of Radiation Monitors @ 600 Coronation Drive Toowong

& ABC News Room @ Mt Coot-tha Channel 10 Studios.

28th July 2008

Summary List of Placements

Monitor Types Numbers Location Comments Radon TLD Badges 8314847 09396 Mt Coot-tha News Room Outside News Editors

Office8314851 09397 Mt Coot-tha News Room In News Exchange Room8314852 09395 600 Coronation Dr

Toowong Ground FloorNear old Chief of Staff desk area

8314848 09394 600 Coronation Dr Toowong Ground Floor

On old News Paper Reading stand

8314846 09393 600 Coronation Dr Toowong Ground Floor

In middle of News Room

8314849 09392 600 Coronation Dr Toowong Level 1

On shelf outside Meeting room


In old studio Control Room area


In middle of old On-Line News office area

09389 57 Coronation Dr Brisbane Level 1

Control Monitor


Placement of Radiation Monitors @ 600 Coronation Drive Toowong & ABC News Room @ Mt Coot-tha Channel 10 Studios.

28th July 2008

ABC News Room @ Mt Coot-tha Channel 10 Studios. Radon 8314847 & TLD 09396

ABC News Room @ Mt Coot-tha Channel 10 Studios. Radon 8314851 & TLD 09397



28th July 2008


Placement of Radiation Monitors @ 600 Coronation Drive Toowong & ABC News Room @ Mt Coot-tha Channel 10 Studios. 28th July 2008

600 Coronation Drive, Toowong, Q 4066: Ground Floor Radon 8314852 & TLD 09395



Placement of Radiation Monitors @ 600 Coronation Drive Toowong & ABC News

Room @ Mt Coot-tha Channel 10 Studios. 28th July 2008




28th July 2008



28th July 2008

600 Coronation Drive, Toowong, Q 4066: Level 1 Radon 8314849 & TLD 09392




28th July 2008



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