Detection of Background Radiation Levels

using Dose Rate and Contamination

Monitors in Perth's Outdoor Areas

Why ?

• Literature is limited and dated concerning the background levels of

radiation in Perth’s outdoor public areas

• One geological study in the region of Perth Australia was conducted using

an ion chamber in 1973

How ?

• Gamma dose sampling at 1 m

– One meter was chosen for gamma radiation readings as it give a valid reading

for a whole body dose

• Contamination monitoring at 2 cm above ground level

• Regular sampling pattern

• Beach radiation levels can drastically vary in radionuclide concentrations

from other outdoor areas; therefore, beach background levels were an area

of interest, followed by parks

Equipment

• A T201 contamination monitor was used to detect alpha and beta radiation

in counts per second (CPS)

• A T202 dose rate monitor was used to detect gamma radiation with a

sensitivity of 59 keV in uSv/h

Homogeneity Proof

• To test the validity of sampling from one point in a park or beach, a test for

homogeneity was conducted

• Measurements in one meter intervals over a five meter by five meter grid

(25 meter squared was covered)

• Each grid spot was measured 5 times

– 1 meter for uSv h-1

– ground level for CPS

5 m

Homogeneity Proof Results

• The park selected for validation was Brian Burke Reserve

• Scarborough Beach was selected for the beach

Scarborough Beach Brian Burke Reserve

uSv h-1 CPS uSv h-1 CPS

Average 0.344 1.471 0.152 0.737

SD 0.046 0.143 0.016 0.075

95 % CI 0.325-0.363 1.413-1.530 0.145-0.159 0.706-0.768

P-value 0.288 0.838 0.999 0.979

Design

• 82 area codes in Perth

• One measurement conducted per area code

• Five readings were taken at 30 second intervals to account for fluctuations

that can arise from environmental conditions

• Beach's chosen over Parks

• If no beaches existed within the area code, the largest accessible park was

then selected

• Readings were taken at the approximate centre of each chosen beach or

park using the T201 and a T202

Shielding

• Water on the surface of the ground can block alpha and potentially beta

radiation

• Before any measurements were taken, the ground was dry with no rain

having fallen two days before any T201 contamination monitor

measurements were taken.

Quadrants

• Perth separated into four quadrants designated

– North West

– North East,

– South West

– South East

• East and West are determined as East and West of Perth city

• the Kirwan freeway south of Perth used as the dividing line

• Natural boundary lines of area codes used north of the river

• North and South where determined by the outdoor recreations area position relative

to the Swan River.

Area codes into Quadrants

Park Land

Measured Area Code

Non-measured Area Code

Ocean

Parks vs Beach's

• Beaches were found to have significantly higher uSv h-1 and CPS readings

(p < 0.001) compared to parks average reading.

uSv h-1 CPS

Beach

Avg (SD) 0.625 (0.245) 1.035 (0.304)

95% CI 0.490 - 0.761 0.867 - 1.204

Park

Avg (SD) 0.275 (0.148) 0.529 (0.379)

95% CI 0.240 - 0.312 0.437 - 0.621

P value <0.0001 <0.0001

Beach North vs Beach South

• uSv h-1 and CPS of beaches North of the Swan River compared to beaches

South

• No difference were found (p = 0.112, p = 0.259) between CPS or uSv h-1.

uSv h-1 CPS

Northern Beach

Avg (SD) 0.591 (0.213) 0.995 (0.238)

95% CI 0.448 - 0.734 0.835 - 1.154

Southern Beach

Avg (SD) 0.72 (0.335) 1.149 (0.468)

95% CI 0.186 - 1.254 0.404 - 1.893

P value 0.112 0.259

Parks North vs South

• uSv h-1 and CPS of parks north of the Swan River compared to parks south

of the Swan River.

• A significant difference (p < 0.001) was observed in both uSv h-1 and CPS

between northern and southern parks.

uSv h-1 CPS

Northern Parks

Avg (SD) 0.217 (0.119) 0.430 (0.272)

95% CI 0.179 - 0.255 0.343 - 0.517

Southern Parks

Avg (SD) 0.367 (0.144) 0.664 (0.471)

95% CI 0.310 - 0.423 0.478 - 0.851

P value <0.0001 <0.0001

Discussion

• Typical background gamma levels measured for outdoor areas in Perth by government officials is 0.3 uSv h-1, which equates to approximately 2.6 mSv a year

• The average Perth parks dose rate measured in this study was 0.275 uSv h-1 which is slightly below the recorded governmental values

• Parks measured in the south were slightly higher than the northern parks (0.367 uSv h-1) with radiation levels slight higher than governmental measurements

• One possible explanation into the discrepancy could be due to the geology of the north.

– The northern region of Perth consisted of wetlands before urbanisation

– Both the original wetland make up and the subsequent reclamation process could have resulted in dissimilar soil types and mineral concentrations being deposited compared to South Perth.

– A more detailed investigation into the different radiation values measured is warranted

Difference in Studies

• Yeats and King (1973) investigated undisturbed sand background radiation

in Perth and found it to be approximately 4 times less (0.15 uSv h-1) than

the results of this study and half the governments average predicted

background

• This difference could be attributed to Yeats and King’s investigation being

– conducted over bitumen or granite surfaced roads and concrete sidewalks

– height of 75 cm because the original organ weighting factor for gonads was

greater in 1973 than it is today

– high pressure ion chamber calibrated to Ra-226

– warrant investigation for future studies

Summary

• A difference in dose rate and CPS was found between beaches and parks

in Perth

• Perth parks dose rates being similar to WA government predicted average

outdoor background levels

• Perth Beach’s were twice this level.

• It is hoped that a better understanding of radiation levels in local area

codes parks and beaches will aid in overcoming the challenge in

communicating realistic radiation risk.