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Activity of Caesium-137 in Sha Tau Kok Air Sample

Sampling Period(i)

Activity of Caesium-137 (micro Bq/m3 )

8 to 15 March 2011

Not Detected

15 to 22 March 2011

Not Detected

22 to 29 March 2011

Not Detected

29 March to 5 April 2011

Not Detected

5 to 12 April 2011

64 (1/39,000,000 of DIL(ii))

Since 12 April 2011

Not Detected

Remarks:

(i)   Daily air samples are collected at King's Park from 25 March to 25 May 2011 and weekly air samples are collected from 26 May onwards.  Daily air samples are collected at Yuen Ng Fan from 25 March to 11 May 2011 and weekly air samples are collected from 12 May onwards.  Weekly air samples are collected at Sha Tau Kok.
 
 
(ii)   The concentration level required for taking protective actions is called Derived intervention level (DIL).  The DIL for inhalation of Iodine-131 and Caesium-137 from the air is 661.38 and 2,480 Bq/m3 respectively (Reference: Report No. 1 of the Radiological Protection Advisory Group, HKSARG: Derived Intervention Levels).
 
 
(iii)   Half-life of artificial radionuclide Iodine-131 is 8 days. This means that after 8 days, the radioactivity of Iodine-131 drops to half of its original level, and after 16 days to a quarter and so on.
 
(iv)   Half-life of artificial radionuclide Caesium-137 is 30 years. This means that after 30 years the radioactivity of Caesium-137 drops to half of its original level, and after 60 years to a quarter and so on.
 
(v)   The amount of radioactive iodine and caesium detected in the air sample is very minute and will have no effect on public health.
 
Last revision date: <21 Dec 2012>