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Activity of Iodine-131 in Yuen Ng Fan Air Sample

Sampling Period(i)

Activity of Iodine-131 (micro Bq/m3 )

25 March to 26 March 2011 (noon to noon)

Not Detected

26 March to 27 March 2011 (noon to noon)

Not Detected

27 March to 28 March 2011 (noon to noon)

Not Detected

28 March to 29 March 2011 (noon to noon)

274 (1/2,400,000 of DIL(ii))

29 March to 30 March 2011 (noon to noon)

471 (1/1,400,000 of DIL(ii))

30 March to 31 March 2011 (noon to noon)

419 (1/1,600,000 of DIL(ii))

31 March to 1 April 2011 (noon to noon)

239 (1/2,800,000 of DIL(ii))

1 April to 2 April 2011 (noon to noon)

Not Detected

2 April to 3 April 2011 (noon to noon)

Not Detected

3 April to 4 April 2011 (noon to noon)

Not Detected

4 April to 5 April 2011 (noon to noon)

Not Detected

5 April to 6 April 2011 (noon to noon)

168 (1/3,900,000 of DIL(ii))

6 April to 7 April 2011 (noon to noon)

245 (1/2,700,000 of DIL(ii))

7 April to 8 April 2011 (noon to noon)

Not Detected

8 April to 9 April 2011 (noon to noon)

Not Detected

9 April to 10 April 2011 (noon to noon)

Not Detected

10 April to 11 April 2011 (noon to noon)

Not Detected

11 April to 12 April 2011 (noon to noon)

Not Detected

12 April to 13 April 2011 (noon to noon)

Not Detected

13 April to 14 April 2011 (noon to noon)

86 (1/7,700,000 of DIL(ii))

Since 14 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>