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Half life

Iodine-131 [131I] is present in fission products of uranium. It is a beta (β) emitter with a half-lifeof 8 days. When absorbed into the body it concentrates in the thyroid gland increasing the riskof thyroid cancer. After the nuclear disaster in Japan, people living in the area were given non-radioactive iodine-127 [127I] supplement tablets to reduce their intake of iodine-131 that leaked from the reaction

question - Calculate for how long people had to take the iodine supplement tablets until the activityof iodine-131 reduced to approximately 3% of its original value just after a leak.

I got 36 days




The mark scheme? doesnt even tell me anything, it just says give one mark for ''-5'' and one mark for ''x8''

what does that even mean???
0 days 100%
8 days 50%
16 days 25%
24 days 12.5%
32 days 6.25%
40 days 3.125%

amount of iodine 131 is approximately 3% original level after a period of 5 half lives, length of a half life period is 8 days... answer is 5x8 days

that's the sort of working they'll be looking for at gcse IMO.
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Avatar for TSR George
TSR George
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Original post by Joinedup
0 days 100%
8 days 50%
16 days 25%
24 days 12.5%
32 days 6.25%
40 days 3.125%

amount of iodine 131 is approximately 3% original level after a period of 5 half lives, length of a half life period is 8 days... answer is 5x8 days

that's the sort of working they'll be looking for at gcse IMO.


thank you, i've made a mistake with the calculation by the looks and wasnt aware the 5 stood for the amount of half life. i get it now :u:

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