Radioactivity questions | form four Physics

A radioactive element has a half life of 3 minutes. If the initial count rate is 512 per minute, find the time needed to reach a count rate of 8 per minute.

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A radioactive element has an initial count rate of 1200 counts per minute measured by a scale and this falls to 150 counts per minutes in 15 hours.
(i) Determine the halflife of the element.
(ii) If the initial number of atoms in another sample of this element is , how many atoms will have decayed in 25 hours?

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What is meant by the halflife of a radioactive element?

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The half-life for the β-decay of thorium – 234 is 24 days. The Physics Department has brought a sample of this thorium from England. On the day of the dispatch its activity was 4 x 10⁵ disintegrations per second.
(i) What was the activity of the source 72 days later?
(ii) What safety precautions should the suppliers take to ensure that none of the dock-workers could be harmed?

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A particular radioactive source has a halflife of 2.0 hours. A sample gives a count of 2400 per second at 11:00 a.m. When will the count have dropped to approximately 300 per second in the same counting system?

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