Half-life and radioactive decay

Question 1

What is the half-life of a radioactive isotope (2 definitions)

Answer 1

Time taken for number of nuclei in sample to halve
or
Time taken for count rate/activity from sample to fall to half of its initial level

Question 2

When does half life occur specifically

Answer 2

It is random

Question 3

Why is it impossible to tell when a particular nucleus will decay

Answer 3

Trillions of nuclei per block of radioactive material likely to decay at different times

Question 4

If radioactive decay is random, how is half-life calculated

Answer 4

Scientists are able to calculate when a certain number will decay in certain time

Question 5

Why does the count rate of radioactive material never drop to zero

Answer 5

0 isn’t the half of anything

Question 6

If the half life of carbon-14 is 5730 years and a tree contains 64 grams of radioactive carbon, how many grams of radioactive carbon will it contain after 17190 years

Answer 6

8g

Question 7

If the half life is 3 days, what is four half lives

Answer 7

12

Question 8

What 3 ways can the remaining amount of a sample be represented

Answer 8

1) fraction
2) decimal
3) ratio

Question 9

Give four half lives as a decimal

Answer 9

4 half lives = 1/2 x 1/2 x 1/2 x 1/2 = 1/16

1/16 = 0.0625 of the original sample