1. Radio-carbon dating is used to estimate the age of objects that were once living as all living things contain a small amount of Carbon-14, which has a half-life of 5700 yrs. By measuring the activity (counts min-1) of the dead tissue its approximate age can be determined. Show all the steps in your working out.

a. A sample of living wood has an activity of 16 counts min-1 per gram. Calculate the activity of a 20g sample of living wood.

b. Calculate the activity of 20g sample of wood from a tree that died 17100 years ago. State the correct units in your answer

c. A 5g of old wood from an archaeological site has an activity of 20 counts min-1, what was the activity of the wood when it was living? How long ago did the tree died?

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answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.