Solutions: Radioactivity Questions
(a) An unstable nucleus, , can decay by emitting a β– particle.
(i) What part of the atom is the same as a β– particle?
A orbital electron
(ii) State the changes, if any, in A and Z when X decays.
A is the nucleon number - that does not change as a neutron changes into a proton when beta decay occurs.
Z is the proton number - that will increase by one as a neutron changes into a proton when beta decay occurs.
(b) In the process of β– decay an anti-neutrino is also released.
(i) Give an equation for this decay.
n → p + e- + ̅ν̅e
n → p + β- + ̅ν̅e
d → u + e- + ̅ν̅e
X → + e- + ̅ν̅e
(ii) State and explain which conservation law may be used to show that it is an anti-neutrino rather than a neutrino that is released.
Conservation of lepton number because the beta particle is a lepton (an electron). The total lepton number of the left hand side of the equation is zero; therefore to balance the right hand side needs an antilepton with lepton number -1 to cancel out the electron lepton number of +1.
(iii) What must be done to validate the predictions of an unconfirmed scientific theory?
To validate the predictions of an unconfirmed scientific theory the hypothesis needs to be tested by experiment. That experiment must be repeatable or hypothesis will be rejected and the theory not shown to be valid.
(Total 8 marks)