State

(i) what is meant by an elementary particle.

(ii) to which class of elementary particles the electron belongs.

An electron is one of the particles produced in the decay of a free neutron into a proton. An exchange particle is also involved in the decay.

(i) State the name of the exchange particle.

(ii) The weak interaction has a range of the order of 10^–18m. Determine, in GeVc^–2, the order of magnitude of the mass of the exchange particle.

(iii) It is suggested that the exchange particle in the weak interaction arises from the decay of one type of quark into another. With reference to the quark structure of nucleons, state the reason for this suggestion.

(i) particle that has no internal structure/is not made out of any smaller constituents;

(ii) leptons;

(i) intermediate vector boson/W boson;

(ii) \(m = \frac{h}{{4\pi Rc}}\);
\( = \left( {\frac{{6.6 \times {{10}^{ - 34}}}}{{4 \times 3.14 \times {{10}^{ - 18}} \times 3.0 \times {{10}^8}}} = } \right)1.75 \times {10^{ - 25}}{\rm{kg}}\);
\( = \frac{{1.75 \times {{10}^{ - 25}}{c^2}}}{e} = 109{\rm{GeV}}{{\rm{c}}^{ - 2}} \approx 10^2{\rm{GeV}}{{\rm{c}}^{ - 2}}\);

(iii) the neutron quark structure is udd and the proton uud;
a d quark in the neutron changes to a u quark by emitting a W boson;