Physics: Nuclear and Particle Physics

Method

1. To estimate nuclear radius from an electron diffraction pattern, use the angle of the first minimum of intensity, θ, in the relationship sin(θ) = 1.22 x λ / (2 x R), where λ is the de Broglie wavelength of the electrons (found from λ = h / (m x v) or λ = h / p) and R is the nuclear radius; rearrange to make R the subject.To estimate nuclear radius from an electron diffraction pattern, use the angle of the first minimum of intensity, theta, in the relationship sin(theta) = 1.22 x lambda / (2 x R), where lambda is the de Broglie wavelength of the electrons (found from lambda = h / (m x v) or lambda = h / p) and R is the nuclear radius; rearrange to make R the subject.
2. Use R = r0 x A^1/3 to estimate the radius of a nucleus of nucleon number A, where r0 is a constant given in the question if needed; to compare the radii of two different nuclides, the ratio of their radii is simply the cube root of the ratio of their nucleon numbers, since r0 cancels.Use R = r0 x A^(1/3) to estimate the radius of a nucleus of nucleon number A, where r0 is a constant given in the question if needed; to compare the radii of two different nuclides, the ratio of their radii is simply the cube root of the ratio of their nucleon numbers, since r0 cancels.
3. For pair production, recognise that a high-energy photon can convert into a particle-antiparticle pair (for example, an electron and a positron) only if its energy is at least equal to the combined rest energy of the pair; find this minimum (threshold) photon energy using E = 2 x m x c², where m is the rest mass of one of the particles produced, then use E = h x f to find the corresponding minimum (threshold) frequency.For pair production, recognise that a high-energy photon can convert into a particle-antiparticle pair (for example, an electron and a positron) only if its energy is at least equal to the combined rest energy of the pair; find this minimum (threshold) photon energy using E = 2 x m x c^2, where m is the rest mass of one of the particles produced, then use E = h x f to find the corresponding minimum (threshold) frequency.
4. For annihilation, recognise that a particle and its antiparticle can annihilate to produce two photons, never just one, since a single photon cannot conserve both energy and momentum; if the particle and antiparticle have negligible kinetic energy before annihilation, the two photons share the total rest energy equally, so each photon has energy E = m x c², where m is the rest mass of one of the particles.For annihilation, recognise that a particle and its antiparticle can annihilate to produce two photons, never just one, since a single photon cannot conserve both energy and momentum; if the particle and antiparticle have negligible kinetic energy before annihilation, the two photons share the total rest energy equally, so each photon has energy E = m x c^2, where m is the rest mass of one of the particles.
5. For a fission or fusion reaction energy calculation, use given atomic or nuclear mass data to find the mass difference between the total mass of the reactants and the total mass of the products, then convert this mass difference directly to energy released using E = (δ m) x c², converting any mass given in atomic mass units (u) to kilograms first, or working entirely in u and MeV using the conversion 1 u = 931.5 MeV.For a fission or fusion reaction energy calculation, use given atomic or nuclear mass data to find the mass difference between the total mass of the reactants and the total mass of the products, then convert this mass difference directly to energy released using E = (delta m) x c^2, converting any mass given in atomic mass units (u) to kilograms first, or working entirely in u and MeV using the conversion 1 u = 931.5 MeV.
6. Distinguish antiparticles from their corresponding particles: an antiparticle has identical mass and identical magnitude of any other quantum property (such as baryon number or lepton number) to its particle, but has opposite charge (where the particle is charged) and opposite value of properties such as lepton or baryon number.
7. In control of a fission chain reaction, as in a nuclear reactor, link a named component to its function: control rods (made of a neutron-absorbing material such as boron) are raised or lowered to absorb a variable proportion of the neutrons produced, keeping the chain reaction steady (critical) rather than increasing (supercritical) or dying out (subcritical).

Practice questions

Try each question, then tap to reveal the answer.

Free printable worksheet