Topic 8 Nuclear and particle physics Flashcards
At the beginning of the 20th century, Rutherford carried out large-angle alpha particle scattering experiments using gold foil.
The vast majority of the alpha particles went straight through the foil whilst a few were deflected straight back.
Describe how the model of the atom changed, as a consequence of these experiments. (4)
Before the experiment:
-Atom containing equally distributed mass/charge.
After experiment:
-Very small nucleus containing almost all the mass of the atom.
-Atom mainly empty space.
-Nucleus is charged.
A series of experiments was carried out in the 1970s to investigate the structure of protons using the linac at Stanford, USA.
Explain how an electron is accelerated in a linac. (6)
-Set of metal drift tubes in a line.
-Electrons accelerated by electric field.
-Acceleration takes place in gaps between tubes.
-Adjacent tubes connected to opposite terminals of power supply.
-P.D is alternating so that as electron emerges from one tube, the next tube is positive.
-Time spent in each tube must be same so as electron travel faster tubes must be larger.
A series of experiments was carried out in the 1970s to investigate the structure of protons using the linac at Stanford, USA.
The electron leaves the accelerator with a high energy.
Explain why electrons need high energies to investigate the structure of a proton. (2)
-High energy electrons will have a short de Broglie wavelength.
-Wavelength needs to be comparable/smaller than proton size.
Proton beam therapy is being introduced in the UK as a new cancer treatment.
A beam of protons is accelerated by a cyclotron to an energy of 23 MeV and is then focused onto a tumor.
Explain how the cyclotron produces the high-energy proton beam. (6)
-There is an alternating P.D/electric field.
-P.D/electric field accelerates protons between Dees.
-Magnetic field perpendicular to plane of Dees.
-Proton path curved by magnetic field.
-As V of proton increases, radius of path in Dees increases.
-Time for which a proton is in Dee remains constant.
Rutherford’s alpha-scattering experiment gave evidence that changed our understanding of the structure of the atom. Alpha particles were fired at a thin sheet of gold foil and their paths
observed.
Explain how the observations of the different paths taken by the alpha particles as they passed through the gold foil led to a new model of the atom. (4)
-Most alpha particles pass through undeflected.
-Very small number of particles are deflected at a angle larger than 90.
-Suggests alpha particles are deflected by a charged nucleus that has a very small diameter compared to that of the atom rather than the charge being distributed throughout atom.
-Most of the mass of the atom is concentrated at nucleus rather than the mass being distributed throughout atom.
How do you convert a proton of mass M in kg to GeV/c^2?
(M(3x10^8)^2)/(1x10^9)(1.6x10^-19)
How do you convert a proton of mass M in MeV/c^2 to kg?
(M(1.6x10^-19)(1x10^6))/(3x10^8)^2
The discovery of the Higgs particle was an important contribution to our understanding of particle physics.
Describe the standard model for subatomic particles. You should identify the fundamental particles and the composition of the particles we can observe. (5)
-Quarks and leptons are fundamental particles.
-Baryons are made up of three quarks.
-Mesons are made up of a quark and antiquark.
-6 quarks/6 leptons.
-Each particle has an antiparticle.
The Higgs particle was discovered using the Large hadron collider in 2012. Two beams of very high energy protons moving in opposite directions, were made to collide.
Explain the need for such high energy collisions. (3)
-Energy required to overcome electrostatic forces of repulsion between protons.
- E=mc^2
- C^2 is very large therefore energy must be large.
Describe what happens in pair production and when it occurs.
-One photon turns into A particle~Antiparticle pair.
-Only occurs when photon has energy greater than total rest energy of both particles.
-Excess energy converted to kinetic energy of particles.
Describe what happens in annihlation.
-When a particle meets an antiparticle.
-Their masses are converted into two equal photons.
-This energy along with kinetic energy of the two particles is released in form of two photons moving in opposite directions in order to conserve momentum.
