24, Particle Physics Flashcards
What did Rutherford’s experiment, what were the results and what did this mean?
The experiment was firing alpha particles at a very thin gold leaf and measuring the amount of particles leaving at different angles with a microscope, he found about 1999/2000 particles experienced almost no scattering at all but some particles were being scattered through angles of more than 90°, this implied atoms were mostly empty space but with highly concentrated points of charge (counters the plum pudding model).
How could Rutherford predict the size of gold nucleus?
By knowing the velocity of the alpha particles he could find the K.E. of them and use this to find the max electric potential energy allowing him to calculate the remaining distance to the atoms giving an upper limit on the radius.
What do we write to represent a specific isotope of an atom?
Superscript A, subscript Z before X, where A is the nucleon number (Z+N), Z is the proton number (or atomic number) (N is the neutron number), X represents the element symbol.
What is an atomic mass unit?
Atomic mass unit (u) is 1/12 * the mass of a carbon-12 atom (includes electrons) and is approx the mass of a neutron/proton in an atom.
What does the equation R = r_0 A^(1/3) mean?
Radius of a nucleus is given by r_0 * nucleon number ^ 1/3 where R_0 is a constant roughly equal to the radius of a proton.
What does the graph of net force against distance for two protons over a short distance look like?
High and steep curve where EM force dominates then the strong force takes over, as r tends to 0 the force tends to 0 from below the axis (i.e. still attractive).
What properties does the strong force have?
Acts between all hadrons but not leptons and acts over a very short range but with high strength.
How does the strong force put an upper limit on nucleus size?
Because it acts over a very short range the nuclei could become larger than the range it takes effect over allowing the EM force to dominate.
What is the definition of a hadron?
A particle like protons which can take part in strong interaction.
What is the definition of a lepton?
A particle like electron which does not interact through the strong force.
What happens during a matter-antimatter collision?
The two particles are annihilated producing a pair of gamma photons such that momentum and energy is conserved.
What is the notation used for antimatter?
The regular matter symbol with a bar across the top.
Why is a anti-neutrino’s emitted in beta minus decay?
To counter the positive “leptonicness” of the electron.
