C24 - Particle Physics Flashcards
How was Rutherford’s alpha-scattering experiment carried out?
A narrow beam of electrons (of the same kinetic energy) from a a radioactive source were targeted at a thin piece of gold foil (only a few atomic layers thick).
The alpha particles were scattered by the foil and detected on a zinc sulfide screen mounted in front of a microscope.
Each alpha particle hitting the fluorescent screen produced a tiny speck of light.
The microscope was moved around in order to count the number of alpha particles scattered through different values of angle per minute (from 0° to 180°).
What were the observations made from Rutherford’s alpha-scattering experiment?
- Most alpha particles passed straight through the thin gold foil with very little scattering. Approx 1/2000 alpha particles were scattered.
- Very few particles were deflected through angles greater than 90° (1/10,000).
What were the conclusions made from Rutherford’s alpha-scattering experiment?
(Since most of the particles passed straight through the gold) - most of the atom is empty space with most of the mass concentrated in a small region [the nucleus].
(Few particles were deflected above 90° therefore) - the nucleus has a positive charge as it repelled the few positive alpha particles that came near it.
What is the simple nuclear model of the atom?
It has a nucleus with protons and neutrons.
What does the letter A represent? (Nucleus)
The nucleon number / total number of protons and neutrons / atomic mass
What does the letter Z represent? (Nucleus)
Atomic number / number of protons
What equation shows the radius of a nucleus?
R = r0A¹/³
R is radius
r0 has an approximate value of 1.2 fm (1.2 * 10 ⁻¹⁵ m)
A is the nucleon number / atomic mass
What is 1 fm?
1 * 10 ⁻¹⁵ m
What force overcomes the force of repulsion between protons in nuclei and stops them flying apart?
The strong nuclear force / strong force
What is the strong nuclear force?
A strong form which acts between all nucleons.
It’s very short range, effective over just a few femtometres (1 * 10⁻¹⁵ m).
It keeps the protons and neutrons together.
How does the strong nuclear force vary between 2 nucleons with distance/separation r?
(Like an l shape from positive to negative then towards zero N)
- At very small separation, the force is large and repulsive but quickly decreases with increasing separation (up to approx 0.5 fm).The force then increases/becomes more negative and attractive (min at approx 1 fm). It then decreases/becomes less negative (still attractive) and tends towards zero newtons.
At what separation (between nucleons) is the strong nuclear force repulsive?
Below approx 0.5 fm (0.5 * 10 ⁻¹⁵ m).
It is shown as a positive force in the graph.
At what separation (between nucleons) is the strong nuclear force attractive?
Approx between 0.5 - 3 fm (10 ⁻¹⁵ m).
Force is 0 above 3 fm.
What’s an antiparticle?
The antimatter counterpart of a particle, with the opposite charge to the particle (if the particle has charge) and exactly the same rest mass as the particle.
If a particle and its corresponding antiparticle meet, they completely destroy each other by annihilation and the masses of both are converted to a high energy pair of photons.
What’s the antiparticle of an electron?
The positron (with a charge of +e).
(Most antiparticles are symbolised by a bar over the letter for the particle).
