Chapter 24 - Particle Physics

Question 1

What are the requirements for the alpha particle experiment?

Answer 1

Same slow speed
Evacuated chamber
Very thin foil
Long half-life

Question 2

Why must alpha particles have the same slow speed?

Answer 2

Slow speeds allow them to be deflected more than faster ones
Same speed guarantees speed has nothing to do with differences

Question 3

Why must the chamber be evacuated?

Answer 3

Alpha particles would be stopped by air molecules

Question 4

Why must the gold foil be very thin?

Answer 4

Otherwise, alpha particles will be deflected more than once

Question 5

Why must the alpha source have a long half-life?

Answer 5

Readings remain the same following later repeats

Question 6

What are the number of alpha particles that followed each interaction?

Answer 6

Most passed straight through
1 in 2000 were deflected by small angles
1 in 10000 were deflected greater than 90^o

Question 7

What assumptions can be made because of the alpha-particle experiment?

Answer 7

Most of the mass is concentrated in the small, positive nucleus in the centre

Question 8

When did the alpha particles get rebounded back?

Answer 8

At the distance where KE = PE

Question 9

What formula gives the distance at which alpha particles get rebounded back?

Answer 9

1/2 * m * v² = Q * q / 4 * pi * E₀ * r

Question 10

What is the radius of the atomic nucleus?

Answer 10

10^-14m

Question 11

What are hadrons?

Answer 11

Hadrons can interact through strong forces - protons, neutrons, mesons, baryons
If charged, they experience the EM force
They decay by the weak nuclear force

Question 12

What are leptons?

Answer 12

Leptons cannot interact through strong forces - Electrons, muons, neutrinos
If charged, they experience the EM force

Question 13

What are baryons?

Answer 13

Made up of 3 quarks - part of hadrons

Question 14

What are mesons?

Answer 14

Made up of two quarks, one anti, and does not decay into protons

Question 15

What are the different quarks and their charge?

Answer 15

up +2/3
down -1/3
strange -1/3

Question 16

What are two commons mesons?

Answer 16

Kaons decay into pions

Question 17

What are neutrinos?

Answer 17

A chargeless, massless lepton that occurs due to a particle transformation inside of an unstable nuclei

Question 18

What is beta minus decay?

Answer 18

Neutron —> Proton + Electron + Electron antineutrino
d —> u + ⁰_-1e + v_e

Question 19

What is beta positive decay?

Answer 19

Proton —> Neutron + Positron + Electron neutrino
u —> d + ⁰₁e + v_e

Question 20

What are the fundamental forces?

Answer 20

Strong nuclear - Acts on nucleons
Electromagnetic - Acts on any charged particle
Weak nuclear - Beta decay
Gravitational - Acts on particles with mass

Question 21

What is the difference between the weak and strong nuclear forces?

Answer 21

Strong holds quarks together to form hadrons and binds them in the nucleus
Weak is part of certain types of radioactive decay, like beta decay, where a neutron changes into a proton (and vice versa)

Question 22

What is the relationship between radius and mass?

Answer 22

r³ / m = Constant

Question 23

What is the formula for nuclear radius?

Answer 23

R = r₀ x A^1/3

Radius = 1.2fm * (Atomic Number)^1/3

Question 24

What is the difference between relative strength and range of the fundamental forces?

Answer 24

Strong nuclear, 1, 10^-15
Electromagnetic, 10^-3, infinite
Weak nuclear, 10^–6, 10^-18
Gravitational, 10^-40, infinite