24. Particle physics

Question 1

What was the plum pudding model?

Answer 1

An atom contained negative electrons (the plums) embedded in a uniform sea of positive charge (the dough)

Question 2

Describe Rutherfords alpha scattering experiment

Answer 2

• A narrow beam of alpha particles, all of the same kinetic energy, from a radioactive source were targeted at a thin piece of gold foil.
• The alpha particles were scatted by the foil and detected on a zinc sulfide screen
• Each alpha particles hitting this fluorescent screen produced a ting speck of light
• The microscope was moves around in order to count the number of alpha particles scattered through different values of the angle per minute, for ø from almost 0 to 180

Question 3

What 2 observations did the alpha scattering experiment lead to?

Answer 3

1. Most of the alpha particles passed straight through the thin gold foil with very little scattering.
   THEREFORE MOST OF THE ATOM WAS EMPTY SPACE WITH MOST OF THE MASS CONCENTRATED IN A SMALL REGION - THE NUCLEUS
2. Very few particles were deflected through angles of more than 90˚
   THIS LEAD TO THE CONCLUSION THAT THE NUCLEUS HAS A POSITIVE CHARGE

Question 4

Define Isotope

Answer 4

Nuclei of the same element that have the same number of protons, but different numbers of neutrons

Question 5

What is the equation for the radius of a nucleus?

Answer 5

R = r0A^1/3

R = Radius
r0 = 1.2fm (rough radius of proton)
A = Nucleon number

Question 6

What is the density of a nucleus?

Answer 6

10^17kgm^-3

Question 7

What is the strong nuclear force?

Answer 7

Force that acts between all nucleons

• very short range
• attractive to about 3fm
• repulsive below about 0.5fm