The Nucleus

Question 1

Rutherford scattering experiment
What was the model of the atom before the experiment?

Answer 1

Plumb pudding model

Question 2

Rutherford scattering experiment
Method

Answer 2

• Alpha particles fired at gold foil in a narrow beam
• The number deflected through different angles was measured

Question 3

Rutherford scattering experiment
Why is the experiment carried out in a vacuum?

Answer 3

Alpha particles would collide with air molecules and would not reach the detectors

Question 4

Rutherford scattering experiment
Why is the alpha particle beam narrow?

Answer 4

So that the angle of deflection could be measured accurately

Question 5

Assumptions made when calculating nuclear radius from distance of closest approach of alpha particles

Answer 5

• Alpha particle is a point charge
• Nucleus does not recoil and gain some KE
• Alpha particle starts at infinity so has no PE due to nucleus
• Alpha particle does not get close enough to be effected by the strong force

Question 6

De Broglie wavelength for noticeable electron diffraction pattern

Answer 6

Around the same size as the nucleus

Question 7

Why is electron diffraction more accurate than alpha scattering for calculating the size of the nucleus?

Answer 7

• Calculates radius, not just upper estimate
• Electrons are closer to point charges than alpha particles
• Less recoil of nucleus with electrons
• Electrons aren’t effected by strong interaction, which is not as well understood
• Easier to control energy of electrons

Question 8

How can the energy of alpha particles be changed?

Answer 8

By using a different source

Question 9

Range for the radius of the nucleus

Answer 9

1-10fm