The evidence for the nucleus

Question 1

What was the Rutherford scattering experiment?

Answer 1

• An Alpha source was placed in a lead container directed towards gold foil.
• The angles the particles deflected at were measured, and each time they hit a florescent screen, a flash of light was emitted.
• A small amount of particles were deflected at 150 degrees, or greater.

Question 2

What conclusions did this lead to?

Answer 2

• The atom has a small positive nucleus(much smaller than the atom)
• The nucleus contains the majority of the mass of the atom(If it didn’t it would be moved by the alpha particles.)

Question 3

How do you calculate the nucleus size?

Answer 3

Ek = (Q1Q2)/4piε0r

Question 4

What is the empirical formula for the radius of the nucleus?

Answer 4

r = r0*A^1/3

Question 5

What is one atomic mass unit( u )?

Answer 5

1.67*10^-27

Question 6

What is a becquerel

Answer 6

The unit of activity( which is the number of particles emitted in a second)

Question 7

What are alpha particles and their features?

Answer 7

• They are the nuclei of Helium atoms(2 protons and two neutrons)
• Mass of 4u and +2e
• Strongly ionising and can be stopped by paper
• can travel about 4cm in air

Question 8

What are beta particles and their features?

Answer 8

• They are fast moving electrons travelling just less than the speed of light.
• Less ionising then Alpha particles
• Absorbed by a few cm thick aluminium
  -can travel about 40 cm in the air

Question 9

What are gamma rays and their features?

Answer 9

• They are EM radiation with the energy of 1Mev
• Very weakly ionising
• Very penetrating
• can travel about 1km in the air

Question 10

How do you detect radiation?

Answer 10

You can detect the type using a gold leaf electroscopes or geigger-Muller tubes.

Question 11

What is the inverse square law for Gamma radiation?

Answer 11

The intensity of gamma rays = a constant/ the distance^2

Question 12

Why is ionising radiation dangerous?

Answer 12

It can change the chemistry of our bodies, change functions of enzymes,cells can be damaged or mutated,and DNA can be mutated. Free radicals(H30) can also be produced, which are highly reactive and can change the structure of surrounding molecules.

Alpha particles do the most damage because the most ions aer created in the smallest amount of space.

Question 13

What is a dose of radiation?

Answer 13

D = E/m (energy absorbed/ mass)
The unit is one gray

Question 14

What is a dose equivalent and a sievert?

Answer 14

The measure of damage done, and the unit of dose equivalent.

Question 15

What force or interaction is responsible for Rutherford scattering?

Answer 15

electromagnetic or electrostatic