Radioactivity

Question 1

Describe the results of Rutherford plum pudding model

Answer 1

Most alpha particles past straight through (atom is mostly empty space)
A small amount were deflected by a large angle (atom is positively charged)
Few particles were deflected back by more than 90 degrees (centre was dense and small)

Question 2

How can you identify different types of radiation (used to measure thickness of materials)

Answer 2

Through their penetration power as you can check the count rate if you place a sheet of paper or aluminium or concrete between a source and detector

Question 3

What is the use of gamma radiation

Answer 3

As it is weakly ionising and highly penetrative
- it is used as a detector to help diagnose patients
- used to sterilise equipment by killing bacteria
- used in radiation therapy to kill cancer cells

Question 4

What is the inverse square law for radiation

Answer 4

Intensity = k/x^2

Question 5

What are the safety measure with dealing with radioactive sources

Answer 5

• long handled tongs
• lead lined containers
• keep source far
• never point source towards others

Question 6

When measuring radiation what must you take into account

Answer 6

Background radiation

therefore: corrected rate = total - background rates

Question 7

Name some sources of background radiation?

Answer 7

Nuclear weapon testing
Cosmic rays
Rocks

Question 8

What is the decay constant

Answer 8

The probability of a nucleus decaying per unit time

Question 9

Equation for decay constant

Answer 9

Change in nuclei number/change in time = -decay constant * Initial number of nuclei

Question 10

Equation for half life

Answer 10

T1/2 = ln(2) / decay constant

Question 11

What is activity

Answer 11

Activity is the number of nuclei that decay per second

Question 12

What can half life be used for

Answer 12

Dating of objects

Medical diagnosis - used in medical tracers if they have short half lives in order to limit exposure.

Question 13

Why might a nucleus become unstable

Answer 13

Too many neutrons
Too many protons (decays via beta plus and electron capture)
Too many nucleons (decays via alpha)
Too much energy (decays via gamma)

Question 14

Beyond 20 neutrons and protons why does the graph not increase uniformly

Answer 14

As electromagnetic repulsion becomes stronger than strong nuclear force, more neutrons are needed to distance the protons and decrease electromagnetic if force hence keeping the nucleus stable

Question 15

What is emitted to reach ground state when excited (too much energy)

Answer 15

Gamma radiation

Question 16

How can you calculate nuclear radius

Answer 16

When a particle with kinetic energy becomes zero where Ek is converted to electric potential energy

electric potential energy = k *Q/r * Q2