Atomic Structure Physics

Question 1

Isotope

Answer 1

An atom of the same element with a different number of neutrons

Question 2

Nuclear model (alpha scattering experiment)

Answer 2

1. Most particles went straight through - mostly empty space, nucleus small compared to whole atom
2. Some particles deflected several degrees - nucleus positively charged as positive particles were repelled
3. A few particles deflected almost 180 degrees - nucleus contains most of the mass of the atom
   Conclusion: the mass of the atom is concentrated at the centre (nucleus) and the nucleus is charged

Question 3

Plum pudding model

Answer 3

The atom is a ball of positive charge with negative electrons embedded in it

Question 4

Niels Bohr’s nuclear model

Answer 4

Electrons orbit the nucleus at specific distances - his theoretical calculations agreed with experimental observations

Question 5

Radioactive decay

Answer 5

A random process in which an unstable atomic nucleus give out radiation as it changes to become more stable

Question 6

Alpha particle

Answer 6

Two neutrons and two protons, the same as a helium nucleus

Question 7

Beta particle

Answer 7

A high speed electron ejected from the nucleus as a neutron turns into a proton

Question 8

Gamma ray

Answer 8

Electromagentic radiation from the nucleus

Question 9

What are the 4 types of nuclear radiation?

Answer 9

Alpha particle, beta particle, gamma ray, neutron

Question 10

Alpha radiation - absorber materials, range in air, ionising power

Answer 10

1. Thin sheet of paper
2. About 5cm
3. Most ionising power

Question 11

Beta radiation - absorber materials, range in air, ionising power

Answer 11

1. Aluminium sheet (5mm), lead sheet (2 - 3mm)
2. 1m
3. Medium ionising power

Question 12

Gamma radiation - absorber materials, range in air, ionising power

Answer 12

1. Thick lead sheet (several cm), concrete (more than 1m)
2. Long range - spreads in air without being absorbed
3. Least ionising power

Question 13

Half-life (2)

Answer 13

1. The time it takes for the number of nuclei in a sample for halve
2. The time it takes for the count rate/activity from a sample containing the isotope to fall to half its initial level

Question 14

Radioactive contamination

Answer 14

The unwanted presence of materials containing radioactive atoms on other materials

Question 15

Irradiation

Answer 15

The process of exposing an object to nuclear radiation; the irradiated object does not become radioactive

Question 16

Why is radiation dangerous?

Answer 16

Radiation causes ionisation which can damage or kill the cell, causing mutations and possibly cancer

Question 17

Why do hazards associated with radioactive materials differ according to their half life?

Answer 17

1. Materials with a longer half life have the potential to be more dangerous as they will be emitting radiation for a long time

Question 18

Risks of using radiation to treat patients

Answer 18

Radiation can ionise both healthy and cancerous cells, causing the patient to feel ill

Question 19

What is nuclear fusion?

Answer 19

The splitting of a large and unstable nucleus (e.g. uranium or plutonium)

Question 20

Describe what happens in a fission reaction

Answer 20

1. Nucleus splits into 2 smaller nuclei roughly equal in size
2. Emits 2 or 3 neutrons plus gamma rays
3. Energy is released

Question 21

What is nuclear fusion?

Answer 21

Nuclear fusion is the joining of 2 light nuclei to form a heavier nucleus. In this process some of the mass may be converted into the energy of radiation.