Atoms , isotopes, radiation

Question 1

What is the radius of an atom?

Answer 1

1 X 10 ^-10m
or
0.1nm

Question 2

How small is the radius of an atom’s nucleus?

Answer 2

1/10,000 of the radius of the atom

Question 3

How did Dalton describe the atom?

Answer 3

.Tiny spheres
.Indivisible and indestructible
.Made up all matter

Question 4

Explain J.J Thomson’s model of the atom

Answer 4

Plum pudding
.Sphere of positive charge with negative electrons stuck in it
.Electrons could be removed

Question 5

Explain Rutherford’s experiment and it’s results.

Answer 5

Alpha scattering experiment
-Fired a beam of alpha particles at thin gold foil expecting (from plum pudding model) for it to go straight through

Results and what it shows:
.Most alpha particles went straight through meaning that most of the atom is empty space
.A small number of alpha particles were deflected at large angles showing there is a concentration of positive charge (alpha= positive and like charges repel)
.A small number of alpha particles came straight back meaning the positive charge and mass are concentrated in a very small nucleus.

Question 6

Who created the first nuclear model?

Answer 6

Ernest Rutherford

Question 7

What did Niels Bohr discover about the atom?

Answer 7

Electrons orbiting the nucleus do so at certain distances called energy levels.

Question 8

What did James Chadwick discover about the atom?

Answer 8

It had particles with no charge (neutron).

Question 9

List the scientist that contributed to the atom in order

Answer 9

John Dalton
J.J Thomsom
Ernest Rutherford
Niels Bohr
James Chadwick

Question 10

What are the relative charges of subatomic particles?

Answer 10

proton: +1
neutron: 0
electron: -1

Question 11

What charge is the nucleus?

Answer 11

Positive

Question 12

What is the charge of an atom?

Answer 12

Neutral

Question 13

Explain how electrons can move within (or sometimes leave) the atom

Answer 13

If the electron gains energy by absorbing EM (electromagnetic) radiation, they move to a higher energy level, further from the nucleus.

If the electron releases EM radiation, it moves to a lower energy level, closer to the nucleus.

Question 14

True or false:
There are the same number of protons and neutrons in an atom

Answer 14

False

same number of protons and electrons

Question 15

What does the mass number show? Is it on top or bottom?

Answer 15

The number of protons and neutrons

top

Question 16

Define an isotope

Answer 16

Atoms of the same element with the same number of protons but different number of neutrons

Question 17

What happens if an atom loses an electron?

Answer 17

It becomes a positive ion (cation)

Question 18

Explain radioactive decay

Answer 18

Some atomic nuclei are unstable. The nucleus gives out radiation as it becomes more stable.

Question 19

Define activity

Answer 19

The rate at which a source of unstable nuclei decays.

Question 20

What is activity measured in?

Answer 20

Becquerels (Bq)

Question 21

Define count rate
What could you measure it with?

Answer 21

The number of decays each second by a detector e.g Geiger-Muller tube

Question 22

Describe the properties/composition of alpha particles including penetration and ionisation.

Answer 22

Alpha particle emitted from the nucleus
.2 protons, 2 neutron
. +2 charge
.travels a few cm in air, stopped by paper or skin
.high ionisation

Question 23

What is a beta particle? What’s it’s charge, penetration, ionisation?

Answer 23

A fast moving electron from the nucleus (neutron turns into a proton inside the nucleus and gives off an electron.

Charge: -1
Penetration: travels a few metres in air, stopped by a thin layer of aluminium
Ionisation: medium

Question 24

What is a gamma particle? What’s it’s charge, penetration, ionisation?

Answer 24

High energy electromagnetic wave. Usually follows alpha or beta decay.

Charge: 0
Penetration: travels kilometres in air, stopped by thick lead or concrete.
Ionisation: low

Question 25

True or false: alpha particles are the same as helium nuclei

Answer 25

True

Question 26

Give and explain an example of alpha radiation.
Why can’t we use beta or gamma radiation for this?

Answer 26

Smoke detectors
-> alpha radiation ionises the air particles causing current to flow. If there is smoke in the air, it binds to the ions, meaning the current stops and the alarm sounds.

Most of the beta and gamma radiation would penetrate smoke and no change in the count rate would be detected.

Question 27

Give an explain an example of beta radiation.
Why can’t we use alpha or gamma?

Answer 27

Testing the thickness of sheets of metal. If the foil is too thick it absorbs more beta particles. The detector receives less beta particles and then sends a signal to the rollers to increase the force on the foil, making it thinner.

If the foil is too thin it absorbs less beta particles. The detector receives more beta particles and then sends a signal to the rollers to decrease the force on the foil, making it thicker.

Alpha radiation would be blocked by even a thin sheet of paper, while gamma radiation will pass through most thin materials

Question 28

True or false: gamma rays change the charge and mass of the nucleus

Answer 28

False. There is no change to the mass number of atomic number.

Question 29

True or false: radiation is random

Answer 29

True

Question 30

Define half life

Answer 30

The time taken for half of the unstable nuclei in a sample to decay .

Question 31

Explain 2 reasons why there is background radiation

Answer 31

1) natural sources such as rocks and cosmic rays from space (mostly from the sun)
2)man-made sources such as the fallout from nuclear weapons
testing and nuclear accidents

Question 32

What is radiation dose measured in?

Answer 32

Sieverts

Question 33

Define irradiation

Answer 33

Exposing objects to beams of radiation

Question 34

True or false: we are irradiated.

Answer 34

True, by background radiation

Question 35

Define contamination

Answer 35

When an object has radioactive material introduced into it.

Question 36

Why is contamination dangerous?

Answer 36

The contaminating atoms might decay, releasing radiation which could cause you harm.

Question 37

How can you avoid contamination?

Answer 37

1) use gloves and tongs when handling sources
2)wear protective suits
3)point source away from you

Question 38

What are the risks to using radiation?

Answer 38

1)radiation can enter living cells and ionise atoms in them which can lead to tissue damage
2)lower doses tend to cause minor damage to cells which can lead to mutations which divide uncontrollably (cancer).
3) higher doses tend to kill cells causing radiation sickness

Question 39

Explain 2 uses for gamma radiation and how it works

Answer 39

1) Medical tracers
radioactive isotopes are injected into people and their progress around the body can be traced by an external detector. A computer shows where the strongest reading is.

2) Radiotherapy-treating cancer
gamma rays are directed at just the right dosage to kill the cancer cells

Question 40

Can nuclear fission be done on earth?

Answer 40

Yes

Question 40

What fuels are mostly used for nuclear fission?

Answer 40

Uranium and Plutonium

Question 42

Explain the