Atomic Physics

Question 1

State the typical size of an atom

Answer 1

1 x 10 -10 m

Question 2

Describe the structure of an atom

Answer 2

A positively charge nucleus containing protons and neutrons surrounded by negatively charged electrons

Question 3

State the size of a nucleus compared to an atom

Answer 3

The radius of the nucleus is less than 1/10000 of the radius of an atom

Question 4

How can electrons move to a higher energy shell/level

Answer 4

By absorbing electromagnetic radiation

Question 5

How can electrons move to a lower energy shell/level

Answer 5

By releasing electromagnetic radiation

Question 6

What is the charge on an atom why?

Answer 6

Atoms are neutral as the number of positive protons is equal to the number of negative electrons

Question 7

What is an Ion?

Answer 7

A charged atom that has gained or lost electrons

Question 8

The same element must always have the same number of…?

Answer 8

Protons

Question 9

Define the atomic number

Answer 9

Number of protons = number of electrons for an atom

Question 10

Define nucleon number

Answer 10

mass mummer = Number of protons + number of neutrons

Question 11

Define an isotope

Answer 11

The same element with the same number of protons but with a different number of neutrons.

Question 12

Describe how the model of the atom has changed with new experimental evidence

Answer 12

Atoms were originally though to be tiny spheres that couldn’t be divided.
The discovery of the electron led to the plum pudding model of the atom.
The alpha particle scattering experiment led to the nuclear model of the atom - a positive nucleus which contained the majority of the mass.
Niels Bohr suggested that electrons orbited the nucleus in shells
James Chadwich discovered the neutron

Question 13

Describe the plum pudding model of the atom

Answer 13

A positive sphere with negative electrons dotted throughout it.

Question 14

Describe the alpha particle experiment.

Answer 14

Alpha Partikels were fired at thin gold in a vacuum.

Question 15

Describe and explain the observations from the alpha particle experiment.

Answer 15

The majority of alpha particles went straight though the gold. so atoms are mainly empty space.
Some alpha particles were defected by the gold foil. there must be something positive which contained the majority of the mass in an atom (the nucleus)
A tiny fraction of alpha particles bounced back where they came from. the nucleus must be a tiny part of the atom

Question 16

How can an unstable nucleus become more stable?

Answer 16

By giving out radiation (alpha, beta or gamma)

Question 17

Define activity

Answer 17

The rate at which a source of unstable nuclei decays

Question 18

State the units of activity

Answer 18

Becquerel (Bq)

Question 19

Define count rate

Answer 19

The number of decays recorded by a detector (GM tube)

Question 20

Describe a alpha particle

Answer 20

Two protons and two neutrons together. A helium nucleus

Question 21

Describe a beta partice

Answer 21

A fast moving electron ejected from the nucleus. This happens after a neutron has decayed into a proton

Question 22

Describe a gamma ray

Answer 22

An electromagnetic wave with no charge or mass.

Question 23

State the penetrating power of alpha, beta and gamma radiation.

Answer 23

Penetrating power is what can stop the radiation.
Alpha - skin, paper 5 - 10 cm of air
Beta - mm’s of aluminium, 1 meter of air
Gamma - reduced by cm’s of lead or m’s of concrete

Question 24

State the ionising ability of alpha, beta and gamma radiation.

Answer 24

Ionising ability is the ability to do damage to our living cells and tissues.
Alpha - highly ionising
Beta - moderately ionising
Gamma - very weakly ionising

Question 25

In decay equations what is the mass number and proton number for an alpha particle?

Answer 25

mass number = 4

proton number = 2

Question 26

In decay equations what is the mass number and proton number for a beta particle?

Answer 26

mass number = 0

proton number = -1

Question 27

In decay equations what is the mass number and proton number for a gamma wave?

Answer 27

mass number = 0

proton number = 0

Question 28

how can the rate of radioactive decay be increased?

Answer 28

It can be affected by physics quantities such as temperature or pressure. it is completely random.

Question 29

Define half life

Answer 29

The time taken for the number of radioactive nuclei in a sample to half.

Question 30

Define contamination

Answer 30

Unwanted presence of radioactive atoms on other materials such as clothes, buildings etc

Question 31

Define irradiation

Answer 31

The process of exposing an object to radiation. the object does become radioactive. e.g. killing bacterial on fruit to increase its shelf life.

Question 32

How should radioactive sources be used safely?

Answer 32

Use only for a short period of time.
Keep source at arms length
Point source away from yourself
Stored in a lead lined box with a radioactive symbol

Question 33

What is background radiation?

Answer 33

Radiation that is around us all the time

Question 34

State some sources of natural background radiation?

Answer 34

Rocks, cosmic rays, food

Question 35

State some sources of man made background radiation

Answer 35

X-rays, nuclear bombs, nuclear power stations