Nuclear Physics

Question 1

What is the radius of an atom?

Answer 1

1 × 10^−10 m

Question 2

Provide some evidence for the distribution of mass in the atom

Answer 2

Scattering of alpha particles by thin metal foil

Question 3

What happens to an electron if it gains energy by absorbing EM radiation?

Answer 3

They can move to higher energy level = further away from nucleus

Question 4

What happens to an electron if it releases EM radiation?

Answer 4

It will move to lower energy level = that’s closer to nucleus

Question 5

What happens if one or more electrons leaves an atom?

Answer 5

Atom becomes positively charged ion

Question 6

What is an isotope?

Answer 6

Atoms with same no. of protons (same atomic number & same charge on nucleus) BUT different no. of neutrons (different mass number)

Question 7

Do all elements have isotopes?

Answer 7

Yes

Question 8

How many roughly stable isotopes do each element have?

Answer 8

1-2

Question 9

What is radioactive decay?

Answer 9

When unstable isotopes decay into other elements & give out radiation as they try to become more stable

Question 10

What can unstable isotopes also release when they decay?

Answer 10

Can release neutrons (n)

Question 11

What is ionising radiation?

Answer 11

Radiation that knocks electrons off atoms, forming positive ions

Question 12

What does the ionising power of a radiation source mean?

Answer 12

How easily it can knock electrons off atoms (forming positive ions)

Question 13

What do radiation substances release?

Answer 13

Radioactive substances spit out one or more types of ionising radiation (e.g. beta, gamma, alpha)

Question 14

Where is radiation given off in a radioactive substance

Answer 14

From the nuclei of their atoms

Question 15

Why can’t you predict exactly which nucleus in a

sample will decay next, or any one of them will decay?

Answer 15

Radioactive decay is entirely random

Question 16

How can radiation can be measured?

Answer 16

By using a Geiger-Muller tube and counter

Question 17

How does Geiger-Muller tube and counter measure radiation?

Answer 17

Records the count-rate i.e. Number of radiation counts reaching it per second

Question 18

What can half-life be used for?

Answer 18

Used to find rate at which a source decays - its ACTIVITY

Question 19

What is activity measured in?

Answer 19

Becquerels, Bq (where 1 Bq is 1 decay per second)

Question 20

Each time radioactive nucleus decays (to become stable nucleus), what happens to its activity?

Answer 20

Its activity as a whole will decrease

Question 21

Do older sources emit more or less radiation?

Answer 21

Older sources emit less radiation

Question 22

Why can’t we measure how long exactly it will take for a nucleus to decay?

Answer 22

The activity never reaches 0

Question 23

What is half-life?

Answer 23

• The time taken for the number of radioactive nuclei in an isotope to halve
• The time it takes for the count rate from a sample containing the isotope to fall to half its initial level

Question 24

What does it mean if a source has a short half-life?

Answer 24

The activity will fall quickly

Question 25

Why would a source have a short half-life?

Answer 25

Because nuclei are very unstable and rapidly decay

Question 26

Why are sources with short half-life dangerous?

Answer 26

Because they emit a high amount of radiation at start

Question 27

What is good thing about sources with a short half-life

Answer 27

Can quickly become safe

Question 28

What does it mean if a source has a long half-life?

Answer 28

Its activity falls more slowly = releases small | amounts of radiation for long time

Question 29

Why would a source have a long half-life?

Answer 29

Because most of nuclei don't decay for a long time

Question 30

Why are sources with long half-life dangerous?

Answer 30

Nearby areas are exposed to radiation for (millions of) years

Question 31

What do nuclear equations show?

Answer 31

Are a way of showing radioactive decay by using element symbols

Question 32

What is the form nuclear equations are written in?

Answer 32

atom before decay → atom(s) after decay + radiation emitted

Question 33

What is the golden rule to remember when writing nuclear equations?

Answer 33

The total mass and atomic numbers must be equal on both sides

Question 34

What happens to an atoms atomic number and mass number when it emits an alpha particle?

Answer 34

Its atomic number reduces by 2 and its mass number reduces by 4

Question 35

Why does the charge of the nucleus decrease when an atom emits an alpha particle?

Answer 35

Its atomic number reduced by 2 = a proton is positively charged and a neutron is neutral

Question 36

How can an alpha particle be written as in a nuclear equation?

Answer 36

As a helium nucleus - see mind map for answer

Question 37

Write out the nuclear equation for Uranium-238 which gives off thorium-234 and an alpha particle

Answer 37

See mind map for answer

Question 38

What happens to an atom when beta decay occurs?

Answer 38

A neutron in nucleus turns in a proton and releases a | fast-moving electron (beta particle)

Question 39

Why does the charge of the nucleus increase (become positive) when an atom emits a beta particle?

Answer 39

The number of protons in nucleus has increased by 1

Question 40

Why does the mass of the nucleus not change during beta decay?

Answer 40

Because the nucleus has lost a neutron and gained a proton during beta decay ∴ mass of nucleus doesn't change (protons and neutrons have same mass)

Question 41

How can a beta particle be written as in a nuclear equation?

Answer 41

See mind map for answer

Question 42

Write out the nuclear equation for Carbon-14 which gives off nitrogen-14 and a beta particle

Answer 42

See mind map for answer

Question 43

How does a nucleus get rid of excess energy?

Answer 43

By releasing it as gamma rays

Question 44

Do gamma rays change the atomic mass or atomic number of an atom?

Answer 44

No

Question 45

How can gamma radiation be written as in a nuclear equation?

Answer 45

See mind map for answer

Question 46

Practice Question on Half-life: The initial activity of a sample is 640 Bq. Calculate the final activity as a percentage of the initial activity after 2 half-life.

Answer 46

= 25% (see mind map for working out)

Question 47

What are alpha particles?

Answer 47

Helium Nuclei

Question 48

What is alpha radiation?

Answer 48

When an alpha particle (α) is emitted from nucleus

Question 49

What is an α-particle made up of (i.e. its no. of neutrons and protons)?

Answer 49

2 neutrons and 2 protons (like a helium nucleus)

Question 50

What is the charge of an alpha particle?

Answer 50

2+

Question 51

How far can an alpha particle travel in air?

Answer 51

Only can travel a few cm in air

Question 52

What will absorb an alpha particle?

Answer 52

A sheet of paper

Question 53

How ionising are alpha particles and why?

Answer 53

Strongly ionising because of their size

Question 54

Give an example how alpha radiation can be used in a home

Answer 54

Alpha radiation can be used in a smoke detector. It ionises the air particles, causing current to flow. If there's smoke in the air, it bind to the ions = meaning current stops and the alarm sounds.

Question 55

What is a beta particle?

Answer 55

Beta particle (β) is a fast-moving electrons released by nucleus

Question 56

How much mass does a beta particle have?

Answer 56

Virtually has no mass

Question 57

What is the charge of a beta particle?

Answer 57

Charge of -1

Question 58

How ionising are beta particles?

Answer 58

Moderately ionising

Question 59

How far can a beta particle travel in the air?

Answer 59

A few meters

Question 60

What will absorb a beta particle?

Answer 60

A sheet of aluminium (around 5 mm thick)

Question 61

How can beta radiation be used (if a beta particle is moderately penetrating)?

Answer 61

Beta emitters are used to test the thickness of sheets of metal as particles are not immediately absorbed by material (like alpha radiation & do not penetrate as far as gamma rays). ∴ Slight variations in thickness affect the amount of radiation passing through the sheet.

Question 62

What are gamma rays (γ)?

Answer 62

Waves of electromagnetic radiation released by nucleus

Question 63

What the penetration of gamma rays and how far will it travel in the air?

Answer 63

They penetrate far into materials without being stopped and will travel a long distance through air

Question 64

What is a gamma ray's charge?

Answer 64

Has no charge

Question 65

How ionising are gamma rays and why?

Answer 65

Weakly ionising because they tend to pass through rather than collide with atoms

Question 66

What will absorb a gamma ray?

Answer 66

Absorbed by thick sheets of lead or meters of concrete