Alpha, Beta, Gamma Radiation

Question 1

Which ionizing radiation produces the greatest number of ion pairs per mm in air

Answer 1

alpha particles

Question 2

What is the typical maximum range in air for alpha and beta particles in metres

Answer 2

alpha - 0.04m

beta - 0.4m

Question 3

Gamma rays have a range of at least 1km in air.
However a gamma ray detector placed 0.5m from a gamma ray source detects a noticeably smaller counter-rate as it is moved a few centimeters further away from the source

Explain this observation

Answer 3

• Inverse square law of gamma radiation

Question 4

Explain the most hazardous aspect of the presence of dust contaminated with an alpha emitter to an unprotected human entering the room

Answer 4

Dust may be ingested causing cells to be damaged

Question 5

Give two sources of background radiation

Answer 5

Rocks
Cosmic rays
Nuclear waste

Question 6

Describe how you would perform an experiment that demonstrates that gamma radiation obeys an inverse square law

Answer 6

GM tube + counter
Measurement of count rate at range of distances + ruler
Suitable range
Determine background radiation and subtract from reading
Safety precautions
Graph of corrected count rate against 1/d^2

Question 7

Explain why gamma radiation obeys an inverse square law but alpha and beta radiation does not

Answer 7

Gamma not absorbed
Spreads uniformly from a point
Area over which it spreads is proportional to radius squared
Alpha and beta are absorbed in addition to spreading out

Question 8

Type of decay Change in mass number
Change in proton number
Change in neutron number

Answer 8

Alpha: -2p-2n = -4
-2p -2n

Beta minus: +1p-1n = 0 n–>p = +1p
n–>p = -1n

Beta plus: -1p+1n=0
p–>n = -1p
p–>n = +1n

Gamma: No change No change
No change

Electron capture: -1p+1n = 0
p–>n = -1p
p–>n = +1n

Question 9

A nuclide AXZ contains how many protons and neutrons, has what charge and has what mass

Answer 9

A-Z neutrons, Z protons

Charge = +Z*e where e is the charge of a proton

Mass = A*u where u is the atomic mass unit

Question 10

Atomic number =

Answer 10

nucleon number = protons + neutrons

Question 11

Radioactive/unstable atoms are trying to become more stable by trying to

Answer 11

obtain a lower energy level

Question 12

What holds the protons and neutrons together in the nucleus

Answer 12

the SNF

Question 13

Types of radiation and what they release (3)

Answer 13

1) Alpha - releases a helium nuclei
2) Beta - releases an electron
3) Gamma - releases a photon/gamma ray

Question 14

Describe the composition and nature of alpha decay

Answer 14

+vely charged alpha particles composing of two protons, two neutrons and zero electrons meaning it is strongly ionising with other atoms making it dangerous as it can damage living cells.
High kinetic energy but slow moving

Question 15

Alpha particle + 2 free electrons =

Answer 15

Helium nucleus (2p 2n) + 2 electrons = helium atom

Question 16

Alpha decay equation

Answer 16

XAZ –> (X-4)B(Z-2) + 4a2

number of protons changes so new element

Question 17

Alpha decay only happens in

Answer 17

very heavy atoms as their nuclei are too massive to be stable

Question 18

Explain what happens to the distribution of kinetic energy in alpha decay

Answer 18

The nucleus recoils when the alpha particle is emitted so the kinetic energy is shared between the alpha particle and the nucleus in inverse proportion to their masses.

Question 19

What happens to an alpha particle in a magnetic field

Answer 19

Slight deflection due to the positive charge caused by the two protons and zero electrons

Question 20

Beta minus particle equation

Answer 20

n –> p + e + electron antineutrino

Question 21

Beta plus particle equation

Answer 21

p –> n + e+ + ve

Question 22

What is beta decay, when does it happen and what happens

Answer 22

beta decay occurs in a neutron-rich (no. neutrons > no. protons) isotope and occurs when a neutron changes to a proton and an electron antineutrino is emitted as the electron is ejected.

Question 23

Beta minus decay equation

Answer 23

AXZ –> AY(Z+1) + 0B(-1) + electron antineutrino

Question 24

A negative beta particle is represented as 0b(-1) because

Answer 24

it has a charge of -e

Question 25

A beta emission makes the nucleus _____ neutron-rich causing it to

Answer 25

less

become more stable i.e. nearer the stability line

Question 26

A positive beta particle is represented as 0b(+1) because

Answer 26

it has a charge of +e

Question 27

Describe beta plus decay

Answer 27

a proton in a proton rich nucleus changes into a neutron and an electron neutrino is emitted as the positron is created.

Question 28

Beta plus decay equation

Answer 28

AXZ –> AY(Z-1) + 0B(-1) + ve

Question 29

Beta deflection in magnetic field

Answer 29

a lot of deflection (in the opposite direction to an alpha particle) as very fast moving

Question 30

Positron naturalness

Answer 30

proton-rich nuclei are not naturally occurring radioactive substances and are created when high energy protons collide with nuclei and so positron decay is artificial

Question 31

Why doesn’t positron decay occur after alpha decay

Answer 31

because it makes the nucleus more neutron rich therefore more unstable

Question 32

How is (kinetic) energy distributed in beta decay

Answer 32

the nucleus, the beta particle and the antineutrino - the kinetic energy of the antineutrino is negligible when the electron has maximum kinetic energy This maximum kinetic energy is < than the energy released because the nucleus recoils in the opposite direction with kinetic energy.

Question 33

How was the wavelength of the photons in gamma radiation discovered

Answer 33

Photons with wavelength < 0.1nm shown via diffraction of gamma radiation through crystals

Question 34

Gamma photons are emitted from excited nuclei with energies of the order

Answer 34

1MeV

Question 35

2 properties of gamma decay

Answer 35

• no change in nucleon/atomic number
• nucleons fall together (due to the SNF) making it more stable
• decrease in potential energy of the nucleus makes energy available to the surroundings so high energy photons/EM waves are emitted to conserve energy

Question 36

Gamma ray deflection in magnetic field

Answer 36

no deflection as chargeless

Question 37

One ways gamma rays are produced (not e capture)

Answer 37

After alpha or beta emission or electron capture, the daughter may be formed in an excited state leading to the emission of a gamma photon allowing the nucleus to lose energy. The excited state is usually short-lived and the nucleus moves to its lowest energy state, its ground state can be represented by an energy level diagram.

Question 38

What is electron capture and how can it produce a gamma ray

Answer 38

Electron capture is where a proton-rich nucleus captures an inner shell electron that interacts with a proton forming a neutron making the nucleus unstable causing it to emit a neutrino which carries away the energy released in the decay. A gamma ray is then emitted when the inner-shell vacancy is filled upon de-excitation.

Question 39

Electron capture particle equation

Answer 39

p + e –> n + ve + y

Question 40

Electron capture decay equation

Answer 40

e + AXZ –> AY(Z-1) + ve