radioactivity

Question 1

nucleons

Answer 1

protons and neutrons are known collectively as nucleons

Question 2

ionisation

Answer 2

• the process of gaining or losing electrons

- can be cause by ionising radiation or in ionic bonding

Question 3

radioactive decay

Answer 3

• if a nucleus is unstable it will eventually emit radiation and decay
• Radioactive decay is random, as it is not possible to predict when an unstable nucleus will decay, and spontaneous, as it occurs without a trigger or cause

Question 4

alpha radiation

Answer 4

symbol: 𝛼 or He
nuclide notation: 4/2He or 4/2𝛼
nature: unstable nucleus emits 2 of its protons and 2 of its neutrons, bound together as a single particle
mass: 4 × proton mass
charge: +2
speed: approx 0.1c (c=speed of light)

Question 5

beta radiation

Answer 5

symbol: β- or e-
nuclide notation: 0/-1β or 0/-1e
nature: a neutron in the unstable nucleus transforms into a proton (which remains in the nucleus) and an electron (which is emitted as a beta particle)
mass: 1/2000 x proton mass
charge: -1
speed: approx 0.8c

Question 6

gamma

Answer 6

symbol: 𝛾
nuclide notation: 0/0 𝛾
nature: excess energy of the unstable nucleus is ejected in the form of gamma radiation
mass: 0
charge: 0
speed: c

Question 7

penetrating ability of alpha radiation

Answer 7

• least penetrating power
• blocked by a sheet of paper
• blocked by human skin
• can typically penetrate a few cm in air

Question 8

penetrating ability of beta radiation

Answer 8

• penetrating power > alpha but < gamma
• blocked by thin metal
• not blocked by human skin
• can penetrate up to several metres in air

Question 9

penetrating ability of gamma radiation

Answer 9

• most penetrating power
• blocked by several cm of very dense material e.g. lead
• can penetrate up to hundreds of metres in air

Question 10

count rate

Answer 10

-the number of radiation impacts detected by the counter per second

Question 11

ionising abilities of radiation types

Answer 11

alpha: most ionising, alpha particles have high momentum and +2 charge, so they are more likely to interact with atoms and cause ionisation
beta: intermediate, beta particles have lower momentum and a single -1 charge
gamma: least ionising, gamma rays have no charge/mass

Question 12

Effects of electric fields on:

Answer 12

alpha: deflected since charged bodies experience forces when in an electric field, deflected in opposite direction to beta particles due to having +ve charge, deflected less than beta particles as alpha particles are heavier
beta: deflected since charged bodies experience forces when in an electric field, deflected in opposite direction to alpha particles due to having -ve charge, deflected more than alpha particles as beta particles are lighter
gamma: not deflected since they have no charge

Question 13

effects of magnetic fields on:

Answer 13

alpha: deflected since moving charges experience forces when in a magnetic field, deflected in opposite direction to beta particles, deflected less than beta particles, because of their much lower mass
beta: deflected since moving charges experience forces when in a magnetic field, deflected in opposite direction to alpha particles, deflected more than alpha particles as beta particles are lighter
gamma: not deflected since they have no charge

Question 14

background radiation

Answer 14

• there is always ionising radiation present at a low level in the environment
• most of it is naturally occurring, some is from human activities
• count rate from source only = count rate measured - background count rate
• from a graph, background count can be determined by finding the rate after the radiation from the source has died away (the end of the curve)

Question 15

hazards of alpha radiation

Answer 15

• inside the body: most hazardous as alpha radiation is highly ionising and will damage nearby cells
• outside the body: not hazardous, because alpha particles cannot penetrate the skin

Question 16

hazards of beta radiation

Answer 16

• inside the body: less hazardous than alpha as it is less ionising, but will still cause some cell damage
• outside the body: hazardous, as beta particles can penetrate the skin and damage the tissue underneath

Question 17

hazards of gamma radiation

Answer 17

• inside the body: less hazardous than alpha and beta as it is less ionising, and much of it will pass straight through cells without damaging them
• outside the body: hazardous, because gamma rays can easily penetrate the skin and cause damage anywhere in the body

Question 18

half life

Answer 18

• the average time taken for half of the nuclei in a sample of an isotope to decay, AND
• the average time taken for the count rate of a sample of an isotope to halve
• the 2 definitions both yield the same time, since the count rate is proportional to the no. of unstable nuclei remaining
• unaffected by the sample size, or the % of nuclei that have already decayed

Question 19

positron beta decay

Answer 19

• a proton turns into a neutron and emits a fast-moving positron
• atomic number decreases by 1
• mass number remains the same

Question 20

activity formula

Answer 20

activity = decay constant x number of remaining atoms

Question 21

radiation definition

Answer 21

the emission of energy via waves or particles