07 Radioactivity And Particles Flashcards
Proton relative charge, relative mass and location
Relative charge = +1
Relative mass = 1
Location = nucleus
Neutron relative charge, relative mass and location
Relative charge = 0
Relative mass = 1
Location = nucleus
Electron relative charge, relative mass and location
Relative charge = -1
Relative mass = 1/1835
Location = shells around nucleus
Atomic number
Small number
- number of protons
Mass number
Large number
- protons + neutrons
Number of neutrons =
Mass number - atomic number
Isotope
Elements with same number of protons but different number of neutrons
- so it has different mass number
What happens when a nucleus is unstable
- it tries to become more stable by ejecting mass (beta/alpha) or energy (gamma)
- the atoms are radioactive
- process of ejecting is called decay
Decay is
Random
Alpha radiation
Helium nucleus emitted from nucleus
- 2 protons 2 neutrons
Beta radiation
Electron emitted from nucleus
Gamma radiation
High energy electromagnetic wave
Alpha ionising and penetration
- very ionising
- low penetration (stopped by paper)
Beta ionising and penetration
- moderate ionisation
- moderate penetration (stopped by aluminium)
Gamma ionising and penetration
- not very ionising
- very penetrating (stopped by lead)
Practical: investigate penetration powers of different types of radiation using radioactive sources
- measure background count for 2 mins using Geiger-Muller (GM) tube and stopwatch —> with no radioactive sources present
- set up source 2cm away from GM tube
- record counts detected from source with no absorbing materials for 5 mins
- place paper between ionising radiation source and GM tube and record counts detected for 2 mins
- repeat with aluminium and lead and record counts
Why do you measure count for at least two minutes
To collect avg value since decay of unstable atoms is RANDOM
Alpha effect on mass/atomic number
4
2
Beta effect on mass/atomic number
0
-1
Gamma effect on mass/atomic number
0
0
Neutron effect on mass/atomic number
1
0
How does GM tube detect ionising radiation
- detects when gas in chamber is ionised by radiation
- every beep is one incidence on radiant (could be gamma/beta/alpha)
How does photographic film detect ionising radiation
When radiation comes into contact with photographic film it DARKENS
- shows presence of radiation
Origins of background radiation
Food and drink
Nuclear power
Medical
Radon gas
Cosmic rays
Food and drink origin
Food and drink: radioactive isotopes decay over time
Nuclear power origin
Nuclear power: from power stations/bombs
Medical origin
Medical: x-rays/gamma ray scans/sterilisation/ cancer treatments
Radon gas
Radon gas: produced by rocks contains small amounts of uranium
Cosmic rays origin
Cosmic rays: radiation from space which is produced in stars
Activity of a sample of radioactive isotopes is measured of
How many radioactive decays happen over a period of time
What is activity of radioactive isotopes measured in
Becquerels (Bq)
Activist of a radioactive source ___ over time
Decreases
Half life
Time taken for half of undecayed nuclei to decay
Half life =
Time taken for activity to half its original value
Large samples of SAME radioactive substance have
Same half life
How to find number of undecayed nuclei in sample
State start number
Go forward half life (divide by 2) and days stated
Repeat until target time passed
Age os isotope
Total number in current sample
Go back half life (x2 sample size)
Repeat until all of sample is radioactive isotope
Smoke detector using radioactivity
- source gives off alpha particles which ionises air particles
- air particles carry current across gas
- when theres smoke the smoke absorbs ions created by source
- alarm sounds when current falls/drops
Use of radioactivity in irradiating food/sterilising equipment
- ionising radiation kills small cells like bacteria
In food gamma rays are used to kill bacteria —> last longer and is safe to eat
In medicine gamma rays kills bacteria on plastic equipment —> sterile and safe to use
Use of radioactivity in gauging thickness
- beta radiation fired through paper/plastic sheets
- amount of radiation passed through is sent to computer
Too much radiation —> paper too thin —> computer tells rollers to move apart
Uses of radioactivity in tracing
Radioactive sources (gamma) added to water supplies to detect leaks
Where water is leaking —> more water —> more radiation
- detected above ground to find leaks without digging
Uses of radioactivity in treatment/diagnosis of cancer
- consume/inject gamma emitter —> passes through body and an external detector than pictures where the tracer has collected in body
- reveals tumours
- gamma is detected since it can pass through skin and tissues
- ionising radiation used on tumour kills cancel cells from outside or inside body
Ions in DNA can cause
Mutations -> result in cell damage or death
Precaution to reduce risk of harm when using radioactive sources
- source shielded when not in use (lead-lined box)
- protective clothing to prevent body contamination
- limiting exposure time with materials
- use tongs to increase distance
- monitor exposure using detector badges
Irradiation
When someone is exposed to alpha/beta/gamma from nearby source
- once they move away irradiation stops
Contamination
Someone gets particles of radioactive source on them or inside their body
- they continue to be posed to radiation until material has all decayed or it is removed
Nuclear waste but be stored in
Sealed containers capable of containing radioactivity for long periods of time
- since they have very long half lives
Danger of radiation
Mutations in living organisms
Damage cell and tissue
Heavy nuclei (e.g. Uranium 235) can be fissioned
- large nucleus absorbs a neutron making it unstable
- nucleus splits (fission)
- energy released as KE of fission products
Products of fission of U-235
- 2 radioactive daughter nuclei and smaller nuclei that are not always identical to each other
- small number or neutrons
Combines atomic mass of daughters and neutrons equal parent
Chain reaction
Extra neutrons at end can induce fission in other atoms
When a coil of wire is toasted in magnetic field it
Induces a voltage
- energy produced from fission is used to make electricity
Neutrons are released in
Chain reaction
Slower neutrons needed for
Fission
Graphite core around reactor in moderator for fission process
Neutrons in moderator are slowed down
- increases rate of fission
Control rods in fission process
Control rods absorb neutrons
Control rods can be moved in and out of reaction —> more or fewer neutrons available
- increases or decreases rate of fission
Reactor vessels made of
Steel
Why is reactor vessels surrounded by concrete in nuclear reaction
Shielding of 5 metres prevents radiation escaping, even neutrons
Fusion
Process of small nuclei forced together to form heavier nucleus
Fusion is energy source for
Stars
Fusion cannot happen at
Lower temp and pressures
Fusion is difficult to make a
Practical fusion power station
Fusion explained
- 2 smaller particles join to form a larger one
- More massive particles are less massive than sum of small parts
- mass becomes energy which is released in fusion
Conditions for fusion and why
VERY high pressure/temp/KE
- needed to overcome electrostatic repulsion between nuclei
Fission reactions used in
Nuclear power stations and submarines
Fusion reactions release energy
Inside stars - unable to generate on earth
Radioactive decay
Processes where unstable nucleus loses energy by emitting ionising particles and radiation
