Topic 6- Radioactivity Flashcards
What happens when an electron changes orbit?
- if move further from nucleus, atom has absorbed EM radiation
- if electron falls to lower orbit (closer to nucleus), atoms has emitted EM radiation
- If electron gains enough energy, can leave atom to form an ion
What is an alpha particle?
- helium nucleus (two protons and two neutrons in nucleus)
- highly ionising
- weakly penetrating ( most dangerous in body)
What is a beta particle?
- two forms of beta decay, β⁻ decay & β⁺ decay,
- beta minus have electrons and beta positive have positrons
- medium ionising & medium penetration
What is gamma radiation?
- from radioactive decay of atomic nuclei
- short wavelength
- low ionising weak penetration
- short wavelength and high frequency
What is background radiation?
- ## Weak And natural radiation that can be detected from natural / external sources like rocks/space and the environment
Examples of background radiation
- Cosmic rays
- Radiation from underground rocks
- Nuclear fallout
- Medical ray
Ways to measure radioactivity
- photographic film
- Film goes darker when absorbs radiation – more radiation absorbed, darker it gets
- used as badges by people who work w/ radiation, check how much exposure they’ve had
Ways to measure radioactivity
- Geiger-Muller Tube
- tube can detect radiation
- when absorbs radiation, transmits electrical pulse to machine, produces clicking sound
- greater number of clicks the more radiation present
How does a beta minus and beta plus decay?
-beta minus
- neutron becomes proton– releases electron
beta plus
- proton becomes neutron – releases positron
What is a half- life?
- time taken for half the nuclei in a radioactive sample to decay
How do smoke alarms work?
-Americium is used in smoke alarms
▪It’s an alpha emitter
o so stopped by a few centimetres of air (as it’s weakly penetrating)
o alpha particles ionise air particles and makes them charged so making a current
o If smoke enters air around the alarm, the current drops in the circuit– causing alarm to sound
uses of radioactivity for irradiating food
- Gamma rays transfer energy to bacteria, killing them and sterilising food
o Also used to delay ripening of fruit
uses of radioactivity for sterilising equipment
- usually gamma, exposed onto equipment to kill all microbes present on equipment, so they’re safe for operations
using radioactivity to trace & gauge thickness
- Beta radiation is mildly penetrating, and can pass through paper
o source receiver placed either side of paper
▪ If there is a drop or rise in received electrons, means thickness of paper has changed – i.e. a defect in the production
o used inside pipes, w/ detector placed externally, to measure thickness of the walls
using radioactivity to diagnose & treat cancer
- gamma emitter, passes through body and external
detector can picture where the tracer has collected in the body, can reveal tumours
o Gamma rays used on tumour, to kill cancer cells - exposing rays on healthy cells can cause them to mutate or cause damage
Dangers of a short half-life
- does not remain strongly radioactive, but initially it’s very radioactive, but quickly dies down, so direct radiation exposure from decay is high and intense
o but presents less of a long-term risk
Dangers of long half-life
- remains radioactive for a long period of time
Differences in contamination and irradiation
- contamination lasts for a long time, irradiation does not last for a long time
- in contamination the source of the radiation is transferred to an object, in irradiation the source emits radiation which reaches the object
- in contamination radioactive dust settles on skin, contaminating it, in irradiation radioactive dusts emits beta radiation which irradiate the skin
External treatment of tumours
- beam of gamma radiation rotates around body
o continually focuses on tumour, only passes momentarily across healthy cells surrounding tumour
o ensures minimal damage on healthy cells, tumour is most affected
-takes long time to fully treat tumour, taking multiple visits
▪ greater risk of long-term side effects, as radiation passes
through healthy tissues
Internal treatment of tumours
- Radioactive material held within a needle, and injected directly into tumour
▪ longer period of time spent in hospital, some radioactive implants are of high radioactivity– you emit radiation
Uses of PET scanners in physics
- Radioactive tracer inserted into body
▪ tracer tagged to desired chemical, and tracer travels
in body where the chemical travels
o scanner records where tracer emits radiation
o produces 3D visualisation of the body
▪ Used to show how effective current treatment is
▪ Or to diagnose cancer, epilepsy, Alzheimer’s etc.
Describe the isotopes used in PET scans
- made locally, because tracer has short half life of 110 mins
What is nuclear fission?
- process of a nucleus splitting into two smaller nuclei after absorbing neutrons, which releases more neutrons
- can be a source of energy
What is radioactive decay?
- when an unstable nucleus decays into two smaller nuclei
- can be a source of energy
Describe nuclear power?
- Uranium fuel splits releasing neutrons, they’re absorbed by uranium nuclei, which split –nuclear fission in a chain reaction
- No carbon dioxide is produced
- safety risk of radiation leaking, or chain reaction become uncontrollable and causing a meltdown
Waste disposal in nuclear power?
- difficult – initially extremely hot, waste needs to be placed deep in ‘cooling ponds’ to cool down, before being stored deep underground
- can be used for nuclear warheads so is a terrorist risk
Describe U-235 in nuclear fission power plants
- absorbs neutrons, and becomes unstable
o causes it to undergo fission & release energy
▪ Forms two ‘daughter’ nuclei
• products are radioactive, they’re strong gamma emitters –some energy released from fission is held by the daughter nuclei
▪ Emitting two or more neutrons as well
What is a chain reaction?
- when a nucleus splits, emitting neutrons, & these neutrons cause further fissions, which release more neutrons
Moderators in a chain reaction?
- usually water/graphite, and slows down emitted neutrons to be absorbed for further fissions (fast moving neutrons cannot be easily absorbed)
Control rods in chain reactions
- boron rods in reactor core, absorbs excess neutrons,
preventing a runaway chain reaction
Unit of activity of a radioactive isotope
Becquerel (Bq)
What is the atomic number
The amount of protons and electrons (number on the bottom)
- smallest number
What is the atomic mass
Amount of protons and neutrons in the nucleus (number at the top)
Net decline equation
Initial no. - number after X half-lives / initial no.
Advantages of nuclear power for generating electricity
- nuclear fuels don’t produce Carbon dioxide
- doesn’t contribute to global warming
- fuel is readily available
Disadvantages of using nuclear power to generate electricity
- unpopular — seen as very dangerous
- expensive to commission and decommission stations
- radioactive waste is difficult to dispose and will remain radioactive for many years
Consequences of an uncontrolled chain reaction
-rate of fission becomes to high and results in the production of too much energy — can lead to a nuclear explosion
How’s electricity produced in a nuclear power station
- reaction releases thermal energy (heat)
- thermal energy (heat) is used to boil water and then produce steam
- steam’s then used to turn a turbine which starts the generator
