SP6 Radioactivity Flashcards
What is an atom?
A positively charged nucleus containing protons and neutrons with smaller, negatively charged electrons surrounding it
What defines an element?
The number of protons present in the nucleus
What is the atomic number?
The total number of protons present in the nucleus
What is the mass number?
The total number of protons and neutrons in an atom’s nucleus
What did the Greeks think matter was made up of?
Millions of tiny uncuttable pieces of the same matter
Who created the plum pudding model?
J.J Thompson
When was the plum pudding model created?
1897
Describe the plum pudding model
An atom consisted of a ‘positive’ dough with negative electrons stuck in it
Describe the experiment that lead Rutherford to discover the atom’s nucleus
- He directed a beam of alpha particles at a thin gold foil suspended in a vacuum
- Most alpha particles went straight through—> established that atoms are mostly empty space
- a small number of alpha particles were deflected—> shows the concentration of positive charges in the nucleus
- tiny number of particles shot back—> reveals that the charge and the mass was concentrated in the nucleus
What are isotopes?
Atoms of the same elements with the same amount of protons in the nucleus but different quantities of neutrons
What are ions?
Atoms which have lost or gained electrons
What type of ion does an atom become when it loses an electron
- positively charged- cation- because there are more protons than electrons
What type of ion does an atom become when it gains an electron
- negatively charged- anion- because there are more electrons than protons
When does an electron jump to a higher orbit?
When it has absorbed EM radiation
When does an electron fall to a lower orbit?
When it has emitted EM radiation
What happens when an electron changes position within its orbits?
It produces light
What is the difference between an emission and absorption spectrum?
Emission spectrum: light emitted by the electron is displayed
Absorption spectrum: light absorbed by the electron is displayed
What is ionising radiation?
Radiation that can cause an ion to form
What is background radiation?
Weak radiation that can be detected from natural/ external sources
What are some examples of background radiation?
- cosmic rays
- radiation from underground rocks
- nuclear fallout
- medical rays
What are the ways of measuring radioactivity?
- photographic film
- Geiger-muller tube
Describe how to measure radioactivity using the photographic film
- film that goes darker when it absorbs radiation
- the more radiation it absorbs, the darker it gets
- worn as badges by people who work with radiation to check the amount of exposure they’ve had
Describe how to measure radioactivity through a Geiger-Muller tube
- Each time the tube absorbs radiation, it transmits an electrical impulse
- This produces a clicking sound
- The greater the number of clicks per second, the more radiation is present
- this is called the count rate
What are the four types of radiation?
- alpha decay
- beta minus decay
- beta plus decay
- neutron emission
Describe what occurs in alpha decay
If the nucleus is unstably large, it will emit a ‘package’ of two protons and two neutrons called an alpha particle—> causes the mass number to decrease by four—> highly ionising—> weakly penetrating
Describe what occurs in beta minus decay
- If the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving electron
- the electron produced is ejected at high speeds and carries away a lot of energy
- causes the atomic number to increase by one but the mass number remains the same
- medium ionising
- medium penetration
Describe what occurs in beta plus decay
- If a nucleus doesn’t have enough neutrons, a proton will turn into a neutron and emit a fast-moving positron
- causes the atomic number to decrease by one but the mass number remains constant
- medium ionising
- medium penetration
Describe what happens in neutron emission
- A neutron is emitted through radioactive decay
- causes the mass number to decrease by one but the atomic number remains the same
Order the types of radiation in terms of their ionising power from the least penetrating to the most
Alpha, beta, gamma ray
Describe the ionising power of alpha decay
- will travel a few cm in air- very ionising - can be stopped by a sheet of paper
Describe the ionising power of beta particles
- will travel a few metres in the air- moderately ionising- can be stopped by 3mm thick aluminium
Describe the ionising power of gamma rays
- will travel a few km in air- weakly ionising- needs thick lead/ several metres of concrete to stop it
What is nuclear activity?
- the number of decays in a sample per second
- initially very high but decreases exponentially over time
- measured in becquerels
What is half-life?
Time taken for half the nuclei in a sample to decay
What affects radioactive decay?
The stability of a nucleus, the more stable a nucleus, the lower its activity
What can radioactivity be used for?
- irradiation
- in smoke alarm
- to monitor thickness of paper
Describe irradiation
Irradiation is exposing objects to beams of radiation. If a source has been irradiated using radioactive decay it can damage living cells
Give an example of how irradiation is used in real life
- It can be used to preserve fruit sold in supermarkets by exposing the fruit to a radioactive source
- This will destroy any bacteria on the fruit without changing the fruit significantly
- Doctors can also use irradiation to sterilise equipment
- the process of irradiation doesn’t cause the irradiated object to become radioactive
What are the advantages of irradiation?
- Sterilisation can be done without using high temperatures- can be used to kill bacteria on things that would melt
What are the disadvantages of irradiation?
- may not kill all the bacteria on the object- can be harmful: standing in an environment here irradiation is occurring could expose people’s cells to damage and mutation
How does a smoke alarm use radioactivity?
- measures the movement of alpha particles across a small gap
- if smoke enters the detector, it will absorb the particles and the detector will measure a drop in the number getting across the gap
- this will trigger a sound
- americium is used in smoke alarms as it is weakly penetrating
How is radioactivity used in monitoring thickness of paper?
- beta radiation is mildly penetrating and can just pass through paper
- a source and a receiver are placed on either side of the paper during its production
- if there is a drop/ rise in the received electrons, that means that the thickness has changed and there is a defect in the production
What is contamination?
If an object has radioactive material introduced to it
What is the difference between contamination and irradiation?
- Irradiation occurs when an object is exposed to a source of radiation outside the object- Contamination occurs when the radioactive source is on or in the object- irradiation stops as soon as the source is removed, whereas if an object has become contaminated, the radiation can’t be blocked
How do we reduce the risk of radiation from radioactive sources?
- holding the source with tongs
- storing the source in lead lined containers
How can we reduce the risk of radiation in hospitals?
- shielding the source
- maintaining distance from the source
- minimising time spent with source
How can radiation be used in the medical field?
- Gamma rays can be used to do a variety of things:—> kill cancerous tumours deep inside the body—> used to detect tumours—> tracers to make soft tissues show up through medical imaging processes- PET scanners
How do PET scanners work?
- Radioactive tracer is inserted into the body. The tracer is tagged to the desired chemical and the tracer therefore travels alongside the chemical
- the scanner records where the tracer emits radiation
- this produces a 3d visualisation of the body
Where are the isotopes for the PET scanner made and why?
In the hospital because they have a short half-life
What are the two types of nuclear reactions that are used as a large-scale energy source?
- nuclear fission: large nuclei break up to form smaller nuclei and release energy
- nuclear fusion: two small nuclei fuse together to form a larger nucleus
What are the safety risks of nuclear fission?
- radiation leaking- chain reaction becoming uncontrollable + causing a meltdown
Which type of large scale energy source can be used by humans on Earth?
Nuclear fission
What are the disadvantages of nuclear fission?
- security risk: can be used by terrorists
- safety risk: hazard of leaking or having a meltdown
- negative public perception
- tricky waste disposal
Describe a nuclear fission reaction
- slow-moving neutron is absorbed into an unstable nucleus (typically uranium-235)
- the entire nucleus splits into two large fragments called ‘daughter nuclei’
- Two or three neutrons also explode out of the fission reaction
- exploded neutrons collide with other uranium nuclei causing a chain reaction
What are the parts of a fission reactor?
- nuclear fuel- moderator- control rods- coolant- concrete shield
What does the nuclear fuel do in a fission reactor?
- provides energy for the reaction- held in rods so that the neutrons are released will fly out and cause nuclear fission in other rods
What is the role of the moderator in a fission reactor and how is it adapted to its role?
- slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod
- it has a graphite core
What is the role of the control rods in a fission reactor?
- raised and lowered to stop neutrons from travelling between fuel rods- change the speed of the chain reaction
What is the role of the coolant in a fission reactor?
- heated up by the reactions
- used to boil water to drive turbines in the power stations
What is the role of the concrete shield in a fission reactor?
The daughter products of fission reaction are radioactive and can be a hazard
Describe what occurs in nuclear fusion
When two small, light nuclei join together to make one heavier nucleus
Where does nuclear fusion occur?
In stars such as our sun
How is energy generated through nuclear fusion?
When the nuclei join together, some of the mass is lost and instead converted into energy, which is radiated by stars
Why don’t we use nuclear fusion as an energy source on Earth?
The electrostatic repulsion of hydrogen protons in the two different nuclei means that a lot of energy is required to overcome said forces and overcome this repulsion. This energy is present in stars at high temperatures and pressureAlthough this could be recreated on Earth, it wouldn’t be practical
