radioactivity Flashcards
What are atoms considered to be?
The building blocks of all matter
What is located at the center of an atom?
nucleus
What particles orbit around the nucleus of an atom?
Electrons
What is the relative atomic mass of protons?
One unit
What particles are found in the nucleus of an atom?
- Protons
- Neutrons
What is the charge of a neutron?
No charge
What is the total charge in an atom?
Zero
What happens when an atom loses electrons?
It is said to be ionised
What does nuclear notation describe?
Particular nuclei by their element symbol, atomic number, and mass number
What is the atomic number of an element?
The number of protons in an atom
Why is the atomic number important?
It determines which element an atom is
What is the mass number of an atom?
The total number of particles (protons and neutrons) in the nucleus
How can the number of neutrons be calculated?
Mass number - atomic number
What is an isotope?
An atom of the same element with an equal number of protons but a different number of neutrons
What is an example of an unstable isotope of carbon?
Carbon-14
What are the three types of radiation emitted from unstable nuclei?
- Alpha (α) particles
- Beta (β) particles
- Gamma (γ) radiation
What is radioactive decay?
The process by which unstable nuclei emit radiation to become more stable
What is the nature of alpha particles?
They are the same as a helium nucleus
What are beta particles?
High-energy electrons produced when a neutron changes into a proton and an electron
What type of radiation has the highest energy?
Gamma rays
What is the penetrating power of alpha radiation?
Stopped by paper
What is the penetrating power of beta radiation?
Stopped by a few millimeters of aluminum
What is the penetrating power of gamma radiation?
Partially stopped by thick lead
What is the purpose of the Geiger-Muller tube in radiation experiments?
To measure the count rate of a radioactive source
Fill in the blank: The total number of protons and neutrons in an atom is called its _______.
Mass number
True or False: The mass number is equal to the number of protons plus the number of electrons.
False
What must be equal for an atom to have no overall charge?
The number of protons and electrons
What is the purpose of taking readings with absorbers in radiation experiments?
To determine the type of radiation emitted by a source based on the reduction in count rate
What type of radiation is indicated if the count rate reduces when paper is present?
Alpha radiation
What does it suggest if the count rate reduces with a few mm of aluminium present?
Beta radiation
If some radiation can penetrate a few mm of lead, what type of radiation is being emitted?
Gamma radiation
What should be ensured to avoid systematic errors during radiation experiments?
Sources must be stored away from the counter and experiments should be conducted in the same location
What can improve the accuracy of radiation experiments?
Using reliable sources with a long half-life and activity above natural background levels
What is a key safety consideration when handling radioactive sources?
Use tweezers or tongs and keep a distance from the source
What does the acronym SCREAMS stand for in the context of conducting experiments?
- S: Same variable kept constant
- C: Variable changed
- R: Reliability measures
- E: Equipment and equations used
- A: Result analysis
- M: Measured variable
- S: Safety precautions
What happens during alpha decay?
An alpha particle is emitted, forming a new element and decreasing both mass and atomic numbers
What is an alpha particle composed of?
2 protons and 2 neutrons
In alpha decay, how are the mass number and atomic number affected?
Mass number decreases by 4 and atomic number decreases by 2
What occurs during beta decay?
A neutron changes into a proton and an electron, emitting the electron
How does beta decay affect the mass number and atomic number?
Mass number remains the same; atomic number increases by 1
What is emitted during gamma decay?
A gamma ray
How does gamma decay affect the atomic and mass numbers?
Neither the mass number nor the atomic number changes
What is neutron emission?
A process where a nucleus emits a neutron, decreasing the mass number by 1 without changing the atomic number
How is a decay equation structured?
It shows particles before the decay on the left and particles produced after the decay on the right
What is background radiation?
The radiation that exists around us all the time from natural sources
Name two natural sources of background radiation.
- Radon gas
- Cosmic rays from space
What are artificial sources of background radiation?
- Nuclear medicine
- Nuclear waste
- Nuclear fallout
- Nuclear accidents
How can background radiation be accounted for in laboratory readings?
By measuring the count rate with no radioactive source and subtracting it from the total count rate
What does a Geiger-Müller tube measure?
Radiation by counting decays and transmitting pulses to a counting machine
What happens to photographic film when it absorbs radiation?
It becomes darker upon development
What is the significance of the corrected count rate?
It provides an accurate measurement of radiation by accounting for background radiation
Fill in the blank: The atomic number decreases by _____ during alpha decay.
2
Fill in the blank: During beta decay, the atomic number increases by _____
1
True or False: Gamma decay results in a change in the mass number of the nucleus.
False
What is the corrected count rate?
The count rate measured with a radioactive source present, minus the background count rate
This calculation helps isolate the radiation from the source being studied.
How can the background count rate be measured?
Using a Geiger-Müller (GM) tube with no source present
This provides a baseline measurement of radiation in the environment.
If a Geiger counter records 24 counts in 1 minute without a source, what is the background radiation count rate in counts per second?
0.4 counts per second (cps)
Calculation: 24 counts per minute / 60 seconds = 0.4 cps.
What is the formula to find the corrected count rate when a source is present?
Count rate of the source - Background count rate
This helps in determining the actual radiation from the source.
What would be the corrected count rate if a Geiger counter records 285 counts in 1 minute with a source present and the background count is 24?
261 counts per minute (cpm)
Calculation: 285 - 24 = 261 cpm.
How can the accuracy of count rate measurements be improved?
- Repeating readings and taking averages
- Taking readings over a long period of time
These methods help mitigate random errors and fluctuations.
What is the background radiation count when the source is moved back far enough that it is all absorbed by the air?
15 counts per minute
This is the amount of radiation detected solely from background sources.
What are the significant natural sources of background radiation?
- Radon gas from rocks and buildings
- Food and drink
- Cosmic rays
These sources contribute substantially to the background radiation levels.
True or False: The background radiation is the amount of radiation received only when a radioactive source is present.
False
Background radiation is always present, regardless of radioactive sources.
What are objects containing radioactive nuclei called?
Sources of radiation
How is the activity of a radioactive source defined?
The rate at which the unstable nuclei decay
In what unit is activity measured?
Becquerels (Bq)
What does 1 Becquerel represent?
1 nucleus in the source decaying in 1 second
How does activity vary with time for a radioactive source?
The activity decreases with time
What is the process of radioactive decay?
A random process
What device is used to measure the count rate of a radioactive source?
Geiger-Muller (GM) tube
What is the activity of a source if it is 2000 Bq?
2000 nuclei decay every second
What is half-life?
The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half
Can the half-life of different isotopes vary?
Yes, it can vary from a fraction of a second to billions of years
What is the half-life of uranium-235?
704 million years
What is the half-life of carbon-14?
5700 years
What happens to the amount of a radioactive isotope after each half-life?
The amount remaining decreases by half
How can half-life be calculated using a graph?
By measuring the time it takes for the activity to decrease to half its original value
What is the activity of a radioactive sample that drops from 880 Bq to 220 Bq?
2 half-lives have passed
What is the half-life of a sample if it drops to 220 Bq in 1 year?
3 months
What are some uses of radioactivity?
- Smoke detectors
- Monitoring the thickness of materials
- Medical procedures
- Sterilising food
- Determining the age of ancient artefacts
What type of radiation is used in smoke detectors?
Alpha particles
Why are beta particles used to measure the thickness of materials?
They are partially absorbed by the material
What is radiotherapy?
The treatment of cancer using radiation
What is a tracer in medical terms?
A radioactive isotope used to track the movement of substances in the body
What does irradiation mean?
The process of exposing a material to ionising radiation
What is contamination?
The accidental transfer of a radioactive substance onto or into a material
What is the risk of contamination?
It is particularly dangerous if a radioactive source gets inside the human body
How can exposure to radiation be minimized?
- Using shielding
- Wearing protective clothing
- Limiting time of exposure
Which type of radiation is most dangerous inside the body?
Alpha sources
Which type of radiation is the most penetrating?
Gamma sources
What is the difference between irradiation and contamination?
- Irradiation: Exposure to radiation without becoming radioactive
- Contamination: Becomes radioactive due to radioactive material
How does the risk of irradiation differ between short and long half-lives?
Irradiation poses a greater risk with shorter half-lives
How does the risk of contamination differ between short and long half-lives?
Contamination poses a greater risk with longer half-lives
What can ionising radiation cause to living cells?
Damage to DNA and mutations that can lead to cancer
What practices can be followed to minimize the risks of contamination?
Keeping radioactive sources in a shielded container, wearing gloves, using tongs, wearing protective clothing, limiting exposure time.
For example, a lead-lined box can be used to store radioactive sources safely.
How can the risks of irradiation to workers be minimized?
By monitoring their exposure to radiation.
This includes measuring the dose received during different activities.
What is a dosemeter?
A device that measures the amount of radiation in particular areas and is often worn by radiographers.
It is also referred to as a radiation badge.
How should alpha-emitting nuclear waste be stored?
In plastic or metal canisters.
What is the storage requirement for beta-emitting nuclear waste?
It must be stored inside metal canisters and concrete silos.
How should gamma-emitting nuclear waste be stored?
In lead-lined, thick concrete silos.
Why must radioactive waste be stored securely for a long time?
Because it emits dangerous levels of radiation for many years.
Where should waste with the highest levels of radioactivity typically be buried?
In secure, geologically stable locations underground.
What are the characteristics of containers used for radioactive waste disposal?
They must be strong, resistant to rust and corrosion, and able to withstand harsh conditions.
What should be ensured about the disposal site for radioactive waste?
It must have high security and a low risk of natural disasters.
What is one method to minimize the concentration of radioactive materials in waste?
Diluting it in large volumes of seawater.
Fill in the blank: A student should keep the gamma source in a _______ until it is needed.
lead lined container
What should a student use to move a gamma source instead of handling it directly?
Tongs.
What should be recorded after using a gamma source?
The date and the time that the radiation has been used.
True or False: The time that the source is being used should be maximized.
False.
List four actions a student should take to minimize risks when using a gamma source.
- Keep the source in a lead lined container until needed
- Use tongs to move the source
- Keep the source as far from themselves as possible
- Minimize the time the source is used
What is nuclear energy?
The energy contained in the nucleus of an atom, which can be harnessed for power.
What is nuclear fusion?
The process when two small nuclei join together to produce a larger nucleus.
Where does nuclear fusion occur naturally?
In stars.
What isotopes of hydrogen are involved in fusion reactions on Earth?
Deuterium and tritium.
What is the energy equivalent of 1 kg of hydrogen undergoing fusion?
Equivalent to burning about 10 million kilograms of coal.
What is nuclear fission?
The process when one large nucleus splits into two smaller nuclei.
What is a parent nucleus in the context of nuclear fission?
The large nucleus that splits during fission.
What are daughter nuclei?
The smaller nuclei produced from the fission of a parent nucleus.
What is spontaneous fission?
Fission that occurs without additional energy being put into the nucleus.
What is induced fission?
Fission that occurs when an unstable nucleus absorbs a neutron.
What is the half-life of uranium-235?
700 million years.
What happens during the fission of uranium-235?
It absorbs a neutron, becomes uranium-236, and then splits into smaller nuclei and neutrons.
What is critical mass?
The minimum amount of fissile material required to maintain a chain reaction.
What are control rods used for in a nuclear reactor?
To absorb neutrons and control the rate of fission.
What is the purpose of a moderator in a nuclear reactor?
To slow down neutrons.
What materials are commonly used for shielding in a nuclear reactor?
Steel and concrete.
What is the main difference between fusion and fission?
Fusion involves nuclei joining together, while fission involves nuclei splitting apart.
What are the conditions required for nuclear fusion?
Extremely high temperatures and pressures.
What is a major advantage of fusion reactors over fission reactors?
Fusion produces no long-lived nuclear waste products.
What is a disadvantage of fusion reactors?
The conditions for nuclear fusion are much harder to achieve and maintain on Earth.
Which isotopes of hydrogen are used in fusion reactions in stars?
Deuterium and tritium.
What is thermal equilibrium in the context of nuclear reactors?
When neutrons are slowed down to react efficiently with the uranium fuel.
Fill in the blank: Nuclear fission reactions produce _______ nuclei that are usually unstable and radioactive.
smaller daughter
True or False: Nuclear fusion is currently a commercially viable method for generating electricity.
False.
What happens to the mass during fusion reactions?
A small amount of mass is converted into energy.
What is the purpose of shielding in a nuclear reactor?
To absorb hazardous radiation.
What type of neutrons are required to induce fission?
Thermal neutrons.
Fill in the blank: The process of nuclear fusion requires _______ to maintain the reaction.
extremely high temperatures
What is the significance of hydrogen in stars?
It is the fuel for nuclear fusion that produces energy.
What are the products of fission when a uranium-235 nucleus splits?
Two smaller daughter nuclei, two or three neutrons, and gamma rays.
