P6 - Radioactivity Flashcards
What is an isotope?
Atoms of the same element with the same number of protons but different number of neutrons - they tend to be unstable and radioactive (they give out nuclear radiation and decay into other stable elements).
What are the 3 types of radiation?
Alpha radiation:
-An unstable nucleus emits an alpha particle (2 protons and 2 neutrons) -> mass number decrease by 4 and atomic number decrease by 2
Beta radiation:
-If nucleus has too much neutrons, a beta particle (electron) is emitted and a neutron in the nucleus will turn to a proton. Atomic number increases (proton added) and mass number remains the same (1 proton gained and 1 neutron lost)
Gamma radiation:
- After spitting out beta or alpha particle, nucleus may need to rid of extra energy by emitting gamma rays. Nothing happens to the mass or proton number.
Types of radiation and their penetration power:
Alpha radiation have low penetration: they can be stopped by paper as alpha particles are large colliding with atoms slowing them down.
Beta radiation have medium penetration: they can be stopped by thin aluminium as they are a smaller size than alpha particles so they can travel further without colliding with atoms
Gamma radiation have high penetration: they can be stopped by thick lead as they travel the furthest without hitting atoms.
Types of radiation and their ionisation power:
Alpha radiation have high penetration: they are the largest therefore they can’t travel far without hitting atoms and knocking off electrons
Beta radiation have medium ionisation: are smaller than alpha particles so they can travel further before hitting atoms and knocking off electrons
Gamma radiation has low ionisation: Gamma rays are just energy therefore there is the lowest likelihood of hitting atoms and knocking off electrons.
Nuclear equations - Alpha radiation
Nucleus emits alpha particles (2 protons and 2 neutrons) so mass number decreases by 4 and atomic number decreases by 2
Eg 266,88 Ra -> 222,86 Rn + 4,2α
Nuclear equations - Beta radiation
Nucleus emits electron and a neutron becomes a proton therefore mass number the same (1 proton gained and 1 neutron lost). Atomic number increases as proton in atom increases by 1
EG 14,6 C -> 0,-1e- + 14,7 N
Nuclear equations - Gamma radiation
The mass number and atomic number doesn’t change
EG 234,91Pa -> 234,91Pa + γ
What happens when an electron absorbs an electromagnetic wave in an atom?
- An electron can move up shells when they gain energy (become excited) from absorbing an electromagnetic wave supplying them with enough energy to move up an energy shell
- The electron will move back to their original shell and all excess energy is released in doing so. The same amount of energy which was absorbed by the electron to move up energy level will be released when doing so.
How do florescent lights work?
- Ultraviolet has a high frequency and when absorbed by electron it has enough energy to become excited and move up multiple energy levels
- When electrons moves back to its original shell it doesn’t go back in one step so it moves back energy level by energy level releasing little amounts of energy as it goes as visible light
What is the absorption spectrum?
- Rainbow colored rectangle from red to violet with black lines
- > the black lines are the amount of energy the electron absorbed to move up energy levels
What is the emission spectrum?
- Black rectangle with coloured lines
- > the coloured lines are the energy released from electron when returning to its original shell
Activity equation?
Activity (*Bq) = Number of decays / time (s)
*Bq = Becquerels
What is the experiment to measure decay?
The geiger muller experiment
- The geiger muller tube detects alpha, beta and gamma radiation as they hit it
- When they hit it the geiger muller tube beeps and allows us to count the decay per seconds (activity)
What is half life?
The time taken for half the radioactive substance to decay to half.
What does a long and short half life mean?
Long half life: activity falls slowly as most of the nuclei makes a long time to decay
Short half life: activity falls quickly as most of the nuclei decays in a short amount of time
Half-life on a graph:
Y axis: Activity
X axis: Time (s, min or hr)
1) Halve the total activity and draw a line from there to the curved line. When it hits the line draw down and find the time.
2) The next half life is half the previous half-life’s activity and draw down to find the time
- To note: If the activity never reaches 0 then there is background radiation which shouldn’t be taken into consideration when working out half-life
Some half life Questions:
Q1) The count rate of a substance is measured as 640 counts a minute. Two hours later it has fallen to 40 counts per minute. Find half life?
Q2) The half life of a substance is 60hr. Find the activity after 240hr, if it is originally 480 Bq?
Q3) A radioactive substance has half life of 15hrs. A tube contains 8mg of isotopes. What is the mass after
a) 15 hrs
b) 45 hrs
Q1) 640 -> 320 -> 160 -> 80 -> 40
4 half lives = 2 hours
1 Half life = 30 minutes
Q2) 480 -> 240-> 120-> 60-> 30->
1 half life = 60
4 half lives = 240
30 Bq at 240hr
Q3) 8mg -> 4mg -> 2mg -> 1mg
1 half life = 15hr
3 half lives = 45hr
15 hrs = 4mg
45hrs = 1mg
Where does the background radiation formed -> percentages
37% = radon and thoron gas released from soil, rocks and building materials 19% = gamma rays from rocks and soil 17% = radiation from bodies 14% = cosmic rays from space 11.5% = medical industry 0.5% = other (like travel) 0.5% = nuclear weapons 0.4% = work related 0.1% = from nuclear power industry
What are the dangers of radioactivity?
-> Can cause ionisation (especially alpha radiation) knocking off electrons and forming ions
Lower doses: radiation damages cells by causing mutations in DNA causing uncontrollable cell division (cancer)
Higher doses: kill living cells entirely and cause radiation sickness
Radiation dangers from different places:
OUTSIDE THE BODY
Beta and gamma radiation are most dangerous due to there high penetration power to enter body
INSIDE BODY:
Alpha radiation is most dangerous as it has high ionisation power meaning it can knock off electrons due to large size
What is irradiation?
- Occurs when an object is exposed to a source of radiation outside the object.
- > it can be shielded or moving object away prevents irradiation
Likeliness of irradiation:
- If gamma irradiation: a higher likeliness as there is a higher range it can reach
- If alpha irradiation: lower likeliness as it has a shorter range than gamma radiation.
What is contamination:
Occurs when radiative substance is in or on the object
-> It cannot be shielded or blocked as substance is in contact with the object and is hard to remove all contamination
Likeliness of contamination:
- If substance is a solid: there is no contamination risk as long as the substance doesn’t touch the object
- If substance is a gas, there is high contamination risk as it can move
Half life and radioactive danger?
Shorter half lives are safer
Longer half lives are more dangerous
Medical uses of radiation?
-Tracers: (short half life gamma ray emitters) are injected or swallowed to see how organs work or how things move in the body
Short half life: Relatively short half life to be as safe as possible so radiation disappears quickly but enough to be detected
Gamma rays: due to high penetration power they can penetrate out the body to be detected by gamma detectors
Cancer treatments with radiation?
RADIOTHERAPY:
- To treat cancer externally
1) Gamma rays concentrated on the tumor
2) The beam - producing gamma rays- is rotated around patient with tumor at centre, minimising damaging to living cells
3) Treatment taken in intervals to allow living cells to repair and grow
BRACHYTHERAPY:
- To treat cancer internally:
1) Implants containing beta particles are placed inside tumor.
2) Beta particles damage the tumor cells but have a short enough range not to damage living cells
3) Alpha emitters can be injected in as they have high ionisation power and short range causing lots of damage to tumor
What is nuclear fission:
When an unstable nucleus splits into two releasing lots of energy
What 2 ways can nuclear fission occur:
1) Spontaneously
2) By absorbing a slow moving neutron causing it to become unstable and split
How does nuclear fission of Uranium work?
1) When.a slow moving neutron is absorbed by the uranium the nucleus becomes unstable and splits
2) The uranium-235 nucleus splits to krypton-89, barium-144, 3 neutrons and gamma rays (if there is excess energy)
3) The 3 neutrons can be absorbed by other Uranium nuclei causing fission and a chain reaction
Advantages and disadvantages of nuclear power?
ADV
1) It doesn’t release CO2 emissions - no global warming contribution
2) It is extremely reliable -> there are lots of uranium - 235 and it produces lots of energy
DIS
1) Nuclear power stations contain highly dangerous radioactive materials which can cause disastre if released
2) Decommission of nuclear power stations take very long and very expensive
3) Generates large amounts of radioactive waste which must be stored away for thousands of years
How does nuclear power stations produce electricity?
IN THE REACTOR CORE
1) Fissionable atoms like Uranium -235 are present and once one neutron is absorbed a chain reaction occurs
2) Moderator: is water and it keeps fission occurring as the 3 neutron emitted in each fission reaction have a lot of energy (they are too fast) therefore the neutrons collide with the H20 molecules slowing them down allowing fission to occur
3) Control rods: they allow us to control number of fission reactions occurring (if control rods lowered they stop neutrons from reach other nuclei slowing it down and vice versa for raising control rods)
4) Surrounded by thick lead to prevent escape of gamma radiation - which can be stopped by lead
IN THE HEAT EXCHANGER
1) The hot water (from energy from fission in reactor core) runs in tube through container of water in heat exchange
2) This transfers energy to the water in heat exchange producing steam as it boils
3) The steam travels up pipe and spins a turbine converting heat energy into electrical energy
IN THE PUMP
1) Pump helps supply heat exchange with constant supply of water as the water in heat exchanger changes state to steam
What is nuclear fusion?
Two smaller nuclei joining together to form a larger nuclei
Why does nuclear fusion release more energy than nuclear fission?
- Due to the difference in mass from before fusion and after fusion
- Before nuclear fusion the nuclei will always have more mass than after so the extra mass is converted into energy released as gamma radiation
How does nuclear fusion of 2 Hydrogen work?
Two hydrogen nuclei combine to form He (Helium) releasing energy as well
(this occurs in the sun)
Advantages and disadvantages of nuclear fusion?
ADV
1) It doesn’t create radioactive waste
2) There is plenty of hydrogen available for fusion
3) Produces more energy than fission
DIS
1) Requires extremely high temperatures and pressures and a very strong magnetic field
Carbon isotope percentage in every living organism?
Carbon - 14 (10%)
Carbon - 12 (90%)
Over time the carbon -14 will decay to carbon - 12. We can use this to find age of organisms like trees.
