Topic 6 Flashcards
Done except for a few specpoints
6.1
Describe an atom (include where mass is concentrated)
-Positive nucleus that has protons and neutrons
-Most mass in nucleus
-Surrounded by negatively charged electrons on energy levels
6.1 6.2
a) State the radius of an atom (include units)
b) State the radius of a nucleus (include units)
c) How many times bigger is the atom than the nucleus inside it?
a) ~ 1×10^-10 m
b) ~1×10^-15 m
c) 100,000 times
6.3 6.4
Define the term isotope
Atom with same number of protons but different number of neutrons
6.5
State the relative masses and charges of the 3 main subatomic particles
CHARGES:
p: +1
n: 0
e: -1
MASSES:
p: 1
n: 1
e: 0.0005
6.6
Why is the overall charge of an atom neutral?
-Equal number of protons and electrons
-Cancel out
6.7
In an atom, how do electrons orbit around the nucleus?
In energy levels, at different set distances from the nucleus & each other
6.8
Describe what happens when an atom absorbs and then emits radiation. What type of radiation is emitted?
-Absorbs: electron gets excited, moves up energy level
-Emits: electron loses energy, jumps down energy level
-EM radiation
6.9
How do atoms form ions?
-Lose electrons to become positive cations
-Gain electrons to become negative anions
6.10
Where is alpha, beta minus, beta plus, gamma rays and neutron radiation emitted from?
Unstable nuclei in a random process
6.11
Name 4 types of ionising radiation
-Alpha
-Beta minus
-Beta plus
-Gamma
6.11
Define the term ionising radiation
Has enough energy to ionise atom (remove electrons from it)
Explanation (don’t need to know): Electron given more energy than needed to reach outermost shell, so will transfer elsewhere and atoms becomes ion
6.12
What is meant by background radiation?
-Ionising radiation around us all the time
-Caused by number of sources
-Some = naturally occurring
-Some = human activities
6.12
How much of background radiation is made up of radon gas?
49%
6.13
Describe how radon gas is produced
Unstable uranium in rocks underground decaying and emitting radiation
6.13
State the origins of background radiation
-Radon gas
-Medical
-Ground & buildings
-Cosmic rays
-Food & drink
-Nuclear and other
Why can radioactive substances decay so easily?
They are unstable
What causes a nucleus to be unstable?
Having a higher mass
What is released in the process of a nucleus becoming more stable?
Radiation
6.14
Give 2 ways we can detect/measure radioactivity
-Geiger-Muller tube
-Photographic film
6.15
a) What is an alpha particle equivalent to?
b) What is a beta particle?
c) What is a gamma ray?
a) Helium nucleus
b) Electron emitted from nucleus (neutron breaks down into proton & electron but proton stays)
c) EM radiation
6.16
Rank the ionising radiations in terms of how ionising and penetrating they are
-IONISING most to least:
Alpha, Beta, Gamma
-PENETRATING most to least:
Gamma, Beta, Alpha
6.16
What affects the amount of ionising power of the radiation?
Mass & charge
6.16
State the materials that stop each radioactive decay
-Paper stops alpha
-Aluminium stops beta
-Lead (almost) stops gamma
6.17
Name and draw the first 4 atomic models and who created them
-DALTON’S SPHERE (JOHN DALTON)
-A sphere
-PLUM PUDDING MODEL (J.J. THOMSON)
https://www.ecosia.org/images?q=plum%20pudding%20model#id=2D8F9F323DE56D626F3F876EC7F7009BD7654A21
-NUCLEAR MODEL (ERNEST RUTHERFORD)
Nucleus (as a ball) with electrons orbiting around it RANDOMLY (not on shells)
-ELECTRON SHELL MODEL (NIELS BOHR)
Nucleus in middle with protons and neutrons. Electrons in fixed orbits around nucleus
6.17
Explain why the atomic model has changed over time (include dates)
-1803 Dalton
-1897 J.J Thomson discovered electrons with use of cathode ray tube
-1911 Rutherford fired alpha particles at thin gold foil. Some detected by detectors, others reflected, some deflected so came to conclusion of tiny, heavy, positive nucleus
-1913 If Rutherford’s model was true, atom would have collapsed so Niels Bohr came up with electron shells
6.17
Explain what Rutherford suggested the atom was composed of
-Mostly empty space
-Positive, tiny, heavy nucleus
6.18
Describe the process of Beta minus decay
-Neutron -> proton + electron
-Beta particle (electron -> negative charge) emitted
6.19
Describe the process of Beta plus decay
-Proton becomes neutron + positron
-Positron (positive charge) emitted
6.19
State the relative mass and charge of a positron
Mass = 0.0005
Charge = +1
(Basically a positive electron)
6.20
Describe the effects of each radioactive decay on an atom
α:
Mass = Decreases by 4
Atomic number = Decreases by 2
β-:
Mass = Same
Atomic number = Increases by 1
β+:
Mass = Same
Atomic number = Decrease by 1
ɣ:
Mass = Same
Atomic number = Same
neutron emission:
Mass = Decreases by 1
Atomic number = Same
6.21
What happens to the atom when it emits a high frequency gamma wave?
Atom remains same but loses some energy
6.22
State the equation symbols for:
-Alpha particle
-Electron
-Positron
-Gamma ray
4 OR 4
α He
2 2
0 OR 0
β e
-1 -1
0 OR 0
β e
+1 +1
0
ɣ
0
6.22
Radium-226 emits an alpha particle. What is the other product?
226 4 222
Ra –> He + Rn
88 2 86
6.22
Uranium 238,
238
U
92,
emits an alpha particle to become what nucleus?
238 4 234
U –> α + Th
92 2 90
6.23
What does the ‘activity of a substance’ mean?
The number of radioactive decays per second
6.23
Describe how the activity of a radioactive source decreases over a period of time
It halves each time
6.24
State the unit used for the activity of a radioactive isotope
Becquerel, Bq
6.25
Define the term half-life
t taken for 1/2 of unstable nuclei in sample of radioactive isotopes to decay
6.26
What is radioactive decay? Can it be predicted? How can half-life be useful here?
-Unstable nuc emitting radiation to become stable
-No. It is a random process
-Predict activity of large amounts of nuclei
6.27
Describe how to work out the half life of an isotope from a graph of its activity over time
-Starting point = 0 minutes/years etc. Say activity is 100
-Go down to activity of 50 and see how long it has taken to get there
-Keep doing
-That’s the half life
6.27
A radioactive isotope has a half-life of 15 days and an initial count-rate of 200 counts per second. Determine the count rate after 45 days
Start = 200
15 days = 100
30 days = 50
45 days = 25
25 counts per second
6.28P
State 6 uses of radiation
-Killing micro-organisms in food (micro-organisms cause food to decompose -> food poisoning. Makes safer to eat)
-Sterilising equipment
-Detecting leaks
-Diagnosing cancer
-Checking paper thickness
-Smoke alarms
6.28P
Give a short description of how radiation (include which type) can be used to sterilise equipment
-Equipment sealed in bag & irradiated with gamma rays to kill micro-organisms
-Alternative to heating
6.28P
Give a short description of how radiation (include which type) can be used to detect leaks underground
-Gamma source added to water
-GM tube follows path of pipe & detects higher levels of radiation where leak is present
6.28P 6.34P
Give a short description of how radiation (include which type) can be used to diagnose cancer
-Patient injected with radioactive tracer
-Radioactive isotope concentrates in particular organ/cancerous tumour
-Emits positron which interacts with electron in body, releases gamma rays
-Detected by detector
6.28P
Give a short description of how radiation (include which type) can be used to check paper thickness
-Beta particles
-Detector on opposite side of sheet detects count rate of radiation travelling through paper
-Too thin = high count rate
-Too thick = low count rate
-Computer corrects force on rollers
6.28P
Give a short description of how radiation (include which type) can be used for smoke alarms
-Alpha particles
-Detector has electrical circuit w/ gap between 2 electrically charged plates
-Alpha particles ionise molecules in air -> current flows across gap (completes circuit)
-Smoke interferes -> current slows (ions have slowed) -> alarm sounds
6.29
State the (8) dangers (effects) of ionising radiation
-Radiation sickness
-Diarrhoea
-Vomiting
-Weak immune system
-Burns & blisters
-Sepsis
-Cataracts
-Cancer
6.30P 6.31
How can we protect ourselves from radiation?
-Increase distance from source
-Minimise time spent near source
-Shielding (Putting barrier between source & person for radiation to be absorbed by)
-Wear a dosimeter to monitor exposure
-Limit dose & use source with short half-life
6.32
Define the term irradiated
Define the term contaminated
-Exposed to nearby radiation
-Particles of radioactive material on skin/inside body
6.32
Compare irradiation and contamination (2 things)
-Irradiation ends when source is removed, contamination ends when all material has decayed
-Irradiation does not cause object to become radioactive, contamination does
6.33P
How can a tumour be treated internally? What is a benefit to this?
-Beta emitter inside/very close to tumour to destroy it
-Benefit: Precise to tumour, less damage to healthy tissue
6.33P
How can a tumour be treated externally? What is a problem with this?
-Beams of radiation directed at tumour from different directions to destroy it
-Con: Healthy tissue may also be damaged
6.34P
Why are different tracers used to diagnose problems in different areas of the body?
Different parts of the body absorb different tracers
6.35P
Explain why isotopes used in PET scanners have to be produced nearby and what they are produced in
-Cyclotrons
-Need to have short half-life to MINIMISE RISK OF RADIOACTIVITY to patient
-Will fully decay in short time so need to be used quickly
6.36P
Evaluate the advantages and disadvantages of nuclear power
ADVANTAGES:
-Low emission of CO₂ (only releases when building power plants)
-Reliable
-Extremely energy efficient
-Saves more lives than it takes
DISADVANTAGES:
-Accidents & disasters
-Nuclear waste difficult to dispose of
-Used to create nuclear bombs -> pollution
6.37P
What can nuclear fission, fusion and radioactive decay be used for?
Supply energy
6.38P
Define the term daughter nuclei
Smaller nuclei that atom breaks down into
6.38P 6.44P
Describe the process of nuclear fission using uranium-235 as an example
-Neutron fired at high speed to hit U-235 nuc
-Nuc -> unstable bc gained neutron
-Nuc splits -> 2 smaller daughter nuclei
-Energy & multiple neutrons released
6.39P
Describe what will happen if the neutrons hit too many fuel rods in a reactor
Reactor overheats -> core melts
6.40P
State 3 features of a nuclear fission reactor
-Fuel rods
-Control rods
-Moderator
6.40P
Describe the role fuel rods play in a reactor
-Neutrons leave fuel rods at high speeds
-Move through moderator
-Absorbed by control rod/another fuel rod -> another reaction
6.40P
Describe the function of the control rods in a reactor
-Control r. reaction (lowered & pulled up)
-Lowered: absorb more neutrons -> ↓ r. reaction
6.40P
Describe the function of the moderator in a reactor
Slows neutrons -> ↑ likelihood will be absorbed by fuel rods and -> split nuc
6.41P
a) Explain how thermal energy from the chain reaction in a reactor is used to generate electricity in a nuclear power station
b) Which energy transfer is present here?
a) -Superheated water from reactor passes through heat exchanger
-At ↑ pressure
-Produces steam
-Turns turbine
-Turns generator
b) KE->electrical
6.42P
Use one word to describe the products of nuclear fission
Radioactive
6.43P
What is the energy source for stars?
Nuclear fusion
6.43P 6.44P
What is nuclear fusion?
Small nuceli combine -> 1 large nuc
Releases E
6.45P
Why are high temperatures & pressures necessary for carrying out nuclear fusion?
-All nuclei = + (bc protons) -> strong electrostatic F of repulsion
-↑ pressure squeezes nuclei together
-↑ temp = enough E to overcome F of repulsion
6.46P
State 3 disadvantages of nuclear fusion
-Very ↑ temp & pressure needed -> difficult to sustain
-Expensive
-So far none of experimental reactors produced more E than was used to heat H₂ nuclei
