Topic 6 - radioactivity Flashcards
Isotope
Element with the same number of protons but a different number of neutrons
Ionising
Causes an atom to lose or gain electrons
Unstable atoms
Wrong number of protons to neutrons causing it to emit radiation in the form of energy or mass
Stable atom
Have the right balance of neutrons to protons
Radiation
Emission of mass or energy
Rutherfords gold leaf experiment of alpha particles. Observations:
Most alpha particles passed through
Some got detected
A few bounced back
Conclusions of Rutherfords gold leaf experiment
Atom is mostly empty space
There was a positive charge at the centre
The mass was concentrated at the centre
How is an ion formed?
If an electrons absorbs enough energy it will make up all the shells and leave the atom
What radioactive particles are emitted from an unstable atom?
Alpha =α. Beta= β. Gamma= γ and neutron radiation
What is background radiation?
Radiation that is naturally occurring all the time
Sources of background radiation
Food, rocks, medical, food.
Main source in the uk for background radiation
Radon gas, nuclear power stations + space
What is a Geiger - Müller tube?
Detects ionising radiation when a charged particle (from an ionised atom) completes a circuit.
How do you accurately measure the radioactivity of an object?
1) take 3 readings of background radiation in the room without object being present. Find the average.
2) take 3 readings with object present + find average.
3) subtract background radiation reading from average reading of object
Bohr’s model of the atom
Passed high current through gases + they emitted light - set number of colours. If only certain frequencies (colours) are present then electrons only moving between set energy levels. -> electrons shells must be set distances from nucleus.
What is half life?
The time taken for the activity of a radioactive substance to reduce by a half.
Can you predict half life?
No, it’s unpredictable + random. You can’t say which nucleus will decay or when. You can’t cause it to decay or slow down.
What are the dangers of ionising radiation?
If alpha, beta or gamma ionise the nuclei in the atoms that make up your DNA your cells can mutate and cause cancer
Contamination
The source of radiation is on or in you
Irradiation
The source of radiation is near you
Safety measures when dealing with types of radiation
Barriers + distance. Eg long handled tongs, gloves, using sources with short half life
What is the approximate size of an atom?
x10-^10m
Describe the atom
A positively charged nucleus with protons + neutrons surrounded by negatively charged electrons. Almost all mass in nucleus
What is the relative mass of a proton?
1
What is the relative charge of a proton?
+1
What is the relative mass of a neutron?
1
What is the relative charge of a neutron?
0
What is the relative mass of an electron?
1/2000
What’s the relative charge of an electron?
-1
How is an atom neutral?
Because the number of protons equals the number of electrons
What happens to electrons when there is an absorption or emission of electromagnetic radiation?
They can move up to a higher energy level if it absorbs EM radiation with right amount of energy. It then quickly falls back + emit same amount of energy absorbed + often visible light is released
What is an alpha particle?
They’re helium nuclei. They have two neutrons + two protons.
Describe how ionising + penetrable alpha particles are
They don’t penetrate very far into materials + stopped quickly. Travel few cm in air + absorbed by paper.
Due to their size they’re highly ionising
What is a beta particle?
Beta minus is an electron emitted from nucleus.
Beta plus is a positron from nucleus (the antiparticle of the electron)
Describe how ionising and penetrable beta particles are
They’re moderately ionising. Beta minus have range in air of few meters + absorbed by 5mm aluminium
Positrons have smaller range as when they hit electron the two destroy each other + produce gamma rays.
What are gamma rays?
Waves of EM radiation released by the nucleus that carry away this energy.
Describe how ionising and penetrable gamma rays are
They penetrate far into materials without being stopped + travel long distance in air.
Weekly ionising as they pass though rather than collide with atoms
Absorbed by thick lead or concrete.
Describe the process of β– decay
A neutron becomes a proton plus an electron
Describe the process of β+ decay
A proton becomes a neutron plus an electron
What is the unit of activity of a radioactive isotope?
Becquerel, Bq
Explain the effect of alpha decay on the charge + mass of an atom
The mass number decreases by 4
The atomic number decreases by 2
Explain the effect of beta minus decay on the charge + mass of an atom
Neutron changes into a protons + electron so:
Mass number doesn’t change as it lost neutron but gained proton
Atomic number increases by 1
Explain the effect of beta plus decay on the mass + charge of an atom
Mass number doesn’t change as it’s lost a proton but gained a neutron
Atomic number decreases by 1 as it has one less proton
Explain the effect of neutron emission on the mass + charge of an atom
Mass number decreases by 1
Atomic number stays the same
Explain the effect of gamma radiation on the charge and mass of an atom
Gamma rays agents rid of excess energy from an atom
Mass + atomic numbers stay the same gayer gamma ray has been emitted
What happens to nuclei that have undergone radioactive decay?
They often undergo nuclear rearrangement with a loss of energy as gamma radiation
How does the radioactivity of a source decrease over time?
Each time radioactive nucleus decays one more radioactive nucleus disappears. As unstable nuclei steadily disappear, activity as a whole will decrease.
What is half life?
The time taken for half the undecayed nuclei to decay.
