Radioactivity And Particles Flashcards
What are isotopes?
Atoms with the same number of protons but a different number of neutrons.
What is at the centre of every atom?
A nucleus
Radioactivity is …………….
A random process
Can you do anything to make decay happen?
No
What are the sources of background radiation?
Cosmic rays from outer space⬆️
Nuclear waste / activity➡️
Rocks and soil⬇️
Remember:
⬆️
➡️
⬇️
Nuclear radiation causes …………….
Ionisation by bashing into atoms and knocking electrons off
What can we use to detect ionising radiation?
Photographic film
Geiger muller tube detector
What nuclei do alpha particles have?
Helium He4 OR 2 protons + 2 neutrons
2
Which particles cannot penetrate any materials and are stopped quickly, and why?
Alpha particles because they are too big.
Why are alpha particles deflected by electric and magnetic fields?
They have a positive charge (+2)
What happened to the atomic and mass number when alpha particles are emitted?
Mass number - decreased by 4
Atomic - decrease by 2
What are beta particles?
Fast electrons
What happens to the atomic number and mass number when a beta particle is emitted form the nucleus?
Mass number stays the same
Atomic number increased by 1
How strong is the penetration of beta particles?
Moderately
What stops a beta particles?
Thin metals such as 1mm aluminium
How far do gamma rays penetrate?
A long way without being stopped, thick lead or concrete only reduces them.
Gamma rays are ,………….. Ionising
Very weakly
Why do gamma rays have no deflection?
Because they have no charge (0).
What effect does a gamma ray have on the atomic mass and number?
No effect
What blocks gamma rays?
Nothing.
Thick lead and concrete only reduces it.
What is activity?
The number of decays per second measured in becquerels
What is half life?
The time taken for half the radioactive nuclei to decay.
What do medical tracers use?
Beta and gamma particles
What are the dangers of ionising radiation?
Cause mutations by damaging DNA
Damage cells and tissue
What are the problems of disposing radioactive waste?
Long half life - active for thousand of years
Highly penetrating - must be stored in a thick container
How can the risks of disposing radioactive waste be reduced?
Using deep redundant mine shafts
Areas which are stable
When working with radioactive materials what cautions need to be taken?
Don't allow skin contact Avoid looking at the source Keep sources in a lead box Lead screens Be exposed for as little time as possible
What is nuclear fission?
- Occurs in nuclear reactors
- Splitting of a Uranium-235 nucleus into two daughter nuclei which releases energy
How does nuclear fission cause a chain reaction?
- slow moving neutron collides with uranium-235 nucleus
- uranium-235 nucleus splits into two daughter nuclei and a few neutrons
- energy is released in the process (kinetic)
- the neutrons collide with more uranium-235 nuclei and they split and so on, making more daughter nuclei and neutrons causing more collisions to happen
What do moderators do in the fission process of generating electricity?
Slows neutrons down so they can more successfully collide with uranium-235 nuclei and sustain chain reaction
What do control rods do in the fission process of generating electricity?
Limit the rate of chain reaction by absorbing excess neutrons
Beta particles are……….. Ionising
Weakly
Alpha particles are……… Ionising
Strongly
What is a gamma ray?
An electromagnetic wave
What is the charge of a beta particle?
-1
Out of alpha particles, beta particles and gamma rays, which is bent by electric or magnetic field lines?
Alpha
Beta
Not gamma because they have no charge
What are the symbols for the units becquerel, centimetre, hour, minute, second?
Bq cm h min s
Describe the structure of an atom.
Nucleus in centre:
+ve protons and neutral neutrons inside
Surrounding and on shells:
-ve electrons
Where is the atomic mass number on a chemical symbol?
Where is the atomic proton number on a chemical symbol?
The top smaller number.
The bottom smaller number.
What is the atomic mass number?
The number of protons + neutrons.
What is the atomic proton number?
The number of protons in the nucleus
Which is the same as the number of electrons
Describe the use of radioactivity in medical and non medical tracers.
Medical:
- radioactive sources added to chemicals, then taken into the body and allow certain parts of body to be viewed from outside
- short half life of beta and gamma sources are used so doesn’t damage body but can penetrate skin.
Non medical:
- radioactive sources can also be used to track leaks in pipes, radioactive source, when added into pipes under rocks, can be tracked from above to locate leaks without digging road.
Describe the use of radioactivity in radiotherapy.
- radioactive sources can be used to stop cancer cells growing
- beams of radiation directed at cancer affected area
What is radio carbon dating?
Finding the age of a sample that was once living by finding the proportion of 14C in it now compared to when it was alive.
Describe the use of radioactivity in dating of archaeological specimens and rocks.
- percentage of carbon 14 in air is stable and known, doesn’t change
- percentage of carbon 14 in trees is kept constant by photosynthesis
- when trees / plants die + stop photosynthesising, carbon 14 in them decays
- by calculating percentage of carbon 14 present in sample, and knowing half life of carbon 14, the age of the artefact can be calculated by working out how many half lives have elapsed.
Describe the results of Geiger and Marsden’s experiments with gold foil and alpha particles.
- alpha particles directed at gold foil
- most passed straight through
- some deflected through angles
- very few bounced back
- suggest atom has a nucleus that is positive (so that positive alpha particles repelled off it)
- but this positive nucleus must be small as only a few alpha particles bounced back.
How do you do half life calculation questions?
Working out amount of sample left after specific time with half life of it:
E.g. Half life of 8 days. If start with 12g, how much left after 24 days?
Write table of time and amount:
T A
0days. 12
8days. 6
16days. 3
24days. 1.5g
= 1.5g.
So keep going down table til you halved enough to get to amount of time want to have passed.
Describe Rutherford’s nuclear model of the atom based on Geiger and Marsden’s discoveries.
Majority of atom is empty space
(as most alpha particles passed straight through)
Atom has a tiny positive nucleus
(as few alpha particles did reflect backwards)
What are the uses of radioactivity?
Medical and Non medical tracers
Radiotherapy
Radioactive dating of archeological specimens and dating of rocks
What is half life measured in?
Becquerels, Bq
What are alpha, beta and gamma rays, where do they come from?
They are ionising radiations emitted from the nucleus of an unstable atom in an attempt to make it more stable.
What can radiotherapy be used for?
Stop cancer cells growing
How do beta particles move?
Fast
How does a medical tracer work?
Penetrates body tissues can be detected externally
Computer coverts to an onscreen display
Used to check if organs are working
Need short half life
How does industrial tracers work?
In cracked pipes
Gamma will collect outside the pipe detecting extra high radioactivity
What can be used to date rocks and archaeological specimens?
Half life
What happens in a nuclear reactor ?
The free neutrons collide with atoms causing the temperature to rise
What happens to the mass number and atomic number when a gamma ray is emitted from the nucleus?
Everything stays the same.
