1. Radioactivity

2. Henri Becquerel
Becquerel put some uranium crystals on a photographic plate and left it away from sunlight for a few days.
He discovered that a strong image of the uranium crystal appeared on the photographic plate.
He concluded that uranium was giving off rays which became known as radioactivity.
He was an engineer from a very educated family and he took over from his father as a physisist at the local college
His first experiment involved leaving the plate in sunlight for a few days as he thought that the sunlight might make phosphorescent compounds emit x-rays.
The paper on the plate was to stop the sunlight affecting the plate.
The image did show through onto the plate.
Was cloudy in Paris for a few days so he put the equipment away and that’s how he got these results. .
All uranium cmpds had the same property of radiation, with proportionality to how much uranium was present.
Pichblende was the exception – emitted way more radiation that would be expected – he wondered what was causing this!

3. The mystery of Pitchblende ore
Becquerel could not understand why Pitchblende ore gave off such a high amount of radiation.
Although it did contain uranium it still was giving off more radiation than even pure uranium gave off!
It is found in silver mines, especially in the czech republic. Name means blackdeceiver

4. Marie Curie
Marie Curie, and her husband Pierre, found that Pitchblende ore not only contained Uranium but also contained two new elements which she called Radium and Polonium
Radium and Polonium are both more radioactive than Uranium
A polish scientist
Radium means radiation and polonium after Poland
She was the first person to use the term radioactivity

5. Nobel Prizes
The Nobel Prize in Physics Becquerel and the Curies shared the Nobel prize for the “discovery of spontaneous radioactivity“ and “joint research on the radiation phenomena discovered by Professor Henri Becquerel”
Curie was the first female to win a Nobel prize in Chemistry for her research on radium and Polonium.
Pierre died in a car crash
Marie curie, a school teacher, a researcher, a single mother! With two daughters!
Radiation damage to researchers…
Marie Curie (66) died from leukaemia in 1934
Becquerel (55) died from radiation burns in 1908

6. X N Notation Mass number:
The number of protons plus the number of neutrons in a neutral atom. A X N
Element symbol
Atomic number:
The number of protons (which is the same as number of electrons) in a neutral atom.

7. Name the elements shown and calculate the numbers of protons, neutrons and electrons for the elements: 12 C 6 75 As 33
127 I 53

8. Calculate the number of protons, electrons and neutrons shown below -12 C 6 13 C 6 14 C 6
What do we call isotopes that are unstable and emit radiation to become more stable?
What do we call atoms of the same element with different numbers of neutrons?
These are all the element carbon, what is the difference between them?
They have different numbers of neutrons.
Radioisotopes
Isotopes

9. There are three different types of radiation:
Radioactivity
The emission of radiation caused by spontaneous disintegration of unstable nuclei.
There are three different types of radiation:
Alpha (α) Particles
Beta (β) particles
Gamma (γ) rays
They can all be detected by the Geiger counter

10. Geiger-Muller Tube
The detector is a metal tube filled with gas. The tube has a thin wire down the middle and a voltage between the wire and the casing.
collision & ionisation
radiation
Argon gas
Argon gas
mica window
When the radioactivity enters the tube, it ionises the gas in the tube. This produces a pulse of current which is amplified and passed to a counter.
counter
124
125

11. Alpha (α) Particles
Alpha particles can be emitted from an unstable nucleus when it disintegrates.
They are made up of two protons and 2 neutrons.
They have a positive charge of +2.
It is usually represented as
Americium-241 emits alpha particles and low energy gamma rays (60 keV, giving a dose at 1 metre of mSv/yr). The alpha particles are absorbed within the detector, while most of the gamma rays escape harmlessly. The americium is present in oxide form in the detector.
The alpha particles emitted by the Am-241 collide with the oxygen and nitrogen in air in the detector's ionisation chamber to produce charged particles called ions. A low-level electric voltage applied across the chamber is used to collect these ions, causing a steady small electric current to flow between two electrodes. When smoke enters the space between the electrodes, the alpha radiation is absorbed by smoke particles. This causes the rate of ionisation of the air and therefore the electric current to fall, which sets off an alarm.
The alpha particles from the smoke detector do not themselves pose a health hazard, as they are absorbed in a few centimetres of air or by the structure of the detector.
Plutonium-241, which is about 12% of the one percent content of plutonium in typical spent fuel from a power reactor, has a half life of only 14 years, decaying to Am-241 through emission of beta particles.  Am-241 has a half life of 432 years, emitting alpha particles (see above) and intense gamma radiation to become neptunium-237.

12. Label the helium atom and fill in the table:
eutron {
E_____
lectron
N_____
ucleus
P_____
roton
Particle
Mass
Charge
Proton
Neutron
Electron 1 +1 1
none
1/1840th -1

13. What we used to think… It was believed that atoms were:
Spheres of positive charge.
With negative charges spread through it.
This resembled a plum-pudding, so it was called the ‘Plum –pudding’ model.
This was wrong!
How did we discover current ideas about the structure of the atom?

14. Rutherford’s team:
Ernest Rutherford and his team of scientists performed a famous experiment in Manchester:
They fired some alpha particles at a piece of thin gold foil (only a few atoms thick):
If the ‘Plum Pudding’ model of the atom was correct, the alpha particles should pass straight through and only be slightly deflected.
This did not happen.

15. What Rutherford’s team observed……..
Most of the alpha particles went straight through the foil.
Some alpha particles were deflected through large angles.
3. A very few alpha particles were reflected straight back.

16. Rutherford’s conclusions
Observation
Conclusion
Most alpha particles went straight through the foil.
A few were deflected through large angles.
A very few were reflected straight back.
Atoms are mostly space.
The nucleus is very small compared to the size of the atom and it contains most of the mass and all the positive charge.

17. Americium-241
Americium-241 is a radioactive isotope that emits alpha particles.
Americium-241 is found in smoke detectors.
The alpha particles it emits ionise the air molecules, which then can conduct an electric current between two terminals.
If smoke is present it will cling to the air molecules inside the smoke alarm and slows them down so the current decreases and a switch activates the alarm.
Half life is 400 years so its te battery that runs out not the radioactive isotope

18. Alpha (α) Particles - a nuclear reaction
Higher level
Alpha (α) Particles - a nuclear reaction
Mass number: Number of protons + neutrons
Atomic number: Number of protons
An alpha particle
This is called a nuclear reaction
When an alpha particle is emitted the mass number of the atom goes down by four and the atomic number goes down by two.
A new element is made!

19. Alpha (α) Particles
When Alpha particles are emitted they move quite slowly and can be stopped by human skin or a few sheets of paper

20. Beta (β) Particles
Beta particles can be emitted from an unstable nucleus when it disintegrates.
What happens:
a neutron changes into a proton and an electron.
The proton stays in the nucleus and the electron leaves.
Americium-241 emits alpha particles and low energy gamma rays (60 keV, giving a dose at 1 metre of mSv/yr). The alpha particles are absorbed within the detector, while most of the gamma rays escape harmlessly. The americium is present in oxide form in the detector.
The alpha particles emitted by the Am-241 collide with the oxygen and nitrogen in air in the detector's ionisation chamber to produce charged particles called ions. A low-level electric voltage applied across the chamber is used to collect these ions, causing a steady small electric current to flow between two electrodes. When smoke enters the space between the electrodes, the alpha radiation is absorbed by smoke particles. This causes the rate of ionisation of the air and therefore the electric current to fall, which sets off an alarm.
The alpha particles from the smoke detector do not themselves pose a health hazard, as they are absorbed in a few centimetres of air or by the structure of the detector.
Plutonium-241, which is about 12% of the one percent content of plutonium in typical spent fuel from a power reactor, has a half life of only 14 years, decaying to Am-241 through emission of beta particles.  Am-241 has a half life of 432 years, emitting alpha particles (see above) and intense gamma radiation to become neptunium-237.
The beta particle is the electron that leaves the nucleus.
They have a negative charge of -1.

21. Beta (β) Particles
When Alpha particles are emitted they move quickly and are more penetrating than alpha particles
They can go through paper but are stopped by 2 -3mm of Aluminium

22. Beta (β) Particles - a nuclear reaction
Higher level
Mass number: Number of protons + neutrons
Atomic number: Number of protons
An beta particle
When an beta particle is emitted the mass number of the atom stays the same and the atomic number goes up by one.
A new element is made!

23. Nuclear reactions
We have already seen two examples of nuclear reactions involving alpha particles and beta particles
Nuclear reactions cause changes in the nucleus – they involve protons and neutrons
They cause elements to change into other elements
In chemical reactions elements combine with one another to form compounds, compounds break up to form elements and elements in compunds rearrange to change one element into another
Nuclear reactions are very different to chemical reactions
where one element cannot be changed into any other

24. Carbon-14 is a radioactive isotope that emits beta particles when it decays.
Carbon dating is a method used for estimating the age of materials that contain carbon – like paintings, fabric and wood.
When an organism is alive it contains carbon-12 and carbon-14 in the proportions it is present in the air
After the death of an organism the unstable carbon-14 decays but the stable carbon -12 stays the same.
By measuring the ratio of carbon-12 levels to carbon-14 levels in an object the age can be estimated.
Carbon-14 is an isotope of carbon that has a half life of 5700 years.
When an organism is alive it will have same levels of carbon in it as the atmosphere

25. Gamma (γ) rays
Gamma rays can be emitted from an unstable nucleus when it disintegrates.
They are made up of electromagnetic radiation
They have no mass or charge
They can go through paper or aluminium but can be stopped by Lead

26. Effects of radioactivity

27. Ionising radiation
What happens if radiation is incident upon a living cell?
Radiation can ionise cells which causes cellular damage.
If the exposure is high, it can kill the cell.
If the exposure is lower it can cause cancer.
The higher the exposure, the higher the risk of cancer.

28. Radiotherapy
A carefully controlled beam of gamma rays can be used to kill cancer cells. It must be directed carefully to minimise the damage to normal cells.
However, some damage is unavoidable and this can make the patient ill.
It is therefore a balancing act - getting the dose high enough to kill the cancerous cells, but as low as possible to minimise the harm to the patient.

29. Gamma (γ) rays
Cobalt-60 is a radioactive isotope that emits gamma rays.
It is used in radiotherapy – the treatment of cancer with radiation.
The cancerous cells are more susceptible to radiation damage than normal cells.
The radiation is especially directed onto the tumour so the dose it receives is much higher than in normal cells

30. The penetration power of the three types of radiation.

31. The effects of a field on radiation
Beta radiation has a –1 charge and a small mass so is strongly deflected
Gamma radiation has no mass or charge so it is not deflected.
Alpha radiation has a +2 charge but a RAM of 4 so is only weakly deflected.
The effect of a magnetic or electric field on radiation depends upon the nature of the radiation.

32. Radioisotopes
Most elements have isotopes, sometimes the isotopes are radioactive.
Unstable radioactive isotopes are called radioisotopes
Examples –
Carbon – 14
Americium -241
Caobalt - 60

33. Half life It is impossible to tell when a radioactive atom will decay
Def Half life is the time taken for half of the radioactive atoms in a sample to decay.
Half life's vary : radium-214 has a half life of 20 minutes while raduim-226 has a half life of 1,620 years!
It is useful to be able to predict approximately how many radioactive atoms will decay in a certain period of time

34. Graphical representation of half life
Decay rate (counts/min)
What is the half life of the radioisotope represented by the following graph? 80 60 40 20
The time it takes the count rate to decrease from 80 per min to 40 per min is what?
2 mins
Time (min)
The half life of the radioisotope is 2 mins.

35. Is safe disposal of such material achievable?
Some of the radioactive waste from nuclear power plants has a half life of millions of years….
Is safe disposal of such material achievable?

36. Radioactive waste
The current solutions are:
Store it at the nuclear power station until is filled up.
Dump it far out at sea.
Store it deep underground in non-permeable rock.

37. Background radiation
Background radiation is the radiation all around us. Working in pairs try to think of five possible sources of background radiation.
You have FIVE minutes!!
Rocks
Air
Building materials
Outer space
Food

38. Radioactivity is widespread…
We are surrounded by a low level of ionising radiation all the time…
Source of radiation
Percentage
Radon gas
60%
Rocks and soil
10%
Food and drink
Cosmic rays
Medical 9%
Nuclear waste
Less than 0.1%
known as background radiation
Radon gas: comes from rocks in the ground - Enters the soil from the soil beneath the house or from the buildings themselves – can be breathed into the lungs and stay there for some period of time.

39. Radon:drak red over 20%, light red 10 -20% dark yello 5-10% light yellow 1- 5% white less than 1%

40. Nuclear Power - fission
Fast neutron from previous decay cause the Uranium nucleus to split.

41. Nuclear Power Kr n
Fission
More
decays n n
Uranium n
In the reaction above a neutron from a previous decay can lead to more and more decays. Ba
This is called a chain reaction.

42. The penetration power of the three types of radiation.  
Skin or paper
stops ALPHA
Thin aluminium
stops BETA
Thick lead
reduces GAMMA
Thin mica