P2.5.2 Atoms and Radiation

P2 Physics

KS4 ADDITIONAL SCIENCEMr D Powell

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Connection

• Connect your learning to the content of the lesson

• Share the process by which the learning will actually take place

• Explore the outcomes of the learning, emphasising why this will be beneficial for the learner

Demonstration

• Use formative feedback – Assessment for Learning

• Vary the groupings within the classroom for the purpose of learning – individual; pair; group/team; friendship; teacher selected; single sex; mixed sex

• Offer different ways for the students to demonstrate their understanding

• Allow the students to “show off” their learning

Activation

• Construct problem-solving challenges for the students

• Use a multi-sensory approach – VAK• Promote a language of learning to

enable the students to talk about their progress or obstacles to it

• Learning as an active process, so the students aren’t passive receptors

Consolidation

• Structure active reflection on the lesson content and the process of learning

• Seek transfer between “subjects”• Review the learning from this lesson and

preview the learning for the next• Promote ways in which the students will

remember• A “news broadcast” approach to learning

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What is this all about? SThere was a time when ladies could buy skin cream which contained small amounts of radioisotopes.

The skin would feel warm and have a lovely pink look.

It worked by actually killing the skin cells, just like if you were burned.

Many women died too because of skin cancer.

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Further...

using hot-cross buns to show the ‘plum pudding’ model

using dice to demonstrate probabilities involved in half-life

using Geiger counters to measure the penetration and range in air of the radiation from different sources.

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P2.5.2 Atoms and Radiationa) Some substances give out radiation from the nuclei of their atoms all the time, whatever happens to them. These substances are said to be radioactive.

b) The origins of background radiation.

c) Identification of an alpha particle as two neutrons and two protons, the same as a helium nucleus, a beta particle as an electron from the nucleus and gamma radiation as electromagnetic radiation.

d) Nuclear equations to show single alpha and beta decay.

e) Properties of the alpha, beta and gamma radiations limited to their relative ionising power, their penetration through materials and their range in air.

f) Alpha and beta radiations are deflected by both electric and magnetic fields but gamma radiation is not.

g) The uses of and the dangers associated with each type of nuclear radiation.

h) The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level.

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Cartoon Video.....

a) Some substances give out radiation from the nuclei of their atoms all the time, whatever happens to them. These substances are said to be radioactive.

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Plenary.... M

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Your skin – a barrier? MYou might think that alpha was the least dangerous because it can't even get through paper. When handled carefully it is safe.

It is most dangerous when it comes in contact with the skin or gets inside the body.

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Geiger Muller Tube / Detectors - recap

This rock is radioactive. It must contain at least one unstable isotope and as this isotope decays it emits nuclear radiation. The ratemeter clicks as it detects the radiation and gives us a reading in counts per second.

The blue badge above contains a piece of photographic film when it is exposed to radiation the film, which starts white, is blackened. The darker it gets the more radiation has fallen on it.

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Geiger Muller Tube in Detail...

mica window

Argon gas

counter

collision & ionisation

radiation

124125

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.

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.

The Argon contains a little

bromine to act as a quenching agent and

prevent continuous discharge.

Good at detecting alpha and beta, not as good at detecting gamma.

Argon gas

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b) The origins of background radiation.

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Background Radiation....

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c) Identification of an alpha particle as two neutrons and two protons, the same as a helium nucleus, a beta particle as an electron from the nucleus and gamma radiation as electromagnetic radiation.

d) Nuclear equations to show single alpha and beta decay.

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AlphaThese are very small, heavy, positively charged particles. They are made up of a little cluster of 2 protons and 2 neutrons stuck together.

They do not travel as fast as the other 2 types of radiation. When moving through the air they bash into anything near them and do a lot of damage but lose their energy very quickly. Alpha particles are like cannon balls.

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Beta

These are very small, light, very fast moving negatively charged particles. They are actually electrons which have come from the nucleus. (even though there aren't any in there!) Because they travel very fast they travel further than alpha particles. The damage they do is much more spread out. Beta particles are like bullets from a rifle.

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Gamma

These are similar to X Rays. They are not particles but electromagnetic waves so they have no mass or charge and travel at the speed of light.

They go through most things easily but can be stopped by thick lead

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Quick Summary

1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 neutrons – the nucleus of a helium atom)

2) Beta () – an atom decays into a new atom by changing a neutron into a proton and electron. The fast moving, high energy electron is called a beta particle.

3) Gamma () – after or decay surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed.

Unstable nucleus

Unstable nucleus

Unstable nucleus

New nucleus

New nucleus

New nucleus

Alpha particle

Beta particle

Gamma radiation

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Copy and Complete....

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Extension for Fun!

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e) Properties of the alpha, beta and gamma radiations limited to their relative ionising power, their penetration through materials and their range in air.

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Your skin – a barrier? MYou might think that alpha was the least dangerous because it can't even get through paper. When handled carefully it is safe.

It is most dangerous when it comes in contact with the skin or gets inside the body.

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Which word links all of these images... S

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Penetration Power....

Thin mica Thin aluminiumstops BETA

Thick leadreduces GAMMA

Skin or paper stops ALPHA

The radiation can be stopped or “absorbed by different substances in different ways...

MMake a note of this in your book...

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Summary Questions...

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Thickness control...

Hydraulicram

detector

Electronic instructions to adjust rollers.

Beta Source

The source strength controls the hydraulic ram as the substance gets thicker or thinner. It is negative feedback!

Make a note of how this works in your book, include a diagram to help you explain it…

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Sterilising Food

Gamma rays are used to kill bacteria, mould and insects in food. This can be done even after the food has been packaged. It can affect the taste, but supermarkets like it because it lengthens the shelf life.

Gamma rays are also used to kill bacteria on hospital equipment. It is particularly useful with plastic equipment that would be damaged by heat sterilisation.

Gamma Sourceunsterilised sterilised

Make a note of how this works in your book, include a diagram to help you explain how it works…

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Smoke Detectors

Alpha radiation

Air molecules Ionised atoms current

smoke ions current

lower Goes off

Bacteria and fungi

Gamma radiation can be used to sterilise the food in plastic containers or vacuum packs. The gamma kills the bacteria and fungi.

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Multichoice Questions.... P

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f) Alpha and beta radiations are deflected by both electric and magnetic fields but gamma radiation is not.

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Field Effects

Gamma radiation has no mass or

charge so it is not deflected.

Beta radiation has a –1 charge and a small mass so is strongly

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.

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Three Types Main Summary - recap

There are 3 types of nuclear radiation that we need to know about.

They are named after the first 3 letters of the Greek alphabet; alpha, beta and gamma.

The three types of radiation have different properties. You should learn the table below.

How far they can

travel in air

What is needed to stop them

Are they deflected by magnetic & electric fields

charge / mass

alpha particles α a few cm paper yes +2/4 =+2

Beta particles β 20 - 30 cm thin metal Yes (strongly) -1/(1/1840) =-1840

gamma rays γ several m thick lead no 0/0

TASK

Make a note of this table – think about why they deflect?

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g) The uses of and the dangers associated with each type of nuclear radiation.

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Formation of Ions

When an electron is removed from an atom the overall charge will increase by +1 as an electron is -1 charged

When an electron is added to an atom the overall charge will decrease by -1 as an electron is -1 charged

This example shows the formation of a simple ionic crystal, sodium chloride. A Chlorine atom steals one from a sodium, forming ions and an attraction strong enough to bond them together.

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Radiation Effects - Ionisation

Radiation can produce this effect as it is high energy.

Gamma does this by high energy rays knocking out an electron from the atom. (1/10000 chance)

TASK

Can you write a sentence to explain how each effect might happen. Gamma is done for you (including diagram..)

1. Alpha (charged +2) (1/10 chance)

2. Beta (charged -1 is in fact an electron) (1/100 chance)

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Ionisation MNuclear radiation is dangerous. It is dangerous because it damages the molecules in our cells so that they don't work properly. The cell may die. If you are exposed to a lot of radiation then a lot of cells may be killed and you would be very ill.

The molecules are damaged because atoms which make up the molecule are ionised. This means that when the radiation bashes into them it knocks off electrons from the outside of the atom. They become ions. One alpha or beta particle has enough energy to cause thousands of ionisations.

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Types of Radiation...

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Multichoice.. M

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Decay Equations....

Can you complete the four equations using conservation of mass laws....

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Put a-j in your book and do T/F S

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Quick Questions M

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Multichoice.... P

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Cancer I

What would happen if nobody died? Imagine also that the people alive kept having children. What would happen to the planet?

Most of the cells in our body are only supposed to last for a certain time. A months or a few years at the most.

Their life cycle is controlled by genes in the nucleus of the cell. Sometimes these genes don't work properly and the cells multiply rapidly and don't die. This is what cancer is.

It is very hard to fight cancer because it our own body cells which are the problem so our immune system doesn't recognise them as a threat.

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Cancer II

Cancer may be caused by a number of things.

Some people inherit faulty genes off their parents which increase the chances of them getting cancer at some time in their life.

Some chemicals can cause cancer. There are lots of these in cigarette smoke.

Ionising radiation can cause cancer if it damages the molecules in our genes.

The more radiation you are exposed to the greater the risk of cancer.

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Using Tracers M

C/D

TASK

Imagine you are the radiographer carrying out the procedure Can you explain what each of the technical terms mean in this article. Write them out like a glossary!

Christine is an athlete hoping to compete at international level. She has trained long and hard in order to compete in the long jump at the European Championships. Unfortunately, she has suffered recurring pain beneath her right knee. X-rays at her local hospital have revealed no evidence of injury. Her surgeon suggests that she visits the Nuclear Physics Department to undergo further investigation. As part of the investigative procedure, Christine is injected with a solution of a radioactive isotope called technetium-99. Technetium-99 is a gamma emitter. The solution was delivered to the operating theatre in a special lead-lined protective container. The movement of the solution in her bloodstream was traced. When the solution reached her knee joints a gamma camera was used to take a photograph. The particular isotope used has a short half-life. The photograph revealed an increased absorption of the isotope in Christine’s right knee when compared to the same location in her left knee. The consultant diagnoses a strain injury that requires prolonged rest.

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h) The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level.

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Half-life – Curse of the Mummy

The activity of a radioactive source decreases with time because the number of unstable nuclei is decreasing.

The half-life of a source is a measure of how long it takes for the activity of a source to reach half of its initial value.

Learning about the process of Carbon dating.

Analysing Science writing and “truths” in modern media articles.

Lessons 2

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Quick Radioactive Questions

1) What is the charge on a beta particle? (electron)

2) What is the charge on a proton?

3) Where do you find a neutron?

4) Where are electrons found in an atom?

5) What is an alpha particle?

6) What do we mean by the term “gamma radiation”

1) -1

2) +1

3) In the nucleus

4) Orbiting the nucleus

5) 2p & 2n

6) A high energy wave emitted during radioactive decays.

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Carbon Dating

• This method of scientific dating is used for samples which were once alive i.e. bone, charcoal and woven materials.

• All the above examples contain carbon, a proportion of which is radioactive C14, an isotope that is continuously being formed in the upper atmosphere.

• As living organisms take up radioactive carbon along with other carbon atoms, the ratio between the two forms remains constant.

• However when they die the radioactive carbon decays and is not replaced.

• Since it decays at a known constant rate, the decreasing concentration of C14 can be measured and the date when the material died estimated.

FACT?

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Half Life Graphs

For the radioactive carbon in this reed matting it takes 5730 years for half the sample to decay. Then a further 5730 years for half of the new sample to decay.

This continues for about 10 “half lives” until all the C14 has decayed.

This is called the half-life of the material and is a constant.

Different isotopes have different half-life times which we can use in all sorts of processes.

0

5000

10000

15000

20000

25000

30000

0 10000 20000 30000 40000 50000 60000

Time in Years

Rad

iio

acti

ve C

ou

nts

FACT?

Movie

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On November 4th, 1922 Howard Carter discovered the tomb of Tutankhamun (1336-1327 BC) in the Valley of the Kings, Luxor, Egypt.

When Carter arrived home that night his servant met him at the door. In his hand he clutched a few yellow feathers. His eyes large with fear, he reported that the canary which he had used to help them find the tomb had been killed by a cobra. Carter, a practical man, told the servant to make sure the snake was out of the house.

The man grabbed Carter by the sleeve and said "The pharaoh's serpent ate the bird because it led us to the hidden tomb! You must not disturb the tomb!"

Scoffing at such superstitious nonsense, Carter sent the man home.

The Curse of the Mummy

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Carter immediately sent a telegram to his backer Lord Carnarvon and waited anxiously for his arrival.

Carnarvon arrived several days later and watched as Carter made a hole in the door to the tomb. Carter leaned in, holding a candle, to take a look. Behind him Lord Carnarvon asked, "Can you see anything?" Carter answered, "Yes, wonderful things."

The tomb was intact and contained amazing treasures. The day the tomb was opened was one of joy and celebration for all those involved. Nobody seemed to be concerned about a curse.

However, a few months later tragedy struck.....

The Curse of the Mummy

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Lord Carnarvon, 57, was taken ill and rushed to Cairo.

He died a few days later. The exact cause of death was not known, but it seemed to be from an infection started by an insect bite.

Legend has it that when he died there was a short power failure and all the lights throughout Cairo went out.

On his estate back in England his favourite dog howled and dropped dead.

The Curse of the Mummy

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Even stranger was that when the mummy of Tutankhamun was unwrapped in 1925, it was found to have a wound on the left cheek in the same exact position as the insect bite on Carnarvon that caused his death.

By 1929 eleven people connected with the discovery of the Tomb had died early and of unnatural causes. This included two of Carnarvon's relatives, Carter's personal secretary, Richard Bethell, and Bethell's father, Lord Westbury. Westbury killed himself by jumping from a building. He left a note that read, "I really cannot stand any more horrors and hardly see what good I am going to do here, so I am making my exit."

The press followed the deaths carefully attributing each new one to the "Mummy's Curse."

The Curse of the Mummy

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By 1935 they had credited 21 victims to King Tutankhamen. Was there really a curse? Or was it all just the ravings of a sensational press? Or perhaps, the power of a curse is in the mind of the person who believes in it.

Howard Carter, the man who actually opened the tomb, never believed in the curse and lived to a reasonably old age of 66 before dying of entirely natural causes.

Carbon dating tests have confirmed historical records to show the mummy of Tutankhamen to be about 3400 years old

The Curse of the Mummy

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Answers....

Victim Circumstances surrounding death Scientific conclusions…

Tutankhamun Had a wound on cheek when found

Not sure how he died but wound could have been a reason

Canary Eaten by Cobra, feathers left Snakes eat birds this is not uncommon

Lord Carnarvon Insect infected bite on cheek before dead

In Egypt bites could become infected without antibiotics and cause blood

poisoning

Lord Carnarvons Dog

Just howled and dropped dead!

May have had any number of different problems just coincidence

Lord Westbury Committed suicide by jumping

Sounds like he was upset by his own circumstances more than a curse!

Howard Carter Natural Causes aged 66At that time lots of people did not live

past 66 years old and this was a normal age to die

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Answers....

2) How many people in total were said to have died from the curse? 21

3) Does the article give enough scientific reasoning for any of the deaths you looked at to form a valid conclusion?

3) No it does not as all the reasons were coincidental and could be explained away by other things. They did not even link or have a pattern.

4) Would a conclusion drawn from the evidence have any degree of certainty?

4) No as the article did not give enough background detail about the cases to say that there definitely was not a pattern. But if you tried to say there was a pattern you could not really back it up so there would be no certainty that you result was valid.

5) The media often feature such reports which lack scientific detail is this a right or wrong thing to do?

5) Wrong this to do as they are trying to lead the reader into believing something which cannot be backed up by evidence. If you are not careful you start to think things are true which are not.

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Your Task

• You decide if this curse is real by looking at the scientific evidence on your worksheet. (Answering the questions will help you).

• You must try and work out the fact from the fiction and reason it all out.....

FACT?

FICTION?

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Questions...

There are 5 suggested decay patterns from isotopesA-E in the table show below.

1) Only one of the isotopes is real, can you pick out which one is real?

2) What is the half-life time?

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Questions...

The graph shows how a sampleof 16 grams of Strontium-90decays?

3) What percentage of atoms would be left after 84 years?

4) What mass of atoms would be left after 28 years?

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Questions...

5) If the y-axis is scaled in grams for this isotope. How many grams of material have decayed and are safe after 240 seconds?

6) Would this isotope be suitable for carbon dating?

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Questions...

A human female died thousands of years ago in the central rift valley in Kenya. Her body was buried with her stone tools and some clothing made of woven water reeds. Some time later in 2006 a team of archaeologists excavated her remains and tried to work out how long ago that she died.

7) What items could they test for carbon content?

8) What about the stone tools?

9) If she died about 40,000 years ago. Roughly how many times would the radioactive count halved?

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Questions...

10) Is there any truth in this joke?

“Don’t worry if you can’t remember your age Granddad we’ll get you carbon dated”

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HSW - Graph Skills

1. The table shows the activity of a sample of a radioactive source. What type of data is the activity?

2. On a fullsize A4 piece of graph paper plot the graph to show how the activity changed over the 16 hours. Think about which type of graph you should plot and why.

3. Use the graph to determine the half life of the source. (try several calculations)

4. Estimate the activity of the source after 18 hours.

5. Comment on the dangers of the source over 16 hours?

Answers3. 3.2 hours4. At 18 hours

activity 15-205. The danger

reduces

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Graphs Match Up PB-D

C

D

A

E

B

F

Complete

Gamma sterilisation

Atomic Bombs

29y

5700y

8 days

6 hours

4500 mill years

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Quick Multichoice

P2.5.2 Atoms and Radiation