Radiation True or False?

1. You are being bombarded with radiation right now.

2. You are giving off radiation right now

3. Your breakfast was irradiated with deadly radiation

4. You can see radioactivity

5. You can feel radioactivity

6. Radioactive substances are only harmful if you touch them

7. If you are irradiated then you become radioactive

8. Radioactivity is not very useful

9. We completely understand what causes radioactivity

10. Do you know the three types of radioactivity. Write them down..

True

True

True ??

False

False

FalseFalse

False

False

?

DP 5.1: Distinguish between stable and radioactive isotopes and describe the conditions under which the nucleus is unstable.

Alpha radiation - or 42He

Helium nuclei

Description:

2 neutrons, 2 protons (helium nuclei)

Electric Charge:

+2

Relative Atomic Mass:

4

Penetration power:

Stopped by paper or a few cm of air

Ionisation effect:

Strongly ionising

Effects of Magnetic/Electric Field:

Deflected towards the negative ?

Beta radiation - or 0-1e

high energy electron

Description:

High energy electron

Electric Charge:

-1

Relative Atomic Mass:

1/1860

Penetration power:

Stopped by few mm of aluminium

Ionisation effect:

Weakly ionising

Effects of Magnetic/Electric Field:

Strongly deflected towards the positive

positron radiation - or 01e

high energy positron

Description:

High energy electron

Electric Charge:

+1

Relative Atomic Mass:

1/1860

Penetration power:

Stopped by few mm of aluminium

Ionisation effect:

Weakly ionising

Effects of Magnetic/Electric Field:

Strongly deflected towards the negative

Gamma radiation -

Electromagnetic radiation

Description:

High energy electromagnetic radiation

Electric Charge:

0

Relative Atomic Mass:

0

Penetration power:

Reduced by several cms of lead or several metres of concrete

Ionisation effect:

Very weakly ionising

Effects of Magnetic/Electric Field:

NO deflection

Thin mica Thin aluminiumstops BETA

Thick leadreduces GAMMA

Skin or paper stops ALPHA

The penetration power of the three types of radiation.

Which type of radiation is…..

1. The most penetrating?

2. The least penetrating?

3. Least dangerous outside the body?

4. Most dangerous inside the body?

5. High energy electrons?

6. Has a negative charge?

7. Is weakly ionising?

8. Has zero charge and zero mass?

9. Only reduced in intensity by lead and concrete?

Gamma

Alpha

Alpha

Alpha

Beta

Beta

Beta

Gamma

Gamma

So what exactly does cause this radiation?

First we need to look at the structure of the atom

Draw diagrams to represent:

How did you go?

6 protons

7 neutrons

6 electrons

6 protons

8 neutrons

6 electrons

6 protons

6 neutrons

6 electrons

What do we call these?

6 protons

7 neutrons

6 electrons

6 protons

8 neutrons

6 electrons

6 protons

6 neutrons

6 electrons

Atoms of the same element containing the same number of protons but different numbers of neutrons in their nuclei.

Isotopes

Because they have the same number of electrons there is NO difference to their chemical behaviour.

Stable and unstable Isotopes

• Over 2000 different isotopes have been discovered so far.

• If the nucleus of the isotope spontaneously emits radiation it is said to be unstable or radioactive.

• Unstable isotopes are called radioisotopes (or radioactive isotopes).

• Radioactive isotopes are unstable. They emit radiation as they spontaneously release energy. This is called radioactive decay. .

.

Stable and unstable Isotopes

p = n

For light elements, stable nuclei have a proton:neutron ratio close to 1:1.

For heavy elements the stable nuclei have a proton:neutron ratio close to 1:1.5Most nuclei out of these ranges are unstable

Stable and unstable Isotopes

All nuclei with p >83 are unstable.

alpha emission

• When a nucleus emits an alpha particle it loses 2 protons and 2 neutrons, the same as a helium nucleus.

• Gamma rays are often emitted along with alpha decay. Radon, plutonium, polonium all have alpha emitting isotopes.

• Example:

• 23892U 4

2He + 23490Th

• Now try these…

• 22086Rn

• 23994Pu

42He + 216

84Po

42He + 235

92U

beta emission

• During beta decay, the nucleus emits an electron. But how?

• A neutron decomposes into a proton and an electron, as follows… 1

0n 1+1p + 0

-1e

• Example: 60

27Co 0-1e + 60

28Ni

• Now you try:

• 146C

• 31H

0-1e + 14

7N0

-1e + 32He

Beta decay is also accompanied by gamma ray emission. Gamma rays are not emitted on their own but accompany alpha or beta decay

positron emission

• During positron, the nucleus emits a positron. But how?

• A proton decomposes into a neutron and a positron (a positive electron), as follows… 1

1P 1on + 0

1e

• Example: 38

19K 01e + 38

18Ar

• Now you try:

• 127N

• 4823V

01e + 12

6C0

1e + 4822Ti

During alpha decay, which of the following is true?

A. Relative atomic mass increases by 2

B. Relative atomic mass decreases by 2

C. Relative atomic mass increases by 4

D. Relative atomic mass decreases by 4

During beta (-) decay, which of the following is true?

A. Atomic number increases by 1

B. Atomic number decreases by 1

C. Atomic number increases by 2

D. Atomic number decreases by 2

Now you try…

• Pg93, Q1, 2, 3 + 5.

Half-life• The time taken for half of the number of atoms in a

sample of radioisotope to decay is called its half-life. Eg.

• The half-life of fluorine-20 is 11 seconds. • The half-life of carbon-14 is 5.7x103 years. • The half-life of uranium-238 is 4.5x109 years.

Radioactive half-life

What is the half life of Carbon-15?

Decay of carbon 15

02468

10

0 1 2 3 4 5 6 7 8 9 10

Time / s

Car

bo

n 1

5 / g

Nu

mb

er o

f ca

rbon

-15

atom

s p

rese

nt

(x 1

08)

Radioactive half-life

The average time taken for half of the substance to decay is called the radioactive half-life.

Decay of carbon 15

02468

10

0 1 2 3 4 5 6 7 8 9 10

Time / s

Car

bo

n 1

5 / g

% A

tom

lef

t u

nd

ecay

ed 100

80

60

40

20

0

DP 5.5Identify one use of a named radioisotope: in industryin medicine

DP 5.6Describe the way in which the above named industrial and medical isotopes are used and explain their use in terms of their properties.

Hydraulicram

detector

Thickness Control Mill

Electronic instructions to adjust rollers.

Beta Source

A radioactive source is on one side of the material and a detector on the other.

If too much radioactivity is getting through, then the material is too thin and the rollers open up a bit to make the material thicker.

If not enough radioactivity is detected then the rollers compress to make the material thinner.

This method is used in the manufacture of lots of sheet materials: plastics, paper, sheet steel.

Leak detection in pipes

The radioactive isotope is injected into the pipe. Then the outside of the pipe is checked with a Geiger-Muller detector, to find areas of high radioactivity. These are the points where the pipe is leaking. This is useful for underground pipes that are hard to get near.

The radioactive isotope must be a gamma emitter so that it can be detected through the metal and the earth where the pipe leaks. Alpha and beta rays would be blocked by the metal and the earth.

The radioactive isotope must be a gamma emitter so that it can be detected through the metal and the earth where the pipe leaks. Alpha and beta rays would be blocked by the metal and the earth.

The isotope must have a short half life so the material does not become a long term problem.

The isotope must have a short half life so the material does not become a long term problem.

GM tube

Cobalt-60 Sterilisation

Gamma rays are used to kill bacteria, mould and insects in ood. Also used to kill bacteria on hospital equipment.

This is useful particularly on packaged food or on plastic items which would be damaged by heat sterilisation.

It can affect the taste and the vitamin content, but it lengthens the shelf life.

Gamma rays are used to kill bacteria, mould and insects in ood. Also used to kill bacteria on hospital equipment.

This is useful particularly on packaged food or on plastic items which would be damaged by heat sterilisation.

It can affect the taste and the vitamin content, but it lengthens the shelf life.

Gamma Sourceunsterilised sterilised

Sterilisation

Cobalt-60 is used as it is a gamma emitter – very penetrating.

It has a half life of 5.3 years so the machines can run cheaply without regular maintenance.

You don’t need external power to produce the gamma rays as you do with x-rays

Cobalt-60 is held in a chemically inert form in a sealed container.

When the cobalt-60 is exhausted it can easily be replaced.

Cobalt-60 is used as it is a gamma emitter – very penetrating.

It has a half life of 5.3 years so the machines can run cheaply without regular maintenance.

You don’t need external power to produce the gamma rays as you do with x-rays

Cobalt-60 is held in a chemically inert form in a sealed container.

When the cobalt-60 is exhausted it can easily be replaced.

Gamma Sourceunsterilised sterilised

Named radioisotopes - industry• Industry - cobalt-60 • Cobalt-60 is used to sterilise food because when it decays by

beta decay it also releases gamma radiation. • Gamma rays are used to kill bacteria, mould and insects in food.

They are also used to kill bacteria on hospital equipment, dressings and bandages.

• This is useful particularly on packaged food or on plastic items which would be damaged by heat sterilisation.

• There are arguments for using cobalt-60 to sterilise food are that it prolongs freshness and so reduces wastage. Arguments against say that it does not effectively kill all bacteria and destroys vitamin content. It may also cause harmful products in the food.

• Cobalt-60 is used because It has a half life of 5.3 years so the machines can run cheaply without regular maintenance. It produces low energy gamma rays which do not make the food radioactive.

• You don’t need external power to produce the gamma rays as you do with x-rays

Where does it come from?

•Co-60 is artificially generated.

Co-59 is bombarded with a neutron in a nuclear reactor59Co + 1n → 60Co

Co-60 is installed in the machine and decays by negative beta and two gamma rays.60Co → 60Ni + 0B + γ + γ

The gamma rays are used to kill bacteria / microbes

27 27

42 43 -1

0

Use of Technetium 99m in medicine

Tc-99m is bound to a carrier molecule

Tc-99m

Technitium-99m is useful because it is a transition metal and chemically binds easily with non-bonding electron pairs on atoms (such as N) in a range of biological molecules which are specific to different organs. It can also be bound to immune system proteins which bind to cancer cells.

It also has a half life of 6 hours so it does not expose the patient to radiation for any significant length of time.

In all other respects the carrier molecule is identical to normal biological equivalent

Tc-99m

The biological molecule is introduced into the body

The Tc-99m is carried to the specific organ (depends on the molecule)

Special gamma cameras then take pictures of the gamma rays emitted by the technetium

Higher signals will be recorded where there is a build up of the radioisotope either in a blood clot, tumour, or constrictions in blood vessels.

The benefits: surgeons and doctors can make an accurate diagnosis without performing surgery

•The problems: Tissue damage – leading to sickness and ultimately death for high exposureCan cause cancer – leukemia/lung – up to 20 years after treatmentGenetic damage causes deformities in offspring.

Where does it come from?

•Tc-99m is artificially generated but has a ½ life of only 6 hours which means it is impractical to deliver it to a hospital.

Mo-98 is bombarded with a neutron in a nuclear reactor98Mo + 1n → 99Mo

Mo-99 is delivered to hospitals where it decays ½ = 66 hrs99Mo → 99mTc + 0B

the Tc-99m is chemically extracted and used 99mTc → 99Tc + γ

The gamma ray is v. low energy and therefore very safe – weakly ionising

42 42

42 43

43 43

-1

0

PM S5 P6 – Use available evidence to analyse benefits and problems with the use of radioactive isotopes in identified industries and machines.

Benefits:

•Non-invasive diagnostic procedures

•Treatement of cancers

•Sensitive monitoring of inductrial processes

•Sterilisation

•Non-invasive examination of pipes / aircraft etc.

Benefits:

•Non-invasive diagnostic procedures

•Treatement of cancers

•Sensitive monitoring of inductrial processes

•Sterilisation

•Non-invasive examination of pipes / aircraft etc.

Problems:

•Tissue damage for people exposed

•Risk of cancer if exposed

•Genetic damages to people exposed

•Hard to dispose of some isotopes (long half-life)

Problems:

•Tissue damage for people exposed

•Risk of cancer if exposed

•Genetic damages to people exposed

•Hard to dispose of some isotopes (long half-life)

More benefits and problems

• In either medicine or industry the problems associated with radiation is its effect on living cells.

• Radiation changes the structure of enzymes so they cannot acts as catalysts.

• The structure of membranes can be changed preventing transport in and out of the cell.

• The structure of DNA molecules can be altered so that it cannot function correctly.

• Sex cells can be altered so that changes can result in defects in offspring.

• Other problems are that some isotopes are made in nuclear reactors so there is the problem of waste products to be dealt with. Also security issues concerned with transport and storage of nuclear waste.

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.

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.

Describe how transuranic elements are produced• Transuranic elements have an atomic number

greater than 92 [uranium].

• These elements are synthesised in nuclear reactors and particle accelerators (cyclotrons).

• Most are radioactive and only exist for short periods.

• In a nuclear reactor the nucleus to be used is bombarded with neutrons produced by uranium decay. Neptunium and americium are produced this way.

• In a cyclotron, target nuclei are bombarded with positive particles such as protons or atoms of helium or carbon, at great speed, until they fuse together on collision.

• Very high speeds are necessary because the positive particles have to fuse with a positive nucleus and the two experience repulsion when near each other. High speeds help to overcome this barrier.

Describe how transuranic elements are produced

• Californium is produced in an accelerator in the following way:

• 23892U + 12

6C 24698Cf + 4(1

0n)

• In both cases the new nucleus formed will be unstable and starts to emit particles and/or radiation in order to become stable.

Describe how transuranic elements are produced

• Neptunium is produced in a reactor: 238

92U + 10n 239

92U 23993Np + 0

-1e

(Uranium-238 is not fissile [will not split on bombardment with neutrons] so forms uranium-239 when hit with a neutron). This rapidly decays to neptunium by beta decay.

• Neptunium rapidly decays to plutonium by beta decay 239

93Np 23994Pu + 0

-1e

(Plutonium can be used to make americium. It is used in energy generation and nuclear weapons. It was also used as a fuel in the long distance craft Voyager and Voyager II, which went on missions to Jupiter, Uranus, Neptune and Pluto. It has a half-life of almost 25,000 years).

Describe how transuranic elements are produced

• Americium is produced in a reactor:239

94Pu + 2(10n) 241

95Am + 0-1e

• Americium is used in most domestic fire alarms• Americium has a half-life of 432 years. • It decays by alpha decay to neptunium and also

releases low energy gamma rays, so very, very small amounts are used in fire alarms (0.2microgram)

• Both neptunium and americium are artificial elements made in reactors

Describe how commercial radioisotopes are produced

• There are about 20 widespread commercial radioisotopes in use, produced by cyclotrons and nuclear reactors.

• An accelerator is a machine that allows positive particles [protons, small nuclei] to be accelerated to high speed, fired at nuclei of atoms with controlled energies in order to study nuclear reaction or make radioisotopes. Accelerators produce neutron-deficient isotopes like fluorine-18.

147N + 4

2He 189F

• Fluorine-18 is used in the treatment of cancers.

• Cyclotrons are found in major hospitals in Sydney, Melbourne and Brisbane to produce useful radioisotopes with short half-lives

• Iodine-123 is also made in a cyclotron.

Describe how commercial radioisotopes are produced

• A nuclear reactor is a device that allows a uranium chain reaction to occur safely, releasing neutrons at a slow and controlled rate. A target is bombarded with neutrons to produce a radioactive species with extra neutrons. Nuclear reactors produce neutron-rich isotopes: iodine-131, strontium-90, cobalt-60.

• Example: 5927Co + 1

0n 6027Co

• Example: Technetium-99m is formed from molybdenum-99, which is a fission product of uranium-235 99

42Mo 9943Tc + -1

0e

• Tc-99m is an important medical diagnostic isotope

Commercial radioisotopes – nuclear reactors • technetium-99m: is formed by the decay of

molybdenum-99, which is a fission product of uranium-235 (when uranium-235 atoms are split when bombarded by neutrons). Molybdenum has a half life of 66 hours so it can be made at Lucas Heights reactor and transported to hospitals all over Australia. Technetium-99m has a half life of 6hrs so is suitable to use in medical diagnosis as it decays rapidly causing minimal damage to the patient. It can be attached to biological molecules [eg. incorporated into blood serum] and used to detect blood clots, tumours, damaged heart tissue.

Commercial radioisotopes – n/reactor•Americium-241: recovered from nuclear waste, used in smoke alarms•Plutonium-238: fuel for space probes•Strontium-90: produces beta particles. Used in industry to monitor paper/card thickness. A long half-life means that it doesn’t need replacing too often

• Cobalt-60: produced when cobalt-59 is bombarded with a neutron. cobalt-60 decays and emits beta particles and gamma rays. Has medicinal and industrial uses.