5th radioactivity ppt

7/28/2019 5th Radioactivity Ppt

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Radioactivity


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The nucleus

The best model of the atom was knownas the Thomson or plum pudding model. The atom was believed to consistof a positive material pudding withnegative plums distributed throughout.


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Geiger and Marsden's experiment This experiment changed the way we

think of the atom.Since particle accelerators were yet tobe developed, naturally occurring highenergy particles were used asprojectiles. Alpha particles arespontaneously emitted by certain heavyelements. These particles have speeds ofthe order of 10 7 m/s.


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These were made incident on thin filmsof metals of high atomic weight, such asgold.


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The number of neutrons in the nucleus isless crucial. You can change the numberof neutrons without changing thechemical properties of the atom. So itbehaves in the same way. Atoms with the

same proton number but differentnumbers of neutrons are called isotopes . H, H, H are isotopes of hydrogen

1

12

1

3

1


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Radioactive tracers in plants



Food Irradiation



Food irradiated by exposing it to thegamma rays of a radioisotope -- one that

is widely used is cobalt-60. The energyfrom the gamma ray passing through thefood is enough to destroy many disease-causing bacteria as well as those thatcause food to spoil, but is not strongenough to change the quality, flavor ortexture of the food. It is important to

keep in mind that the food never comesin contact with the radioisotope and isnever at risk of becoming radioactive.



Some meats are irradiated. Pork, forexample, is irradiated to control thetrichina parasite that resides in themuscle tissue of some pigs. Poultry isirradiated to eliminate the chance offood borne illness due to bacterialcontamination.


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Thickness control

Beta radiation sourcescan be used to measurethe thickness ofmaterials. Beta

radiation canpenetrate paper,plastic and other thinmaterials. However

the count will bereduced, and from thisreduction thethickness of thematerial can be gauged.



Radioactivity Some atoms are unstable. They have too

much energy or the wrong mix ofparticles in the nucleus. So to makethemselves more stable, they breakdown(or decay) and get rid of some matterand/or some energy. This is calledradioactive decay and isotopes of atoms

that do this are called radioisotopes .



The process is spontaneous and random.You cant do anything to speed it up orslow it down- spontaneous.

You cant predict when it will happen -random (Cant predict which atom will

decay at any given time. The only reasonwe can do any calculations onradioisotopes is because there are huge

numbers of atoms in most samples so wecan use statistics to accurately predictwhats most likely to happen.



Radioactive Decay is a Random Process

You can NEVERtell when anindividual atom is going to decay.

You can figure out approximatelyhow many atoms in a group aregoing to decay in a certain time,but you cant tell which ones are

going to blow. The timescale for radioactivedecay is described by the quantitycalled a half - life.

Half-lives can be VERY short(helium-5 decays in 7.6 x 10 -22 seconds), or very long (thorium-232 decays in 1.4 billion years).



Precautions for Using RadioactiveMaterial

Label all containers with a radioactive material label andspecify the isotope No eating, drinking or smoking in the laboratory Use spill trays and absorbent covering

Use fume hoods for handling potentially volatilematerial Use glove/ box for handling large quantities of volatile

material

Wear laboratory coat, disposable gloves, and laboratorysafety glasses Use gloves appropriate for the chemicals to be handled Use automatic or remote pipetting devices. NEVER

pipette by mouth.



G-M tube



Cloud Chamber

The cloud chamber , also known as theWilson chamber , is used for detectingparticles of ionizing radiation. In itsmost basic form, a cloud chamber is asealed environment containing asupercooled, supersaturated water oralcohol vapour. When an alpha particleor beta particle interacts with themixture, it ionises it.



symbol Nature Penetrating power Relativemass

RelativeCharge

Relativespeed

Heliumnuclide

Stopped by paper or the skin.

Range in air isshort

4 +2 1/20 thespeedof light

Fastmoving

electrons

Stopped by thinmetal. e.g.

Aluminum foil

negligible -1 Variable- up to90%

speedof light

Electro-magneticradiation

Reduced by manycms of lead or a

few metres of concrete

0 0 Speedof light



Background radiation

Background radiation is the radiation all around us.Working in pairs try to think of five possiblesources of background radiation.

You have FIVE minutes!!

Rocks Air

Building materials

Outer space

Food



Safety first

There are several types of radiation. They differ in whateffects they have and their nature.

All radioactive sources must be handled safely.

Do you know what the hazard symbol for radiation is?

As well as the normal laboratory safety instructions you followare there any extra rules concerning radioactivity?


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h i f h h



Thin mica Thin aluminiumstops BETA

Thick leadreduces GAMMA

Skin or paper stops ALPHA

The penetration power of the three typesof radiation.

Th ff f fi ld di i



The effects of a field on radiation

Gammaradiation has nomass or charge

so it is notdeflected.

Beta radiation has a 1charge and a small mass so

is strongly deflected

Alpha radiationhas a +2 charge

but a RAM of 4 sois only weaklydeflected.The effect of a magnetic or electric field on radiation depends

upon the nature of the radiation.



Effect of Magnetic field

U i l f h i h


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Using your results from the previous threeinvestigations, fill in the table below:

Alpha Beta Gamma

Penetrating power

Range of radiation

Most dangerousoutside of body

Most dangerousinside of body

Affected by amagnetic field

least medium most

Less than10 cm. medium longest

least medium most

most medium least

yes yes no

Al h di ti


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Alpha radiation -

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:

Weakly deflected

B t di ti


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Beta radiation -

high energy electron

Description:

High energy electronElectric Charge:

-1


1/1840th

Penetration power:

Stopped by few mm of aluminium

Ionisation effect:Weakly ionising


Strongly deflected

G di ti


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Gamma radiation -

Electromagnetic radiation

Description:

High energy electromagnetic radiation

Electric Charge:

0


0Penetration power:

R e d u c e d by several cms of lead or several metres of concrete

Ionisation effect:

Very weakly ionising


NO deflection

M t h th di ti


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Match the radiation

Alpha

Beta

Gamma Heliumnuclei

High energyelectron

Electromagneticradiation

Stopped bypaper or skin

Reduced bylead

Stopped byaluminium

Ionising radiation


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Ionising radiation

If the exposure is high, it can kill the cell.

If the exposure is lower it cancause cancer.

The higher the exposure, the higher the

risk of cancer. Alpha is the most ionising radiation, gamma is the least.

What happens if radiation is incident upon a living cell?

Ionising radiation can be used to kill cancer cells.

Radiation can ionise cells whichcauses cellular damage.

Ionisation questions


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Ionisation questions

1. What is ionisation?

2. How is a neutral atom positively ionised?

3. How is a neutral atom negatively ionised?

4. What two effects on living cells can ionisation have?

5. Which type of radiation is the most ionising?

6. Which type of radiation is the least ionising?

When a neutral atom loses or gains electrons and hence charge.

By losing electrons.

By gaining electrons .

Kill cells or cause cancer.

Alpha radiation .

Gamma radiation.


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Uses of radiation


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Uses of radiation

Sterilisation


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Sterilisation

Gamma rays are used to kill bacteria, mould and insectsin food. This can be done even after the food has been

packaged. It can affect the taste, but supermarkets likeit because it lengthens the shelf life.

Gamma rays are also used to kill bacteria on hospitalequipment. It is particularly useful with plastic equipment

that would be damaged by heat sterilisation.

Gamma Sourceunsterilised sterilised

Radiotherapy


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Radiotherapy

A carefully controlled beam of gamma rays can beused to kill cancer cells. It must be directedcarefully 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 dosehigh enough to kill the cancerous cells, but as lowas possible to minimise the harm to the patient.

Leak detection in pipes


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Leak detection in pipes

The radioactive isotope is injected into the pipe. Then theoutside of the pipe is checked with a Geiger-Muller detector,

to find areas of high radioactivity. These are the pointswhere the pipe is leaking. This is useful for undergroundpipes that are hard to get near.

The radioactive isotope must be a gamma emitter so that it can bedetected 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 musthave a short half lifeso the material doesnot become a longterm problem.


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Photographic film


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Photographic film

1. What happens to film when radiation is incidentupon it?

It darkens.

2. Can photographic film tell you the type of radiationincident upon it?

No, just the amount of radiation received.

3. What can this be used for?Can be used in radiation badges, that record theexposure of workers to radiation. Different windowsdetect different types of radiation.

Geiger-Muller Tube


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mica window

Argon gas

Geiger Muller Tube

counter

collision & ionisation

radiation

124125

The detector is a metal tube filled with gas. The tube has a thin wiredown the middle and a voltage between the wire and the casing.

When the radioactivity enters the tube,it ionises the gas in the tube. Thisproduces a pulse of current which isamplified and passed to a counter.

The Argoncontains a little

bromine to act as

a quenchingagent andprevent

continuousdischarge.

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

Argon gas

The Spark Detector


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The Spark Detector

The spark detector consists of a metal grid and a metalstrip. A high voltage is applied between the grid and thestrip. The voltage is increased until electrical arcing(sparking) across the gap just occurs.

When ionising radiation is placed close to the detector there is a marked increasing in the amount of sparking.

High voltagesupply

Which type of radiation willbe detected the best?

Why?

Cloud chamber


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Cloud chamber

Cloud chambers show the actual paths of the ionising particles.They rely on ionisation. The cloud chamber is cooled and then is

super-saturated with alcohol. If an ion is formed a droplet of condensation appears. Best for alpha radiation as alpha mostionising; then Beta which shows faint traces, but cloud chambersare not as good for gamma as gamma is only weakly ionising.

Solid carbon dioxide

Radioactive source Cooled alcohol vapour


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What is a Half-Life? The half-life (t ) is the amountof time that it will take half of

the atoms to decay. This doesnot mean that in twice thatamount of time, all the atoms

will decay. Since this is arandom process, there is nohistory and you have to startover, so in the second half-life,half of the remaining atoms willdecay, leaving a quarter of theoriginal atoms.

Note: All the atoms will still bethere, but the ones that havedecayed will be a differentelement.

. . .

N undecayed atomsTime (T) = 0

N/1024 undecayed atoms1023/1024 x N something else

T = 10 x t

N/8 undecayed atoms7/8 x N something else

T = 3 x t

N/4 undecayed atoms3/4 x N something else T = 2 x t

N/2 undecayed atomsN/2 something else T = t


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Radioactive Decay Kinetics - plot


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The percentage of carbon-14 found inthis wooden bow:

25%What is the age of the bow?


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The percentage of carbon-14 found inthis wooden bow:

12.5%What is the age of the skull?


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Applications of Radioactive Decay Kinetic

Nuclide Half life219Th90 1 s26Na11 1s40

Cl17

1.4 min32P15 14.3 d14C6 5730 y235U92 7.04x108 y238U92 4.46x109 y

Half life is not affected by chemical andphysical state of matter.

Anthropologists, biologists, chemists,diagnosticians, engineers, geologists,physicists, and physicians often useradioactive nuclides in their respectivework.


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Radioactive Decay

What happens to the nucleus ofan atom when it emits a

radiation?


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Alpha Decay

When an unstable nucleus emits an alphaparticle it loses 2 protons and 2neutrons

For example,Radium 226 decays by alpha emission

22688

Ra 22286

Rn + 42

He

Note: The atomic and mass numbers on both sides of the equation balance.


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Beta decay

Beta decay is more complicated. A beta particle is anelectron. But where does this electron come from?

When an unstable nucleus emits an electron a neutronin its nucleus changes into a proton and an electron.The electron is emitted.

For examplePolonium-218 decays by beta emission

21884

Po 21885

At + 0-1

e

Note: The atomic and mass numbers on both sides of the equation balance.


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Gamma Decay

After an alpha or beta particle has beenemitted from the nucleus of an isotope,the nucleus has too much energy.

Too get rid of that excess energy, agamma wave is emitted.


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Summary

Alpha Decay

Beta Decay

22688

Ra 22286

Rn + 42

He

21

884

Po 21

885

At + 0

-1

e


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Which type of radiation is the most penetrating?

A. Alpha

B. BetaC. Gamma

D. X rays


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Which type of radiation is the most damaging

inside the body?

A. Alpha

B. BetaC. Gamma

D. X rays


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Which type of radiation is the most dangerousoutside the body?

A. Alpha

B. BetaC. Gamma

D. X rays


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Which of the following is not a use of radiation?

A. Pre-natal scans

B. RadiotherapyC. Smoke detectors

D. Detecting leaks


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Nuclear Reactions:

AN INTRODUCTION TOFISSION & FUSION

E 2


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Mass

Matter can be changed into Energy Einsteins formula above tells us

how the change occurs

In the equation above:E = Energym = Mass

c = Speed of Light (UniversalConstant)Energy

LightSpeed

E = mc2

E 2


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E = mc2

The equation may be read asfollows:

Energy (E) is equal to Mass (m) multiplied by the Speed of Light (c) squared

This tells us that a small amountof mass can be converted into avery large amount of energybecause the speed of light (c) isan extremel lar e number

H h i b k?


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How much energy in a buck?

A dollar bill has a mass of 1 gram.m = 0.001 kg; c = 3 x 108 m/s; E = ?E = mc2 E = (0.001 kg)(3 x 108 m/s) 2 E = 9 x 1013 J = 90,000,000,000,000 J

E = 12 kilotons of TNT-equivalent

Fi F


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Fiss vs. Fuse

Fiss = break down Start with a larger atom and finish with

two or more smaller atoms

Fuse = build up

Start with two smaller atoms and finishwith one larger atom


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Fission

When atoms are bombarded with neutrons, their nucleisplits into 2 parts which are roughly equal in size.

Nuclear fission in the process whereby a nucleus, witha high mass number, splits into 2 nuclei which haveroughly equal smaller mass numbers.

During nuclear fission, neutrons are released.


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Nuclear Fission

There are 2 types of fission that exist:

1. Spontaneous Fission

2. Induced Fission


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Induced Fission

Nuclear fission can be induced by bombarding atomswith neutrons.

Induced fission decays are also accompanied by the

release of neutrons.

The nuclei of the atoms then split into 2 equal parts.


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U23592n

10

The Fission Process

A neutron travels at high speed towards a uranium-235nucleus.


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U23592n

10

The Fission Process


h


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U23592n

10

The Fission Process


h i i


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U23592n

10

The neutron strikes the nucleus which then captures theneutron.

The Fission Process

Th Fi i P


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U23692

The nucleus changes from being uranium-235 touranium-236 as it has captured a neutron.

The Fission Process

Th Fi i P


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The uranium-236 nucleus formed is very unstable.

The Fission Process

It transforms into an elongated shape for a short time.

Th Fi i P


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The uranium-236 nucleus formed is very unstable.

The Fission Process

It transforms into an elongated shape for a short time.


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Th Fi i P


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It then splits into 2 fission fragments and releasesneutrons.

The Fission Process

14156 Ba

9236 Kr

n10

n10

n10


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Th Fi i P


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The Fission Process

14156 Ba

9236 Kr

n1

0

n10

n10

Th Fi i P


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The Fission Process

14156 Ba

9236 Kr

1

n10

n10


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Nuclear Fission Examples

U235

92 +Ba141

56+ n1

03n

1

0 +Kr 92

36

U235

92 +Cs138

55+ n1

02n1

0 +Rb96

37

Energy from Fission


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Energy from Fission

Both the fission fragments and neutrons travel at highspeed.

The kinetic energy of the products of fission are far greater than that of the bombarding neutron and targetatom.

E K before f ission


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Energy from Fission

U235

92 +Cs138

55+ n1

02n

1

0 +Rb96

37

Element Atomic Mass (kg)235

92U 3.9014 x 10 -25

13855Cs 2.2895 x 10 -25

9637Rb 1.5925 x 10 -25 1

0n 1.6750 x 10 -27

Energy from Fission


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Energy from Fission

Calculate the total mass before and after fission takes place.

The total mass before fission (LHS of the equation):

The total mass after fission (RHS of the equation):

3.9014 x 10 -25 + 1.6750 x 10 -27 = 3.91815 x 10 -25 kg

2.2895 x 10 -25 + 1.5925 x 10 -25 + (2 x 1.6750 x 10 -27 ) = 3.9155 x 10 -25 kg

Energy from Fission


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Energy from Fission

The total mass before fission =

The total mass after fission =

3.91815 x 10 -25 kg

3.91550 x 10 -25 kg

total mass before f ission > total mass after f ission

Energy from Fission


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Energy from Fission

mass difference, m = total mass before fission total mass after fission

m = 3.91815 x 10 -25 3.91550 x 10 -25

m = 2.65 x 10 -28 kg

This reduction in mass results in the release of energy.


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Energy from Fission


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Energy from Fission

E = mc 2

U235

92 +Cs

138

55+n

1

02n

1

0 +Rb

96

37

Calculate the energy released from the following fissionreaction:

m = 2.65 x 10 -28 kg

c = 3 x 108

ms-1

E = E

E = 2.65 x 10-28

x (3 x 108

)2

E = 2.385 x 10 -11 J

Energy from Fission


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Energy from Fission

The energy released from this fission reaction does notseem a lot.

This is because it is produced from the fission of asingle nucleus.

Large amounts of energy are released when a largenumber of nuclei undergo fission reactions.


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Energy from Fission


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Energy from Fission

If one uranium-235 atom undergoes a fission reactionand releases 2.385 x 10 -11 J of energy, then the amountof energy released by 1 kg of uranium-235 can becalculated as follows:

total energy = energy per fission x number of atoms

total energy = 2.385 x 10 -11 x 2.56 x 10 24

total energy = 6.1056 x 10 13 J


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Nuclear Fusion


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Nuclear Fusion

In nuclear fusion, two nuclei with low mass numberscombine to produce a single nucleus with a higher massnumber.

H2

1 +He4

2+ n1

0H

3

1 +Energy


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The Fusion Process


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The Fusion Process

H21

H31


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The Fusion Process


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The Fusion Process

H2

1

H31

The Fusion Process


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The Fusion Process

The Fusion Process


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The Fusion Process

The Fusion Process


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The Fusion Process


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The Fusion Process


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The Fusion Process

He42

n10

The Fusion Process


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The Fusion Process

He42

n10


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The Fusion Process


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The Fusion Process

He42

n10

E f F i


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Energy from Fusion

Element Atomic Mass (kg)2

1H 3.345 x 10 -27

31H 5.008 x 10 -27

42He 6.647 x 10 -27 1

0n 1.6750 x 10 -27

H2

1 +He4

2+ n1

0H3

1 +Energy

Energy from Fusion


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gy

The total mass before fusion (LHS of the equation):

The total mass after fission (RHS of the equation):

3.345 x 10 -27 + 5.008 x 10 -27 = 8.353 x 10 -27 kg

6.647 x 10 -27 + 1.675 x 10 -27 = 8.322 x 10 -27 kg

H2

1 +He4

2+ n1

0H3

1 +Energy

Energy from Fusion


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gy

m = total mass before fission total mass after fission

m = 8.353 x 10 -27 8.322 x 10 -27

m = 3.1 x 10 -29 kg

Energy from Fusion


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gy

E = mc 2m = 3.1 x 10 -29 kgc = 3 x 10 8 ms -1

E = E

E = 3.1 x 10 -29 x (3 x 10 8)2

E = 2.79 x 10 -12 J

H21 +He

4

2+ n1

0H3

1 +Energy

The energy released per fusion is 2.79 x 10 -12 J.

How fission can be used?


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GOOD A controlled chain reaction in a reactor

used in nuclear power plants to produce

electricity.

EVIL

An uncontrolled chain reaction is used tocreate incredibly powerful weapons theatomic bombs dropped on Japan.

Nuclear Fusion


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Nuclear Fusion Build up of nucleus or fusing of two nuclei to

form one large nucleus Occurs at exceptionally high temperatures

over 100 million degrees Laboratory Experiments

Deuterium and tritium accelerated Collide to form one new atom with a larger helium

nucleus and a neutron is released Mass of helium and neutron less than mass of

deuterium and tritium Mass that was lost became

energy

The Sun


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Proton-proton chain reaction Two hydrogen atoms (protons) fuse

together to create deuteron

A third hydrogen atom collides withdeuteron to create a helium isotope Helium isotopes fuse to make beryllium

which breaks down Two protons are released and it starts

again.


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5th radioactivity ppt

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