Chapter 18Chapter 18

The Nucleolus: A The Nucleolus: A Chemist’s ViewChemist’s View

TopicsTopics

Nuclear stability and radioactive decayNuclear stability and radioactive decay The kinetics of radioactivityThe kinetics of radioactivity Nuclear transformationsNuclear transformations Detection and use of radioactivityDetection and use of radioactivity Thermodynamic stability of the nucleus Thermodynamic stability of the nucleus Nuclear fission and nuclear fusionNuclear fission and nuclear fusion Effects of radiation Effects of radiation

IntroductionIntroductionNuclear Reactions vs Chemical ReactionsNuclear Reactions vs Chemical Reactions

Chemical reactions: Changes in the outer electronic Chemical reactions: Changes in the outer electronic structure of atoms or moleculesstructure of atoms or molecules

Nuclear reactionsNuclear reactions: study of changes in structure of : study of changes in structure of nuclei and subsequent changes in chemistry.nuclei and subsequent changes in chemistry.

Radioactive nucleiRadioactive nuclei: spontaneously change structure : spontaneously change structure and emit radiation.and emit radiation.

Differences between nuclear and chemical Differences between nuclear and chemical reactionsreactions::

Much larger release in energy in nuclear reaction.Much larger release in energy in nuclear reaction. Isotopes show identical chemical reactions but different Isotopes show identical chemical reactions but different

nuclear reactions.nuclear reactions. Nuclear reactions not sensitive to chemical environment.Nuclear reactions not sensitive to chemical environment. Nuclear reaction produces different elements.Nuclear reaction produces different elements. Rate of nuclear reaction not dependent upon temperature.Rate of nuclear reaction not dependent upon temperature.

Representation ofRepresentation of atomicatomic nucleinuclei

C126

Mass number- A

Atomic number- Z

C146

Isotopes

12C

14C

Nucleus componentsNucleus components

• NucleonNucleon: any nuclear particle, e.g. protons, p, : any nuclear particle, e.g. protons, p, and neutrons, n. and neutrons, n.

XAZIsotopes: atoms that have identical atomic numbers but different mass numbersNuclide: is a term used to identify an individual atom. Each individual atom is called nuclide

Nuclide

RadioactivityRadioactivity

RadioactivityRadioactivity is a nuclear reaction in which an is a nuclear reaction in which an unstable nucleus decomposes spontaneouslyunstable nucleus decomposes spontaneously

Natural radioactivityNatural radioactivity Natural unstable nuclei Natural unstable nuclei decomposedecompose more stable nuclei more stable nuclei

ArtificialArtificial radioactivityradioactivity

Synthetic unstable nuclei Synthetic unstable nuclei decomposedecompose more stable nuclei more stable nuclei

DecayDecayParentnuclei

Daughter nuclei

Radioactive Decay Series

Decay of P-32 to S-32

18.1 Nuclear stability and radioactive decay18.1 Nuclear stability and radioactive decay

Nuclear stabilityNuclear stability Thermodynamic stabilityThermodynamic stability:: the potential energy of the potential energy of

a nucleus as compared with sum of the potential a nucleus as compared with sum of the potential energies of its components protons and neutronsenergies of its components protons and neutrons

Kinetic stabilityKinetic stability: it describes the probability that a : it describes the probability that a nucleus will undergo decomposition to form a nucleus will undergo decomposition to form a different nucleus- different nucleus- a process called radioactive a process called radioactive decaydecay

• Stability depends upon a balance between repulsive Stability depends upon a balance between repulsive forces (between protons) and strong attraction forces forces (between protons) and strong attraction forces between nucleibetween nuclei

•The stability of a nucleus depends mainly on A, the mass number and Z, the atomic number. Up to the mass number 30 or 40, a nucleus has approximately the same number of neutrons and protons to be stable.

• Bigger nuclei must have more neutrons than protons. As Z gets bigger, repulsive forces get bigger.

•When nucleus gets big enough, no neutron is enough to keep it stable. After, Z= 82, no nuclei is stable. Such unstable nuclei are radioactive, which means they undergo radiations in order to become stable.

Nuclear Stability

•A nucleus having very much protons compared to neutrons will never be stable

• This does not mean that a nucleus with many neutrons and little protons will be stable.

•To understand this we may look at this graph,

Nuclear Stability

Empirical rules for predicting stability of nucleiEmpirical rules for predicting stability of nuclei

• Neutron-to-proton ratioNeutron-to-proton ratio varies with atomic varies with atomic numbernumber

• Light isotopes (small atomic number) have aLight isotopes (small atomic number) have a Neutron-to-proton ratio almost =Neutron-to-proton ratio almost = 1(almost 1(almost stable)stable)

• Nuclei are held together by strong attractive Nuclei are held together by strong attractive forces; but electrostatic repulsion causes forces; but electrostatic repulsion causes large atoms (>83 protons) to be unstable.large atoms (>83 protons) to be unstable.

O N 168

147

126 C

51.1p

n ;206

82 Pb

Nuclides with Nuclides with even even number of nucleons number of nucleons ((p +n)p +n) are are moremore stable than those with stable than those with

oddodd number number Certain number of protons or neutrons Certain number of protons or neutrons

appear to be particularly stable. The appear to be particularly stable. The magic numbers are: magic numbers are:

2, 8, 20, 28,50, 82, 1262, 8, 20, 28,50, 82, 126 These numbers are in parallel to those These numbers are in parallel to those

produce chemical stability: produce chemical stability: 2, 10, 18, 36, 54 and 86 2, 10, 18, 36, 54 and 86

(Noble gas configuration)(Noble gas configuration)

Types of radiation emitted in natural radioactivity

TypesTypes ofof radioactiveradioactive decaydecay radiation = attracted towards radiation = attracted towards negatively charged plate negatively charged plate PositivelyPositively chargedcharged

radiation = attracted towards positively radiation = attracted towards positively charged platecharged plate NegativelyNegatively chargedcharged = =1e1e--

radiation = not attracted to either plateradiation = not attracted to either plate NeutralNeutral.. When emitted it does not change atomic or mass numbersWhen emitted it does not change atomic or mass numbers

Very high energy photons; very short wavelengthVery high energy photons; very short wavelength

. Positron is a positive electron . Positron is a positive electron

Positron emission is equivalent to a fall of ePositron emission is equivalent to a fall of e-1-1 in in

nucleusnucleus

He42

e01

e01

NUCLEAR REACTIONSNUCLEAR REACTIONS

RadioactivityRadioactivity: nucleus unstable and spontaneously : nucleus unstable and spontaneously disintegrates.disintegrates.

Nuclear BombardmentNuclear Bombardment: causes nuclei to disintegrate : causes nuclei to disintegrate due to bombardment with very energetic particles.due to bombardment with very energetic particles.

Particles in nuclear reactionsParticles in nuclear reactions::

1. Proton H11 or p1

1 2. Neutron n1

0 3. Electron e0

1 or 0 1

4. Positron e0 1 or

0 1

5. Gamma ray 00

1) Total Nucleon Number (TOP VALUES) =Total number of protons and neutrons

2) Total electric charge (BOTTOM VALUES)

Are kept the same.

Protactinium

Balancing nuclear equations

•Nuclear reaction is written maintaining mass and charge balance.

E.g.

N147

C146

e0 1+ +

Examples of adioactive decayExamples of adioactive decay Beta emissionBeta emission: Converts neutron into a proton : Converts neutron into a proton

by emission of energetic electron; atomic # by emission of energetic electron; atomic # increases:increases:

E.g. Determine product for following reaction: E.g. Determine product for following reaction:

• Alpha emissionAlpha emission: emits He particle: emits He particle..

E.g. Determine product:E.g. Determine product:

epn 0 1

11

10

?K 0 1

4019

He?Ra 42

22688

Positron emission: Converts proton to neutron:

E.g. Determine product of

enp 0 1

10

11

e?Tc 01

9453

Gamma emission: no change in mass or charge but usually part of some other decay process.

E.g. eNC 0

1147

14 6

Electron capture: electron from electron orbitals captured to convert proton to neutron.

nep 10

0 1

11

E.g. Determine product ?eK 0 1

4019

More examples of radioactive decayMore examples of radioactive decay

Alpha production (Alpha production (): helium nucleus,): helium nucleus,

Beta production (Beta production (): ):

92238

24

90234U He Th

90234

91234

10Th Pa e

10 e

Examples of radioactive decayExamples of radioactive decay

Gamma ray productionGamma ray production ( ():):

Positron productionPositron production::

Electron capture: (inner-orbital electron is captured Electron capture: (inner-orbital electron is captured by the nucleus)by the nucleus)

92238

24

90234

002U He Th

1122

10

1022Na e Ne 10 e

80201

10

79201

00Hg e Au

18.218.2 The kinetics of radioactive decayThe kinetics of radioactive decay Nuclear decay is a Nuclear decay is a first order reactionfirst order reaction RateRate amount of radioactiveamount of radioactive isotope present isotope present For a radioactive nuclides, For a radioactive nuclides, the rate of decaythe rate of decay,, that is that is

the the negative changenegative change in the number of nuclides per in the number of nuclides per unit time unit time

is directly proportional to the number of nuclidesis directly proportional to the number of nuclides N N

)(t

N

This is a first order process

N α Δt

ΔN Rate That is

kNΔt

ΔN Rate

kt )N

Nln( o

Original # of nuclides

# of nuclides remaining at time t

Half-LifeHalf-Life

The time required for the number of nuclides to The time required for the number of nuclides to reach half the original value (reach half the original value (NN00/2)./2).

tk k1 22 0 693

/ln( ) .

1/2t

0693t-

o

kt-

o

e N

e N

N

N

Examples of Half-LifeExamples of Half-Life

Isotope Half lifeIsotope Half life

C-15C-15 2.4 sec2.4 sec

Ra-224Ra-224 3.6 days3.6 days

Ra-223Ra-223 12 days12 days

I-125I-125 60 days60 days

C-14C-14 5700 years5700 years

U-235U-235 710 000 000 years710 000 000 years

ExamplesExamples

1. 1. The half-life of Cobalt-60 is 5.26 years how much The half-life of Cobalt-60 is 5.26 years how much of of

the original amount would be left after 21.04 the original amount would be left after 21.04

years? years?

2. Tritium decays by beta emission with a half-life of 2. Tritium decays by beta emission with a half-life of

12.3 years. How much of the original amount 12.3 years. How much of the original amount

would be left after 30 years? would be left after 30 years?

3. If a 1.0 g sample of tritium is stored for 5.0 years, 3. If a 1.0 g sample of tritium is stored for 5.0 years,

what mass of that isotope remains? what mass of that isotope remains?

k = 0.563/yeark = 0.563/year. .

18.3 Nuclear Transformation18.3 Nuclear Transformation

The change of one element into another The change of one element into another Bombard nuclei with nuclear particles to Bombard nuclei with nuclear particles to

convert element to another one to convert element to another one to become become more stable through radioactivity is more stable through radioactivity is transmutation.transmutation.

1327

24

1530

01Al He P n

98249

818

106263

014Cf O X n

RutherfordHOHeN 11

178

42

147

Irene Curie

• Nuclear transformation can occur by alpha or beta radiation, or some other nuclear reactions such as nuclear bombardment• Nuclear transformation is achieved mostly using particle accelerator• Accelerators are needed when positive ions are used as the bombarding particles• The particle is accelerated to a very high velocity thus it can overcome the repulsion and can penetrate the target nucleus • Neutrons are also used often as bombarding particles • Neutrons are uncharged, thus they are not repelled and readily absorbed by many nuclides• Using neutron and positive ion bombardment made possible to extend the periodic table

p N U 0

1 U 0

1-23893

23892

23892 pn

• Since 1940, elements with atomic numbers 93 through 112 have been synthesized• These elements are called transuranium elements

Schematic diagram of a cyclotron

Nucleus

Positive ion

A Schematic Diagram of a Linear Accelerator

44 . .Detection and uses of radiationDetection and uses of radiation

• Geiger countersGeiger counters detect charged particles produced from interaction detect charged particles produced from interaction

of gas with particles emitted from radioactive of gas with particles emitted from radioactive material. The device detects the current flowmaterial. The device detects the current flow

• Scintillation countersScintillation counters detect particles from radioactive material by detect particles from radioactive material by

measuring intensity of light when these particles hit measuring intensity of light when these particles hit substances such as ZnS. substances such as ZnS.

• UnitsUnits: : 1 curie (Ci)1 curie (Ci) = 3.7x10 = 3.7x101010 disintigrations×s disintigrations×s11

A representation of a Geiger-Müller counter.A representation of a Geiger-Müller counter.

High energy particles produced from radioactive decay produce ions when they travel through matter

Ar(g) Ar+(g) + e-

Scintillation counters

Carbon-14 DatingCarbon-14 Dating

Carbon-14 is formed naturally at a fairly constantCarbon-14 is formed naturally at a fairly constant

rate by bombardment of atmospheric nitrogen byrate by bombardment of atmospheric nitrogen by

cosmic rays (high energy neutrons).cosmic rays (high energy neutrons).

and then over time C-14 decays 14

6C 147N + 0

-1e

147N + 1

0n 146C + 1

1 H

Dating by radioactivity

Age of organic materialAge of organic material

As long the plant or animal lives theAs long the plant or animal lives the C-14/C-12 C-14/C-12 ratio in its molecules remains the same as ratio in its molecules remains the same as

in the atmosphere (1/10in the atmosphere (1/101212) because of the continuous ) because of the continuous uptake of carbon.uptake of carbon.

When the plant/animal dies, C-14 decays and the When the plant/animal dies, C-14 decays and the ratio decreasesratio decreases

• tt1/2 1/2 for C-14 = 5730 yrfor C-14 = 5730 yr• If C-14/C-12 found in the old wood is ½ of that in a If C-14/C-12 found in the old wood is ½ of that in a

currently living plant, then its age is 5730 yr. currently living plant, then its age is 5730 yr.

• This assumes that the current This assumes that the current C-14/C-12 ratio is the C-14/C-12 ratio is the same as that in the ancient plant same as that in the ancient plant

Age of rocks/Age of earthAge of rocks/Age of earth

• U-238U-238 present in certain rocks slowly decays to present in certain rocks slowly decays to Pb-206Pb-206• Pb-206 was not present originallyPb-206 was not present originally• As time progresses the amount ofAs time progresses the amount of U-238 U-238 decreases and Pb- decreases and Pb-

206 increases206 increases• By measuring the ratio of By measuring the ratio of Pb-206 / U-238Pb-206 / U-238 scientists can scientists can

determine the age of a rockdetermine the age of a rock• The oldest rocks can then be used to determine the The oldest rocks can then be used to determine the

minimum age of the earthminimum age of the earth• It is assumed that It is assumed that

• Pb-206 was not present originallyPb-206 was not present originally• All of the decay products are retainedAll of the decay products are retained

Medical applications of radioactivityMedical applications of radioactivity

Radioactive nuclides can be introduced into Radioactive nuclides can be introduced into organisms in food or drugs where their paths can organisms in food or drugs where their paths can bebe tracedtraced by monitoring their radioactivity by monitoring their radioactivity

Radioactive tracers provide sensitive methods for: Radioactive tracers provide sensitive methods for: learning about biological systems, learning about biological systems, detection of disease, detection of disease, monitoring the action and effectiveness of monitoring the action and effectiveness of

drugs, drugs, early detection of pregnancy,early detection of pregnancy,

Medical applications of radioactivity

18-5 Thermodynamic Stability of the Nucleus18-5 Thermodynamic Stability of the Nucleus

We can determine the thermodynamic stability of a We can determine the thermodynamic stability of a nucleus by calculating thenucleus by calculating the change in potential change in potential

energyenergy that would occur if thatthat would occur if that nucleusnucleus were were formed formed from its constituent from its constituent protons and neutronsprotons and neutrons..

For example, the hypothetical process of formingFor example, the hypothetical process of forming

nucleus from eight neutrons and eight protons:nucleus from eight neutrons and eight protons:O186

What is the change in energy that correspond to the formation of What is the change in energy that correspond to the formation of 1 mol of O-16 from its protons and neutrons?1 mol of O-16 from its protons and neutrons?

Thus, Thus,

= (-1.366X10= (-1.366X10-4-4 kg/mol)(3.00X10 kg/mol)(3.00X1088 m/s m/s22) = -1.23X10) = -1.23X101313J/molJ/molConsequently:Consequently: Nuclear processes are accompanied with extremely large Nuclear processes are accompanied with extremely large

energy compared to chemical and physical changesenergy compared to chemical and physical changes Nuclear processes constitute a potentially valuable energy Nuclear processes constitute a potentially valuable energy

resourceresource

2mcE

molgmsmc /1366.0;/1000.3 8

molKgm /10366.1 4

Thermodynamic stability of a particular nucleus is Thermodynamic stability of a particular nucleus is represented as energy released per nucleonrepresented as energy released per nucleon

Calculate the energy released per a nucleon of O-16Calculate the energy released per a nucleon of O-16

nucleonMeVJX

MeVnucleonXJX/98.7

106.1

1/1028.1

13

12

nucleusJXmolnucleiX

molJX/1004.2

/10022.6

/1023.1nucleus Oper ΔE 11

23

1316

8

nucleonJXnucleusnucleons

nucleusJX/1028.1

/16

/1004.2 Ofornucleon per ΔE 12

1116

8

nucleonMeVJX

MeVnucleonXJX/98.7

106.1

1/1028.113

12

Thus, 7.98 MeV of energy per nucleon would be released if O-16 were from neutrons and protons

Thus, 7.98 MeV of energy per nucleon would be Thus, 7.98 MeV of energy per nucleon would be releasedreleased if O-16 were from neutrons and protons if O-16 were from neutrons and protons The energy required to The energy required to decomposedecompose the above the above

nucleus into its components has the same quantity nucleus into its components has the same quantity but with but with +ve sign+ve sign : This is the : This is the binding energybinding energy per per nucleon for O-16 nucleon for O-16

Calculation of binding energyCalculation of binding energy

Calculate the binding energy per nucleonCalculate the binding energy per nucleon

for nucleus.for nucleus.

(Atomic masses =4.0026 amu, (Atomic masses =4.0026 amu,

1.0078 amu)1.0078 amu)

We must calculate the mass defect for We must calculate the mass defect for

He-4He-4

He42

He42

H11

Nuclear binding energyNuclear binding energy

It is the energy required to decompose nucleus into It is the energy required to decompose nucleus into protons and neutrons or it is the energy released protons and neutrons or it is the energy released when protons and neutrons combine together to when protons and neutrons combine together to form nucleusform nucleus

The NBE is a measure of the stability of the nucleus The NBE is a measure of the stability of the nucleus towards decomposition. Large NBE means more towards decomposition. Large NBE means more stability. Atoms of intermediate masses have larger stability. Atoms of intermediate masses have larger NBE than either the very light atoms or the very NBE than either the very light atoms or the very heavy ones heavy ones

18.6 Nuclear fission and nuclear reaction18.6 Nuclear fission and nuclear reaction The graph above has very important implications for the The graph above has very important implications for the

use of nuclear processes as sources of energy. use of nuclear processes as sources of energy. Energy is released, that is,Energy is released, that is, E E is negativeis negative, , when a when a

process goes fromprocess goes from aa less stable to a more stable stateless stable to a more stable state nuclei nuclei

The higher a nuclide is on the curve, the more stable it is. The higher a nuclide is on the curve, the more stable it is. This means that two types of nuclear processes will be This means that two types of nuclear processes will be

exothermicexothermic 1.1. Combining two light nuclei to form a heavier, more Combining two light nuclei to form a heavier, more stable nucleus. This process is called stable nucleus. This process is called fusion.fusion. 2. Splitting a heavy nucleus into two nuclei with smaller 2. Splitting a heavy nucleus into two nuclei with smaller mass numbers. This process is called mass numbers. This process is called fission.fission.

Because of the large binding energies involved in holding Because of the large binding energies involved in holding the nucleus together, both these processes involve the nucleus together, both these processes involve energy changes energy changes more than a million timesmore than a million times larger than larger than those associated with chemical reactions.those associated with chemical reactions.

The Binding Energy Per Nucleon as a Function of Mass NumberThe Binding Energy Per Nucleon as a Function of Mass Number

Highest stability

Sta

bili

ty o

f n

uc

lei i

ncr

ea

sin

g

• 56Fe has highest Eb and is most stable isotope.

•Energy sources:

–Fission for large radioactive elements, such as U-235

–Fusion of very light nuclei such as deuterium producing He. Not yet accomplished.

–Atoms of Z=50-80 (intermediate masses have the largest NBE.

Nuclear fusion

Nuclear fission

Fusion of light nuclei and fission of heavy nuclei are exothermic processes

Nuclei of Nuclei of heavy atomsheavy atoms will gain more will gain more stability if they are fragmented (stability if they are fragmented (fissionfission into intermediate ones). They will give into intermediate ones). They will give off energy when the fission occursoff energy when the fission occurs

Nuclei of Nuclei of lightlight atomsatoms will gain more will gain more stability if they are fused together stability if they are fused together ((fusionfusion) to give atoms of intermediate ) to give atoms of intermediate NBE. Energy will be given off when NBE. Energy will be given off when fusion occurs. fusion occurs.

Both Fission and Fusion Produce More Stable NuclidesBoth Fission and Fusion Produce More Stable Nuclides

Nuclear FissionNuclear Fission

Several isotopes of the heavy elements Several isotopes of the heavy elements undergo fission if undergo fission if bombarded with neutronsbombarded with neutrons of high enough energyof high enough energy

In practice attention was paid toIn practice attention was paid to

and and U235

92uP239

94

The discussion will focus on

That is only 0.7% of the naturally occurring U

U23592

U23892

is most abundant isotope and does not go fission

FissionFission

2352359292U + U + 11

00n n 2362369292UU**

and 10and 10-14-14 seconds later... seconds later... 236236

9292UU** 92923636Kr + Kr + 141141

5656Ba + Ba + 3 3 1100nn + + ENERGYENERGY

50 possible sets of fission products (sum of 50 possible sets of fission products (sum of atomic numbers = 92)atomic numbers = 92)

3 neutrons released for 3 neutrons released for ONEONE 2352359292U (too many for U (too many for

stability, thus fragmentation continues to reach stability, thus fragmentation continues to reach stability) stability)

U23592

Fission ProcessFission Process

Chain Fission ReactionsChain Fission Reactions Produced neutrons will attack more and Produced neutrons will attack more and

more forming chain reactionmore forming chain reaction This chain reaction occurs in the atomic This chain reaction occurs in the atomic

bomb. Energy is evolved in successive bomb. Energy is evolved in successive fissions that will lead to tremendous fissions that will lead to tremendous explosionexplosion

For the chain reaction to occur must be For the chain reaction to occur must be large large (critical mass),(critical mass), thus most neutrons are thus most neutrons are capturedcaptured

Critical mass for is 1 to 10 KgCritical mass for is 1 to 10 Kg

U23592

U23592

U23592

• If the sample is too small most neutrons escape braking the chain

Fission Produces a Chain ReactionFission Produces a Chain Reaction

Nuclear FissionNuclear Fission

Event

NeutronsCausingFission Result

subcritical < 1 reaction stopscritical = 1 sustained reactionsupercritical > 1 violent explosion

A self-sustaining fission process is called a A self-sustaining fission process is called a chain reactionchain reaction..

Fission Produces Two NeutronsFission Produces Two Neutrons

Nuclear reactorsNuclear reactors Because of the tremendous energies involved, it is Because of the tremendous energies involved, it is

desirable to develop the fission process as an desirable to develop the fission process as an energy source to produce electricity. energy source to produce electricity.

To accomplish this, reactors were designed in which To accomplish this, reactors were designed in which controlled fission can occur. controlled fission can occur.

The resulting energy is used to heat water to The resulting energy is used to heat water to produce steam to run turbine generators, in much produce steam to run turbine generators, in much the same way that a coal-burning power plant the same way that a coal-burning power plant generates energy.generates energy.

A schematic diagram of a nuclear power plant is A schematic diagram of a nuclear power plant is shown shown

In the reactor core, uranium that has been enriched to In the reactor core, uranium that has been enriched to approximately 3% U-235(natural uranium contains only 0.7% approximately 3% U-235(natural uranium contains only 0.7% U-U-235) 235) is housed in cylinders. is housed in cylinders.

A moderator surrounds the cylinders to slow down the A moderator surrounds the cylinders to slow down the neutrons so that the uranium fuel can capture them more neutrons so that the uranium fuel can capture them more efficiently. efficiently.

Control rods, composed of substances that absorb neutrons, Control rods, composed of substances that absorb neutrons, are used to regulate the power level of the reactor. The reactor are used to regulate the power level of the reactor. The reactor is designed so that should a malfunction occur, the control are is designed so that should a malfunction occur, the control are automatically inserted into the core to stop the reactionautomatically inserted into the core to stop the reaction

A liquid that is usually water is circulated through the core to A liquid that is usually water is circulated through the core to extract the heat generated extract the heat generated

The energy can then passed on via a heat exchanger to water The energy can then passed on via a heat exchanger to water in the turbine system in the turbine system

A Schematic Diagram of a Nuclear Power PlantA Schematic Diagram of a Nuclear Power Plant

A Schematic Diagram A Schematic Diagram

of a Reactor Coreof a Reactor Core

Breeder ReactorsBreeder ReactorsFissionable fuel is produced while the reactor Fissionable fuel is produced while the reactor runs runs

is changed (split) to fissionable is changed (split) to fissionable

92235U

94239 Pu0

192

23892

239

92239

93239

10

93239

94239

10

n U U

U Np e

Np Pu e

U23892 94

239 Pu

This reaction involves absorption of neutrons

• As the reactor runs and U-235 is split some of the excess neutrons are absorbed by U-238 to produce Pu-239• Pu-239 is then separated and used to fuel another reactor• This reactor, thus breeds nuclear fuel as it operates

Breeder Reactors

Fissionable fuel is produced while the reactor runs ( is split, giving neutrons for the

creation of ):94

239 Pu

01

92238

92239

92239

93239

10

93239

94239

10

n U U

U Np e

Np Pu e

U23892

FusionFusion

Large quantities of energy are produced by Large quantities of energy are produced by the fusion of two light nuclei to give a heavier the fusion of two light nuclei to give a heavier oneone

Stars and sun produce their energy through Stars and sun produce their energy through nuclear fusion. nuclear fusion.

Our sun, which presently consists of 73% Our sun, which presently consists of 73% hydrogen, 26% helium, and 1 % other hydrogen, 26% helium, and 1 % other elements, gives off vast quantities of energy elements, gives off vast quantities of energy from the fusion of protons to form helium:from the fusion of protons to form helium:

Energy n He 10

42

31

11 HH

Proposed mechanism for reactions on the sun

T 1X109 oC; E 1X1019 kJ/day

How does fusion take place?How does fusion take place? The major stumbling block in having these fusion The major stumbling block in having these fusion

reactions feasible is that high energies are required reactions feasible is that high energies are required to initiate fusion. to initiate fusion.

The forces that bind nucleons together to form a The forces that bind nucleons together to form a nucleus are effective only at very small distances nucleus are effective only at very small distances ((1010-13-13 cm). cm).

Thus, for two protons to bind together and thereby Thus, for two protons to bind together and thereby release energy, they must get very close together. release energy, they must get very close together.

But protons, because they are identically charged, But protons, because they are identically charged, repel each other electrostatically. repel each other electrostatically.

This means that to get two protons (or two This means that to get two protons (or two deuterons) close enough to bind together (the deuterons) close enough to bind together (the nuclear binding force is not electrostatic), they must nuclear binding force is not electrostatic), they must be "shot" at each other at speeds high enough (10be "shot" at each other at speeds high enough (1066 m/s) to overcome the electrostatic repulsion.m/s) to overcome the electrostatic repulsion.

High temperatures are expected from various High temperatures are expected from various sources that are under studysources that are under study

Effects of RadiationEffects of Radiation

Factors that make the biological effectsFactors that make the biological effects 1.1. The energy of the radiation. The energy of the radiation.

The higher the energy the more damage it can The higher the energy the more damage it can cause. Radiation doses are measured in radscause. Radiation doses are measured in rads ((radiation absorbed doseradiation absorbed dose),), where 1rad corresponds where 1rad corresponds to 10to 10-2-2 J of energy deposited per kilogram of tissue. J of energy deposited per kilogram of tissue.

2. The penetrating 2. The penetrating ability ability of the radiation.of the radiation.

The particles and rays produced in radioactive The particles and rays produced in radioactive processes vary in their abilities to penetrate human processes vary in their abilities to penetrate human tissue:tissue: rays are highly penetrating,rays are highly penetrating, particles particles can penetrate approximately 1 cm, andcan penetrate approximately 1 cm, and particles particles are stopped by the skin.are stopped by the skin.

3. The ionizing 3. The ionizing ability ability of the radiationof the radiation Extraction of electrons from biomolecules to form ions is particularly Extraction of electrons from biomolecules to form ions is particularly

detrimental to their functions. The ionizing ability of radiation varies detrimental to their functions. The ionizing ability of radiation varies dramatically. For example, dramatically. For example, rays penetrate very deeply but cause only rays penetrate very deeply but cause only occasional ionization. On the other hand, occasional ionization. On the other hand, particles, although not very particles, although not very penetrating, are very effective at causing ionization and produce a dense trail penetrating, are very effective at causing ionization and produce a dense trail of damage.of damage.

Thus ingestion of an Thus ingestion of an particle producer, such as plutonium, is particularly particle producer, such as plutonium, is particularly damaging.damaging.

4. The chemical properties of the radiation source 4. The chemical properties of the radiation source When a radioactive nuclide is ingested into the body, its effectiveness in When a radioactive nuclide is ingested into the body, its effectiveness in

causing damage depends oncausing damage depends on its residence timeits residence time. . For example, Kr-85 and Sr-90 For example, Kr-85 and Sr-90 are both are both -particle producers. -particle producers.

However, since krypton is chemically inert, it passes through the body However, since krypton is chemically inert, it passes through the body quickly and does not have much time to do damage.quickly and does not have much time to do damage.

Strontium, being chemically similar to calcium, can collect in bones, where it Strontium, being chemically similar to calcium, can collect in bones, where it may cause leukemia and bone cancer.may cause leukemia and bone cancer.

The energy dose of the radiation and its effectiveness in causing biological The energy dose of the radiation and its effectiveness in causing biological damage form the source for the term rem (roentgen equivalent for man)damage form the source for the term rem (roentgen equivalent for man)

Number of rems = (number of rads X RBE (relative effectiveness of radiation Number of rems = (number of rads X RBE (relative effectiveness of radiation in causing biological damage)in causing biological damage)

• In the linear model, even a small dosage causes a proportional risk. • In the threshold, risk begins only after a certain dosage

The two models for radiation damage