The Fission Mechanism And Nuclear Energy

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The Fission Mechanism And Nuclear Energy

Nuclear Power06.12.2011

The Fission Mechanism And Nuclear Energy

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FISSION

1. Fission Mechanism, Spontaneous Fission

2. Neutron-Induced Fission, Chain Reaction

3. Nuclear Energy

The Fission Mechanism And Nuclear Energy

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FISSION

1. Fission Mechanism, Spontaneous Fission

2. Neutron-Induced Fission, Chain Reaction

3. Nuclear Energy

The Fission Mechanism And Nuclear Energy

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Fission Mechanism: fission barrier

spherical nucleus

r1

~

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Spontaneous Fission: Fissility(derivation: Demtröder 4, p.164)

• surface:• Coulomb:

spontaneous fission:

→ fissility:

→ spontaneous fission: or

example: :

CCCC

SSSS

EEEE

EEEE

0

510

0520

²1

²1

… deformation

00 2 SCSC EEEE

AZ

E

Ex

S

C

50²

2 0

0

Bethe-Weizsäcker-formula

1x 50² AZ

14623892 U

36238

²92

The Fission Mechanism And Nuclear Energy

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50²

,1 AZ

x

25²

,5.0 AZ

x

14623892 U

The Fission Mechanism And Nuclear Energy

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FISSION

1. Fission Mechanism, Spontaneous Fission

2. Neutron-Induced Fission, Chain Reaction

3. Nuclear Energy

The Fission Mechanism And Nuclear Energy

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Neutron-Induced Fission

1934 Enrico Fermi: new elements by impact of neutrons on

Uranium → β-active products1939 F. Straßmann, Lise Meitner, O. Hahn:

- discovered Barium as one of these products => fission:

3n Kr Ba U U n 9236

14456

23992

23892

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Neutron-Induced Fission

neutrontarget

fissioningnucleus

6.9 5.4 -1.5

6.6 5.7 -0.9

even number of neutrons => => fission by motionless neutrons

5.3 6.0 0.7

4.8 6.5 1.7

odd number of neutrons => => fission by kinetic neutrons

)U( 192

AeE fbE efb EE

U23392 142

23492 U

U23592 144

23692 U

U23492 143

23592 U

U23892 147

23992 U

fbe EE

fbe EE

Plutonium

Uranium

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Neutron-Induced Fission: Fission Fragments200MeV 43.2 Ba Kr U U 5636

23692

23592 nn

minimum:

maximum:

12

1 AA

32

2

1 AA

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Chain Reaction

B A X X nn

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Chain Reaction

• chain reaction:

→ since , a multi-plicative effect canoccur

→ number of neutronswill be multiplied

→ reaction rate incrases

1

The Fission Mechanism And Nuclear Energy

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Chain Reaction: Multiplication Factor

supercritical regime → chain reaction• sub-critical regime → no chain reaction

critical regime → constant reaction

• dependency:- - non fissioning absorbtion- diffusion- …- mass (k=1 => critical mass)

1

1

1

k

,...)3,2,1( 1 iN

Nk

i

i

k

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FISSION

1. Fission Mechanism, Spontaneous Fission

2. Neutron-Induced Fission, Chain Reaction

3. Nuclear Energy

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Nuclear Energy

• exothermic nuclear reactions:

– α-decay:

– fission:

• energy release for :

→ … sum of the kinetic energies of the fission fragments

MeV262.4 Th U 234238

Q

fisAZ

AZ

AAZZ QXXX

2

2

1

1

21

21

²)],(),([²),( 22112121 cZAmZAmcZZAAmQ fis

fisQ

MeV200 Ba Kr U 563623692

fisQ

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Binding energy per nucleon

B/A(240) = 7.6MeV

B/A(120) = 8.5MeV

216MeV

MeV6.7240MeV5.81202

fisQ

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The Fission Mechanism And Nuclear Energy

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Picture Credits

• http://www.zamandayolculuk.com/cetinbal/nuclearchemistry.htm• A.Junghans• http://frank.mtsu.edu/~phys3110/Syllabus/Examples/CH_11/

EX_11_VII/ex_11_vii.html• W. Demröder: (Springer, Heidelberg, 1998) Kern-, Teilchen- und

Astrophysik 4• http://www3.mpch-mainz.mpg.de/~elbert/geschichte.htm• J.Grehn, J.Krause: (Schroedel Verlag, Hannover, 1998) Metzler Physik• http://clautechonolgyblog.wordpress.com/• http://thushararadioactivity.blogspot.com/• J.L.Basdevant, J.Rich, M. Spiro: (Springer, Heidelberg, 2005)

Fundamentals in Nuclear Physics• http://www.nucleonica.net/wiki/images/d/d4/NuclideChart.pdf

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References

• J.L.Basdevant, J.Rich, M. Spiro: (Springer, Heidelberg, 2005)Fundamentals in Nuclear Physics – From nuclear structure to cosmology

• W. Demröder: (Springer, Heidelberg, 1998)Kern-, Teilchen- und Astrophysik 4

• Horst Hänsel / Werner Neuman: (Spektrum, Akad. Verl.,Heidelberg, Berlin, Oxford, 1995)Physik – Atome, Atomkerne, Elementarteilchen

• Dr. Arnd Junghans (Helmholtz-Zentrum Dresden-Rossendorf,Institute of Radiation Physics)