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Review of Fundamentals

Nuclear Reactions

Day 1 – Lecture 6

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Objective

• To learn various kinds of nuclear reactions

• To discuss health physics significance and energy considerations of nuclear reactions

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Content

• Properties of neutrons• Nuclear decay processes• Cross section• Neutron interactions• Charged particle reactions• Spallation• Fission• Fusion

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Chadwick, 1932, alpha bombardment

He + Be C + n + Q

Neutron Discovery

Thermal (0.0025 eV)Slow (1 - 100 eV)Epithermal (100 eV – 100 keV)Fast (100 keV – 1 MeV)Ultrafast (>1 MeV)

Neutron Classification

Properties of Neutrons

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Neutron Characteristics symbol - n no charge rest energy 939.507 MeV has a magnetic moment it is a fermion

Neutron Interaction with matter Scattering (2 mechanisms) Absorption (>4 mechanisms)

Properties of Neutrons

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Nuclear ReactionsNuclear Decay

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Nuclear ReactionsAlpha Decay

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Nuclear ReactionsBeta Decay

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Nuclear ReactionsPositron Decay or Electron Capture

Electron Capture

Positron Emission

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Nuclear ReactionsSummary of Major Decay Mechanisms

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Cross Section

where

= cross section

R = number of reactions per unit time per nucleus

I = number of incident particles per unit time per unit area

=RI

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Nuclear ReactionsFast Neutron Interactions

• Elastic scattering - neutrons interact with particles of approximately the same mass such as protons (billiard ball analogy)

• Occurs in materials rich in hydrogen such as water, wax, concrete

• Accounts for about 80% of fast neutron dose to tissue

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Inelastic scattering – neutrons interact with particles of much greater mass, for example, iron (table tennis ball vs bowling ball analogy)

Nuclear ReactionsFast Neutron Interactions

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Nuclear ReactionsElastic Scattering of Neutrons

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Nuclear ReactionsInelastic Scattering of Neutrons

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Neutron Reactions

(n, CP) QHeLiBn 42

73

105

10

CoCon 605910

(n, gamma)

LiMoUUn 1399523692

23592

10 *

(n, fission)

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Nuclear ReactionsNeutron Absorption, Charged Particle

n + 10B 7Li(*) +

7Li(*) 7Li + soft gamma (480 KeV)

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Fission

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Breeding 239Pu from 238U Neutron Capture

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Details of 239U Decay to 239Pu

239U (23.5 min) 239Np (2.3 d) 239Pu

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Nuclear ReactionsCharged Particle Bombardment

p + 68Zn 67Ga + 2n

+ 16O 18F + p + n

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Nuclear Fusion ReactionsUtilize Isotopes of Hydrogen

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Nuclear ReactionsFusion

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Deuteron – Deuteron Fusion

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Tritium – ProtonProduction from Fusion

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3He with Neutron Production from Fusion

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Fusion - Tokamak

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Energy ProductionReactions in Stars

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Summary

• Various examples of nuclear reactions were discussed

• Students learned about properties of neutrons, nuclear decay processes, cross section, neutron interactions, and various kinds of nuclear reactions including charged particle reactions, spallation, fission and fusion

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Where to Get More Information

Cember, H., Johnson, T. E, Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2009)

International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources (PGEC), Training Course Series 18, IAEA, Vienna (2002)