PRACTICAL RADIATION PHYSICS FOR EMERGENCY MEDICAL PERSONNEL Module III

Module III

What is radiation?

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Ionizing radiation

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Electromagnetic radiation

VISIBLE IONIZING RADIATON X-RAYS COSMIC MICROVAVES TV, RADIO INFRARED ULTRAVIOLET Decreasing wave length Increasing frequency Increasing photon energy GAMMA

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Forms of ionizing radiation

Directly ionizing Particulate radiation consisting of atomic or subatomic particles (electrons, protons, etc.) which carry energy in the form of kinetic energy of mass in motion Indirectly ionizing Electromagnetic radiation in which energy is carried by oscillating electrical and magnetic fields travelling through space at speed of light

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Origin of radiation

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What is the relationship between atom structure and radiation production?

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Atom anatomy

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Electron Proton Neutron

Nucleons - 7

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Isotopes

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Why are some nuclides radioactive

?

Neutron to proton ratio

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Half-life

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Activity

The number of decaying nuclei per unit of time The Systéme International (SI) unit of radioactivity is the Becquerel (Bq) One Bq = 1 disintegration per second

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Non-SI unit of radioactivity is the Curie (Ci) One Ci = 3,7 x 10 10 transformations per second One milicurie (mCi) = 3,7 x 10 7 s -1 One microcurie (μCi) = 3.7 x 10 4 s -1 1 Bq = 2.7 x 10 -11 Ci

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Atomic symbols

A MASS NUMBER (

the number of protons and neutrons)

Z X SYMBOL OF ELEMENT N

The number of neutrons

ATOMIC NUMBER (

the number of protons) Example:

131 53 I 78 131

I or I-131

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Mass-energy relationship

Measured Mass Calculated Mass

E= mc

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Fission

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Nuclear reaction and energy production

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Module III Mechanisms of radioactive decay - 16

Alpha (α

++

) decay

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A Z X A-4 Z-2 Y + 4 2 He e.g. 238 92 U 234 90 Th + 4 2 He

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Beta (



) decay

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n p + e + υ A Z X



A Z+1 Y +e +



e.g. 131 53 I



131 54 Xe+e +

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Positron (



+

) decay

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p n + e +

+ υ

A Z X



A Z-1 Y+e + +



e.g. 18 9 F



18 8 O+e + +

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Electron capture

p + + e -



n +



A Z X



A Z-1 Y +



125 53 I



125 52 Te+

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Gamma (



) emission

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Nuclear energy levels: gamma radiation

SIMPLIFIED NUCLEAR MODEL Gamma ray

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How does radiation interact with matter?

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Excitation

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Ionization

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Electron removal by ionization

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Alpha particle interaction

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Interaction of alpha radiation with living matter: external deposition



Alpha radiation is not external hazard.



The maximum range in tissue is <0.1 mm



All alpha radiation is absorbed in stratum corneum

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Interaction of alpha radiation with living matter: internal deposition Prime danger is inhalation and ingestion of

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alpha emitter

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Beta interaction with matter

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Interaction of beta radiation with living matter Cell nucleus Cell diameter 1.7 MeV beta 100 cell diameter alpha 0.15 MeV beta beta 5.3 MeV alpha Auger

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I I I I I ı 0.001 0.01 0.1 1 10 100 mm

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Positron interaction:

annihilation reaction

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Neutron interaction

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Neutron activation

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Interaction of gamma radiation with matter



In terms of ionization, gamma radiation interacts with matter in three main ways 1. Photoelectric effect 2. Compton scattering 3. Pair production

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Module III Gamma interaction by photoelectric effect - 35

Module III Gamma interaction by Compton scattering - 36

Module III Pair production - 37

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Extranuclear energy release



Bremsstrahlung radiation



Characteristic X rays



Auger electrons

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Bremsstrahlung radiation

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Importance of bremsstrahlung X rays in radiation safety practice

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Characteristic X rays

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Module III Difference between X rays and gamma rays - 42

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Internal conversion: Auger electrons

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Specific ionization and linear energy transfer (LET)

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Penetrating power of radiation

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Review points



Characteristics of representative types of ionizing radiation



particulate, charged, and directly ionizing radiation of alpha and beta particles



particulate, uncharged, and indirectly ionizing radiation of neutrons



electromagnetic, uncharged, and indirectly ionizing radiation of gamma rays and X rays.



Radiation interacts with matter via two main processes: ionization and excitation



Energy, which comes in many forms, can be converted from one form to another



Nuclear potential energy is converted into kinetic energy through nuclear fission



Conversion of mass to energy was predicted by Albert Einstein in his mass-energy equation, E = mc 2



Penetrating power of ionizing radiation is relative to radiation type and energy

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