fok radprot atomic 2020vds5 - semmelweis.hu · 1/39 radiationprotection atomicstructure,...

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Atomic structure, radioactivity, ionizing radiationRadiation Protection

Radiation ProtectionAtomic structure, radioactivity, ionizing radiation

2020. February 5.

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Lectures: Wednesday at 14:45 – 15:55

Other: ask Dr. SZABÓ Bence Tamás

http://semmelweis.hu/oralis-diagnosztika/en/education/radiation-protection/

Subject: Radiation Protection

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Why to learn Radiation Protection? – the „Big Picture”

Obtain InformationBased on radiation(Radiology)

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Knowledge on PROTECTION & Measure

(Radiaton Protection - Dosimetry)


For PatientFor DentistFor Environment


+ „Side effect”

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For PatientFor DentistFor Environment


+ „Side effect”

+ Certificate….

Knowledge on PROTECTION & Measure

(Radiaton Protection - Dosimetry)

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Effect – Interaction –needed

HOW? – the „Big Picture”

Usefull Information

+ „Side effect”+ Protection+ Measurement

Energy absorption (transfer) - Energy

dental structure

+ other structures+ lead, aluminium+ detector

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Usefull Information



Energy : radiation

Source of radiation

dental structure


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Usefull Information



Energy : radiation

Source of radiation

dental structure


Certificate (exam)question:

Describe and characterize the ionizing radiations

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Interaction – general theory

1. Energy absorption via IONIZATION

+

-

+ Energy

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Interaction – general theory

1. Energy absorption via IONIZATION

+

-

Usually means: create a FREE electron

(2. Energy absorption via other methods)

+

+

+ Energy

+ Energy

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Ionization by radiation

+ Energy (E): could be a radiation

Radiation: energy flow through a matter without „mediation”

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Pure energy flow (photon (EM-wave) – „particle” with no rest mass)Eg. gamma, X-ray radiation

Particle flow („real” particle – has a rest mass)Eg. alpha, beta, neutron radiation

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Pure energy flow (photon (EM-wave) – „particle” with no rest mass)Eg. gamma, X-ray radiation

Particle flow („real” particle – has a rest mass)Eg. alpha, beta, neutron radiation

If high enough to free an electron: ionizing radiationE > bounding energy = ionization energy aka „work function” ~10eV

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Ionization by charged particles (electrons…)

Coulomb interaction

Direct ionization: caused by a charged particle

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Ionization by photons

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high Ephoton

„primary” electrons

high Eelectron Ionization by electrons (see before!) – indirect ionization

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Ionization by photonsWhich one? (Photoeffect, Compton-scattering, Pair production)

Given PROBABILITYDepends: Ephoton, matter

Importance: different image quality, scattering – radiation NOT in a linear direction - PROTECTION

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Ionization by photonsWhich one? (Photoeffect, Compton-scattering, Pair production)

Given PROBABILITYDepends: Ephoton, matter

Importance: different image quality, scattering – radiation NOT in a linear direction - PROTECTION

+ „interaction” : elastic scattering

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Interactions by „others” Neutrons:

gamma radiation, charged particles orheavy charged particles created

via nuclear force (strong interaction - see later)

…. Other: not relevant for dentistry students

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Characterisation

How many ions are created in a material - at a unit distance

The amount of E transfered to the materialat a unit distance LET value: linear energy transfer

Depends on: the type and energy of the radiationWhy is it important??? (see next lecture)

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Usefull Information



Energy : radiation

Source of radiation

Certificate (exam)question:

The stability of the nucleus,

The law of radioactive decay,

Decay lines

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Source of radiation – atomic structureModels:

Thomson: ~ plum pudding (paired positive-negative particles)Rutherford: ~solar system (positive at the middle - nucleus)Rutherford - Bohr: + quantum restrictions

Nucleus: positrons (p+) and neutrons (n0) – called nucleons

Cloud (envelope, shells):electrons (e-)

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Source of radiation – atomic structureModels:

Thomson: ~ plum pudding (paired positive-negative particles)Rutherford: ~solar system (positive at the middle - nucleus)Rutherford - Bohr: + quantum restrictions

Nucleus: positrons (p+) and neutrons (n0) – called nucleons

Cloud (envelope, shells):electrons (e-)

NuclearNotation: ��

� A: mass number (Z+N)Z: atomic number (number of p+)X: chemical symbol of the elementN: neutron number (number of n0)

Iso: sameIsotop: same ZIsoton: same NIsobar: same A

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Source of the radiation

1. Processes in the electron cloud („envelope”) of the atom: result: photons - called X-ray photons

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Source of the radiation1. Processes in the electron cloud („envelope”) of the atom:

result: photons - called X-ray photons

a) deceleration/acceleration of charged particleeg. Brehmstrahlung of electrons (X-ray device) +

Xray

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1. Processes in the electron cloud („envelope”) of the atom: result: photons - called X-ray photons

a) deceleration/acceleration of charged particleeg. Brehmstrahlung of electrons (X-ray device)

different energies! – continous spectrab) „hole” of electron in the inner shell – *characteristic X-ray radiation created

Reasons: I. ionization in the inner shell because of electron, photon, neutron, other particles

eg. electron – electron Coulomb interaction in an X-ray deviceII. electron capture (see later)III. … not relevant

*depends on the E differece of shells – line spectra(type of material)

+

+

+

I.

II.+

Xray

Xray

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2. Processes in the nucleus of the atom – radioactive decay

result: photons – called gamma photonsalpha-particlesbeta-particles…

Note: X-ray photons = gamma photons ; only the source is different(Energy range of X-ray and gamma overlaps)

1,5. Other processes (eg. pair-production) – near to the nucleus

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Source of the radiation: nucleus

No balance (not at minimal energy): unstable nucleus:too much p+ or n0 or +„energy”

Forces:Coulomb-force (repulsive): between p+ and p+

nuclear force (aka strong force or nucleaon-nucleon interaction)(attractive): between nucleons – act at very small distances

Balanced via number of nucleons and the „structure” („arrangement of nucleons”)

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Source of the radiation: nucleusUnstable nucleus : emits (radiates) proton or neutron and „remnant” energy = radioactive

Z

N

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Radioactivity - decay

� =∆�

∆

RadioActivity (A): number of emitted (radiated) particles (∆N) at unit time (∆t) - frequency

Unit: [Bq] ; SI base unit: [1/s]

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� =∆�

∆



- depends on the number of unstable atoms (N)!! Emitting a particle is random (stochastic) event!

– given probability: specific for the isotope !

– expected value (mean) could be given () - decay constant

� =∆�

∆= − · �

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!! Changing in timeHow does it change? Decay law of radioactivity:

� =∆�

∆



- depends on the number of unstable atoms (N)!! Emitting a particle is random (stochastic) event!

– given probability: specific for the isotope !

– expected value (mean) could be given () - decay constant

� =∆�

∆= − · �

� = �� · ��·

� = �� · ��·

� = �� · 2�

�

�

� = �� · 2�

�

�

T: half life time

N or A (%)

N0 or A0

T

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Alpha decay

Reason of unstability: too heavy nucleus; solution: emitting 4 particlesEmitted particle: alpha = 2 protons + 2 neutrons (=nucleus of He)

�� + (2�� + 2��)��

��

�� !

�� !��"

�� !��

Always the same energy! (line spectra)

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Beta decay(s)

Reason of unstability: too much neutron; solution: neutron converted to proton

Emitted particle: beta = electron and (anti)neutrino (#̅) [biologically not relevant in interactions]

1. '� = ��

�� ( + �� + #̅�

��(�

��+ �� + #̅��

*+,,(-.

/�,!(-."

/�,!(-.

Separately emitted particles!Energy same for the sum!Electron energy in a range! (continous spectra)

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Beta decay(s)

Reason of unstability: too much protons; solution: proton converted to neutronEmitted particle: beta = pozitron and neutrino (#) [biologically not relevant in interactions]

2. '� = ��

�� ( + �� + #�

��(�

��+ �� + #��

01(

2 (

Separately emitted particles!Energy same for the sum!Positron energy in a range! (continous spectra)

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Electron capture

Reason of unstability: too much protons; solution: proton + electron converted to neutronEmitted particle: -- (neutrino (#) [biologically not relevant in interactions])

But hole in the electron cloud in the inner shell!

an outer shell electron fills itEnergy difference emitted as a photon (characteristic X-ray)or Energy difference enough to free an outer electron (Auger-electron)

�� ( + #�

��(�

�� + #�� + ��

*3��,(

4�-,(

+�3�5 63 �7�836�

Always the same energy!

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Decay series (lines)

Natural ancient decay series:Thorium series (T=14 billion years)

Neptunium series (T=2.1 million years)Uranium 238 series (T=4.5 billion years)Uranium 235 series (T=710 million years)Potassium 40 series (T=1.3 billion years)

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Gamma decay(s)

Reason of „unstability” – not at energy minimum: AFTER alpha or beta: nucleon is at excited state

Emitted particle: gammaa) promt gamma – T < microsecond after alpha/betab) isomeric transition – T > microseconds

metastable energy levelprohibited transition = small probability

�� + 9�::��

�

;8�-11"

;8�-11

Always the same energy! (line spectra)

fok radprot atomic 2020vds5 - semmelweis.hu · 1/39 radiationprotection atomicstructure,...

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