Base of protection. Radiation Protection. Radiation. Structure of the atom. (ionizing radiations: α-,β-, γ-radiation, X-ray) J E

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Base of protection Radiation Protection Properties of the radiations Interaction with matter Physical step: ionization (ionizing radiations: -,β-,

possible definition: propagatation of energy. strength of the radiation: intensity.

1 Base of protection Radiation Protection Properties of the radiations Interaction with matter Physical step: ionization (ionizing radiations: -,β-, γ-radiation, X-ray) Particle ( and β) Electromagnetic (γ and X-ray) Chemical reaction Biological consequenties Radiation Structure of the atom possible definition: propagatation of energy. strength of the radiation: intensity. nucleus proton J E ΔE ΔA Δt Amount of the energy propagating through ΔA surface during Δt time (perpendicular to it). Electron cloud neutron Atomic number (Z): no. of protons or electrons Mass number: No. protons and neutrons

Stability of the nucleus Isotopes Coulomb force repulsive force (long range) Nuclear force

!! hydrogen deuterium tritium Ratio of the no. of protons and neutrons are important!

Stability of the nucleus small atomic number: N ~ Z higher value: N > Z Unstable atoms Decay:

2 Stability of the nucleus Isotopes Coulomb force repulsive force (long range) Nuclear force Attractive force (short range) Same atomic number, different mass number. Coulomb force!!! hydrogen deuterium tritium Ratio of the no. of protons and neutrons are important! Less or too many neutrons: unstable atom. Stability of the nucleus small atomic number: N ~ Z higher value: N > Z Unstable atoms Decay: transformation of the atom. Radioactive decay: the atom emits a radiation. Bound energy/nucleon (MeV) decay: (mainly at higher atomic number) β decay: (mainly at lower atomic number mass number

(He nucleus) According to the quantummechanics, there is a small probability being out.

3 -decay -radiation The energy state is quantized in the nucleus! parent daughter Line spectrum. (energy distribution of the particles) tunnel-effect: Atomic number decreases by Mass number by 4. (He nucleus) According to the quantummechanics, there is a small probability being out. Path: linear High kinetic energy: a few MeV Negative β-decay spectrum of the β-radiation we expect: experiment Continuous spectrum!!! There is no electron in the nucleus! 0 n + p + 0 e no. of β-particles Surprising: the energy state is quantized! The spectrum should be line, (see: -radiation.) kinetic energy?

Atomic number decreases by, mass number is the same. Only in the case of artificial isotopes.

4 Anti-neutrino Positive β-decay 0 n + p + 0 e +υ anti-neutrino: particle of the anti-substance. + 0 p n + + e +ν 0 Quantized energy is shared between electron and antineutrino. particle ν: neutrino Continuous spectrum is possible. Atomic number decreases by, mass number is the same. Only in the case of artificial isotopes. electron-positron pair γ-radiation Spectrum of the γ-radiation If the nucleus has excess energy after - or β-decay. Metastable state: excess energy. energy γ-radiation (e.m. radiation) Line spectrum: corresponding to the quantized energy states. radiation energy(kev) ratio 37 Cs β - 73,(max) ~ 5% β - 5,6(max) ~ 95% 37m Ba γ 66,6

5 Decay law ΔN N λ Δt N N 0 e λt Activity: no. of decays during unit time. Unit: /s (Bq Bequerel) A A Observation: activity is proportional to the no. of atoms. N no. of undecayed atoms. ΔN no. of decays during Δt. λ decay constant. N 0 No. of. Atoms at the beginning of the observaton. N No. of undecayed atoms t time later. Meaning of the λ Decay rate relatíve decay rate ΔN ΔN / Δt λ N λ Δt N N 0 / N 0 /e Graphic representation ln λ T ln λ T λ τ ΔN Δt A Activity: no. of decays during unit time. T τ T half-life (no. atoms decreases by ) τ lifetime (no. atoms decreases by factor e)

half-life a natural isotopes half-life of a few isotopes used in medical practice atom 38 U 34 U Rn 8 Po 4 Po 0 Po decay Half-life 4.5 million year 45 thousand year 3.8 day 3.05 minutes 0.

6 half-life a natural isotopes half-life of a few isotopes used in medical practice atom 38 U 34 U Rn 8 Po 4 Po 0 Po decay Half-life 4.5 million year 45 thousand year 3.8 day 3.05 minutes secons 38.4 day atom C 3 I 59 Fe 5 O 99m Tc decay β + β - β - β + metastable Half-life 0.3 min day 45 day 4 sec hour Radioactive decay families in equilibrium: Frequently the daughter is also unstable. λ N λ N λ 3 N 3 β 38 U 34 Th 34m Pa equilibrium: e.g. Th is produced and decays with the same rate. Decay rate condition: λ N λ N ΔN λ N Δt

Electron cloud Energy states of electrons Principle of minimum energy Pauli principle Being as close to the nucleus as possible. In the atom there is no two electrons in the same energy state.

7 Electron cloud Energy states of electrons Principle of minimum energy Pauli principle Being as close to the nucleus as possible. In the atom there is no two electrons in the same energy state. potential energy excited states vibrational levels The energy state is quantized. Only discrete energy levels are allowed. groundstate Tranzitions between states Energy of the emitted photon internal conversion vibrational relaxation M-series ΔE E i -E j hν energy L-series excitation and ionization K-series emission frequency depends on the transition. excitation fluorescency phosphorescency

8 Electromagnetic spectrum Production of X-ray I anode ev: kinetic energy of an electron accelerated by volt. ( ~.6x0-9 J) X-ray γ-ray anode anticathode X-ray X-ray tube cathode ray U anode anode holder cathode I heating anode cathode Acceleration of electrons, kinetic energy Speed of the electron Electric field Work of electric field example: U 60 kv m v e e W m e 9,. 0-3 kg e C W Fi Δsi Q i i E Δs i i W U e V C 0 4 J Voltage: work done on unit charge. W J U, V Q C v W m e 9. 0 J kg m s

9 ΔE mev Brehmstrahlung (breaking radiation) deaccelerating an electron or breaking. m v e free electron: the energy change is not quantized. Spectrum of the Brehmstrahlung e U λ min h c λ min h c e U heat electromagnetic radiation (X-ray) e.t.c. continuous spectrum Duanne-Hunt law λ min k U Power and efficiency Characteristic X-ray P total c U x ray I Z efficiency: at higher accelerating voltages. accelerated electron c constant U accelerating voltage I - anode current Z atomic number of the anode η P P x ray electric cu IZ UI cuz knocks out an electron (ionize the atom) (P electric UI) M-series L-series the third electron emits radiation efficiency usually is below %! K-series excitation and ionization emission energy is quantized line spectrum

10 Spectrum of the characteristic radiation (Cu-anode) relative intensity The line spectrum superimposes the breaking radiation. (dashed line the original part of the breaking spectrum) wavelength

Some nuclei are unstable Become stable by ejecting excess energy and often a particle in the process Types of radiation particle - particle

Some nuclei are unstable Become stable by ejecting excess energy and often a particle in the process Types of radiation particle - particle Radioactivity George Starkschall, Ph.D. Lecture Objectives Identify methods for making radioactive isotopes Recognize the various types of radioactive decay Interpret an energy level diagram for radioactive