Energy Absorption in Radiobiology Ionization vs. Excitation Ionizing Versus Non-ionizing Radiation Absorption Mechanisms Ionization by alpha particle, Xray & neutron

1. RADIATION
ABSORPTION
MADe By: DR. ISHA JAISWAL
MODeRATOR: DR. S.P MISHRA
DATe : 25 NOv. 2013

2. eNeRgy ABSORPTION IN
RADIOBIOLOgy
The enrgy is absorbed in form of
small discrete packets: PHOTONS
 The energy deposition is uneven,
discrete & nonuniform.
 Lead to chemical & biological
changes.
Absorption of radiation may lead
to ionization or excitation of atoms

3. IONIzATION vS.
excITATION
EXCITATION: raising of electron to
higher energy level without
ejection.
IONIZATION:ejection of orbital
eletron from atom resulting in
production of ion pair

4. IONIzATION vS.
excITATION

5. TyPeS Of RADIATION
• Radiation is classified into:
–Ionizing radiation
–Non-ionizing radiation

6. Ionizing Versus Non-ionizingIonizing Versus Non-ionizing
RadiationRadiation
Ionizing RadiationIonizing Radiation
– Higher energy electromagnetic waves (gamma) orHigher energy electromagnetic waves (gamma) or
heavy particles (beta and alpha).heavy particles (beta and alpha).
– High enough energy to pull electron from orbit.High enough energy to pull electron from orbit.
Non-ionizing RadiationNon-ionizing Radiation
– Lower energy electromagnetic waves.Lower energy electromagnetic waves.
– Not enough energy to pull electron from orbit, butNot enough energy to pull electron from orbit, but
can excite the electron.can excite the electron.

8. Primary Types of IonizingPrimary Types of Ionizing
RadiationRadiation
PARTICULATE RADIATIONPARTICULATE RADIATION
Alpha particlesAlpha particles
Beta particlesBeta particles
NeutronsNeutrons
ELECTROMAGNETIC RADIATIONELECTROMAGNETIC RADIATION
Gamma rays (or photons)Gamma rays (or photons)
X-Rays (or photons)X-Rays (or photons)

9. PARTIcuLATe vS.
eLecTROMAgNeTIc RADIATIONS
Particulate Radiations are sub-
atomic particles with mass.
(e.g., alpha and Beta particles,
electrons, neutrons).
EM Radiations have no mass and
no charge.
(eg. X-rays and gamma rays)

10. Types of Ionizing RadiationTypes of Ionizing RadiationTypes of Ionizing RadiationTypes of Ionizing Radiation
β
α
γ or X-
rayneutron

11. PRODucTION Of ALPHA & BeTA
RAyS

12. Production of gamma rays

13. absorPtion mechanisms
Radiation can be classified as
directly or indirectly absorption.
Direct absorption -
charged particles
Indirect absorption -
photons, neutrons

14. directly vs indirectly
ionizing radiation
Charged particles
can directly
distrupt the atomic
structure of the
atom through
which they pass &
produce chemical
and biological
damage.
• EM radiation &
neutron when
absorbed in
matter give up
their energy to
produce fast
moving charged
particle which in
turn produce
effect.

15. directly vs indirectly
ionizing radiation

16. sPecific ionization
• No of ion pairs produced per unit
length of charged particle is called as
specific ionization.
• Depend on charge & mass of particle.

17. Ionization by alpha particle,
Xray & neutron

18. linear energy
transfer
Energy absorbed in medium per
unit length of particle is called
LINEAR ENERGY TRANSFER
Expressed in kev/um
LET determines rate of energy
absorption in medium

19. low let radiations
Properties:
From x or gamma rays
Sparsely ionizing
Low specific ionization
They do not give up their energy
quickly:longer range in air
More penentration
Indirectly ionizing

20. high let radiation
Properties:
From particles that do possess mass
and charge
High specfic ionization
Their energy is exhausted sooner
than that of an x or gamma ray
Less penentration
Directly ionizing

21. low vs high linear energy
transfer

23. Absorption of EM rADiAtion
 Indirect ionization
 depends on
 energy of incident photon
 Chemical composition of absorber.
Three ways of energy absorption
PHOTOELECTRIC EFFECT
COMPTON EFFECT
PAIR PRODUCTION

24. photoElEctric EffEct
Interaction between photon & bound
electron
 all energy transferred.
 More likely for low-energy photons
Photon absorption proportional to Z3 (z is
atomic no of absorber)
 Inner-shell electron is ejected
Vacancy filled with outer orbital electron
Characterisic x ray & auger electron

26. coMpton scAttEr
 interaction betweenphoton & free
electron
photon strikes a free or loosely-bound
orbital electron (outer shell)
 transfers portion of kinetic energy
More likely at intermediate photon
energies
Photon absorption is independent of Z
of absorber, thus energy absorption by
this mechanism is similar for soft tissue,
muscle and bone

28. pAir proDuction
Interaction between photon & nucleus
high-energy photon produces
positron/electron pair
Increases with square of atomic no. of
medium
Threshold energy of this process: 1.02MeV
Ultimately, the positron annihilates and
produces two 0.511 MeV photons

30. Absorption of chArgEDpArticlEs
Directly ionizing
Larger mass than electrons
Greater KE deposited over a
shorter path length: short range
Greater specific ionization.
greater LET than photons

31. Absorption of nEutron EnErgy
Uncharged,
Indirect ionizing
Generate fast
recoil protons,
alphas, and
heavy
fragments

33. DNA and Radiation

34. Ionizing Radiation at the
Cellular Level
• Causes breaks
in one or both
DNA strands or;
• Causes Free
Radical
formation

36. Direct Ionization Caused By:
Protons
Alpha
Particles
Beta
Particles
Positron
Particles

37. DIRECT IONIZATION

38. Indirect Ionization
Caused By:
• Neutrons
• Gamma Rays
• X-Rays

39. INDIRECT IONIZATION