photon /xray interaction with matter.pptx

photon interaction with matter

1. PHOTON INTERACTION WITH MATTER DARSHAN BS MEDICAL IMAGING TECHNOLOGIST KIDWAI MEMORIAL INSTITUTE OF ONCOLOGY BANGALORE

2. content Nature of radiation,Types . Attenuation Absorption scattering Photon Interaction with matter

3. NATURE OF RADIATION The term radiation applies to the emission &propagation of energy through space or material TYPES OF RADIATION 1)Electromagnetic Radiation(ex .light wave,heat waves,xray,Y rays ) -defined by Maxwell in terms of oscillating electrical &magnetic field. EM rays range from 10-7 M( radiowaves to 10 -13 (ultra high energy xray ) 2)Particulate radiation

4. 2)Particulate radiation - Refers to energy propagated by traveling corpuscles which have definite rest mass -elementary atomic particles eletron,protons,Neutron -positron , neutriono are subatomic particles

5. Nature of matter

6. RADIATION INTERACTION

7. Photon Beam may undergo the following 4 process

8. ATTENUATION Attenuation is the product of absorption and scattering. It is the removal of photons from the beam due to absorption and scattering. it is given by the relation I is the number of transmitted photons, I0 is the number of incident photons, e is the base of natural logarithm and µ is the linear attenuation coefficient of the absorber material

9. Linear Attenuation Coefficient The linear attenuation coefficient is defined as the reduction in the radiation intensity per unit path length and its unit is cm–1 . It refers the fractional reduction produced in any mono enegetic photon-beam is constant for any given material per unit thickness . This constant is know as the linear attenuation coefficient . linear attenuation coefficient express of the probality of the photon being removed by a given material. linear attenuation coefficient is related to the half value layer by following expressing µ=0.693/HVL or

10. Mass Attenuation Coefficient The mass attenuation coefficient is obtained by dividing the linear attenuation coefficient by the density P has the symbol µ/p and unit cm2/g The mass attenuation coefficient is independent of density

11. The half value layer (HVL) The half value layer (HVL) is the thickness required to reduce the beam intensity to half of its original value The linear attenuation coefficient is related to the term half value layer as follows: HVL = 0.693/µ HVL is an indirect measure of photon energies . Varies material used for measurement of HVL Generator energy <30KV 30-150KV 120-600KV 500KV-2MV material cellophane aluminium copper lead

12. X-RAY AND GAMMA -RAY INTERACTIONS or photon beam attenuation When traversing matter, photons will penetrate without interaction, scatter, or be absorbed There are four major types of interactions of x-ray and γ ray photons with matter, the first three of which play a role in diagnostic radiology and nuclear medicine

13. THERE ARE FIVE BASIC WAYS THAT AN X-RAY PHOTON CAN INTERACT WITH MATTER Coherent scattering Photoelectric effect Compton scattering Pair production Photodisintegration

14. COHERENT SCATTERING "coherent scattering" is given to those interactions in which radiation un dergoes a change in direction without a change in wavelength. For this reason, term "unmodified scattering" is sometimes used. There are two types 1) Thomson scattering-Thomson scattering a single electron is involved in the interaction 2) Rayleigh scattering-Ray leigh scattering results from a cooperative interaction with all the electrons of an atom Both types of coherent scattering may be described in terms of a wave-particle interaction, and are therefore some times called "classical scattering.

15. Low-energy radiation encounters the electrons of an atom and sets them into vibration at the frequency of the radiation This is the only type of interaction between x rays and matter that does not cause ionization no ionization occurs with coherent scattering. Its only effect is to change the direction of the incident radiation coherent scattering occurs throughout the diagnostic energy range, but it never plays a major role it produces scattered radiation which contributes to film fog, the total quantity is too small to be important in diagnostic radiology.

16. Coharent scattering properties

17. PHOTOELECTRIC EFFECT

18. COMPTON SCATTERING

19. PAIR PRODUCTION When a photon having energy > 1.02 MeV, passes near the nucleus of an atom, will be subjected to strong nuclear field. The photon may suddenly disappear and become a positron and electron pair r. For each particle 0.511 MeV energy is required and the excess energy > 1.02 MeV, would be shared between the positron and electron as kinetic energy