Lesson3_1

Lesson3_1 - Lesson 03 Quantities for Describing the...

This preview shows pages 1–6. Sign up to view the full content.

Lesson 03 Quantities for Describing the Interaction of Radiation with Matter MP200 Radiation Physics - 2010 Duke Medical Physics Graduate Program 1

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Kerma ( K ) Kerma stands for the k inetic e nergy r eleased per unit ma ss in the matter. This is a nonstochastic quantity only relevant to the fields of indirectly ionizing radiation. K = d tr dm tr = expectation value of the energy transferred in the finite volume V for a time t . d tr = sum of initial kinetic energies of secondary charge particles in a mass dm of the infinitesimal volume of dv . Kerma is the first step of dissipating energy by indirectly ionizing radiation. definition Kerma is the expectation value of the energy transferred to charged particles per unit mass at a point of interest, including radiative loss energy but excluding energy passed from one charged particle to another. Units of Kerma is J.kg - 1 or Gy . Exponential Attenuation Figure 1: Exponential Attenuation 3

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
n = number of interactions in distance dx n dx and n N n = μNdx μ = linear attenuation coefficient μ = ( n N ) dx Units of μ are m - 1 or cm - 1 Definition of μ Probability of a photon interaction with matter by one process or another per unit distance traversed. μ depends on the density of material and the photon energy. Change in number of photons, dN = ( N - n ) - N = - n = - μNdx N N 0 dN N = L 0 - μ.dx N = N 0 e - μL N = number of photons passed through material without interaction. Mass Attenuation Coefficient μ divided by the density of the material is defined as the mass attenuation coefficient. Mass attenuation coefficient = ( μ ρ ) Units: cm 2 .g - 1 4
Definition of ( μ ρ ) ( μ ρ ) = ( n N ) ρdx The probability of an interaction per unit thickness in g.cm - 2 of material tra- versed.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern