Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

1

cos11 20

'

cmhh

h

20

21cmh

hEc

cos11

cos1

20

20'

cmhcmh

hhhEe

In the figure:• Photoelectric suppressed.• Single Compton (effect of crystal dimensions).• Below 1.022 MeV.

Compton ScatteringCompton Scattering.Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

2

Reproduce the graph.

cos11 20

'

cmhh

h

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

3

• Compton scattering is predominant for energies typical of radioisotope sources.

• “Probability” per atom increases linearly with Z (Why).• Electron density.• Effect of binding energy.• Effect of polarized photons.• Compton fraction. Klein-Nishina formulaKlein-Nishina formula

Let the recoil electron be emitted at an angle , calculate cot() as a function of tan(/2).

HW 4HW 4

20cm

h

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

4

Note tendency for Note tendency for forward scattering forward scattering at high energies.at high energies.

Considerations for shields and detectors? Sources vs. accelerators???shields and detectors? Sources vs. accelerators???

HW 5HW 5 What is Thomson scattering.What is Thomson scattering.

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

5

If you need to measure gamma ray yield from nuclear reactions (using particle accelerators), the photon energies could be as high as 10 MeV. What is the typical Ge detector to be used?

Prepared with Monte Carlo simulations.

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

6

Single peak if electron and positron “kinetic” energies are captured by the

detector. But annihilation!2

02 cmhEEee

Rest mass of electron and positron. Gamma must have 1.022 MeV

minimum energy for PP to occur.

Two annihilation photons are then created when positron recombines with an electron. These photons may or may not be captured, causing single and double escape peaks in the spectrum (effect of crystal dimensions).

Pair ProductionPair Production.

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

7

Low-energy gamma.Low-energy gamma. High-energy gamma.High-energy gamma.

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

8

Probability of pair production.

Dependence on Z?

Recoil nucleus,Why?Why?

Effect of Effect of screening?screening?

HW 6HW 6

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

9

Principles of Spectrometry

Importance in Linacs?

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

10

Very large detector. All secondary radiation, including Compton scattered gamma rays, Bremsstrahlung, x-rays and annihilation photons, are captured in detector volume

Large photofraction (fraction of full energy events) is desired in any detector

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

11

Very small detectors. All secondary radiation, including Compton scattered gamma rays and annihilation photons, are not captured in detector volume (escaping).

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

12

A typical detector.

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

13

Effect of surrounding material. Detectors are normally shielded to minimize as much as possible the counting of ambient background radiation.

X-rays and

lining.

Principles of Spectrometry

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

14

Principles of Spectrometry

• Efficiency and resolution.• Summing effects.

Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).

15

HPGeHPGe

Principles of Spectrometry

Resolution