7.1 Basic Concepts and Formulae 377
Bremsstrahlung
When a relativistic particle of massm, chargezemoves close to a target nucleus
of chargeZe, it undergoes acceleration which is proportional tozZ/m, and emits
radiation known as bremsstrahlung. Thus the radiation losses for electrons under
identical conditions, are 3× 106 times greater than for protons. Since energy loss is
a one-shot process, the law of energy degradation is exponential. IfE 0 is the initial
energy then at distancex
<E>=E 0 exp(−x/X 0 ) (7.36)Radiation lengthX 0 is defined as that absorber thickness which reduces the particle
energy by a factore.
Passage of radiation through matter
When electromagnetic radiation passes through matter the type of interaction depends
on (1) photon energy (2) Z of the material (3) particle or field with which the photon
interacts. The important processes in Nuclear physics are
- Compton scattering
- Photoelectric effect
- Electron–positron pair production
- Nuclear resonance fluorescence
The compton effect
The process of elastic scattering of photon by a free electron with reduced frequency
(or increased wavelength) is known as Compton scattering, Fig. 7.8
Fig. 7.8Compton scattering
Shift in wavelength
Δλ=λ−λ 0 =(h/mc)(1−cosθ) (7.37)The Compton wavelengthλc=h/mc= 2. 43 × 10 −^12 m (7.38a)