Detection of γ-rays from nuclear decay:

0.1 < Eγ < 20 MeV

γ-ray interaction

γσ EZpp ln2≈

ionization occurs in limited regions of the absorber

Ge

µ

ppCph σσσµ ++=

Linear attenuation coefficient (probability per unit path)

γ

γσEE

ZC

ln≈

54

5.3

−=

≈

n

EZ n

phγ

σ

I/I0

t

e-µt

= hν

= c/ν=hc/E

Eγ = hν

Derivation of Compton Scatterig Formula

Detector response We detect recoil electrons

and NOT photons !

)(256.02

/21

22

2

cmEifMeVcm

cmEE

EEE

ee

eCEgap

>>=≈

+=−=

γ

γ

γγ

Egap

Important characteristics: §  energy resolution: δEγ/Eγ = FWHM/Eγ

§  peak-to-total: P/T = Areapeak/Areatotal

Egap

Study of Detector response

Accurate study of detector response

is done with MonteCarlo GEANT simulations

133Ba in-beam spectrum

after unfolding

Backscattering peak: θ=π ⇒ (Εγ)min ~mec2/2 =256 keV important for θ≥ 1100