05 - Radioactive properties Flashcards
Z
A
Element
Z
number of protons
= atomic number
N
number of neutrons
A
= protons + neutrons
= mass number
isotope
same proton number
various neutron number
various number of mass
beta- decay
neutron to
–> Proton, Negraton and antineutrino
daughter: Z+1, N-1, Z+1+N-1=A
e. g. 87Rb -> 87Sr
beta+ decay
positron decay
Proton to
–> Neutron, Positron, Neutrino
daughter: Z-1, N+1, Z-1+N+1 =A
e. g. 18F -> 18O
e- capture decay
Electron -> split proton
–> Neutron & Neutrino
daughter: Z-1, N+1, Z-1+N+1
e. g. 40K -> 40Ar
alpha decay
2 Protons + 2 Neutrons
- -> charge 2+
- -> 4He-nucleus
daughter: Z-2, N-2, Z-2+N-2=A-4
e. g. 238U -> 234Th
Decay chains
U and Th isotops can’t reach stable via a single decay
!!
Dacay of unstable isotopes
!!
(formula)
N = N0 * e^( -lambda * t )
N = numer of remaining mother isotopes at time t
N0 = number of mother isotopes at time t=0
lambda = isotope specific decay constant
half life time
for daugther isotopes
D* = N0 * /1-e^(-lambda*t)
t = 1/lambda * ln( D* / N + 1 )
depth of penetration
of
radiation
extremely small
for apha & beta particles
thats why gamma ray is used
which radioactive decays produse measureable gamma rays?
uranium-radium series
(4.4 * 10^9 years half life)
Thorium series (1.4 * 10^9 years half life)
Potassium K40 (1.3 * 10^9 years half life)
characteristic peak
Potassium
1.46 MeV
characteristic peak
Thorium
2.62 MeV
