2.9 - Nuclear decay
Background radiation
Natural sources (85%)
● Air, underground radon gas (~50%)
● Ground, buildings (concrete) (13%)
● Cosmic rays (12%)
● Food & drinks (eg bananas) (10%)
Artificial sources (15%)
● Hospitals (14%)
● Industrial sources (1%)
Radiation hazards
● ***Irradiation: exposure to radiation; NO radiation once source is removed
● ***Contamination: deposition of radioactive material on surfaces/into bodies;
surface/body continues to irradiate surroundings after source is removed
● How to minimise:
○ Keep sources which emit ionising radiation ≥30 cm away from body
(minimises irradiation)
○ Limit time of use of sources (minimises irradiation)
○ Do NOT touch/inhale source (otherwise contamination)
○ Wash hands after working with source (prevents contamination)
Types of ionising radiation (& decay)
●
Alpha (α ) Beta minus ( Beta plus ( Gamma ( γ ) Neutron (n)
−¿¿ +¿¿
β ) β )
Composition He nucleus electron positron photon neutron
Mass 6.6446573357(20)e-27 kg 9.1093837015(28)e-31 kg 0 1.67492749804(95)e-27 kg
4.001506179127(63) u 5.48579909065(16)e-4 u 1.00866491588(49) u
3.7273794066(11) GeV c-2 0.51099895000(15) MeV c-2 939.56542052(54) MeV c-2
Charge +2e -e +e 0 0
Reason of Strong nuclear force fails N : Z too high N : Z too low Too much
decay to balance electrostatic (too many energy in
repulsion between neutrons) nucleus
nucleons
Speed ~0.05c ~0.99c c
Typical 3~7 MeV 0~12 MeV 100 eV~100 keV
energy
1
, Relative 10000 100 1
ionising
power
Penetration/ Few cms of air Few mms of Al Few cms of Pb
range
Deflection in Small Large No
electric +
magnetic
fields
Eg of decay
❑241 237
95 Am →❑93 Np+❑
❑4 90
2 He
90
38 Sr →❑39 Y❑38
19 K →❑18 Ar
38
0
0 ¿¿
+❑−1 e +❑01 e +¿+❑ ν ¿
0 e
2
Background radiation
Natural sources (85%)
● Air, underground radon gas (~50%)
● Ground, buildings (concrete) (13%)
● Cosmic rays (12%)
● Food & drinks (eg bananas) (10%)
Artificial sources (15%)
● Hospitals (14%)
● Industrial sources (1%)
Radiation hazards
● ***Irradiation: exposure to radiation; NO radiation once source is removed
● ***Contamination: deposition of radioactive material on surfaces/into bodies;
surface/body continues to irradiate surroundings after source is removed
● How to minimise:
○ Keep sources which emit ionising radiation ≥30 cm away from body
(minimises irradiation)
○ Limit time of use of sources (minimises irradiation)
○ Do NOT touch/inhale source (otherwise contamination)
○ Wash hands after working with source (prevents contamination)
Types of ionising radiation (& decay)
●
Alpha (α ) Beta minus ( Beta plus ( Gamma ( γ ) Neutron (n)
−¿¿ +¿¿
β ) β )
Composition He nucleus electron positron photon neutron
Mass 6.6446573357(20)e-27 kg 9.1093837015(28)e-31 kg 0 1.67492749804(95)e-27 kg
4.001506179127(63) u 5.48579909065(16)e-4 u 1.00866491588(49) u
3.7273794066(11) GeV c-2 0.51099895000(15) MeV c-2 939.56542052(54) MeV c-2
Charge +2e -e +e 0 0
Reason of Strong nuclear force fails N : Z too high N : Z too low Too much
decay to balance electrostatic (too many energy in
repulsion between neutrons) nucleus
nucleons
Speed ~0.05c ~0.99c c
Typical 3~7 MeV 0~12 MeV 100 eV~100 keV
energy
1
, Relative 10000 100 1
ionising
power
Penetration/ Few cms of air Few mms of Al Few cms of Pb
range
Deflection in Small Large No
electric +
magnetic
fields
Eg of decay
❑241 237
95 Am →❑93 Np+❑
❑4 90
2 He
90
38 Sr →❑39 Y❑38
19 K →❑18 Ar
38
0
0 ¿¿
+❑−1 e +❑01 e +¿+❑ ν ¿
0 e
2
