Actinide (An)
𝜶 radiation (particle): 𝟒𝟐𝑯𝒆𝟐# , very energetic due to high mass, not very penetrating, as alpha particles being
heavy and doubly charged, interact intensely with electron and nuclei of atoms they encounter, causing them to
lose energy quickly and limit penetration depth.
𝜷 radiation (particle): high energy electron emission, having small mass and being charged, interact with electron
in material, leading to moderate penetration.
𝜸 rays (electromagnetic): short wavelength < 0.1 Å, higher in energy than X-rays, having no mass and charge,
allow them to penetrate materials deeply without being deflected or reflected.
Mass balance radio decay
𝜶 decay: Atomic number decrease by 2, mass number decrease by 4.
%&'
→ %&)
$%𝑈
)
$(𝑇ℎ + %𝐻𝑒
𝜷 decay: Atomic number increase by 1, mass remain, with a 𝜸 rays.
𝜸 decay: Atomic number remain, mass remain, release energy in forms of 𝜸 photon.
Units of sample activity
The activity of a radioactive sample is measured by the rate at which unstable atoms in the sample disintegrate.
Classic Unit: Curie (Ci) based on radioactivity of 226Ra
1 Ci = 2.22 * 1012 disintegration per min
1 Ci = 3.7 *1010 disintegration per second
SI Unit: Becquerel (Bq)
1 Bq = 1 disintegration per second
1 Ci = 3.7 * 1010 Bq
Units of radiation dose
Classic Unit: Roentgen (R)
Measurement of quantity of X-rays or 𝜸-rays produced by ionizing radiation in air. Unit related to energy.
1 R = quantity of radiations that produces ions carrying a charge of 2.58 * 10-4 coulombs per kg of air
1 R = 89.6 ergs per g air = 96 ergs per g human issue
Classic Unit: Radiation absorbed dose (Rad)
The energy deposition by any type of radiation in any material.
1 Rad = 100 erg per g absorber
SI Unit: Gray (Gy)
1 Gy = 100 Rad = 10000 erg/g = 107 erg/kg = 1 J/kg
Classic Unit: Radiation Equivalent Man (Rem)
Measure dose equivalent by considering the biological effectiveness.
- Relative biological effectiveness
1 Rad of 𝛼-particles > 20 Rad of 𝛾-rays
- Rem dose = Rad dose * quality factor
SI Unit: Sievert (Sv)
1 Sv = 100 Rem measure of dose equivalent
, Activity Versus half-life
Activity: first-order reaction kinetics, Activity is inversely proportional to the half-life.
![#]
= −𝑘 [𝑥], rate of decay of isotope is proportional to the number of radioactive nuclei present.
!%
Integration give: [𝑥] = [𝑥]!"# exp (−𝑘𝑡), 50%[𝑥] = [𝑥]!"# exp (−𝑘𝑡)
ln 2 ln 2
𝑡$ = ,𝑘 =
% 𝑘 𝑡$
%
𝑑[𝑥] ln 2 [𝑥]
= −
𝑑𝑡 𝑡$
%
Radioactivity Versus distance and mass
I ∝ 1/ d2, intensity of radiation inverse proportional to distance squared.
Radioactivity (disintegration per second, Bq) ∝ m
Dose ∝ radiation time ∝ radiation level
Discovery
Discovery from Pitchblende uranium ores by Maire Curie:
1898, Marie Curie found that thorium and uranium compound emits Becquerel rays (𝜸-rays) and invent the word
“radioactivity”. She found that two uranium containing ores, Pitchblende and Chalcolite, were much more
radioactive than pure uranium. She suggests this may be due to presence of other radioactive element, they used
different radiation levels to monitor separation of the element.
Polonium (Po) and Radium (Ra): discovered by Curies as they refined pitchblende.
Actinium (Ac): discovered by colleague of Curies, also in pitchblende
Non-fission Applications
th
19 Century application:
1. Thorium oxide gas mantles (in gas lamps)
Produce a bright and white light in a gas flame. Material filament soaked in Th salts and form an oxide upon being
burned, It’s very fragile. Now replaced by CeO2.
2. Uranium glass
Vaseline glass, used in vase, bowls and wine glasses. Depends on oxidation states, U4+ green, UO22+ yellow.
3. Uranium glazes for ceramics
Produced during mid of 19th centuriy, contain uranium and Lead mixture, produce bright orange color, used as
glazing pigment and ceramic picture tiles.
20th Century application:
1. 241Am smoke detectors
Use 241Am, a radioisotope that emits 𝜶-particles, and ionize air in the detection chamber. Any smoke particles
entering the chamber absorbs the 𝛼-particles, reducing the ionization current and triggering the alarm. The half-
life of 241Am is very long, ensures that the smoke detector does not need frequent replacement due to decay.
238
2. Pu Nuclear batteries
238
Pu emits high energy 𝜶-particles, which can generate heat due to its kinetic energy. The heat is converted into
electricity using thermoelectric material (PbTe). Used to power heart pacemakers, 5 times longer than
