Fundamentals of Radiation Flashcards
(31 cards)
Minimum energy for an alpha from radioactive decay
3.8 MeV
Alpha particles are emitted with a _________ energy level.
Discrete. Alpha particles are essentially mono energetic and emit at certain energy levels. If the radioisotope doesn’t emit an alpha at the max energy it is left in an excited state and releases a gamma to return to ground state
Beta deacy happens in…
Isotopes too rich in neutrons
Beta energies
Beta energies are continuous from low energies up to the theoretical max energy. The average beta energy is usually 30-40% of the max. The extra energy goes to the neutrino.
What is secular equilibrium?
Secular equilibrium is when the parent decay activity is equal to the daughter products. This can only happen when the parent has a longer half live (1000s of times greater) than the daughter. Usually equilibrium is reached in 5-10 daughter product half life’s
What is transient equilibrium?
Transient equilibrium is when the parent half life is higher but not magnitudes higher than the daughter. After 5-10 daughter half lifes the activity ratio of the daughter and parent will be greater than one and the activity will be driven by the parent half life
Is there equilibrium in a decay chain if the daughter products has a longer half life than the parent?
No
The three main sources of radiation?
Cosmic, terrestrial, and man-made
Examples of cosmic radiation:
H-3, C-14
A major source of cosmic radiation is from the sun.
87% protons
11% alpha
2% heavy nuclei and electrons
How is Carbon-14 made?
Cosmic radiation interacts with the atmosphere creating thermal neutrons that interact with Nirtogen-14 ejecting a proton and creating C-14
At sea level how much annual dose is created by cosmic radiation?
26 mrem
For every 2000 meter increase in elevation the dose doubles
Dose increases to a max of 10% more at the poles due to the magnetic field of the Earth
Terrestrial Radiation is comprised of these decay Isotopes Decay chains:
Th-232 Thorium
U-238 Uranium
U-235 Actinium
Most the dose comes from Rn-222 and its progeny
All terrestrial decay chains include:
- Starts with a nuclide with a long half-life
- contains an isotope of Radon
- End result is stable lead
Thorium series progeny atomic mass remainder:
no remainder (4n)
Uranium series progeny atomic mass remainder:
Two (4n+2)
Actinium series progeny atomic mass remainder:
remainder of three (4n+3)
Characteristics of the artificial series:
Begins with Pu-241
Ends with Bi-209
Does not have an isotope of Radon
4n+1
Longest lived is Np-237
2.14E6 yr half life
Terrestrial radiation annual dose contribution:
274 mrem
~ 200 mrem due to airborne radionuclides
Air sampling issues caused by NORM
- Constant NORM in air sampling
- Can wait several hours for NORM to decay but if COC is a short lived isotopes will also decay
- Air sample results are delayed
- Could use gamma spec
Time to recount if Rn-222 is suspected
Count ASAP and then 35 minutes later.
If counts are one-half the original value, radon is suspected.
Isotopic analysis should be done to confirm
EPA guidelines for Radon
0-4 pCi/L - No action
4-20 pCi/L - radon reduction systems
20-200 pCi/L sampling done 3 months
200+ pCi/L - immediate reduction methods
What is a WL?
WL or working level us a unit used to measure the short lived radon decay products in air.
30 CFR 57.5039
41 CFR 50-204.36
The concentration of short-lived radon daughters in 1 liter of air that will result in the ultimate emission of 1.3 × 10⁵ MeV (million electron volts) of potential alpha energy during their complete decay to stable lead-210.
100 pCi/L of Radon - 222
WL limits ( 30 CFR § 57.5037 )
Exposure does not exceed 1.0 WL or 4 WLM (working level months) per year
WLM
Working level month:
The cumulative exposure from breathing air containing a radon progeny concentration of 1 Working Level (WL) for 170 working hours, which is equivalent to one working month (based on a 40-hour workweek over approximately 4.25 weeks).
WLM = WL x Exposure Time (hours) / 170
