Radionuclides Flashcards
Radioactivity
Refers to emission of radionuclides
Radionuclides in the aquatic habitat
unstable nuclei which emit particles or radiation
Basic types of radiation
-Alpha
-Beta
-Gamma
All are ionising radiation
Can knock electrons off molecules they encounter and can therefore damage biologic tissue (especially nucleic acids)
Alpha radiation
Emission of a helium nucleus (2p and 2n)
- nucleus left behind has a nuclear charge 2 units less and a mass # 4 units less
- Becomes another element plus a helium nucleus
- eg. Thorium becomes Radium
Beta radiation
Electron formed when a neutron ‘splits’ into a proton and an electron
- nuclear charge increases by 1
- no change in mass #
- eg. lead-214 becomes Bismuth-214 + 1e-
Gamma radiation
Highly energetic form of EM Radiation emitted by a nucleus in an excited state
-No change in atomic or mass #’s
Paths of energetic particles in biologic tissue
Alpha - 0.005cm
Beta - 3cm
Gamma - 20cm
*protective layer of skin is 0.007cm thick so may be able to protect from alpha
Decay Kinetics
1st order
- Proportional to the # of radionuclides
- Differential Rate Law: Rate (dn/dt) = k[A] where n is # radionuclides, t is time of reaction, k is rate constant, A is the subject
- Integrated Rate Law: ln[A]t=ln[A]o - kt OR At=Aoe^-kt
- Decay Rate: -dn/dt = lambda x N where lambda is decay constant
Half-life, t1/2
The time taken for 1/2 of the original radionuclides to disintegrate
t1/2 = 0.693/lambda
lnNt = lnNo - lambda(t) OR Nt = Noe^-lambda(t)
So: Nt/No = e^-lambda(t)
Important radionuclides in the aquatic envr and t1/2’s
Iodine-127: 8 days
Cesium-137: 30 years
Strontium-90: 28 years
- Top 3 from nuclear reactor accidents and nuclear fall out
Radium-226: 1620 years (from U-238 decay series)
What is a reason for Cesium to be an issue for people?
It is similar to Na and K and therefore readily uptaken by the body
Under ordinary circumstances, what is the most likely radionuclide contaminant of water supply and can it be easily removed?
Ra b/c Ra2+ (produced as part of the U-238 decay series) is water soluble and similar to Ca2+ and is an alpha emitter
- problem in uranium mining areas
- can be removed by water softeners again b/c of similarity to Ca2+
Units of radioactivity
measure of disintegrations per unit time
What is a Curie (Ci)?
Large unit (radioactivity of 1g of pure Radium) 1 Ci = 3.7 x 10^10 disintegrations per second - often use picoCurie (pCi) = 10^-12 1 pCi = 3.7 x 10^-2 disintegrations per second
MCL
Maximum Contaminant Level
What is MCL of radioactivity of drinking water in US?
5 pCi/ L of drinking water
Bq
Becquerel
1 Bq = 1 disintegration/second
Name 3 notable Nuclear reactor accidents
- Three Mile Island US March 28th 1979
Total emitted radioactive material = 15 Ci - Chernobyl USSR (present day Ukraine) April 26th 1986
Reactor meltdown = 100MCi (100,000,000Ci or 4 x 10^18Bq) - Fukushima Japan April 2011, associated w/ Tsunami
9.0 x 10^17 Bq
What is the result of the energy emitted by alpha and beta particles in living organisms?
Can result in ionization of molecules
What particle can cause sever damage in the body and why?
Alpha particle, 20x more damaging to tissue than beta particle
- release of energy is concentrated around point of emission
- damages DNA –> all death or mutations that can cause cancer
Example of alpha particle poisoning
Alexander Litvinenko: London 2006, Polonium-210 (nuclear reactors), died w/in 2 weeks, Dose = 10ug (200x the lethal dose of 50ng)
Sub-lethal levels of radiation: symptoms and long-term effects
- Radiation Sickness
- Earliest observed in areas of high rate of cell division (bone marrow, stomach lining, which = nausea and low white blood cell count)
- Longer-term = genetic damage, cancer, birth defects
How to quantify dose of radiation received
Old unit: 1 rad (Radiation Absorbed Dose) = quantity of radiation that deposits 0.01Joule of energy into 1kg of body tissue
- but doesn’t discriminate btwn alpha and beta
New unit: rem (Roentgen Equivalent Man) (Roentgen German who discovered x-rays)
or
Sievert (1 Sv = 100rem)
What is the background exposure of humans from radiation?
approx 0.3 rem/year
Sources of background radiation
Anthropogenic (eg. x-rays): 18% Radon-222: 55% Cosmic Rays: 8% Rocks: 8% Natural Isotopes in body(K-40, C-14): 11%
Acute exposure of radiation: Levels and effect in body
25 rem: low white blood cell count
>100 rem: nausea/ hair loss
500 rem: lethal dose in 50% of population
