Radionuclides

Question 1

Radioactivity

Answer 1

Refers to emission of radionuclides

Question 2

Radionuclides in the aquatic habitat

Answer 2

unstable nuclei which emit particles or radiation

Question 3

Basic types of radiation

Answer 3

-Alpha
-Beta
-Gamma
All are ionising radiation
Can knock electrons off molecules they encounter and can therefore damage biologic tissue (especially nucleic acids)

Question 4

Alpha radiation

Answer 4

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

Question 5

Beta radiation

Answer 5

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-

Question 6

Gamma radiation

Answer 6

Highly energetic form of EM Radiation emitted by a nucleus in an excited state
-No change in atomic or mass #’s

Question 7

Paths of energetic particles in biologic tissue

Answer 7

Alpha - 0.005cm
Beta - 3cm
Gamma - 20cm
*protective layer of skin is 0.007cm thick so may be able to protect from alpha

Question 8

Decay Kinetics

Answer 8

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

Question 9

Half-life, t1/2

Answer 9

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)

Question 10

Important radionuclides in the aquatic envr and t1/2’s

Answer 10

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)

Question 11

What is a reason for Cesium to be an issue for people?

Answer 11

It is similar to Na and K and therefore readily uptaken by the body

Question 12

Under ordinary circumstances, what is the most likely radionuclide contaminant of water supply and can it be easily removed?

Answer 12

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+

Question 13

Units of radioactivity

Answer 13

measure of disintegrations per unit time

Question 14

What is a Curie (Ci)?

Answer 14

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

Question 15

MCL

Answer 15

Maximum Contaminant Level

Question 16

What is MCL of radioactivity of drinking water in US?

Answer 16

5 pCi/ L of drinking water

Question 17

Bq

Answer 17

Becquerel

1 Bq = 1 disintegration/second

Question 18

Name 3 notable Nuclear reactor accidents

Answer 18

• 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

Question 19

What is the result of the energy emitted by alpha and beta particles in living organisms?

Answer 19

Can result in ionization of molecules

Question 20

What particle can cause sever damage in the body and why?

Answer 20

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

Question 21

Example of alpha particle poisoning

Answer 21

Alexander Litvinenko: London 2006, Polonium-210 (nuclear reactors), died w/in 2 weeks, Dose = 10ug (200x the lethal dose of 50ng)

Question 22

Sub-lethal levels of radiation: symptoms and long-term effects

Answer 22

• 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

Question 23

How to quantify dose of radiation received

Answer 23

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)

Question 24

What is the background exposure of humans from radiation?

Answer 24

approx 0.3 rem/year

Question 25

Sources of background radiation

Answer 25

Anthropogenic (eg. x-rays): 18%
Radon-222: 55%
Cosmic Rays: 8%
Rocks: 8%
Natural Isotopes in body(K-40, C-14): 11%

Question 26

Acute exposure of radiation: Levels and effect in body

Answer 26

25 rem: low white blood cell count
>100 rem: nausea/ hair loss
500 rem: lethal dose in 50% of population