NATS 1745 Lecture Notes - Lecture 4: Acute Radiation Syndrome, Nuclear Fusion, Radioisotope Thermoelectric Generator

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17 Feb 2016
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Chapter 4: uclei and Radioactivity
4.1 Radioactivity
4.1.1 Radioactivity (or radioactive decay): the spontaneous explosion of an atom’s nucleus
- a radioactive substance has atoms which naturally decay due to an imbalance among the
forces between nucleons
4.1.2 Half-life (t
1/2
): the time for ½ an atom’s population to decay
- eg, Carbon-14 has t
1/2
= 5730 years (a C-14 atom has a 50% change of decaying in 5730
years)
- the shorter t
1/2
, the more radioactive the atom (more decays each second)
- since a radioactive atom’s population is halved every t
1/2
, the substance becomes less
radioactive over time
4.1.3 Radioactive dating: determining a substance’s age by its amount of radioactive decay
- eg, a rock’s % of Argon yields its age, since Argon is a decay product of a rock’s
Pottasium-40
- used for dating of rocks, fossils and impact craters
4.2 Radiation
4.2.1 Radiation: high-speed particles or high-energy light waves (eg, x-rays, gamma rays)
- radioactive decay is a source of radiation
4.2.2 Causes damage to humans by breaking apart molecules or mutating genes
- secondary radiation: high-speed particles released by the broken molecules, causing
exposure to spread internally
- radiation poisoning: illness due to cell damage from radiation; repairable in low doses,
fatal in large doses
- gene mutations can lead to uncontrolled splitting of abnormal cells (ie, cancer)
4.2.3 REM unit: measures the amount of cell damage from radiation exposure
- “1 rem whole body”: every part of the body has received a dose of 1 rem
4.2.4 Linear Hypothesis (LH): the chance of cancer increases linearly with radiation dose
- eg, since 2500 rem = 100% chance of cancer, then
250 rem = 10% increased risk of cancer
- LH is unproven at low doses (<10 rem)
4.3 Sources of radiation
4.3.1 Medical x-rays: ~0.001-1 rem (not whole body)
- eg, chest x-ray: ~0.015 rem on ~50% of body (0.008 rem whole body 0.0003%
increased cancer risk if LH applies)
- cancer risk unproven because increase is within error bars of normal cancer risk
4.3.2 Radiation Therapy: to destroy cancer cells, a typical amount is 60 grays (6000 rem) in
small doses (~1-2 grays)
- if treatment is applied to 1% of body, 6000 rem = 60 rem full body = ~2% cancer risk
(if LH applies to individual doses)
4.3.3 We receive an average annual whole body dose of:
a) ~0.6 rem from artificial and naturally-occurring radiation in the environment (rocks,
food, water, cosmic rays, x-rays, etc)
b) 0.04 rem from radioactive isotopes in our body (K-40, C-14)
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