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Energy, matter and radiation
(much more interesting than it looks like)(well not really, but shut up and take notes)
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Let’s define each term!
Energy: measured in Joules (J), it corresponds to the ability of a system to do work on another one. It cannot be created or destroyed; the quantity of energy is constant, it can only be transferred from one system to another.
Matter: measured in kilograms (kg), it’s defined by anything that has mass and volume, or, in a more scientist definition, everything that is made up by atoms and molecules.
Radiation: radiations are a process in which energetic particles or energetic waves travel through vacuum or matter. There are two kinds of radiations: ionizing ones and non-ionizing ones.
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A quick reminder on radiations
Many sort of radiations Carry and transmit energy Characterized by their wavelength ()
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Where do radiations come from?
We’re constantly exposed to radiations!
There are a lot of different sources:o Cosmic radiation (radiations from the sun and stars)
o Terrestrial radiation (soil, vegetation…)
o Internal radiation (your own body!)
o X-rays (medicine, airport security…)
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How much radiation are we exposed to?
Source Effective Dose Comment
Cosmic radiation~0.4 (milliSievert/year)
About 100,000 cosmic ray neutrons and 400,000 secondary cosmic rays penetrate our bodies every
hour - and it increases with altitude!
Terrestrial radiation~0.5 (mSv/year)
Over 200 million gamma-rays pass through our body every hour from sources such as soil and
building materials
Internal radiation~0.3 (mSv/year)
About 15 million 40K atoms and about 7,000 natural uranium atoms disintegrate inside our bodies every
hour, primarily from our diet
Radon and other gases~1.3 (mSv/year) About 30,000 atoms disintegrate inside our lungs
every hour as a result of breathing
Estimated maximum dose to evacuees who
lived closest to the Fukushima nuclear
accidents
68 (mSv)
Eating a banana 98 (nSv) Yep, even bananas emit radiations
100 millisievert/year : threshold of danger
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A few formulas (1) Stefan-Boltzmann Law: amount of radiation
given off by a black body.
E : energy radiated per unit surface area ( : Stefan–Boltzmann constant () T : temperature of the body (K)
(in reality, since black bodies don’t exist, the value is always lower)
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A few formulas (2) Wien Law: the wavelength of maximum
emission of any body is inversely proportional to its absolute temperature.
: wavelength of the peak emission (m : Wien's displacement constant () T : temperature of the body (K)
Temperature of a human being = 37°C = 310 K so
λ max=𝑏𝑇
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A few formulas (3) Inverse Square Law: the amount of radiation
passing through a specific area is inversely proportional to the square of the distance of that area from the energy source. It applies when radiation is radiated outward radially in three-dimensional space from a point source, like the sunlight.
: intensity of the radiation (unitless) : Intensity of the radiation at 1 unit of distance d : distance travelled (same unit as )
𝐼 𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦=𝐼𝑑 ²
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A few formulas (3) Inverse Square Law
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What happens when radiation encounters a material?
• Radiations can whether be ionizing or non ionizing.
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Non-ionizing radiations
Non-ionizing radiations: not enough energy to ionize atoms or molecules (visible light, infrared, microwave…)
• Two possibilities o Reflectiono Transmission
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Ionizing radiations Ionizing radiations : enough energy to ionize atoms or
molecules, and therefore deposit energy; absorbed by matter.
Alpha and beta particles : deposit energy through electrical interactions with electrons in the material.
Gamma rays and X rays : liberate atomic (orbiting) electrons, which then deposit energy in interactions with other electrons.
Neutron : deposit energy through collisions with nuclei that contain protons.
Protons : set in motion and, being charged, they again deposit energy through electrical interactions.
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Abilities of ionizing radiations to
penetrate solid matter
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Let’s recap!
Matter
RadiationsEnergy
Emits
Carry
Affects