energy, matter and radiation (much more interesting than it looks like) (well not really, but shut...

Energy, matter and radiation

(much more interesting than it looks like)(well not really, but shut up and take notes)

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.

A quick reminder on radiations

Many sort of radiations Carry and transmit energy Characterized by their wavelength ()

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…)

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

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)

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

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

A few formulas (3) Inverse Square Law

What happens when radiation encounters a material?

• Radiations can whether be ionizing or non ionizing.

Non-ionizing radiations

Non-ionizing radiations: not enough energy to ionize atoms or molecules (visible light, infrared, microwave…)

• Two possibilities o Reflectiono Transmission

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.

Abilities of ionizing radiations to

penetrate solid matter

Let’s recap!

Matter

RadiationsEnergy

Emits

Carry

Affects