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