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: • Cosmic radiation (radiations from the sun and stars) • Terrestrial radiation (soil, vegetation…) • Internal radiation (your own body!) • X-rays (medicine, airport security…)
How much radiation are we exposed to? 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
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 )
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 • Reflection • 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.
Let’srecap! • Matter Affects Emits • Energy • Radiations Carry