Radiation Physics - PDF

## Radiation physics ### Contents 1. Oscillatory motion. Waves. Electromagnetic waves 2. Non-ionizing radiations 3. Biological effects ## Oscillatory motion. Waves - Vibrations and waves are essential, because of them we can hear and see, thus it is important to understand the physics of waves -...

## Radiation physics ### Contents 1. Oscillatory motion. Waves. Electromagnetic waves 2. Non-ionizing radiations 3. Biological effects ## Oscillatory motion. Waves - Vibrations and waves are essential, because of them we can hear and see, thus it is important to understand the physics of waves - The two animations below are examples of oscillatory motion. - How can you describe the movement of these bodies? - How much does such a motion last? - What similarities and differences are between the two examples? - How can we explain such motions? ## Oscillatory motion. Waves - What causes this motion? - The equilibrium position (rest) is the position in which the body stays still. We say that the body is in an equilibrium state, the total force acting on the body is zero. - But when we apply an external force, then the equilibrium state is perturbed and the body starts oscillating. ## Oscillatory motion. Waves - The force is applied for a short time, the object starts its repetitive movement around the equilibrium position, each time on a shorter distance, up to the moment when it stops again in the equilibrium position. - Such a motion is called attenuated oscillation or damped oscillation. - Damping is the tendency of oscillating objects to lose or dissipate the energy in time. To keep the movement, the external force should act again. ## Oscillatory motion. Waves - Other oscillating bodies: - pendulum - tuning fork - elastic string ## Oscillatory motion. Waves - A motion that regularly repeats is called periodical movement. - If we place a motion detector under the body hang on the string and register its position in time, what dependence would we get? - The equilibrium position is 0.6 cm above the detector. - We can observe the periodic nature of the motion: from the equilibrium position, A, the body reaches the maximum height, B, then goes back through the equilibrium position towards the position closest to the detector, D. A full cycle lasts 2.3 seconds. ## Waves - Examples: - Sound waves - Visible light - Radio waves - The waves on the water surface - Choc waves - How are produced? - What properties they have? - How can we physically describe waves? ## Waves - A wave can be defined as a perturbation that propagates in space, usually through an environment. - The environment is a material or solution that carries a wave. - The wave propagates inside the environment from one place to another through the particles in the environment. - The wave transports energy DOESN'T transport matter!!!! ## Waves - The waves can be categorized depending on their properties: - The direction of motion - Transverse waves - The particles in the environment move perpendiculary to the direction on which the wave propagates. ## Waves - Direction of motion - Transverse waves - Longitudinal waves - The particles of the environment move on a parallel direction with the direction of propagation. ## Waves - Ability of transferring the energy through vacuum: - Electromagnetic waves - are able to transport the energy through vacuum - are produced by the vibrations of electrically charged particles - Ex.: light - Mechanical waves - ARE NOT able to transport the energy through vacuum; - need matter to transfer their energy - Ex. sound (doesn't propagates in vacuum) ## Characteristic parameters of waves - O transverse wave propagates by moving the particles perpendicular to the direction of energy transfer. - The amplitude of a wave represents the maximum displacement of a particle from the environment with respect to the equilibrium position. - The wavelength of a wave represents the length of a complete cycle. ## Characteristic parameters of waves - The frequency of a wave shows how many times a particle from the environment vibrates in one second when the wave passes through the environment. - Waves transport energy. - The amount of energy transported by a waves is direct proportional with the square of the amplitude of the wave ## Characteristic parameters of waves - The propagation speed of a wave is the distance rode by the wave in the unit of time (wavelength divided by period). - depends on the propagation environment - is independent on the properties of the wave - velocity=frequency * wavelength ## Electromagnetic (EM) waves - The moving electrical charges (=electrical currents) produce magnetic fields - A variable magnetic field generates a variable electric field - Electric and magnetic fields can reciprocal be generated. - An electromagnetic wave is an oscillation of an electric field and a magnetic field that propagates with the speed of light. ## Electromagnetic waves - The energy of the electromagnetic wave is stored in the oscillating electric and magnetic fields (oscillations take place in 2 perpendicular planes which are also perpendicular on the propagation direction) - Electromagnetic waves are transverse waves - Maxwell assumed their existence (1864). Heinrich Hertz (1887) demonstrated it and determined the speed and other properties ## Electromagnetic waves spectrum - Continuous range of frequencies of the electromagnetic waves ## Ionization - The process by which an atom (electrically neutral) loses one or more electrons from its electronic cloud due to the absorption fo electromagnetic radiation - Atom + electromagnetic wave energy -> ion -> ionizing radiation - The radiations that don't have enough energy to produce ionizations are called non-ionizing radiations ## Biological effects of EM waves - The biological effects of EM waves are critical for: - Understanding the potential risks and developing standards to: - Use different devices (phones, wireless networks, tv, radios, medical devices, etc.) - Development of medical technologies - Ex: ultrasounds, nuclear magnetic resonance (NMR), ionophoresis. - Analyze the biological effects of the electromagnetic radiations at cellular level. - At macroscopic scale (dosimetry) - At microscopic scale ## The effects of non-ionizing radiations - The non-ionizing radiations DON'T have enough energy to ionize the matter BUT they have enough energy to EXCITATIONS of the atoms/molecules - They can be: - Natural (sunlight, lightning, etc.) - Produced by humans(wireless communications, medical and scientific applications, etc) ## Non-ionizing radiation sources - Radiation sources: - natural (the sun, atmosphere phenomena, etc.) - artificial (communications, industry, scientific, medical) - The spectra is divided in 2: - Electromagnetic fields (EM) - Optic radiations ## Effects of non-ionizing radiations - A biological effect appears when we can detect a change in a biological system after it was the subject of some stimuli. - Atention! Observing a biological effect doesn't necessary suggest the existence of a danger for the health of the organism. - If the changes induced alter the health or integrity of the organism, then the biological effect becomes a hazard. - Biological effects can be: - physiologic - biochemical - behavioral changes (of the organism, tissue or cell) ## Effects of non-ionizing radiations - The biological effects depend on a multitude of factors such as: - The incident radiations (which determines the penetration depth from the surface of the body) - The power density of the EM field - The characteristics of the source emitting the radiations - The exposure time - The environmental conditions - The spatial orientation of the irradiated tissue - The biological characteristics of the irradiated tissue ## Effects of non-ionizing radiations - Non-ionizing radiations: - have a wavelength higher than about 100 nm - are divided in 4 approximate regions: - static electric and magnetic fields 0 Hz - very low frequency fields 0-300 Hz - radiofrequency (RF) and microwaves (MW) 300 Hz - 300 GHz - optic radiations: infrared (IR), visible (VIS), and ultraviolet (UV) ## Effects of non-ionizing radiations 1. Static fields 0 Hz - can produce vertigo and charge accumulation 2. Very low frequency fields 0-300 Hz -are present around the electric appliances, electronics, cables, power lines, transformers, etc. - Produce charge accumulation on the surface of the body - The induction currents can interfere with the function of the nervous central system and perturb the function of muscles and nerves ## Professional exposure to non-ionizing radiation ## Effects of non-ionizing radiations 1. Static fields 0 Hz 2. Very low frequency fields 0-300 Hz 3. radiofrequency (RF) and microwaves (MW) 300 Hz - 300 GHz -radiowaves (RF) are used in telecommunications and tv -MW-telecommunications, radar, satelite, mobile technologies, microwave oven, TV transmitters -the main effect is heating Medical applications: -diatermia şi hyperthermia ## Effects of non-ionizing radiations - Diatermia = the heat is electrically induced with high frequency electromagnetic currents - Used in medicine for: - muscle relaxing, - tissue heating, - rehabilitation physical therapy; - surgery (the heat is used to destroy tissues on a surface, cauterization of small blood vessels especially in neurosurgery and eye surgery) - Hypertermia = MW (434 și 915 MHz) are used to increase the temperature of deep tissues up to 45°C; therapy used for short term management of skeletal muscle injuries - electrocauterization(cutting or cauterization of blood vessles) ## SAR - SAR = Specific Absorption Rate rata specfică de absorbţie a energiei ## Optic radiations - The action of optic radiations is mainly directed to the exposed parts: the skin and the eyes. - The optic radiations produce changes: - Thermal - Photochemical - pigmentations, erythema, cancer - Photo-cataract, lesions of retina and cornea - heating of the body surface ## Optic radiations - 3.Infrared - are caloric radiations - are the main way of heat exchange of bodies with the environment - it is used in spectroscopic analysis (check the lecture on instrumental analysis) - insolation, caloric shock, muscle cramps - on the skin- produce vasodilation, change the sensitivity of nervous terminations (analgesic and regeneration effects) - on the eyes - high intensity can produce burns and cataract ## Optic radiations - 4.Visible radiations - have wavelengths between 390 nm and 780 nm - stimulate the brain activity, activate the metabolism, the circadian rhythm - can make the skin photosensitive - Responsible for seeing! ## Ultraviolet radiations - Wavelengths between 10 and about 400 nm - Less than 10% of the solar radiation - stimulate the metabolism (enhance the basal methabolism) - on the skin - eritema, pigmentation, melanoms - on the eyes - photoconjuctivitis, cataract - Molecular effects: destruction of DNA molecules, proteins, lipids, cell membrane - The action of UV produces free radicals - atoms or molecules with an unpaired electron (can be free radicals of oxygen, nitrogen, aromatic compounds, etc.) - are highly reactive