Webster s Dictionary The act or process of radiating The process of emitting radiant energy in the form of waves or particles Dictionary.com the process in which energy is emitted as particles or waves. the energy transferred by these processes.
Ionizing Radiation: is a kind of energy emitted from radioactive atoms, and have sufficient energy to overcome the binding energy between an electron and an atom to cause ionization. Non-ionizing radiation Radiation that does not have sufficient energy to ionize an atom is (NIR) (less than 10-12 ev)
Ionizing Radiation Alpha, Beta Gamma Neutron Non-ionizing Radiation Microwave UV Radiofrequency Laser
IONIZING RADIATION
Ionization Radiation, h e Ionization is the removal of an electron from an atom or an ion, resulting in an ion pair. Ionization is the primary cause of radiationinduced biological damage.
Radioactive Atom (Radionuclide) An atom is consisted of the nucleus and electrons orbiting around it. The nucleus is consisted of protons and neutrons. The ratio of the numbers of protons and neutrons determines the stability. If there are too many or too few neutrons for a given number of protons, the resulting nucleus will have too much energy and will not be stable. The unstable atom will try to become stable by giving off excess energy in the form of radiation (particles and/or photons).
Radioactive Decay (Disintegration) Radioactive decay is a process of radioactive atoms releasing radiation over a period of time trying to become stable. The daughter may be stable or unstable.
Physical Half-life (T ½ ) The time in which half the atoms of a radioactive substance disintegrated to another nuclear form. A = A o e t where A is activity at time t, is decay constant, t is time taken. When t = T ½, then A = 1/2 A o
Basic Types of Ionizing Radiation Common types of ionizing radiation: Alpha particles Beta particles, electrons Gamma/X ray Neutrons
Alpha Particles Alpha particles are helium nuclide (Z=2, A=4) with a heavy mass, and they carry a positive charge (+2). Because of their heavy mass and positive charge, their ranges are short: 1 to 2 inches in air, 40 to 70 m in tissue (cannot penetrate the dead layer of skin). They can be stopped by even a piece of paper.
Beta Particles and Electrons Common beta emitters are 3 H, 14 C, 35 S, 32 P,... Beta particles are electrons emitted from the nucleus, so they carry a negative charge ( 1). Beta particles are emitted with an energy spectrum, with the average energy equals to about 1/3 of the maximum energy. They have longer ranges than alpha particles: 10 20 feet in air, several mm in human tissue.
Gamma and X Ray Their range in air is long: several hundred feet. A significant fraction can pass through the human body.
http://www.hko.gov.hk/education/cyber_exh_hall/eng/exhibit02_intro_eng.htm
Shielding Use proper and sufficient shielding: Radiation Alphas Betas Gamma/X ray Neutrons Shielding Materials Almost anything (e.g., even a sheet of paper) Low atomic number materials (e.g., plastic) Dense or heavy materials (e.g., lead, concrete) High H content materials (e.g., water)
Radioactivity The quantity for an amount of radioactive atoms decay in a given energy state at a given time. Conventional unit: curie (Ci) 1 Ci = 3.7 x 10 10 disintegrations/sec SI unit: becquerel (Bq) 1 Bq = 1 disintegration/sec 1 Bq = 27 pci
Sources of Radiation Manmade: 18% Occupational: less than 0.3% Natural Background: 82%
Sources of Radiation Natural Background - radiation received from: 1. Cosmic Rays ( 宇 宙 射 线 ) 2. Terrestrial Radiation ( 陸 地 輻 射 ) 3. Food 4. Radon ( 氡 氣 ) Background is generally the main source of radiation exposure to a population
Sources of Radiation Man-made Radiation The 4 major sources of man-made radiation exposure are: 1. Medical Radiation ( 医 疗 辐 射 ) 2. Radioactive Fall out ( 核 爆 扩 散 ) 3. Industrial Applications ( 工 业 应 用 ) 4. Consumer Products ( 消 费 产 品 )
Health Effect
Health Effects Deterministic Effect: Causally determined by preceding events. Generally a threshold level of dose exists. Biological effect which increases in severity with increasing radiation dose above a threshold dose. Stochastic Effects: Probability of the effect occurring increases continuously with increasing absorbed dose while the severity of the effect, in affected individuals, is independent of the magnitude of the absorbed dose. (no threshold) All-or-none response (cancer). The induction of stochastic effects (cancers and genetic effects) is considered to the principal effect that may occur following exposure to low doses of ionizing radiation. Generally assumed that the higher the dose, the higher risks of biological effect.
Deterministic vs Stochastic Effect Per cent Response Stochastic Effect Threshold Dose Deterministic Effect Dose
Factors Affecting Biological Damage Total Dose Dose Rate Types of Radiation Area of the Body Irradiated Cell Sensitivity Individual Sensitivity
Reduction of External Radiation Dose (a) Time (b) Distance (c) Shielding (d) Source Reduction
Radiation Monitoring Personal and work area monitoring are needed. It ensures that radiation exposure at both personal and working area are less than the regulatory dose limit.
Non-ionizing Radiation Radiation that emits insufficient amount of energy to cause ionization. e.g. IR, visible light, microwave, ultrasound. Exposures to non-ionizing radiations will induce heat
EMF Wave Physics Wavelength ( ) is the length of one complete cycle, in m Frequency (f) is number of cycles per second, in hertz (Hz), 1 Hz = 1 cycle per second Speed of light (c) is a constant: c = 3 x 10 8 m s -1
Energy Transfer to Water Generates Heat
Object Size
Interactions with Matter Low frequency (long wavelength) e.g. 50/60 Hz High penetration. Little absorption Medium frequency (medium wavelength) e.g. 10-300 MHz High penetration. Maximum absorption High frequency (short wavelength) e.g. 300 MHz - 300 GHz Low penetration. Little absorption. Surface absorption predominant Absorption is most important (generates heat) Interactions depend on electrical properties, object size and polarization (all frequency dependent)
Known and Proven Effects Direct Effects: Mainly thermal Indirect Effects: Contact and Induced Currents: spark discharges, shocks and burns They serve as the basis for the current exposure guidelines
Ionizing vs Nonionizing Radiation Ionizing Radiation Nonionizing Radiation Ionization is the main mechanism for damage by ionizing radiation Can cause direct and indirect damages and cancer at high dose. Also increases the risks of cancer at low dose. Co-60 photon: about 1 MeV RF radiation does not have sufficient energy for ionization Causes thermal effect and induces body current Microwave-oven photon: about 10-5 ev Not a confirmed human carcinogen.
*
Laser - acronym Light Amplification by Stimulated Emission of Radiation Laser - a safety definition A highly collimated source of extremely intense monochromatic electromagnetic radiation *
Classification based on the ability of the primary laser beam to cause biological damage to the eye or skin. There are four laser classes. *
* Class I Not hazardous, even if output is gathered by optics Exempt from any control or other forms of surveillance Class II Emits in the visible portion of the spectrum (0.4 to 0.7 um) Average power < 1 mw Eye protection is normally afforded by the aversion response. Hazard would exist if viewer stifled aversion reflexes, i.e. blinking and looking away.
* Class III Moderate-Power Laser Can cause harm to eye in less time than it takes to blink (1/4 second), skin and diffuse reflection hazards not important
* Class IIIR Potentially hazardous under some direct and specular reflection viewing condition Not harmful at a glance, collecting optics needed to cause harm
* * Class IIIB * May be hazardous under direct and specular reflection viewing conditions * Bare beam could injure eye
* Class IV High-Power Laser >500 mw Can cause eye damage by diffuse reflection, also skin injury and fire hazard May also produce laser generated air contaminants (LGAC) and hazardous plasma radiation This class requires serious controls.
*
* The eyes are the most vulnerable The lens can focus light by 100,000 times to a 20um size point on the retina. Injury is frequency dependent. The retina, cornea and lens of the eye can be damaged by some laser frequencies but not all.
*
* UV-B, UV-C and far-ir radiation is absorbed at the cornea UV-A radiation is primarily absorbed in the lens Visible and near-ir radiation is refracted at the cornea and lens and absorbed at the retina
* 315 nm-1mm wavelength beams absorbed by the skin Thermal effects range from mild reddening (erythema) to blistering and charring Primarily minor burns Only with high-power lasers
*
* Wavelength Intensity of radiant exposure Angle of beam incidence Direct beam/specular reflection/diffuse reflection Duration of exposure Pulsed verses continuous wave (CW) more damaging, including retinal hemorrhaging
Beam Hazard Eye Skin Electrical Dye Gas Other hazards *
* Enclose beam as much as possible Terminate beam at the end of useful path Barriers to beam - walls, partitions, curtains Area control - locked doors/interlocks Electrical earthing Gas cabinet
* Procedures Laser Operating Safety Procedures (OSP) Identify hazards and controls General Safety no jewelry or shinny tools, avoid beam viewing, electrical safety, etc. Warning lights and signs Training
* Specific for wavelength(s) of beams Optical density (OD) rates attenuation Should always be worn when working with exposed beams Should never be used for direct beam viewing Chemical goggles for dye mixing/cylinder changing Chemical-resistant gloves for dyes and solvents