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Assorted FactsBy George W. Dowell
2.54 cm = 1 inch. 30.4 cm = 1 foot. 2.83E4 cc = 1cubic foot. The atom is the smallest part of an element that can be separated by chemical reaction. Atomic number is the number of protons. This is known as the Z number. Atomic mass number is the sum of the number of protons and neutrons in the nucleus. This is known as the A number. Protons and Neutrons are called Nucleons. One atomic mass unit (AMU) is equal to 1/12 the mass of a carbon-12 nucleus. (1.6604E-24 g.) (Also called a Dalton.) Radioactivity is the process by which the nucleus of unstable nuclides disintegrates with the resulting emission of nuclear radiation. Becquerel discovered radiation. Half-Life is the term in which half of the atoms of a particular radioactive substance decay to another nuclear form, or element. Ionization is the general process of producing Ions by the passage of high energy particles. Chronic radiation exposures are those involving continuous or repeated exposures over a relatively long time interval. Acute radiation exposures are involving relatively large doses in a short time. Somatic effects refer to the individual that received the exposure. Isotopic abundance is the amount of the isotope (percentage) present in a normal natural mixture of the element. Isotopes are defined as atoms with the same atomic number (Z) but different atomic mass number (A). Linear Attenuation Coefficient: " A fraction decrease in energy through absorption of material inverse of the mean free path". This is the name that describes the number of interactions per unit length. The unit for energy in nuclear reactions is the electron volt (ev), which is the amount of energy gained by an electron when accelerated through a potential difference of one volt.1 Mev is 1E6 ev. A Curie is 3.7E10 dps (one dps is equal to one Becquerel) or 2.22E12 dpm. A Pico Curie is 2.22 dpm The Roentgen is a measure of Exposure of air to gamma and x-rays. The energy absorbed by one gram of air exposed to one Roentgen of gamma rays is 87 ergs. There is no SI equivalent. The RAD is used as a unit of measurement for the energy deposited by any radiation in any material. 1 Rad = 100 ergs/gm any radiation in any material. 100 Rad = 1 Gray. REM is Dose Equivalent resulting from any type of radiation exposure. Rem is the unit of measure for internal exposure. REM Dose = RAD Dose x Quality Factor. 100 Rem = 1 Sievert. Quality Factor is used to convert Absorbed Dose (RAD) to Biological Effect (REM). QF: Gamma = 1, Beta = 1, Thermal Neutron = 2 (NEU) to 3 (DOE), Fast Neutron = 10, Alpha = 20, Proton = 10. The new 10 CFR 20 and 10 CFR 835 is based on ICRP #26. A major change in dose limits between the old and revised 10 CFR 20 is that the old limits are based on calendar quarter time period and the revised limits are based on an annual time period. An individual must be supplied with a personnel monitoring device if entering the restricted area and will receive or is likely to receive an exposure in excess of 10% of the (federal) limit. A minor will be allowed 10% of an adults limit per year. When entering a high radiation area, you need personnel monitoring devices. TODE, Dose limit for the extremities as per 10 CFR 20 is 50 Rem/yr. DDE, deep dose equivalent, is dose to the whole body (WB) from 'external' radiation exposure. TEDE, total effective dose equivalent, is the sum of all internal and external dose. CDE is the dose equivalent from Internal exposure to an individual organ or tissue, as calculated over a 50 year period after the exposure. CEDE equates risk from organ to risk from whole body dose. WF, weighting factor, is the equivalent whole body exposure from exposure of all organs due to radioactive material intake. According to the ICRP "ALI" stands for Annual Limit on Intake. 1 ALI = 2000 DAC Hrs = 5 Rem. The annual PSE limit for TEDE is 5 Rem. PSE = Planed special exposure. The NRC must be notified prior to any PSE. A radiation area is posted at 5 mr/hr @ 30 cm. The revised 10 CFR 20 specifies that radiation levels be measured at 30 cm. Black lettering is now ok for Radiation signs. -- The nucleus carries a positive charge. -- Protons and Neutrons are collectively known as "Nucleons". -- The diameter of the nucleus is relatively small compared to the diameter of the atom. -- Electrons carry a negative charge. -- Electrons, protons, and neutrons ARE NOT all about the same size. -- The nucleus contains 99.9% of the mass of the atom and about 10E-10 of the volume. -- The number of orbital electrons is equal to the number of protons in electrically neutral atoms. -- A Proton is an elementary particle that is identical with the nucleus of a Hydrogen atom and carries a positive charge. -- C0-60: The element is Cobalt, with 60 nucleons, 27 protons, 33 neutrons. -- An atom of a Carbon-12 has six protons, and six neutrons. If a Carbon-12 atom and an alpha particle were fused together, an Oxygen-16 isotope would result. -- 95Am-241 has 95 protons and 146 neutrons. -- 38Sr-90 decays by emission to Y-90. You would add 1 to the number of protons, so the scientific nomenclature of the daughter is 39Y-90 -- The highest to lowest relative penetration of 1 MeV Alpha, Beta, and Gamma rays is: Gamma, Beta, Alpha. -- Charged particles interact with matter by Excitation and Ionization. -- Ionizing radiation interacts with the orbital electrons of an atom and creates two particles of opposite charge, these particles are called ion pairs. -- The primary mechanisms whereby charged particles lose energy in transversing materials are ionization and excitation affecting the electronic structure of the material atoms. -- Alpha Particles (a) are Helium Nuclei emitted from the nucleus of an unstable atom. -- The interaction between alpha particles and atoms is most through columbic. (electrostatic) -- A 7 Mev Alpha particle travels in air 2 inches. -- The range of beta particles in air depends on the energy of the particle. -- The range of 1Mev beta particle in air is about 10 ft. (12ft actual per Mev) -- A beta particle can be either a positively or negatively charged electron. -- The electron has a negative electrostatic charge, and is equal in charge intensity to the proton. It's mass is 1/1838 that of a proton. -- A beta particle is an electron (1/1838 mass of a proton) emitted from the nucleus of a radioactive isotope. -- Bremsstrahlung radiation is originated by a high energy beta particle as it decelerates near a heavy nucleus. -- The secondary radiation produced when beta particles are stopped by shielding is bremsstrahlung. -- The difference between X-rays and gamma photons of the same energy is their origins. -- Nuclear radiation refers to the emanation of the energetic particles and/or the electromagnetic wave from the nucleus of the atom. -- Atomic radiation refers to electromagnetic waves emitted from the electron shell. -- A single quanta of electromagnetic energy is called a photon. -- Gamma photons originate in the nucleus of the atom. -- After undergoing Compton Scattering, a gamma photon is deflected off at an angle with reduced energy. -- Pair Production is when a high energy photon enters the vicinity of an atoms nucleus, the photon energy is converted into an electron-positron pair. (1.022MeV.) -- Pair production is when a high energy photon (more than 1.022 Mev) enters the vicinity of an atom's nucleus, the photon energy is converted into an electron-positron pair. -- X-rays come from electromagnetic ionizing radiation emitted by an orbital electron as it moves from the L shell to the K shell (changing energy levels). -- X-ray radiation refers to electromagnetic waves associated with electronic energy transition. (electron cloud) -- During photoelectric effect, a gamma photon gives up all of its energy to orbital electrons. -- The photon (gamma) interaction where a portion of the photons kinetic energy is transferred to an atom's orbital electron is called Compton scattering. -- The minimum energy photon in theory for a pair production is 1.022 Mev, however, this type of interaction in not observed for photons having energies less than about 2.5 Mev. -- Neutrons can cause ionization indirectly by knocking charged particles out of the nucleus. (Protons out of H-1) -- A Neutron has no charge. -- Fast Neutrons are the most severe external radiation hazard. -- H-1 (Hydrogen) has the most effect on the thermalization of fast neutrons as far as biological chemicals. -- In soft tissue, fast neutrons lose 80% to 90% of their energy by interacting with hydrogen. -- The chief difference between fast and slow neutrons is their (kinetic) energy. --- Elastic scattering slows down neutrons because it causes a neutron to lose kinetic energy without exciting the target nucleus. -- After an inelastic scattering process, the excited nucleus will emit a gamma photon. -- A neutron is absorbed and a gamma is released, is the best description of the method of inelastic scattering pertaining to neutrons. -- Beta decay process: During radioactive decay, a nucleus emits an electrically charged particle equal in mass to an electron. Part Three: Detectors and Meters -- (MDC) Minimum detectable counts is the smallest number of sample counts that are statistically greater than the background counts and are a result of radioactivity in the sample. -- (MDA) Minimum detectable activity is the minimum activity present in a sample that may be detected by a particular instrument. -- The purpose of the chi-squared test is to ensure that the instrument's results lie within a normal Gaussian Distribution. -- Pulse height determines which source it is. Alpha pulses are the highest. -- You don't check the desiccant for a initial check on instruments prior to use, or the beta shield calibration (duh). -- The following checks are made on a survey instrument prior to use: check the instrument for date calibrated (calibration expiration date), proper battery condition, and a response check. -- The principal that explains the operation of most radiation detection instruments is the radiation causes ionization in the detector which is converted into a meter reading. -- Radiation is not measured directly, but is measured instead by its effect on the detector walls or the material within the detector. -- In a gas filled detector, radiation ionizes the fill gas releasing electrons that are attracted to the positively charged anode and measured by the electrical circuitry. -- The ratio of intensity measured by the detector (intensity of the primary beam and scatter radiation) to the calculated actual intensity is the buildup factor. -- The type of gas used would affect the sensitivity of an ion chamber detector because some gases ionize more easily than others. -- An ion chamber produces output based on the ions produced in the wall of the chamber. -- In the ionization chamber, the detector output is approximately equal to the amount of primary ionization produced in the gas. -- An ion chamber survey instrument is used to ascertain the amount of exposure personnel would receive as it accounts for all the ionization events occurring. -- The instrument used for the best tissue equivalent dose rate is the ion chamber. -- The Dead Time for GM detectors is the period in which a second pulse will not be detected. -- Unless some type of quenching gas is used, a Geiger-Mueller detector will re-trigger its avalanche because of electrons released while the positive ions interact with the outer wall. -- When compared to ion chambers, proportional counters and fission chambers, the Geiger-Mueller detectors are the most sensitive to low level gamma fields, but not more accurate. -- In the Geiger-Mueller detector the output pulse is approximately independent of the type and energy of the radiation entering the detector. -- Proportional counters operate at higher voltages than ionization chambers. (RIPLGC) -- A proportional counter system can tell the difference between alpha and beta radiation because the size of the pulse caused by the alpha interaction will be much higher than the pulse caused by the beta interaction. -- The main advantage of using a proportional counter is it is able to differentiate between different types of radiation. -- The function of the Photo Cathode in a photo-multiplier (PM) tube is to release electrons when it is struck by light emitted from scintillation. -- In a scintillation detector, the photomultiplier tube converts and amplifies the electrons freed by ionization in the scintillation crystal to a larger light output. -- In general, scintillation detectors are more sensitive then gas-filled detectors for gamma radiation because they contain material with a higher density for gamma's to interact. They are often used for counting measurements in laboratories. -- Surface medium for scintillators, alpha is zinc sulfide (ZnS), beta is anthracene, and gamma is sodium iodine (NaI). -- The GeLi is a Semi Conductor Detection System. The middle section is composed of germanium and lithium mixture. Pure germanium is on one side of the mixture and pure lithium on the other side. When a gamma enters the center region of the crystal it undergoes an interaction that frees an electron from one of the atoms in the crystal. When this happens, a vacancy, or hole is left in the inner electron shell around the nucleus. -- The center region is the part of the semiconductor crystal that is sensitive to ionizing radiation. -- When a gamma ray is detected by a semi-conductor crystal a flow of free electrons is initiated toward the positive end of the crystal. -- For a semiconductor material to detect radiation, the voltage applied to the detector must be large enough to separate the positive charges from the negative charges to form a depletion region. -- In Germanium crystal detectors, the flow of free electrons towards the positive electrode and the apparent movement of holes toward the negative electrode create a current flow in the circuit. -- A whole body counter is for measuring internal gamma emitters. -- In-vivo or whole body counting, determines the amount of a radionuclide deposited in an individual by liquid or solid crystal scintillation detectors. -- It is important to add moderating materials to shield for a fast neutron source since the absorption cross section for most elements increases as the velocity or energy of the neutron decreases. -- A good thermal neutron absorber used in the portable detectors is cadmium. -- The neutron interaction used in portable survey instrumentation is neutron capture with the emission of a charged particle. -- Neutron detectors are easy to design because there are a large number of materials with large cross sections for absorption. -- Paraffin is used to attenuate fast neutrons. -- Individual dosimeter placement could be described as an error associated with relating a dosimeter reading to an actual dose. -- Beta and gamma exposure is determined in a Beta-Gamma Radiation field using film/TLD dosimetry by subtracting the closed window (shielded) film reading from the open window (unshielded) film/TLD reading. -- Finger rings don't have a need for neutron sensitivity. -- Minute by minute update on exposure is not an error or problem in relating TLD readings to the actual dose received by the body. -- A TLD's disadvantage is that it is expensive to use. -- Recognize the Decay Formula and the Decay Constant. (l) ln2/t1/2. -- In an atom prior to Beta Minus Decay, there will be excess neutrons in the atoms nucleus. -- Materials with a low Atomic Number (such as water, plastic, and paraffin) are used in making neutron shields because their atomic size allow for greater transfer of the neutrons energy per collision. -- Shallow dose equivalent applies to the external exposure of the skin or an extremity and is taken as a dose equivalent at a tissue depth of 0.007cm averaged over an area of 1 cm2. -- Using the assumption that 2" of lead equals one tenth thickness, the amount of shielding required to reduce a Cs-137 gamma beam of 100 mr/hr intensity to 1 mr/hr would be 4". (1/100) -- The mathematical expression which expresses the relationship between the radioactive decay constant and the half-life of an isotope is, T 1/2 = ln2/ Decay constant. -- The decay process emitting an alpha particle can be described as when a positively charged particle with a mass equal to a Helium nucleus is emitted from a nucleus during radioactive decay. -- To determine shielding, build up factors is not a valid reason to perform a radiation survey. -- If you shield a beta source with a higher atomic number shielding material, you will create more X-rays. (Bremsstrahlung). -- Shielding material with a high atomic number attenuates radiation more effectively than a lower atomic number material because, more electrons are available for interactions. -- The decay constant and the half-life are constants for a given radionuclide. -- The effective half-life formula is Teff = (TR x TB) + (TR + TB). The result will always be shorter than the shortest half-life. -- Beta shielding is better accomplished by aluminum than lead due to the production of Bremsstrahlung radiation. -- The actual decrease in the intensity of a beam of gamma rays passing through a wall is less than the theoretical decrease because some gamma interactions result in other gamma rays of lower energy being given off, this is called buildup. -- The shielding half value thickness for 1 Mev gamma of: lead is 0.5 inches, concrete is 4 inches, and water is 8 inches. The shielding tenth value thickness for 1 Mev gamma of: lead is 1.5 inches, concrete is 12 inches, and water is 24 inches. The shielding half value thickness for 6 Mev gamma of: lead is 0.7 inches, steel/iron is 1.3 inches, concrete is 8 inches, and water is 16 inches. The shielding tenth value thickness for 6 Mev gamma of: lead is 2 inches, steel/iron is 4 inches, concrete is 24 inches, and water is 48 inches. -- For lines and equipment containing reactor water, or primary steam with hold-up times of less than five minutes, you would use 6 Mev gamma 1/10 shielding (lead 2", water 48").
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