What is Radiation? The transfer of energy in the form of particles or waves from one object to another though a medium. Module #2

Types of Radiation Particulate vs Electromagnetic Photon Alpha Particle Beta Particle Alpha, beta and neutrons have mass and volume and if one had good enough eye sight one could see them. Where as the x-ray and gamma rays are just electromagentic waves without mass or volume. Neutron Module #2

Electromagnetic Radiation Oscillating electric and magnetic fields that transfer energy to matter via photon or wave interactions 10-12 10-10 10-8 10-6 10-4 10-2 100 102 104 106 108 1010 Ultra - Violet Infrared Micro - waves Radio waves Electric X-Rays & Gamma Rays Visible Light Ionizing Non-ionizing Wavelength (cm) Note the only difference between x-rays and gamma waves and other waves such as light or radiowaves is the wavelength. X-rays and gamma rays have a very short wavelength. Module #2

Types of Radiation Charged vs. Uncharged Photon Alpha Particle Neutron Alpha particles have a ++ electrical charge and beta particles have a - charge. Neutron Beta Particle Module #2

Types of Radiation Ionizing vs. Non-Ionizing Has enough energy to completely remove an electron from an atom Non-Ionizing Not enough energy to completely remove an electron from an atom Module #2

Pair Production A photon of at least 1.022 MeV energy may spontaneously form a positron-electron pair The positron and electron interact with matter as energetic charged particles The positron will eventually combine with an electron and produce two 511 keV photons Module #2

Exposure The sum of the charges of one sign produced by photons in given mass of air The SI unit of exposure in the coulomb/kilogram (C/kg) The traditional unit is the roentgen ® 1 R = 2.58 x 10-4 C/kg This unit is only defined for photons of less than 3 MeV energy in air Symbol is X Module #2

Absorbed Dose The energy deposited in (absorbed) by an object per unit mass The SI unit of absorbed dose is the Gray (Gy) The traditional units is the rad 100 rad = 1 Gy = 1 J/kg Applies to all radiations at all energies in all absorbers. Symbol is D Exposure by definition is in air. Absorbed dose is in matter. It could be air, concrete, a desk top, or our bodies. Module #2

Dose Equivalent The energy deposited is an object per unit mass multiplied by a “quality factor” that accounts for the different biological effectiveness of different types of radiation Symbol is H H = D * Q The SI unit of dose equivalent is the sievert (Sv) The traditional unit is the rem 100 rem = 1 Sv Dose equivalent normalizes absorbed dose to a common basis for a given biological effect. If one is evaluating dose equivalent it does not matter whether the radiation was alpha, beta, gamma, x-ray or neutrons. Module #2

Recommended Quality Factors RADIATION TYPE NRC X- and Gamma 1 Beta (except H-3) 1 H-3 1 Thermal Neutrons * Fast Neutrons * Unknown Neutrons 10 Alpha 20 * See 10 CFR Table 1004(b).2 Alpha is very easy to shield. A sheet of paper will stop alpha as will the dead layer of skin that covers our body. However, if alpha is next to live tissue it can traverse 6-10 cell layers. It give up its energy in a very short distance. This fact in part is the reason that alpha has a quality factor of 20. In other words if one has an absorbed dose from an alpha particle; on a biological basis it has the potential to be 20 time more effective in causing potential health effects when compared to gamma. Module #2

Conversions For purpose of radiation protection it is often assumed that 1R = 1rad = 1rem For photons, since R is only defined for photons and the quality factor is 1 for photons; 1R is actually less than 1rad so this is a conservative assumption The actual “conversion” factor is dependent on the absorber (1R = 0.96rad for tissue) Module #2

Other Dose Equivalents Deep Dose Equivalent (Hd) – The dose equivalent at a tissue depth of 1cm due to external radiation Eye Dose Equivalent (Heye) – The dose equivalent at a tissue depth of 0.3cm due to external radiation Shallow Dose Equivalent (H5) – The dose equivalent at a tissue depth of 0.007 cm due to external radiation Deep dose is usually only penetrating radiation like x-ray or gamma. Shallow dose is x-ray and gamma plus beta. Module #2

Other Dose Equivalents * Committed Dose Equivalent (HT50) – The dose equivalent received by a tissue (T) over the next 50 years due to an intake of radioactive material Committed Effective Dose Equivalent (CEDE or HE50) – The sum of the products of the committed dose equivalent to a tissue and a weighting factor for that tissue [HE50 = Sw T HT50]] When one takes radioactive material into the body it does not decay all at once. One receives a dose only when atoms decay. If one knows the physical half-life one can calculate the numbers of atoms that are decaying per unit of time and then one can calculate the dose for a like unit of time. This is further complicated by the fact that most any chemicals (remember radioactive materials are chemicals and their behavior in the body follows their chemical properties) are eliminated from the body via the urine and feces. If we know the elimination rate then by combining this with the physical half-life we can determine dose over time. Regulations specify that we must calculate a committed dose over a 50 year time period. For short half-life materials and materials that are eliminated from the body rapidly, the 50 year committed dose may be received in a matter of a few days. Whereas material with a long physical half-life and which is eliminated from the body slowly may result in a dose over many years. When one takes radioactive material into the body it does not decay all at once. One receives a dose only when atoms decay. If one knows the physical half-life one can calculate the numbers of atoms that are decaying per unit of time and then one can calculate the dose for a like unit of time. This is further complicated by the fact that most any chemicals (remember radioactive materials are chemicals and their behavior in the body follows their chemical properties) are eliminated from the body via the urine and feces. If we know the elimination rate them by combining this with the physical half-life we can determine dose over time. Regulations specify that we must calculated a committed dose over a 50 year time period. For short half-life materials and materials that are eliminated from the body rapidly, the 50 year committed dose may be received in a matter of a few days. Whereas material with a long physical half-life and which is eliminated from the body slowly may resulting a dose over many years. When one takes radioactive material into the body it does not decay all at once. One receives a dose only when atoms decay. If one knows the physical half-life one can calculate the numbers of atoms that are decaying per unit of time and them one can calculate the dose for a like unit of time. This is further complicated by the fact that most any chemicals (remember radioactive materials are chemicals and their behavior in the body follows their chemical properties) are eliminated from the body via the urine and feces. If we know the elimination rate them by combining this with the physical half-life we can determine dose over time. Regulations specify that we must calculated a committed dose over a 50 year time period. For short half-life materials and materials that are eliminated from the body rapidly, the 50 year committed dose may be received in a matter of a few days. Whereas material with a long physical half-life and which is eliminated from the body slowly may resulting a dose over many years. When one takes radioactive materila into the body it does not decay all at once. One receives a dose only when atoms decay. If one knows the physical half-life one can calculate the numbers of atoms that are decaying per unit of tim Module #2

Other Dose Equivalents* Effective Dose Equivalent (HE) – The sum of the products of the dose equivalent to a tissue and a weighting factor (wT) for that tissue [HE = SwTHT] Total Effective Dose Equivalent (TEDE) – the sum of the deep dose equivalent and the CEDE [TEDE = Hd + HE50] Different tissues and organ have varying probabilities for the induction of radiation induced cancer. A weighting factor (WT) take this into account and relate the dose to that of a deep dose having the same likelihood of a radiation induced cancer. Module #2