Louisiana State University Radiation Safety Office Module 2 Fundamentals of Ionizing Radiation

The transfer of energy from one object to another through space. What is Radiation? The transfer of energy from one object to another through space.

Types of Radiation Particulate vs. Electromagnetic Beta Particle Alpha Particle Beta Particle Photon 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 or just elctromagentic waves without mass or volume. Neutron

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.

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

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

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

Exposure The sum of the charges of one sign produced by photons in a given mass of air The SI unit of exposure is the coulomb/kilogram (C/kg) The traditional unit is the roentgen (R) 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

Absorbed Dose The energy deposited in or absorbed by an object per unit mass Applies to all radiation at all energies in all absorbers. The SI unit of absorbed dose is the Gray (Gy) The traditional unit is the rad 100 rad = 1 Gy = 1 J/kg 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.

Dose Equivalent The energy deposited in an object per unit mass multiplied by a “quality factor” (quality factor accounts for the different biological effectiveness of different types of radiation) The SI unit of dose equivalent is the sievert (Sv) The traditional unit is the rem 100 rem = 1 Sv Symbol is H, H = D * Q 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.

Recommended Quality Factors (from the NRC - Nuclear Regulatory Commission) RADIATION TYPE QF X-rays and Gammas 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 (CFR = Code of Federal Regulations) 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 the reason that alpha has a quality factor of 20. In other words if one has an absorbed dose of alpha it on a biological basis has the potential to be 20 time more effective in causing potential health effects when compared to gamma.

Conversions For purpose of radiation protection, it is assumed that 1R = 1rad = 1rem R is only defined for photons The quality factor is 1 for photons The actual “conversion” factor is dependent on the absorber 1R is actually less than 1rad (1R = 0.96 rad for tissue)

Other Dose Equivalents Deep Dose Equivalent (Hd) – The dose equivalent at a tissue depth of 1 cm due to external radiation Eye Dose Equivalent (Heye) – The dose equivalent at a tissue depth of 0.3 cm 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.

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 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.

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 does to that of a deep dose having the same likelihood of a radiation induced cancer.