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Home , Background radiation, Radiation, Radionuclide

APPENDIX B Understanding

This section introduces the general reader to some basic concepts of radioactivity and an understanding of the radiation emitted as radioactive materials decay to a stable state. To better comprehend the radiological information in the Site Environmental Report (SER), it is important to remember that not all are the same and that different kinds of radiation affect living beings differently. This appendix includes discussions on the common sources of radioactivity in the environment, types of radiation, the analyses used to quantify radioactive material, and how radiation sources contribute to radiation dose. Some general statistical concepts are also presented, along with a discussion of that are of environmental interest at BNL. The discussion begins with some definitions and background information on scientific notation and numerical prefixes used when measuring dose and radioactivity. The definitions of commonly used radiological terms are found in the Technical Topics section of the glossary, Appendix A, and are indicated in boldface type here only when the definition in the glossary provides additional details. radioactivity and radiation ionizing or not, may pose health risks. In the All substances are composed of that SER, radiation refers to . are made of subatomic : , neu- Radioactive elements (or radionuclides) are trons, and . The protons and referred to by name followed by a number, such are tightly bound together in the positively as cesium-137. The number indicates the mass charged nucleus (plural: nuclei) at the center of of that element and the total number of neutrons the . The nucleus is surrounded by a and protons contained in the nucleus of the atom. of negatively charged electrons. Most nuclei Another way to specify cesium-137 is Cs-137, are stable because the holding the pro- where Cs is the chemical symbol for cesium in tons and neutrons together are strong enough to the of the Elements. This type of overcome the electrical that tries to push abbreviation is used throughout the SER. them apart. When the number of neutrons in the nucleus exceeds a threshold, then the nucleus Scientific Notation becomes unstable and will spontaneously “de- Most numbers used for measurement and cay,” or emit excess energy (“nuclear” energy) quantification in the SER are either very large or in the form of charged particles or electromag- very small, and many zeroes would be required netic . Radiation is the excess energy to express their value. To avoid this, scientific released by unstable atoms. Radioactivity and notation is used, with numbers represented in radioactive refer to the unstable nuclear prop- multiples of 10. For example, the number two erty of a substance (e.g., radioactive ). million five hundred thousand (two and a half When a charged or electromagnetic million, or 2,500,000) is written in scientific is detected by radiation-sensing equip- notation as 2.5 x 106, which represents “2.5 ment, this is referred to as a radiation event. multiplied by 10 raised to the power of 6.” Radiation that has enough energy to remove Since even “2.5 x 106” can be cumbersome, the electrons from atoms within material (a pro- capital letter E is substituted for the phrase “10 cess called ) is classified as ionizing raised to the power of …” Using this format, radiation. Radiation that does not have enough 2,500,000 is represented as 2.5E+06. The “+06” energy to remove electrons is called nonionizing refers to the number of places the decimal point radiation. Examples of nonionizing radiation was moved to the left to create the shorter ver- include most visible , light, micro- sion. Scientific notation is also used to represent waves, and radio waves. All radiation, whether numbers smaller than zero, in which case a

B- 2008 Site Environmental Report APPENDIX B: understanding radiation

of cosmic radiation from outer , radiation from radioactive elements in and rocks, and radiation from and its decay products in Radon, air. Some people use the term background when 200 Medical, 39 referring to all non-occupational sources com- Manmade monly present. Other people use natural to refer Nuclear only to cosmic and terrestrial sources, and back- Medicine, 14 ground to refer to common man-made sources Consumer such as medical procedures, consumer products, Internal, Products, 10 40 and radioactivity present in the from former nuclear testing. In the SER, the term Cosmic, natural background is used to refer to radiation 26 Terrestrial, 28 from cosmic and terrestrial radiation. Cosmic – Cosmic radiation primarily consists of Figure B-1. Typical Annual Radiation Doses from Natural and Man- Made Sources (mrem). Source: NCRP Report No. 93 (NCRP 1987) charged particles that originate in space, beyond the ’s atmosphere. This includes ionizing minus sign follows the E rather than a plus. For radiation from the , and secondary radia- example, 0.00025 can be written as 2.5 x 10-4 tion generated by the entry of charged particles or 2.5E-04. Here, “-04” indicates the number of into the earth’s atmosphere at high speeds and places the decimal point was moved to the right. . Radioactive elements such as hydro- gen-3 (), -7, -14, and NUMERICAL Prefixes sodium-22 are produced in the atmosphere by Another method of representing very large cosmic radiation. Exposure to cosmic radiation or small numbers without using many zeroes is increases with altitude, because at higher eleva- to use prefixes to represent multiples of ten. For tions the atmosphere and the earth’s magnetic example, the prefixmilli (abbreviated m) means provide less shielding. Therefore, people that the value being represented is one-thou- who live in the are exposed to more sandth of a whole unit; 3 mg (milligrams) is 3 cosmic radiation than people who live at sea thousandths of a gram or E-03. See Appendix C level. The average dose from cosmic radiation for additional common prefixes, includingpico to a person living in the United States is ap- (p), which means trillionth or E-12, giga (G), proximately 26 mrem per year. (For an expla- which means billion or E+09, and tera (T), nation of dose, see effective dose equivalent in which means trillion, E+12. Appendix A. The units rem and also are explained in Appendix A.) Sources of Ionizing Radiation Terrestrial – Terrestrial radiation is released Radiation is energy that has both natural by radioactive elements that have been pres- and manmade sources. Some radiation is essen- ent in the soil since the formation of the earth. tial to , such as and light from the sun. Common radioactive elements that contribute to Exposure to high-energy (ionizing) radiation terrestrial exposure include of potas- has to be managed, as it can pose serious health sium, , , and uranium. The risks at large doses. Living things are exposed average dose from terrestrial radiation to a per- to radiation from natural background sources: son living in the United States is approximately the atmosphere, soil, , food, and even our 28 mrem per year, but may vary considerably own bodies. Humans are exposed to ionizing depending on the local . radiation from a variety of common sources, the Internal – Internal exposure occurs when ra- most significant of which follow. dionuclides are ingested, inhaled, or absorbed – Radiation that occurs through the skin. Radioactive material may be naturally in the environment is also called back- incorporated into food through the uptake of ter- ground activity. Background radiation consists restrial radionuclides by roots. People can

2008 Site Environmental Report B- APPENDIX B: understanding radiation ingest radionuclides when they eat contaminat- Therefore, beta particles have a negative charge. ed plant or meat from that have Beta radiation is slightly more penetrating than consumed contaminated . The average alpha radiation, but most beta radiation can be dose from food for a person living in the United stopped by materials such as aluminum foil and States is about 40 mrem per year. A larger expo- plexiglass panels. Beta radiation has a range in sure, for most people, comes from breathing the air of several feet. Naturally occurring radioac- decay products of naturally occurring radon gas. tive elements such as -40 emit beta The average dose from breathing air with radon radiation. Some beta particles present a hazard byproducts is about 200 mrem per year, but to the skin and eyes. that amount varies depending on geographical Gamma Radiation – Gamma radiation is a form location. An Environmental Protection Agency of electromagnetic radiation, like radio waves (EPA) map shows that BNL is located in one of or visible light, but with a much shorter wave- the regions with the lowest potential radon risk. length. Gamma rays are emitted from a radioac- Medical – Every year in the United States, mil- tive nucleus along with alpha or beta particles. lions of people undergo medical procedures Gamma radiation is more penetrating than alpha that use ionizing radiation. Such procedures or beta radiation, capable of passing through include chest and dental x-rays, mammography, dense materials such as concrete. Gamma radia- heart stress tests, and tumor irradia- tion is identical to x-rays except that x-rays tion . The average doses from nuclear are more energetic. Only a fraction of the total medicine and x-ray examination procedures are gamma rays a person is exposed to will interact about 14 and 39 mrem per year, respectively. with the human body. Anthropogenic – Sources of anthropogenic (man- made) radiation include consumer products such Types of Radiological AnalysEs as static eliminators (containing -210), The amount of radioactive material in a detectors (containing americium-241), sample of air, water, soil, or other material can cardiac pacemakers (containing -238), be assessed using several analyses, the most fertilizers (containing isotopes from uranium common of which are described below. and thorium decay series), and products Gross alpha – Alpha particles are emitted from (containing polonium-210 and -210). The radioactive material in a range of different average dose from consumer products to a per- energies. An analysis that measures all alpha son living in the United States is 10 mrem per particles simultaneously, without regard to their year (excluding tobacco contributions). particular energy, is known as a gross alpha ac- tivity measurement. This type of measurement COMMON TYPES OF Ionizing RADIATION is valuable as a screening tool to indicate the The three most common types of ionizing total amount but not the type of alpha-emitting radiation are described below. radionuclides that may be present in a sample. Alpha Radiation – An is identi- Gross beta – This is the same concept as that for cal in makeup to the nucleus of a helium atom, gross alpha analysis, except that it applies to the consisting of two neutrons and two protons. measurement of gross activity. Alpha particles have a positive charge and have Tritium – Tritium radiation consists of low-en- little or no penetrating power in matter. They ergy beta particles. It is detected and quantified are easily stopped by materials such as paper by liquid scintillation counting. More infor- and have a range in air of only an inch or so. mation on tritium is presented in the section However, if alpha-emitting material is ingested, Radionuclides of Environmental Interest, later alpha particles can pose a health risk inside the in this appendix. body. Naturally occurring radioactive elements Strontium-90 – Due to the properties of the such as uranium emit alpha radiation. radiation emitted by strontium-90 (Sr-90), Beta Radiation – Beta radiation is composed a special analysis is required. Samples are of particles that are identical to electrons. chemically processed to separate and collect any

B- 2008 Site Environmental Report APPENDIX B: understanding radiation strontium atoms that may be present. The col- spread, or distribution, of results will be ob- lected atoms are then analyzed separately. More tained. This spread, known as a Poisson dis- information on Sr-90 is presented in the section tribution, is centered about a mean (average) Radionuclides of Environmental Interest. value. Similarly, if background activity (the Gamma – This analysis technique identifies number of radiation events observed when no specific radionuclides. It measures the particu- sample is present) is counted multiple , it lar energy of a ’s gamma radiation also will have a Poisson distribution. The goal emission. The energy of these emissions is of a radiological analysis is to determine wheth- unique for each radionuclide, acting as a “fin- er a sample contains activity greater than the gerprint” to identify it. background reading detected by the instrument. Because the sample activity and the background Statistics activity readings are both Poisson distributed, Two important statistical aspects of measur- subtraction of background activity from the ing radioactivity are uncertainty in results, and measured sample activity may result in values negative values. that vary slightly from one analysis to the next. Uncertainty – Because the emission of radia- Therefore, the concept of a minimum detection tion from an atom is a random process, a sample limit (MDL) was established to determine the counted several times usually yields a slightly statistical likelihood that a sample’s activity is different result each ; therefore, a single greater than the background reading recorded by measurement is not definitive. To account for the instrument. this variability, the concept of uncertainty is ap- Identifying a sample as containing activity plied to radiological data. In the SER, analysis greater than background, when it actually does results are presented in an x ± y format, where not have activity present, is known as a Type I “x” is the analysis result and “± y” is the 95 error. Most laboratories set their acceptance of percent “confidence interval” of that result. That a Type I error at 5 percent when calculating the means there is a 95 percent probability that the MDL for a given analysis. That is, for any value true value of x lies between (x + y) and (x – y). that is greater than or equal to the MDL, there is Negative values – There is always a small 95 percent confidence that it represents the de- amount of natural background radiation. The tection of true activity. Values that are less than laboratory instruments used to measure radioac- the MDL may be valid, but they have a reduced tivity in samples are sensitive enough to mea- confidence associated with them. Therefore, sure the background radiation along with any all radiological data are reported, regardless of contaminant radiation in the sample. To obtain whether they are positive or negative a true measure of the contaminant level in a At very low sample activity levels that are sample, the background radiation level must be close to the instrument’s background reading, it subtracted from the total amount of radioactivity is possible to obtain a sample result that is less measured. Due to the randomness of radioac- than zero. This occurs when the background tive emissions and the very low concentrations activity is subtracted from the sample activ- of some contaminants, it is possible to obtain ity to obtain a net value, and a negative value a background measurement that is larger than results. Due to this situation, a single radia- the actual contaminant measurement. When the tion event observed during a counting period larger background measurement is subtracted could have a significant effect on the mean from the smaller contaminant measurement, a (average) value result. Subsequent analysis negative result is generated. The negative results may produce a sample result that is positive. are reported, even though doing so may seem When the annual data for the SER are com- illogical, but they are essential when conducting piled, results may be averaged; therefore, all statistical evaluations of data. negative values are retained for reporting as Radiation events occur randomly; if a well. This data handling practice is consistent radioactive sample is counted multiple times, a with the guidance provided in the Handbook of

2008 Site Environmental Report B- APPENDIX B: understanding radiation

Radioactivity Measurements Procedures (NCRP former Hazardous Waste Management Facility, 1985) and the Environmental Regulatory Waste Concentration Facility, Building 650 Guide for Radiological Effluent Monitoring Reclamation Facility and Sump Outfall Area, and Environmental Surveillance (DOE 1991). and the Brookhaven Graphite Research Reactor Average values are calculated using actual (BGRR). analytical results, regardless of whether they are Strontium-90 – Sr-90 is a beta-emitting radionu- above or below the MDL, or even equal to zero. clide with a half-life of 28 years. Sr-90 is found The uncertainty of the mean, or the 95 percent in the environment principally as a result of fall- confidence interval, is determined by multiply- out from aboveground . ing the population standard deviation of the Sr-90 released by weapons testing in the 1950s mean by the t(0.05) statistic. and early 1960s is still present in the environ- ment today. Additionally, nations that were not Radionuclides of Environmental Interest signatories of the Nuclear Test Ban Treaty of Several types of radionuclides are found in 1963 have contributed to the global inventory of the environment at BNL due to historical opera- fission products (Sr-90 and Cs-137). This radio- tions. was also released as a result of the 1986 Cesium-137 – Cs-137 is a fission-produced accident in the former Soviet Union. radionuclide with a half-life of 30 years (after Sr-90 is present at BNL in the soil and 30 years, only one half of the original activ- groundwater. As in the case of Cs-137, some ity level remains). It is found in the worldwide Sr-90 at BNL results from worldwide nuclear environment as a result of past aboveground testing; the remaining is a by- nuclear weapons testing and can be observed in product of reactor operations. The following near-surface at very low concentrations, areas with Sr-90 contamination have been or are usually less than 1 pCi/g (0.004 Bq/g). Cs-137 being addressed as part of the Environmental is a beta-emitting radionuclide, but it can be Remediation Program: former Hazardous Waste detected by gamma because its Management Facility, Waste Concentration , barium-137m, emits gamma Facility, Building 650 Reclamation Facility and radiation. Sump Outfall Area, the BGRR, Former and Cs-137 is found in the environment at BNL Interim Landfills, Chemical and Glass Holes mainly as a soil contaminant, from two main Area, and the STP. sources. The first source is the worldwide depo- The information in SER tables is arranged sition from nuclear accidents and fallout from by method of analysis. Because Sr-90 requires weapons testing programs. The second source a unique method of analysis, it is reported as a is deposition from spills or releases from BNL separate entry. Methods for detecting Sr-90 us- operations. operations produce ing state-of-the-art equipment are quite sensitive Cs-137 as a byproduct. In the past, wastewater (detecting concentrations less than 1 pCi/L), containing small amounts of Cs-137 generated which makes it possible to detect background at the reactor facilities was routinely discharged levels of Sr-90. to the Treatment Plant (STP), result- Tritium – Among the radioactive materials that ing in low-level contamination of the STP are used or produced at BNL, tritium has re- and the Peconic River. In 2002/2003, under ceived the most public attention. Approximately the Environmental Restoration Program, sand 4 million Ci (1.5E+5 TBq) per year are pro- and its debris containing low levels of Cs-137, duced in the atmosphere naturally (NCRP Sr-90, and were removed, assur- 1979). As a result of aboveground weapons test- ing that future discharges from the STP are free ing in the 1950s and early 1960s in the United of these contaminants. Soil contaminated with States, the global atmospheric tritium inventory Cs-137 is associated with the following areas was increased by a factor of approximately that have been, or are being, addressed as part 200. Other human activities such as consumer of the Environmental Remediation Program: product manufacturing and reac-

B- 2008 Site Environmental Report APPENDIX B: understanding radiation tor operations have also released tritium into the HTO, none as elemental tritium. Sources of environment. Commercially, tritium is used in tritium at BNL include the reactor facilities (all products such as self-illuminating wristwatches now non-operational), where residual water and exit signs (the signs may each contain as (either heavy or light) is converted to tritium via much as 25 Ci [925 GBq] of tritium). Tritium bombardment; the accelerator facili- also has many uses in medical and biological ties, where tritium is produced by secondary research as a labeling agent in chemical com- radiation interactions with soil and water; and pounds, and is frequently used in universities facilities like the Brookhaven Linac and other research settings such as BNL and Producer, where tritium is formed from second- other national laboratories. ary radiation interaction with cooling water. Of the sources mentioned above, the most Tritium has been found in the environment at significant contributor to tritium in the environ- BNL as a groundwater contaminant from opera- ment has been aboveground nuclear weapons tions in the following areas: Current Landfill, testing. In the early 1960s, the average tri- BLIP, Alternating Gradient Synchrotron, and tium concentration in surface streams in the the High Flux Beam Reactor. Although small United States reached a value of 4,000 pCi/L quantities of tritium are still being released to (148 Bq/L; NCRP 1979). Approximately the the environment through BNL emissions and same concentration was measured in precipita- effluents, the concentrations and total quantity tion. Today, the level of tritium in surface have been drastically reduced, compared with in New York State is less than one-twentieth historical operational releases as discussed in of that amount, below 200 pCi/L (7.4 Bq/L; Chapters 4 and 5. NYSDOH 1993). This is less than the detection limit of most analytical laboratories. REFERENCES and bibliography Tritium has a half-life of 12.3 years. When DOE Order 5400.5. 1993. of the an atom of tritium decays, it releases a beta par- Public and the Environment. U.S. Department of Energy, ticle, causing transformation of the tritium atom Washington, DC. Change 2: 1-7-93. into stable (nonradioactive) helium. The beta DOE. 1991. Environmental Regulatory Guide for radiation that tritium releases has a very low Radiological Effluent Monitoring and Environmental Surveillance. DOE/EH-0173T. U.S. Department of energy, compared to the emissions of most other Energy, Washington, DC. radioactive elements. In humans, the outer layer NCRP. 1979. Tritium in the Environment. NCRP Report of dead skin cells easily stops the beta radia- No. 62. National Council on Radiation Protection and tion from tritium; therefore, only when tritium Measurements. Bethesda, MD. is taken into the body can it cause an exposure. NCRP. 1985. Handbook of Radioactivity Measurements Procedures, NCRP Report No. 58. National Council on Tritium may be taken into the body by inhala- Radiation Protection and Measurements, Bethesda, tion, ingestion, or absorption of tritiated water MD. through the skin. Because of its low energy NCRP. 1987. Ionizing of the radiation and short residence time in the body, Population of the United States. NCRP Report No. 93. National Council on Radiation Protection and the health threat posed by tritium is very small Measurements. Bethesda, MD. for most exposures. NYSDOH. 1996. Radioactive Contamination in the Environmental tritium is found in two Peconic River. Bureau of Environmental Radiation forms: gaseous elemental tritium, and tritiated Protection, New York State Department of Health, water or water , in which at least one of Albany, NY. the atoms in the H O water molecule NYSDOH. 1993. Environmental Radiation in New York 2 State. Bureau of Environmental Radiation Protection, has been replaced by a tritium atom (hence, its New York State Department of Health, Albany, NY. shorthand notation, HTO). Most of the tritium Society Online. www.radiochemistry. released from BNL sources is in the form of org/nomenclature/index/html, accessed 3-25-04.

2008 Site Environmental Report B-