Introduction
The energy emitted from a source is called radiation. Examples include sun radiation or heat, oven microwaves, X-rays, and other radioactive elements that emit gamma rays. Alpha, beta, and gamma are particles generally emitted in ionizing radiation. Alpha-emitting radioactive elements, both natural and man-made, include: Americium-241, Plutonium-236, Uranium-238, Radium-226, Polonium -210 and Radon-222. The health consequences of exposure to alpha particles vary, based on the particle type and route of exposure. Unlike alpha particles, beta particles are the size of electrons, which penetrate the outer layer of the skin and pose higher health risks than alpha particles. Individuals who expose themselves to the beta particle face the risks of living tissue damage and cell function disruptions. Some of beta emitters include: Tritium, Cobalt-60, Strontium-90, Iodine-129, Iodine-131, and Cesium-137. Gamma particles are light rays with high energy that can travel at the speed of light and cover a large area in a matter of seconds. Beta particles cause gamma-ray emissions. The gamma-emitting radionuclide most frequently used in radiations include Cobalt-60, Cesium-137, and Technetium-99m. Excessive doses of radiation lead to the development of various health complications, from burns to acute radiation syndrome. Ionizing radiation in low doses increases the risks of terminal diseases, such as cancer (WHO, 2012).
The objectives of this laboratory experiment were to understand various types of radiation, their differences, as well as the principles of the proper usage of different equipment for the detection of radiation, its identification, and dose rate measurement.
Materials and Methods
The experiment was performed under the guidance of Dr. John Johnson and Mr. Bob Peterson in the environmental labs 430 and 457 of Chase Hall. All students were divided into two groups of approximately nine students each. Mr. Peterson provided and explained the principles of the radiation equipment to be used in the experiment. Our group started the experiment in laboratory # 457. In the experiment, we used the hand-held sodium iodide radiation detector, Ludlum Model 44-3 sensitive to low energy gamma rays (Figure 1), and Model 44-9 (Figure 2), as well the popular radiation detector, which is very sensitive to alpha, beta and gamma radiation.
While holding the detector, each student searched through cabinets, bench draws, refrigerators, and bio-safety hoods located in the laboratory to find sources of radiations. The Thermo-IndentiFinder-U (Figure 3), a hand-held instrument to find and identify radiation, was also used to identify radiation sources in the laboratory. Each student identified his (her) sources by holding the Thermo-identifier-U close to the source. The detector displayed the identity of the isotope on the green screen. We used the hand-held pressured µR ion chamber survey meter 451P (Figure 4) made by Fluke Biomedical to measure the level of exposure to the sources found in the laboratory. This highly sensitive instrument can measure the rate and dose simultaneously. Each student held the chamber close to the identified source, and the highest reading rate of the isotope was displayed digitally on the green screen face of the chamber. The Standard Geiger counter was provided, but our group never used it in the experiment. After finishing the search and identification of the radioactive material in laboratory #457, we started the same experiment in laboratory #430.
Results
In laboratory #457, using the radiation survey equipment provided, we found the first radiation source in the first drawer of a cabinet next to the bio-safety hood by the right side of the door. We identified the source as Cesium-137, with the highest reading of 0.7mR/hr. Cesium-137 is the unstable and most common radioactive form of Cesium. It is very useful in many industries. However, exposure to the byproducts of Cesium-137 can increase the risks of cancer. Cesium-137 has a half-life of 30.17 years (EPA, 2012). The 0.7mR/hr reading we detected was not hazardous because it was less than the occupational exposure limit of 2mR/hr.
We found the second radiation source in the second drawer of bench # 1 (Appendix 1). We identified the isotope as Cobalt-57, with the highest reading of 0.8mR/hrs. Cobalt-57 is a metal used in medical tests. It emits gamma and x-rays through ingestion, inhalation, or skin contamination, with the lung being the target organ. Cobalt-57 has a half-life of 170.9 days. If properly handled, Cobalt-57 does not pose any serious health risks.
In laboratory #430, using the same procedure and equipment, we found three more sources of radioactive materials. We found the first source in drawer 18 of a cabinet in the smaller room in the back of the laboratory. The source was identified as Barium-133 with the highest dose reading of 0.27mR/hr. Barium-133 decays by double electron capture with a half-life of 10.5 years (U.S. Department of Energy, n.d.). The second source of radiation was found in the freezer of a refrigerator on the back of the laboratory. We identified the source as Gadolinium-153 with the highest dose rate reading of 0.27mR/hr. Gadolinium-153 is a low-energy gamma-emitter with 240.4 half-lives (U.S Department of Energy, n.d.). We found the third radiation source with the highest reading of 0.69mR/hr in a cabinet by the right side of the laboratory door, but we were unable to identify it.
Discussion and Conclusion
Radiation has a wide range of energies and is usually divided into the following categories: ionizing and non-ionizing. Examples of non-ionizing radiation include visible lights and microwaves. Ionizing radiation is strong enough to tear the electrons that are tightly bound from their atoms. It is produced by unstable atoms to achieve a more stable state. Ionizing radiation can come from a natural source, including water and soil, or from medical devices such as X-ray. Radiation also has many useful applications, including cancer treatment, research, and others. However, the growing scope of ionizing radiation increases potential health risks, especially if not handled properly. This is why it was important to learn the basics of radiation detection from a hidden source and discuss its most essential characteristics. The results of this laboratory experiment provide valuable knowledge of radiation, its sources, and potential impacts on health.
Both groups of students, who participated in the experiment, were able to locate and identify all radioactive sources placed in the two laboratories. Because of the sensitivity of the instruments used and the small area covered by the experiment, all isotopes were easily located, except the Gadolinium-153 isotope. It was hidden in an unexpected location (freezer), but it was finally located. In laboratory #457 we found Cesium-137 with 0.8mR/hr dose rate and Cobalt-157 with 0.7mR/hr dose rate. In laboratory #430, we found Barium-137 isotope with a 2.8mR/hr dose rate and Gadolinium-153 isotope with 0.27mR/hr dose rate. We also found an unknown radiation source. Of all the values measured during the survey, none reached any potentially harmful levels.
References
EPA. (2012). Radiation: Non-ionizing and ionizing. Environmental Protection Agency. Web.
U.S. Department of Energy. (n.d.). Gadolinium-153. Isotopes Sciences Program. Web.
WHO. (2012). Ionizing radiation, health effects and protective measures. World Health Organization. Web.
Appendix 1
Identity of the isotope. Source #1: Cecium-137; source #2: Cobalt-57
Highest reading during survey: Cecium-137 = 0.8mr/hr; Cobalt-57 = 0.7mr/hr.
Appendix 2
Identity of the isotope. Source #1: Barium-133; Source #2: Gadolinium-153.
Highest reading during survey. Barium (Ba) = 2.8mr/hr; Gadolinium (Gd) = 0.27mr/hrs.