Radioactivity: The Invisible Pest
William Zhou
Britannia Secondary
Floor Location : S 181 P

Radioactivity is the release of energy and particles from the nucleus, making it more stable. The radiation consists of three main forms: alpha and beta particles, and gamma rays. Alpha particles are charged helium nuclei (emitted commonly from large nuclei), beta particles are energetic electrons (emitted primarily from neutron-rich nuclei) and gamma rays consist of high-wavelength, high energy electromagnetic waves (emitted from energetic nuclei). All three radiations lose energy by ionization, harming humans because ionization can damage chemical bonds in DNA and induce mutations such as cancer. Therefore, radiation must be blocked before reaching humans.rnrnFrom my experiment, I wish to find a correlation between cross-sectional mass (CSM, mass divided by surface area). I hypothesize that larger CSM will weaken radiation, and that chemical composition of the materials will not affect the stopping power. All materials have about the same amount of electrons per unit mass, making the probability of energy loss by ionization similar. Also, I used CSM because radiation penetrates the surface area of a material.rnrnI conducted my experiments at TRIUMF, organized by Dr. Marcello Pavan. For this experiment, I used the alpha source Americium-241, beta source Strontium-90, and gamma source Cesium-137. Also, I amassed many materials of different CSMs and chemical compositions, ranging from thin cloth to lead sheets. I used a zinc sulphide detector for alpha, Geiger counter for beta, and sodium iodide for gamma radiation. During the experiments, I used a personal radiation dosimeter and nitrile gloves when handling the radioisotopes.rnrnThe results of my experiment partially supported my hypothesis, and the particle radiations differed greatly from the electromagnetic radiation. The materials showed no significant difference in stopping power of the alpha and beta radiations, because the data followed a smooth decreasing exponential curve when plotted by CSM vs. amount of radiation penetrated. However, materials with larger CSMs didn't increase stopping power, because all effective radiation has been blocked. Gamma radiation behaved very differently. The chemical composition significantly affected the stopping power of the material, and materials with high nuclear charges (such as lead, +82) stopped radiation more efficiently. I think that these higher nuclear charges hold electrons more tightly, and those electrons will then require more energy to remove. Also, radiation penetration decreased with larger CSM for the same material. However, I did not find a CSM range when radiation completely disappeared with my materials, because the penetration of gamma rays is very high.rnrnMy project found several interesting implications. Firstly, staying indoors during radiation disasters can minimize the amount of exposure, because building materials can block out all alpha and beta radiation, and are effective at blocking gamma radiation. Alpha radiation does most damage to human internal organs. Masks can protect against all effective alpha radiation, wearing them in environments with airborne radiation can protect internal organs from damage. In addition, building radiation shelters under water or ice may be wise, since water and ice are easily and cheaply acquired in the environment, as well as having large cross-sectional areas.