Build a simple ionization chamber that is capable of detecting fairly low levels of radiation
BACKGROUND OF THE STUDY
Radon is a cancer-causing gas. It comes from the natural breakdown of uranium in soil, rock and water and gets into the air you breathe. These radioactive materials “decay” into lighter elements, emitting energetic sub-atomic particles in the process, and one of those lighter elements is Radon. Since radon is a noble gas, it is chemically inert and doesn’t stay bound in the solid the way it’s parent did. It diffuses right through solids and ends up floating freely in the air. Being a noble gas, radon is fairly harmless, itself. You breathe in some radon with every breath but then you breathe it right back out, since it isn’t chemically active or electrically charged. But radon has a short half-life of only about four days, meaning that about half of it will decay within four days, producing new, even lighter radioactive isotopes of other elements like polonium, lead, and bismuth.
Those isotopes keep decaying, until a stable isotope of lead is reached. These radon “daughters” are not noble gasses like radon, they are usually ionized when they are produced, and they will readily stick to anything nearby, like healthy lung tissue. They typically have an even shorter half-life than radon and quickly decay inside the lung, kicking out energetic alpha and beta particles that can cause tissue damage and potentially trigger lung cancer. This unfortunate chain of events is due to the decay chain including a noble gas. Radon gas is considered to be the second leading cause of lung cancer. It can get into any type of building — homes, offices, and schools — and result in a high indoor radon level.
But, we are most likely to get your greatest exposure at home, where we spend most of our time. It typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation. Any home traps radon inside, where it can build up. Any home may have a radon problem. This means new and old homes, well-sealed and drafty homes, and homes with or without basements. These are examples where you can find the noble gas:
1. Cracks in solid floors
2. Construction Joints
3. Cracks in walls
4. Gaps in suspended floors
5. Water supply
It breaks down into solid radioactive elements called radon progeny. Radon progeny can attach to dust and other particles and can be breathed into the lungs. As radon and radon progeny in the air break down, they give off alpha particles, a form of high-energy radiation that can damage our health. Radon daughters will stick to just about anything they encounter, so they are easily collected by drawing air through a dusting cloth with an ordinary fan. After collecting the daughters for about an hour or two, the radiation being emitted from the cloth due to the further decay of the collected radioactive isotopes can be measured with a simple ionization chamber made from an empty coffee can, a single Darlington transistor, and a digital voltmeter.
The deceivingly simple ion chamber is quite sensitive and can detect radon daughters in buildings with radon concentrations below the “action level” recommended by health authorities. A simple ionization chamber is nothing more than a metal can with a wire inside. When a radioactive particle passes through the air in the chamber, many of the molecules of air are ionized, having electrons knocked loose from the outer atomic shells. Applying a positive voltage on the outer can relative to the internal wire, causes these ions to be attracted to the wire and the free electrons to be attracted to the interior wall of the can. This movement of charge is a tiny current that may be amplified to detect the rate at which ions are being generated, and thereby the rate that radioactive particles are passing through the can. The chamber will be detecting mostly beta particles.
BACKGROUND OF THE STUDY
Copper is an essential element for all known living organisms, including humans. You need a small amount of copper in your diet to stay healthy. On average, most people will eat and drink about 1,000 micrograms ( μg) of copper per day—drinking water normally contributes approximately 150 μg per day. Levels of copper found naturally in ground water and surface water are typically very low—about 4 μg of copper in one liter (L) of water or less—however, drinking water may contain higher levels of copper, usually as a result of flowing through copper pipes. High levels of copper can occur if water that is corrosive comes in contact with copper plumbing and copper-containing fixtures. Many factors can make water corrosive for copper pipes: dissolved salts and minerals, bacteria, and suspended solids, such as sand, sediment, and rust. The level of copper in drinking water increases with the corrosivity of the water and the length of time it remains in contact with the plumbing.
If the copper level gets too high, the water may have a metallic taste and you might notice blue or blue-green stains around sinks and plumbing fixtures. It will be highest in the morning because the water will have been exposed to the pipes overnight. If you are being served by a public water system, the owner of the utility will have results of copper sampling, which is a process that has been done in parts of the water-distribution system. In this chemistry science fair project, you will investigate another possible factor in making water corrosive for copper — the pH of the water. You will test the theory that acidic water is more corrosive for copper pipes than non-acidic water.
In the procedure, dingy copper pennies will be placed in either plain water or in water with acetic acid (vinegar). You may know that newly minted pennies have bright, shinny copper but over time the copper and air react and the pennies build up a layer of copper oxide on them. The copper oxide is the dull, dark coloration on well-used pennies. In this experiment, if the water is corrosive enough to strip off the copper oxide then you will see the progress of the reaction by watching the pennies go from dull and dingy to bright and shiny. The pennies get shiny because the copper oxide is being stripped off by a reaction, which results in increasing levels of copper in the liquid. Unfortunately, water that is corrosive slowly eats away at the pure copper, as well as at the copper oxide.
For houses with corrosive water systems, this can result in elevated levels of copper in the drinking water. On a purely practical level, houses with corrosive water systems might find that their copper pipes are springing leaks, and that the whole house needs to be re-piped with plastic pipes! To measure the amount of copper present in the solutions that are used to clean the pennies, you will perform a color-based chemical test. The chemicals for the test are contained in a small tablet, which is dissolved in water. When the tablet is dissolved, the solution turns reddish-orange. If no copper (or very small amounts of copper) is present, the solution remains reddish-orange. If copper is present, the solution will turn blue.