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Published on May 25, 2017

Build a Radiation Geiger Counter


Abstract

The objective: Why don’t we have radiation monitors in our homes. Exposure to radiation can cause cancer. Some other common examples of items that contain low levels of radiation are smoke detectors, antique pottery, radon gas from the ground and rocks. Building a Geiger counter was my project to prove that a simple Geiger counter can be made so it could detect radiation. The hypothesis is that a Geiger counter can be built and the accuracy of the measurement was comparable to a commercially available unit.

Research

Radioactivity refers to the particles which are emitted from the nuclei as a result of nuclear instability. Because the nucleus experiences the intense conflict between the two strongest forces in nature, there are many nuclear isotopes which are unstable and emit some kind of radiation. The most common types of radiation are called alpha, beta, and gamma radiation, but there are several other varieties of radioactive decay. It is the emission of energy through electromagnetic waves or as moving subatomic particles.

In every day houses, it is standard to own a thermostat, and a fire alarm. Why don’t we have radiation checkers in our houses? It could be life-saving just like a fire alarm. Exposure to radiation can cause the electrons in our body to be removed from atoms. The harm of this process can be too much for the body to handle, so it is important to take precautions. Some other common examples of items that contain low levels of radiation are smoke detectors, glow in the dark watches, and rocks. Because of these dangers, a Geiger counter was created so that we could acquire data, and detect danger.

A Geiger counter is a radiation sensor, designed to measure the radiation level in cpm (counts per minute.) With the installation of a mica window, it allows the sensor to measure all the types of radiation. The Geiger–Müller tube is a gaseous ionization detector and uses the Townsend avalanche phenomenon to produce an easily detectable electronic pulse from as little as a single ionizing event due to a radiation particle. It is used for the detection of gamma radiation, X-Rays, and alpha and beta particles. The tube operates in the "Geiger" region of ion pair generation. In simpler terms, the Geiger counter works by having a mixture of gases that surround a central electrode. Voltage is applied, creating an electric field that charges particles that pass through. The particles then collide, producing a wave of electrons. This wave can be registered through the Geiger counter in counts per minute (cpm).

I would like to thank Mr. Conrad Knauer for allowing me to test my Geiger counter along side his Geiger counter and use his vast collection of radioactive materials as the radioactive samples. I would also like to thank my Father for giving me advice and providing materials for building this instrument.

Purpose

Can a Geiger counter be built inexpensively and get similar results to a commercially manufactured Geiger counter?

Hypothesis

The Geiger counter will be successfully made and get similar results as a commercially made Geiger counter. If the Geiger counter circuit works, then the performance can be compared to a commercial unit.

Constants and Variables

Constants: The commercial Geiger counter is the constant that the performance of the home made unit is judged against.

Independent Variable: is the objects that have radiation. The test samples used: Old watch, camera lens, smoke detector, tea pot, Coleman gas mantle, Thorite crystals, Potassium water softener, and several pieces of Uranium glass.

Dependent Variable: is the data collected (counts per minute) which represent the amount of radiation present from the samples.

Build a Radiation Geiger

Control Group

I am comparing the results of my Geiger counter to a commercially made Geiger counter. If the results are similar, then the experiment is a success.

Whilst it is a robust and inexpensive detector, it is unable to measure high radiation rates efficiently, has a finite life in high radiation areas and is unable to measure incident radiation energy, so no spectral information can be generated and there is no discrimination between radiation types.

Procedure

I used the following procedure in chronological order to complete my test:

1. Research different Geiger counter designs. By looking at different designs of Geiger counters, it allows me to choose the best circuits for this project.

2. Choose the best characteristics of each design of each circuit. Then draw the circuit into a schematic diagram.

3. Obtain the parts needed. Purchase some components that are needed.

4. Build the circuits by building it on a prototype board.

5. Test each circuit for correct operation and document results.

6. Confirm unit is working.

7. Optimize high voltage level for GM tube.

8. Take readings of the different objects to ensure an accurate result.

9. Compare the data between the commercial unit and home built. By using Excel spreadsheet program compare and chart the results in a graphical form.

10. Document the results.

Observations

Before testing out the items with my home-built Geiger counter, I had to calibrate the voltage I was going to use. I tested each high voltage and recorded the number of clicks heard for one minute.. I chose 600 as the high voltage level because it’s in the middle of the plateau between no counts and the region with many counts of self-arcing. The reason for doing this is to optimize the best high voltage for optimum operation.

Build a Radiation Geiger

To get a baseline of radiation, numerous items in the home were used to measure the radiation levels. These were deemed to be safe to humans. The following chart shows the range of radiation emitted from the materials.

The Uranium oxide Tea pot had very high radiation levels along with the Fiesta Ware plate. These materials are not used currently because of concern for unhealthy radioactivity, so the range of radiation emitted range from 30 to 10,000 counts per minute.

Conclusion

From the results of the tests, the design and building of the Geiger counter was successful. The comparison of the measured radiation levels using a commercially available Geiger counter was the same as the home built Geiger counter. Although the numbers were off by a few percentage points I think there were two reasons for this. One, the time of measurement was different for each counter.

The homemade Geiger counter was counting every second, while the commercial made one displayed the average every minute. Secondly, the parts were made in different areas of the world so it could have had an impact on the construction of the Geiger Muller Tube. By getting similar results and testing it with a variety of safe radioactive materials. I can confirm that the hypothesis is true. The cost of building the Geiger counter was $28 which is quite reasonable considering commercial units sell for $150-$1000.

Bibliography

• Armentrout, Patricia. The Pulley. Vero beach, FL:Rourke, 1997

• http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/radact.html

• http://en.wikipedia.org/wiki/Geiger%E2%80%93M%C3%BCller_tube

Science Fair Project done By Dennis Lee

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