Project paper

ABSTRACT: Radiation detection field started to take place in radiation science after the discovery of X- rays by Roentgen and the discovery of radiation by Becquerel in 1895 and 1996, respectively. The first type of radiation detector was the ionization chamber. The ionization chamber has a simple operational principle and can be constructed using household materials. In this project, we are building an ionization chamber using a 9- voltage battery. Materials and Methods: Coffee can was used. A hole in the middle of the closed end of the can was made. Into this hole, a stripped electrical wire was inserted. The wire soldered with the base leg of the transistor. The collector leg of the transistor was connected to a 9V battery, and the resistor was connected to the negative terminal on the battery. The negative terminal of the battery was also connected to the input on the multimeter. The second input on the multimeter was connected to the emitter leg on the transistor. Finally, the opened side of the can was covered by the aluminum foil to prevent the excess of background ionization. Results: The ion chamber functioned as expected. It read approximately 0 V without the source and about 0.3-0.5 volt when it placed over the potassium chloride No Salt. INTRODUCION

Ionizing radiation is the type of radiation that can cause neutral atoms or molecules to produce either positive or negative electrical charges. Ionizing radiation has been found in nature (cosmic rays and naturally occurring radioactive materials) but was not well understood by man. Radioactive material emits different types of ionizing radiation; alpha, beta, gamma, X-ray, and neutrons. The kind of radiation emitted and the associated energy is dependent on the radioactive material. This energy can be

deposited partially or entirely in a medium and cause an ionization effect. The detection of ionizing radiation and its energy is based on the detection of the effects in the medium it interacted with (Flakus31).

The principle of detecting ionizing

radiation already existed since the 17th century, but the ionization caused by the ionizing radiation was not measurable in the past. The detection field started to develop dramatically in 1895 when Rontgen discovered x-rays. Rontgen, through his research into x-rays, discovered that x-rays could produce electrical conductivity when it passes through the air. Also, it has been discovered that there is a correlation between the emission of the x-rays and the emitted light (fluorescence). In 1986, Becquerel studied the connection between the emission of light and x-ray using highly fluorescent uranium (Flakus32). Through this experiment, Becquerel discovered radioactivity after he developed a photographic plate that was placed in a dark area with uranium. In 1899, J.J Thomson found that the charges produced when x-ray passes through the air could be collected by producing an electrical field. This was the time when the ionization chamber first used in radiation detection. Marie Curie used Thompson's discovery and repeated Becquerel's experiment using an ionization chamber and electrometer (Flakus32). She found that the intensity of the radiation detected is proportional to the amount of uranium used (Flakus32).

In 1908, a cylindrical electrical

counter was described by Rutherford and Geiger for alpha particle measurement; this counter was improved in 1912 to a spherical counter. In 1913, a beta particle counter was developed. Geiger and Muller worked on developing a gas-filled detector that can measure single radiation events in 1928,

which was then improved in 1930. In 1940, the gridded ionization chamber was designed by Frisch (Flakus34).

The ionization chamber operational principle is known to be the simplest of all gas-filled detectors. The ionization chamber consists of two electrodes: the positively charged electrode, the anode, and the negatively charged electrode, which is the cathode. In some ionization chambers, the outer wall of the chamber used as the cathode. The cathode usually has a cylindrical or spherical shape, while the anode has a rod shape (ORAU). As the radiation passes through the gas, the gas molecule excited and ionized due to interaction effects. When a particle hits a gas molecule, the outer shell electrons absorb a part or full of the energy of the incident particle — this ionization process results in creating ion pair, which consists of a positive ion and a free electron. For the ionization to happen, the incident particle must transfer energy that is at least equal to the ionization energy of the gas to free an electron (Knoll 131). The number of ion pairs created through this process is proportional to the amount of energy deposited in the gas. When a particle has an energy of 1 MeV and the full energy deposited in the gad molecule, this can result in 30,000 ion pairs. The ionization can occur directly when the electron absorbs a sufficient amount of energy from the incident particle or can occur indirectly when the electron absorbs only part of the energy of the incident particle, which only creates excitation. This excited electron then goes through another interaction and produce the ionization. When an external voltage applied to the electrical field, the free electrons accelerated toward the positive anode, and the positive ion accelerates toward the cathode. The accumulated electrons complete the cycle and recorded by the electronics,

Oscilloscope, which is used to observe the result (Knoll 131, 132).

Since Ionization chamber played an important role in radiation detection from the earliest use in the 18th century until today and because ionization chamber can be built with simple and cheap materials, in this project we will experience the ease of how to build an ionization chamber using a nine-volt battery and basic household materials. After building the ionization chamber, the function of the detector will be tested using radioactive material. MATERIALS AND METHODS

To build this ion chamber, we used a large metal cylindrical coffee can (Uline 12575 Uline Drive Pleasant Prairie, WI 53158, USA). This coffee can was used for the purpose of shielding the electronic parts to reduce the external electrical effects on the measurement. Since the inside of the can was covered with a plastic layer as it’s the case in most food tin cans, we had to remove this layer using fingernail polish because the inside of the can must be conductive. Aluminum foil also used to cover the open side of the can to prevent excess background ionization and makes it possible to detect the source. A tape was used to hold the aluminum foil into the can for proper sealing and to hold other parts such as a battery to prevent failing. A 4.7 kΩ resistor (KOA Speer Electronics, Inc. Mfr # MOS1CT528R472J) used to control the intensity of the current and reduces the current flow by 4.7 kΩ to prevent overheating or damage to the components. A Darlington Transistor (ON Semiconductors. NPN polarity. Mfr # BC517-D74Z. Phoenix, AZ, USA) was also used to amplify the electrical power signals. An analog multimeter (GMT-312. Gardner Bender Instruments. Milwaukee, WI USA) was used to measure the voltage, electric current, and

resistance of the produced signals. A soldering iron (Weller Standard Duty. 25 Watts. 750-degree Fahrenheit. Apex Tool Group LLC. 1000 Lufkin Road. Apex, NC 27539 USA) was used for soldering some of the electronic parts as required to establish the connections. An Electrical Repair Solder (Alpha Fry. Item # 51406. Cookson Electronics Assembly Materials, 109 Corporate Blvd. South Plainfield, NJ 07090 USA): this is a fusible metal that was used to help in connecting the electronic parts together. A wire (copper electrical wire. 22 gauge, no manufacturer details available) was used as the cathode. A 9V battery (Amazon Basics alkaline battery. 410 Terry Ave North, Seattle WA, 98109 USA) used to provide a power supply to the detector. Potassium chloride No Salt: sodium-free alternative (French’s. The French’s Food Company. 445 E. Mustard Way. Springfield, MO 65803-9416) used as a radiation source to ionize the air on the chamber.

For building the ion chamber, we

started with making about ¼ inch hole in the middle of the closed end of the coffee can. The Darlington transistor consists of three legs; collector, base, and emitter. We bend the collector and the emitter leg to face outward and make sure that the collector and the emitter leg do not touch the can. Then, we took a stripped of electrical wire (this should not be too long to avoid touching the aluminum foil) and soldered the end of the wire to the end of the base leg using the soldering iron to melt the electrical repair solder. The wire connected to the base leg of the transistor both work as the cathode; this part of the detector will collect the positive ions. The base leg and the wire inserted into the hole. At this point, we had to make sure that the wire does not touch the body of the can. If the wire touched the can, this would result in having a higher reading. Using another piece of wire, we soldered the

collector leg of the transistor to the negative terminal of the 9V battery. This step will provide the negative signal into the base and the wire. One side of the resistor was connected to the positive terminal of the 9V battery using a piece of a wire and the soldering materials. The other side of the resistor was soldered to the can; this will provide the positive signals to the can. The inside of the can work as the anode to collect the negative ions. The positive terminal of the 9V battery also connected to the multimeter into the voltage input terminal using a longer piece of wire and soldering materials. The last piece of wire was used to connect the emitter leg of the transistor to the common ground input terminal of the multimeter. The aluminum foil was used to cover the open side of the can using tape to make sure that we have proper sealing.

At this point, we had a complete

circuit starting from the battery, which creates a negative field on the can and a positive field on the central wire, which is connected to the base leg of the transistor. The negative charges on the can will move toward the cathode. The transistor will work on amplifying the electrical signal and transfer them to the multimeter. Figure1. Shows a simple electrical diagram to represent the setup of the components.

When the reading on the multi-meter

reads a background level, we were to test the function of the detector using the radiation source. The radiation source was placed near the aluminum foil side.

Figure 1. Electrical diagram. RESULTS

It takes three attempts to get the ion

chamber to function. This was due to having poor soldering techniques. We connected all the components, as seen in figures 2-6. After connecting the circuit, the multimeter reads approximately 0 with some fluctuations between 0.1 and 0.2, and when placed over five tablespoons of NUSALT, the multi- meter reads 0.3 to 0.5 volts.

Figure 3. Internal image of the can showing cathode.

Figure 4. External lateral view of the can showing battery and multi-meter.

Figure 2. Top of the can showing transistor and related connections.

Figure 5. Multi-meter background reading.

Figure 6. Multi-meter radioactive source reading.

CONCLUSION

The ionization chamber used in radiation detection since the 18th century. It is known to have a simple operational principle, and it consists of two electrodes; the positively charged electrode, the anode, and the negatively charged electrode, which is the cathode. This type of detector can be constructed easily using simple and cheap materials. In this paper, we built an ion chamber using a 9-volts battery, a large coffee can, aluminum foil, tape, a 4.7 kΩ resistor, a PNP Darlington Transistor, analog multimeter, soldering iron, an electrical repair solder, electrical wire and potassium chloride No Salt. We created a complete circuit using the listed materials. The ion chamber was able to read a background of about 0-0.2 volts. Also, it successfully functioned and read 0.3-0.5 volts when it was placed over the source. REFERENCES

1. BYU College. “How to Buil Your Own Radiation Detector.” PDF file. https://www.et.byu.edu/~mjm82/che4 12/Winter2020/Homework/Homewor k_24b.pdf.

2. Flakus, F. N. Detecting and Measuring Ionizing Radiation- A Short History / IAEA, VOL 23, No 4.

3. Ionization Chambers,

www.orau.org/ptp/collection/ioncha mber/ionizationchambers.htm.

4. Kirk. Make a Cheap and Effective

Radiation Detector (Ion Chamber), madscientisthut.com/wordpress/daily

-blog/easily-make-a-radiation- detector-ion-chamber/.

5. Knoll, Glenn F. Radiation Detection and Measurement / Glenn F. Knoll. Wiley, 2010.