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Homework 3

Type: Group

Title: Literature Review

Assigned: 10/02/14

Due: 10/09/14

1. Identify the types of information needed to be reviewed for a complete understanding of all aspects of the project.

2. For each information type listed in item 1 above, identify the sources you will need to use to obtain the information. This will also serve as a partial reference list for your project. Refer to how to list references in the Senior Project manual for the format for this section.

3. Using the sources identified in item 2, develop a well planned and exhaustive literature review for your project. Make sure you plan the details of the subsections for the literature review section of your project report as part of this assignment, and prepare the literature review report accordingly. References should be properly cited in the literature review, and a list of references provided.

Literature Review

Abstract

The information needed to be reviewed for all aspects of this project include identifying the characteristics of gamma radiation and what makes them detectable. Also there are multiple devices that can detect gamma, alpha, beta, and X radiation and many companies have their own high-tech designs to perform these specific tasks. Since there are time constraints involved in our project, I am looking for ways in which I can detect these forms of radiation in a practical and cost effective way. The device that will be designed will not be one that is too complicated to be completed by our deadline. There are multiple ways to create a simple device that can detect radioactive material. The goal is to understand the importance of explosive detection devices for security measures and to be able to design a device that could possibly do what the multiple high-tech devices can do without spending the same amount of money. It is also important to research and identify any flaws that the current detectors might have in order to find ways to improve them with our design. A possible solution to our design could be to possibly combine multiple practical applications into one fully functional design that meets our design criteria.

Literature 1: The Ionization Chamber

The first simple design found was the ionizing chamber. It could be modified to produce as stronger response, if combined with other elements such as a charge sensitive pre amplifier.

Ionizing chambers consist of two collecting electrodes, the anode and cathode (Oak Ridge 1). The anode is positively charged and the cathode is negatively charges. The outer chamber wall would serve as the cathode (Oak Ridge 1) . There will be a potential difference between the anode and cathode that varies because you can change certain things such as the size of the chamber itself, but it is usually in the 100 to 500v range. One of the physical characteristics of the chamber wall consists of a cylinder which serves as the outer cathode chamber with a rod shaped anode in the center (Oak Ridge 1). The biggest variable as seen in Figure 1 below is the shape of the cathode because there are different materials other than a cylinder that can serve as a cathode to change the potential difference range. When tested, the charged particles transverse the gas inside the chamber during the presence of radiation.

Figure 1: Pictures describing the variable shapes of an ionization chamber. The outer chamber cylindrical wall is the cathode and the anode it the rod in the middle. Other shapes could consist of a cylinder, cone or two parallel flat parallel plates as electrodes.

Literature 2: Characteristics of gamma radiation from the The Photo electric Effect, Compton scattering, and Pair Production

There are three major mechanisms describing how gamma rays interact with matter are the Photoelectric effect, Compton Scattering, and pair production (La Radioactive 1) . The effects are what allow you to be able to determine explosive materials from other organic or polymer materials that contain similar mass densities.

I. Photoelectric Effect

1. The most common form of interaction when the energy of gamma rays is the same order of magnitude as that of the energy binding atomic electrons to the nucleus defines the photoelectric effect (La Radioactive 1) . When this happens the gamma ray can eject and electron away from the atom, so it’s now sharing its energy between the electron and the atom that is excited.

II. Compton Effect

1. The Compton Effect describes gamma photons with higher energies, producing a collision between and incoming gamma ray and an electron (La Radioactive 1) . The photon and electron share the initial energy, which will gradually slow down by ionizing the atom around it.

III. Pair Production

1. A third effect comes into play once the energy of the gamma ray exceeds one million electronvolts (La Radioactive 1) . The photons will interact with a nucleus to produce an electron and positron. Gamma ray energy is transformed into matter with the strong electrical field acting as a catalyst.

Literature 3: The Scintillation Detector

This device uses a special material that glows as a result of radiation reacting with it. Sodium –iodine is the most common (EQUIPCO 1) . The light that is produced from the process of scintillation reflects through a clear window where it interacts with a photomultiplier tube. The first part of the photomultiplier tube consists of the photocathode which produces electrons as a result of light striking its surface (EQUIPCO 1) . As a result, these electrons will be pulled towards plates called dynodes from the application of a positive high voltage. As electrons coming from the photocathode hit the first dynode, the will be several electrons that will be produced for each initial electrons that hits its surface. The arrays of electrons are then pulled towards the next dynode, where there will be more electron multiplication that occurs (EQUIPCO 1). The process will continue until the last dynode is reached, resulting in an electron pulse that will be millions of times larger than it was at the beginning of the tube. Once the end stage is reach the electrons would have been collected by an anode at the end of the tube resulting in the formation of an electronic pulse (EQUIPCO 1). The instrument will detect and display that electronic pulse. Figure 2 below shows each component of the scintillation detector as described.

Figure 2: The block diagram shows the components of a basic radiation detector specifically a common Scintillation Detector as described in detail above.

Literature 4: Charge sensitive preamplifiers

If we are going design a simple, portable explosive detection device, some kind of amplifier will be needed in order to increase the signal intensity for measurement. Research has led me to a particular amplifier called the charge sensitive preamplifier. If an ionization chamber is chosen for our design similar to the one described earlier, this particular amplifier will be very useful when amplifying the current generated for the chamber.

1. When designing readout circuitry for pulse detectors, the charge sensitive preamplifiers are usually the best choice for performing this task. Offering low noise stability, their integrating nature provides and output that is proportional to the total charge flowing from the detector during the pulse event ( Cremat 1). These reasons make the preamplifiers useful in radiation detection applications, where individual detection pulses require measurement with high precision.

2. The fundamental charge sensitive preamplifier design in its most basic form is shown in figure 3 below. As you can see there is a feedback resistor that is between the input and output ( Cremat 1). The purpose of this resistor is to store charge from the detector and the gain of the preamplifier is equal to 1/Cf (Cremat 1). Each pulse of current from the detector will cause the output of the charge sensitive preamplifier to step, so the output is the integral of the detector current. For response to a detection event, the current from the detector may be collected quickly or slowly, but the charge sensitive allows for the final output to remain unaffected by the speed of the charge collection. The result is a response that will be unaffected by stray capacitance attached to the preamplifier (Cremat 1) Figure 3 below shows the circuit diagram just described and the equation showing that the voltage output is proportion to the detector current over time.

Figure3: Basic design of a charge sensitive preamplifier circuit.

Literature 5: What high tech devices are using today, and what is their most essential feature for identifying chemical explosives, radiation and other hazardous materials?

1. One device is the M908. It’s designed to provide the powerful detection capabilities of high-pressure mass spectrometry in a rugged, handheld form (908devices 1). The system selectivity focuses on some of the most critical compounds and extreme hazards in liquid, solid and vapor form without the noise and clutter of other low-threat background chemicals (908devices 1). This machine produces extremely low false alarm rates. It utilizes a well established analytical technique for measuring the mass of charged molecules called Mass spectrometry.

2. What is mass spectrometry?

· The art of measuring atoms and molecules to determine their molecular weight is defined as mass spectrometry. It’s commonly used for detection devices.

· There are four basic components that are considered standard in all spectrometers

1. Sample inlet

2. Ionization source

3. Mass analyzer

4. Ion detector

Some parts of the spectrometry are combined but regardless of the configuration, the molecules will undergo the same process (Scripps 1). When sample molecules are placed into the sample inlet, the sample molecules are converted to ions in the ionization source before they are electrostatically propelled into the mass analyzer (Scripps 1). This results in ions being separated according to their m/z within the mass analyzer. Finally the detector will then convert the ion energy in to electrical signals, which will be transmitted to a computer. This technique although widely used it also complicated to fully explain without extensive research on how useful it is when detecting molecules to determine their molecular weight (Scripps 1). One of the earliest challenges to mass spectrometry was sample introduction. Figure 4 below shows the components of the mass spectrometer as described.

Figure 4: Components of a mass spectrometer.

Summary

The information researched and presented in this literature review consists of both simple and practical applications for gamma radiation detection. A lot of the information that I found simply describes how radiation is detected and what systems can accomplish this task. The photomultiplier tube and the ionization chamber are both devices that are useful for understand the process of how to construct an explosive detection device of our own. Charge sensitive preamplifiers are used to detect small signals for amplification. Circuits like these and its modified versions are very useful for explosive and radiation detection devices. Moving from systems that can be implemented into our design, I reviewed some of the advanced explosive detection devices currently in use. One of them consists of the M908. It provides the powerful detection capabilities of high-pressure mass spectrometry in a rugged, handheld form. While trying to understand the circuit diagrams for the multiple gamma and explosive detection devices, my research consisted of information describing what properties make gamma, alpha, beta, and X radiation detectable.

Works Cited

"An Introduction to Ionization Chambers." An Introduction to Ionization Chambers. Oak Ridge

Associated Universities, 31 July 2009. Web. 28 Sept. 2014.

<https://www.orau.org/ptp/collection/ionchamber/introionizationchamberr.htm>.

"Gamma Rays In Matter." La Radioactive. La Radioactive, n.d. Web. 28 Sept. 2014.

<http%3A%2F%2Fwww.laradioactivite.com%2Fen%2Fsite%2Fpages%2FGamma_Matter.htm>

"Introduction to Radiation Detectors." Introduction to Radiation Detectors. EQUIPCO, n.d. Web. 28

Sept. 2014. <http://www.equipcoservices.com/support/tutorials/introduction-to-radiation-

monitors/>.

"Why Use Charge Sensitive Preamplifiers?" Why Use Charge Sensitive Preamplifiers? Cremat,

Inc, n.d. Web. 28 Sept. 2014. <http://www.cremat.com/Why_use_CSPs.htm>.

"Explosive Detection - 908 Devices." 908 Devices Explosive Detection Comments. 908devices,

n.d. Web. 28 Sept. 2014. <http://www.908devices.com/applications/explosive-

detection/>.

"Scripps Center for Metabolomics and Mass Spectrometry - Mass Spec History." Scripps Center

for Metabolomics and Mass Spectrometry - Mass Spec History. Scripps Center for

Metabolomics, n.d. Web. 28 Sept. 2014.

<http://masspec.scripps.edu/mshistory/whatisms_details.php#Basics>.

Ionizing chamber for gamma ray detection

Photomultiplier for gamma ray detection

Spear detector for gamma ray detection