Variation of cosmic ray detection with shielding material

Research Group: Andrew Brown, Ishan Gauli, and Jarin Manuel

Launch: Whitworth Spring 2017

''The goal of our experiment was to see how lead shielding effects cosmic radiation counts as a Ginger counter gains altitude. We also added on to past group's projects by sending a pressure sensor with the pod in order to see how cosmic radiation counts change related to atmospheric pressure. By establishing the effects of lead shielding on cosmic radiation we hoped to aid future groups in obtaining accurate counts of cosmic radiation efficiently and without the noise of secondary radiation. Unfortunately, the project ran into some mechanical issues and the pod returned without any useful data.''

Background
In 1912, an Austrian Physicist, Victor Hess, discovered a phenomenon with radiation, coining the term: Cosmic Rays. By using an electroscope, an instrument used to measure electric charge, Hess conducted an experiment in a hot-air balloon during a solar eclipse. He found that the electroscope would set off more and more as his altitude increased, and concluded that the radiation ultimately could not be only from the sun, but somewhere beyond it. In 1936 he shared the Nobel Prize.

Cosmic rays are high-energy particles that originate from beyond Earth's atmosphere. About 89-90% of all cosmic rays are protons. They consist mainly of 3 types of cosmic rays: galactic, anomalous, and solar. Galactic cosmic rays tend to be on the higher end of energy and can travel long distances coming from phenomenon such as supernovas, while solar cosmic rays are lower and originate from solar flares/releases of plasma. Anomalous cosmic rays fall in-between the two in terms of energy consisting of colliding ions. As cosmic rays approach the Earth's atmosphere, they go through spallation, and only the heaviest and those with the highest energy hit the surface. We classify those outside of the atmosphere as primary cosmic rays, and those that break off within the atmosphere as secondary. As the balloon gets higher and higher, we expect to receive more and more counts from the secondary cosmic rays since radiation will increase the closer we get to the atmosphere and outer space.

Along with our project, we want to see the difference shielding makes in receiving radiation. We have two Geiger counters that both take in counts of radiation. One is unaffected while the other is totally shielded in lead. As the balloon and the pod get higher, we expect the shielded counter to receive less counts than the unshielded one because less energy will be able to pass through. As we measure the radiation counts, we also will create a more accurate graph of the behavior of cosmic rays. Most graphs only have altitude by number of counts, while we want to also include altitude and see if it changes the shape of the graph.

Mechanical Design
In order to accurately measure the effects of shielding and atmospheric pressure on cosmic radiation, we made use of two Geiger counters, lead plating, an MBED microprocessor, a pressure gauge, and a microchip. One Geiger counter was covered on all sides with lead shielding, using duct tape, and the other was left bare as a control. The Geiger counters were zip tied directly on to the pod. In order to power our pod we used a 7V battery pack. Both the battery pack and the MBED were zip tied to a thin board which was then bolted on to the pod. The Geiger counters were connected to the MBED using telephone wire and the pressure gauge and the microchip were connected directly to the MBED.

To ensure accurate comparison of radiation counts we needed to avoid three problems. First, we did not want the control Geiger counter to give us false counts caused by high energy radiation running into the shielded counter and breaking up into smaller particles still energetic enough to be counted by the control counter. Second, we did not want the shielded counter to block low energy particles from running into the control counter. Third, we did not want the counters to share counts as they encountered high energy radiation capable of traveling through both counters. In order to minimize the chances of these three events occurring we set the counters in the box so that the angle of coincidence between the two counters was as low as possible (Fig 1).

In order to allow the pressure in the box to change with the atmospheric pressure we chose a box with a number of small holes and a larger hole on the wall. We added another large hole on the wall opposite of the first large hole (Fig 2).

Electrical Design


(We are not 100% sure the mbed was working properly when we took this reading)
 * 7V power pack (4 1.5 volt cells)


 * 3500 mAh capacity


 * Approximately 8mA current draw


 * 437.5 hr run time

Overall, our design was pretty good. We were able to keep everything on one breadboard, including two sensors, and cables for two Geiger counters. Also, by using jumper cables instead of the longer, more bendable connections, we were able to keep everything tidy and close to the board. We also went ran analog inputs at every instance using I2C. However, adversely to nice wire placement, we had some faulty wires. We decided to use a battery pack (4 AA batteries) and phone cables that were most likely used in a previous group's project. It seemed to run flawlessly when we tested, however, after the experiment, we found that twisting/pushing the wires a certain way would cause the MBED to turn off. Also, since our first launch was unsuccessful and the pod was taken apart, we were not able to be as cautious putting the pod back together and securing the systems within as well. Possibly choosing to have a custom fritzing board instead of the whole MBED with a superfluous amount of wires would help reduce confusion and displacement of connections. Instead of assuming, actually making sure the wires and MBED work properly together is extremely important to the whole process and for reliability in future experiments.

Code
The code is written in C++ and is used to count the number of radiation counts that hit each of the GM counters at a particular altitude and pressure. The two GM counters were routed to pin 23 and 24, pins 5 through 8 were used for SD card and pins 28 and 29 were used for I2C communication with the MPL3115A2.

Program Flow

 * 1) Signal inputs into pin 23 and 24
 * 2) InterruptIn increments a variable that stores the number of counts for each GM counter.
 * 3) Stores the data for every minute worth of counts.
 * 4) Takes the existing count data, stores it and clears the variable.
 * 5) Timer periodically flushes data onto the SD card.
 * 6) Return to Step Two and repeat.

Validation and Calibration


The first step we took to find how cosmic radiation is effected by shielding was to confirm that our Geiger counters were working. We accomplished this by letting each Geiger counter run for at least five minutes, outputting radiation counts every minute. The Geiger counters we used, when properly calibrated, count 20 to 23 radiation particles per minute. During testing our counters produced numbers very close to this range revealing that they were properly calibrated.

Our next step was to test different types of shielding with a radiation source to see which types of shielding would be most effective. Not surprisingly, lead was the most effective shield-er. Originally, we intended to shield with lead combined with a lighter type of shielding in order to block secondary radiation. Eventually we decided that this would add too much mass to our pot, but the testing data we collected (figure 5.) would have helped us to determine the best candidate for the second type of shielding.

We also had to calibrate the temperature sensor's offsets to zero, also since it was not a mBed direct library we had to redefine variables as signed so as to take negative temperature data. We also made sure that the pressure sensor part of the temperature sensor was working properly by placing the sensor in a vacuum chamber and making sure that the denser reacted to the change in pressure.

Data and Analysis
Due to unforeseen factors with regards to improper placement of wires/breaking wires, we were unable to recover any flight data. In our conclusion we will discuss these problems in greater detail and give some suggestions to avoid similar problems in the future.

Conclusion
Unfortunately, we were not able to receive any sort of data from our launch. Despite rigorous testing weeks prior to launch, we did not end up with any reliable data points. From post-flight diagnostics we came to the conclusion that there was a split in the ground wire from the battery pack to the mBed. Because of this the mBed was not able to reboot properly when the split reconnected and no data was received by the mbed.

Upon post flight analysis we believe that we also observed that the ground wire for Geiger counter #1 (shielded) slipped out of the ground bus and entered the hot bus. Had the Geiger counter been set up properly, we still might not have gotten useful data.

Overall, there are two things that led to our failure to collect data. The first is the split in the wire. For all practicality this was beyond our control, as there is nothing we could have done except buy all new equipment for our experiment or get lucky and find the flaw during testing. The other component to our failure was the ground wire in the wrong bus. This, most likely was caused by our failure to secure the wire properly before launch. This happened because we had two launches. In the first launch, the balloon failed. Because we were ready to go the first time, we were more causal about our preparation for the second launch. The result of our carelessness was a poorly connected ground wire.

For future experiments, this is what we advise. It is absolutely crucial to have everything properly tided down so that when the box is moved around or shaken vigorously everything stays properly connected. It is imperative to test the project beyond a shadow of a doubt. Therefore, do not hesitate to spend time running complete tests. It is also healthy to assume the worst case and conduct possible scenarios on the mBed. It is helpful to use in-code diagnostics like blinking leds or dancing leds. Use the lights to their full potential so that the mBed can communicate to you as many errors as possible. Although the following suggestions do not deal wit not our main problems, they may be helpful to consider: Our breadboard saved us in cost and may have saved us in weight, but it was also very busy, which may have caused some errors, so consider some alternative. Rebuilding the pod may also have been beneficial as it would have allowed us to place the Geiger counters at optimum angles of coincidence.

References/Works Cited
Information about types of cosmic radiation: https://home.cern/about/physics/cosmic-rays-particles-outer-space

Battery Capacity information: http://data.energizer.com/pdfs/l91.pdf

Understanding Shielding Materials 1: http://www.nuclear-power.net/nuclear-power/reactor-physics/atomic-nuclear-physics/radiation/shielding-of-ionizing-radiation/shielding-beta-radiation/

Understanding Shielding Materials 2: http://www.thomasnet.com/articles/custom-manufacturing-fabricating/radiation-shielding-materials

Other Background Information: https://helios.gsfc.nasa.gov/cosmic.html

Jarin's Highschool Research: erase these word words when you put your url in

Dr. Larkin