Cosmic ray reduction through Delrin and gelatin shielding

Research Group: Carla Calderon, Taylor Olp, and Laura Wells

Launch: Whitworth Spring 2019

''The goal of our project was to test the shielding ability of the Gelatin and Delrin shields against cosmic rays in Near Space. We made gelatin with Know gelatin mix at a lower water concentration to replicate ballistic gel. We originally planned for 2 Geiger counters, one for Delrin and one for gelatin shielding but due to weight restrictions, we only sent the gelatin shielded Geiger counter. Unfortunately, the shielding properties of gelatin against cosmic rays were inconclusive because an electrical problem occurred before launch so no data was recorded.''

Background
Radiation is usually thought of as radioactive elements like uranium, x-ray machines, and in appliances like microwaves. All these radioactive sources are composed of Alpha, Beta, Gamma, or electromagnetic rays, among other types of radiation. In space, radiation is at another level of power and intensity. Radiation found in Near Space is comprised of highly energized particles: atoms that have been stripped of electrons and move near the speed of light. Because these cosmic rays are so highly energized they easily pass through materials. Cosmic rays are one of the most damaging types of space radiation because they are primarily protons. It is hypothesized that there will be contact with one of these types of space radiation sources, all of which produce ionizing radiation. These cosmic rays will ionize atoms easily because they knock the electrons out of them at high speeds.

To prevent this electron stripping, shielding for cosmic radiation is being researched and developed. So far, shielding has been most successful when utilizing hydrogen-based materials and magnetic fields. Hydrogen is a one proton/electron element. For this reason, hydrogen better shields against the single protons from cosmic rays. Materials that have large quantities of hydrogen are being researched and considered as shielding agents for the protection of astronauts, space stations, etc.

Hydrogen-rich plastics have been tested for their cosmic ray shielding properties and have proven to be some of the best shielding agents (since 2010). Polyethylene, a heavily hydrogenated plastic, has shown to be particularly effective. Recently, NASA has found that hydrogen/carbon material plastics are efficient and effective for shielding purposes. The association developed a polyethylene based material called RXF1. Interestingly, polyethylene is found in most commonly used plastics (used in trash bags). The RXF1 material itself is challenging to obtain due to the fact that NASA is currently testing with the newly created medium. Considering the possibility of working with this material in the future, a shield may be created through the use of laser cutting and epoxy. In our near space research, 3D printed plastics, such as Delrin, are being considered.

In comparison, Lead has shown to be a good shielding material for Alpha, Beta, and Gamma radiation. However, these types of rays are not cosmic radiation, so it is completely possible that lead may not be a good shield for cosmic rays. This can be seen in previous experiments when Delrin was used. It was shown that Delrin, a lighter material, shielded better than Lead because it received fewer counts when tested in near space. These results could be due to the fact that cosmic radiation ricochets off the lead and is counted again rather than being absorbed. So lead may have received more secondary counts because the energy was not dissipated. Theoretically, Gelatin may be able to shield from cosmic radiation because of its overall structure. Gelatin is a chemical compound of peptides and proteins. Gelatin is made of protein from partial hydrolysis of collagen. Collagen is taken from skin, bones, and connective tissues of animals. Chemically speaking, gelatin consists of carbon, nitrogen, oxygen, and hydrogen. Because it is so rich in hydrogen it is potentially successful shielding material. The half inch gelatin shield created during our research showed promising results against a Strontium radiation source during testing. (Note that Strontium emits a lower level and a different type of radiation compared to cosmic rays). Interestingly, the gelatin shielded better than Delrin plastic. It was hypothesized that when the neutron radiation came into contact with the nucleus of the molecules within the Gelatin, the energy would be absorbed because the nuclei are similar in size, thus the particle would not just bounce off nor lose energy.

In terms of near space, it was predicted that as the balloon rose higher in altitude, the more radiation the pod would come into contact with. This is phenomena occurs because the atmosphere itself is a great cosmic ray shield. The atmosphere protects humans and the environment; however, as we rise in altitude, the atmosphere dissipates, and higher amounts of cosmic radiation are encountered.

Mechanical Design
In the original design of the pod, two shielded Geiger counters and electrical components were incorporated. The motherboard needed to be securely attached to the box, taking up as little space as possible in the box. The next part of the mechanical design was securing the Delrin box and gelatin mold without holding them down beyond removal and not destroying the gelatin. It was not logical to try and strap the gelatin mold in with zip ties because it would just rip the gelatin and destroy the shield. The Delrin and Gelatin shielded Geiger counters were secured to each opposite walls with wooden sticks between 2 foam pieces, creating tension. This method secured the gelatin and Delrin at the same time, eliminating the need for any straps.

In order to maximize space in the box, the breadboard was set into the lid of the box with a border of foam around it to maintain the tightness of the lid. The breadboard was the perfect size to set into the lid and maximize the inside space of the box. In order to make a square hole for the breadboard, the outside foam square of the lid was separated from the inner foam square and the square was cut into four strips. Four screw size holes were drilled into the outside square to secure the breadboard to the foam. Once the holes were made the breadboard was secured to the outside square, with a small cut out into the square for the battery underneath the wiring. The four remaining foam strips were epoxy glued around the breadboard frame. This design allowed the breadboard to be easily removed from the top foam for recharging or fixing, reusing the unnecessary foam of the lid, and kept the motherboard safely secured without the need for a large number of attachments.

A Delrin plastic box had already been created and designed from the previous Near Space group. The Delrin box, however, was held together by duct tape, so the tape was removed and the box was reinforced with epoxy. This gave the box a more sturdy design and made the box more simple. Unfortunately, in the end, the Delrin shielded Geiger counter was removed from the experiment because of weight restrictions. The pod was adjusted for only one Geiger counter with Gelatin shielding before launch.

Gelatin Mold
The gelatin mold completely surrounded the Geiger counter. The mold for the gelatin was designed with 1/2-inch of space around each side of the Geiger counter so the gelatin shield would be 1/2-inch thick. The decision to use this measurement of Gelatin came from the overall weight of the box needing to be as close to 2 pounds as possible, and anything thicker than 1/2 inch would weigh too much.

To start, Knox Gelatin (found at most grocery stores) was used to create the ballistic type gel. One gallon of water for every 13 ounces of Gelatin mix (about a 10% concentration) is required. The liquid gelatin was poured into the mold in 2 separate layers. The first layer was 1/2 inch thickness covering the bottom of the mold to solidify first.

The gelatin mold started off with a foam mold that was modeled after the exact size of the Geiger counter, this would be placed in the gelatin for it to take the shape of a Geiger counter. Then we created another mold that would give 1 inch of space around the Geiger counter mold which the gelatin will be poured into. This mold of 1 inch was made before the thickness of gelatin needed to be reduced so we decided to cut the gelatin instead of remaking the mold. After the creation of both molds, the base layer of gelatin was poured into the large mold to get a layer at the bottom of about 1 inch, which was then refrigerated to take form slightly before the next layer was poured. This is the point where the Geiger counter mold was placed over the first layer and then secured with a stick through the center, in order to minimize movement of the Geiger counter mold. Then the gelatin was poured into the mold until it was 1 inch over the top of the Geiger counter so that at this point, there is 1 inch of gelatin around the Geiger counter mold at every point. Then the molds were placed in the fridge for 1 week.

After the Gelatin mold was removed from the fridge, it needed to be trimmed in order to fit the pod. Each side of the gelatin mold was trimmed to 1/2 inch. Then the actual Geiger counter was wrapped in saran wrap and then placed in the mold. The entire gelatin mold was wrapped in saran wrap to keep the shield together. Finally, a small hole was cut into the side of the gelatin mold to wire to the Geiger counter to the motherboard.

Electrical Design

 * SD and mbed were previously wired to the circuit board and already laid in place.
 * Our team arranged the wiring for two gieger counters.
 * geigerJello: radiation hits through gelatin shielding
 * geigerDelrin: radiation hits through delrin shielding

Code
Here is link to the code.

Validation and Calibration
Geiger counters were calibrated and validated through the use of Strontium as a radiation source and code similar to the code above(previous segment). Two Geiger counters were individually tested first without shielding, then again with either Delrin or gelatin shielding. Both Geiger counters worked effectively although one Geiger counter was slightly more sensitive than the other. Additionally, Delrin and Gelatin shielding proved to be successful shielding agents for the beta-rays emitted from the Strontium radiation source.

Validation data:

Note:
 * front face of Geiger counter was x distance from Strontium radiation source

Data and Analysis
When we recovered the pod after launch, the SD card showed that no data was collected during the launch and flight. This was because the signal wire broke before the balloon launch from the connection For the data analysis of our experiment, we had an unfortunate incident with our pod. After removing the top of the pod too many times, there was a wire that was not pliable enough, so after time and repeated bending, the signal wire for our Geiger counter snapped. Unfortunately, we had no knowledge that this happened. When we did testing the night before, data was collected, which leads us to believe that it happened during launch day. Overall, something that can be improved on our design, and all designs in the future, is to use less rigid wires.

Linear attenuation coefficient of Delrin
Since we did not have any data from the flight, we decided to Linear attenuation value of 2.71565 ± 1.05804

To find the linear attenuation coefficient we used the following equation: ln(IB)= ln(IA) - μx
 * μ = Linear Attenuation Coefficient of Delrin
 * x = thickness of the material
 * IB= the shielded dose rate
 * IA= the initial dose rate

This equation is in a slope-intercept form so graphing the natural log of counts per minute with the natural log of the thickness of the material.

Conclusion
In conclusion, it is hard to know whether the gelatin is an effective shield for cosmic rays; however, the unexpected weight of gelatin is a deterrent for using the gelatin. It may have performed well against the strontium compared to the delrin, but it is not efficient for the lightweight pod style. So, for future research, to make it easier and scientific while picking a material, we included the linear attenuation values of Delrin, and how they were acquired. By including this data we hope that group in the future that choose to do this similar experiment, they are able to pick a better material by testing the effectiveness of the shielding material, can retrieve better results from the experiment, and contribute to scientific research.

References/Works Cited

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 * https://www.nasa.gov/feature/goddard/real-martians-how-to-protect-astronauts-from-space-radiation-on-mars
 * https://www.cnet.com/news/appliance-science-the-firm-chemistry-of-gelatin/
 * https://www.nasa.gov/pdf/284275main_Radiation_HS_Mod3.pdf
 * https://www.nasa.gov/audience/foreducators/postsecondary/features/F_Understanding_Space_Radiation.html
 * https://web.archive.org/web/20100323201842/http://science.nasa.gov/headlines/y2005/25aug_plasticspaceships.htm
 * https://pslc.ws/macrog/pe.htm