LinksPhotos The vacuum chamber. The motor is located at the bottom of the apparatus, the peeling tape is inside.  The apparatus: vacuum chamber at left, power supply at right, pressure gauges on top shelf VideosA video from the journal Nature highlighting research at UCLA into X-ray emission from sticky tape, which inspired this project. | Mid-Term ReportMuch progress has been made on this project regarding X-rays emitted from peeling sticky tape. Schematics for the design of the apparatus are now being implemented, and should soon be complete. In the meantime, Professor Hess and I have been experimenting on the electrostatic and radiological properties of peeling sticky tape. We designed the apparatus and obtained all of the necessary parts earlier in the semester. The first design had the motor that peels the tape as well as the tape itself inside the vacuum apparatus. However, Dr. Clark and Professor Smith, who are very familiar with vacuum chambers, advised us to place the motor outside of the vacuum chamber with a feed-through to unravel the tape inside the chamber. The reason for this precaution is that oil may leak from the motor and contaminate the vacuum, making it difficult to reach the goal pressure of 10-3 torr. We also obtained a Grainger gearmotor, which runs at 0.5 revolutions per minute and requires 12 VDC. From calculations based on the specifications of the motor and experimental data from the rolls of tape, we realize that the torque produced by the motor, 5.65 Nm, is much grater than that required to peel the tape, 0.0225 Nm. However, the motor may not be able to rotate quickly enough, as it only moves at 0.5 rpm. To produce a usable amount of X-rays, we may need to implement some mechanical gears to increase the angular velocity or perhaps even obtain a faster motor. The vacuum chamber itself will be a cylinder constructed of clear plastic, 5.5 inches in diameter and 4.9 inches in height. As mentioned earlier, we will pass a sealed driveshaft from the motor into the chamber to unwind the tape. A screw-top lid will allow the tape to be placed and replaced. We have also obtained and tested two vacuum pumps that allow us to reach a minimum pressure of 10-3 torr. Any experiments beyond this pressure will require more powerful equipment located at the Laboratory for Surface Science and Technology (LASST). Tom Tripp is currently fabricating the vacuum chamber, and should finish the chamber this week for testing. Our X-ray detector is a Reuters-Stokes xenon gas-filled proportional counter. It is more sensitive to X-ray radiation than a Geiger-Mueller counter. The detector operates at 12 kV and will be located outside of the vacuum chamber. The exact position of the detector is arbitrary, as the X-rays radiate outward from the tape. For calibration purposes, we must first test the detector with a known X-ray source. While Tom Tripp has been working on constructing the vacuum chamber, Professor Hess and I have conducted several mini-experiments on peeling tape. The first of these involved unrolling Scotch tape onto a plastic rod connected to a General Electric Electrostatic voltmeter. Rolling the tape by hand allowed us to obtain a maximum voltage of 11 kV. We also noticed a direct correlation between the electrostatic voltage and the speed at which the tape was peeled. This result suggests that we may need to implement a faster motor than our current model to obtain voltages required for X-ray emission. Another mini-experiment was conducted with the aim of further investigating the voltage produced by sticky tape peeling at atmospheric pressure. We wrapped Scotch tape around the anodes of several varieties of vacuum tubes, with the hopes that the voltage from the peeling would cause the vacuum tubes to become illuminated. These experiments were not successful, however, as not enough current was transferred to the tubes. However, when conducting the vacuum tube experiments in a darkened room, we were able to observe significant triboluminescence. White light was emitted from where the tape separated from the roll. The light became visibly brighter when the tape was peeled at a higher rate, again suggesting that we may need to obtain a faster motor for the final apparatus. Our next experiment attempted to create X-rays by peeling tape at atmospheric pressure with the use of an X-ray tube. The X-ray tube is similar to the vacuum tubes used earlier. When a voltage is applied to the vacuum tubes, they emit light of a certain color depending on the gas used in the tube. The X-ray tube simply emits light of the X-ray variety. The apparatus for this experiment consisted of the GE voltmeter, which has an aluminum bar connected to a plastic rod. The tape was unrolled from the plastic rod, and the positive wire was attached from the aluminum segment to the end of the X-ray tube with aluminum foil. A ground wire was soldered from the socket of the tube to the ground of the voltmeter. Any X-rays were measured with a Geiger counter. When we peeled the tape, the voltmeter read over 5 kV, but the detector did not show any counts above background; indicating that we were not producing X-rays. When the tape was switched to electrical tape we did see a small amount of radiation; 24.5 counts per ten seconds compared to a background of 15.0 counts per ten seconds. However, this amount of radiation is still quite small. We later repeated the experiment, with similar results. We tested the X-ray tube with a Welch sparkcoil and were able to obtain significant radiation. However, a possible reason for the lack of radiation from the X-ray tube is poor contact between the positive wire from the unrolling tape to the tube. Looking forward, the prognosis for this project is very good. The completion of the vacuum chamber after spring break will allow us to construct the apparatus and begin attempts to create significant amounts of X-rays at low pressure. The mini-experiments have afforded me a deeper understanding of electrostatic effects and X-ray emissions resulting from the peeling of sticky tape, and will allow us to complete a viable device to produce significant amounts of X-rays using this principle in the second half of the semester. Project DescriptionAn X-ray image taken in a hospital from a typical Bremsstrahlung apparatus costs hundreds of dollars to the patient. However, recent studies have demonstrated that one possible avenue towards achieving cheaper images could be by the unpeeling of sticky tape. While it has long been known that unpeeling sticky tape releases radiation in the form of visible light in a process known as triboluminescence,[1], and in 1953 it was discovered that peeling tape released X-rays [2], recent attempts have demonstrated the correlation between nanosecond, 100mW X-ray pulses and stick-slip peeling events in unrolling tape in a moderate vacuum. This triboluminescence extended to the X-ray region of the spectrum is described in the recent letter to Nature, “Correlation between nanosecond X-ray flashes and stick-slip friction in peeling tape” by Camara, Escobar, Hird and Putterman of the University of California, Los Angeles [3]. The letter demonstrates that X-rays can be produced at a moderate vacuum of 10-3 torr with energies of 15 keV, strong enough to produce crude images. This project hopes to harness this effect to create an effective and economical X-ray imaging device. The apparatus consists of a variable 12 Volt DC motor used to peel a typical roll of sticky tape. The tape roll nests on a stationary spindle while the end to be unrolled attaches around the rotating spindle of the motor. A 4.9 inch tall, 5.5 inch diameter clear plastic cylinder contains the entire tape-motor assembly. A vacuum pump creates the low-pressure environment of at most 10-3 torr required for the release of high-energy X-rays. The wiring for the motor exits the cylinder via a sealed conduit. To detect any emitted X-rays we utilize a Xenon gas Reuter-Stokes proportional counter. The detector utilizes a pre-amp and amplifier and a 3000V power supply. The immediate goal of this project is to construct a functioning X-ray emitting device and test the proportional counter on existing X-ray sources. After construction of the apparatus and familiarization with the detector, the properties of the X-rays emitted from the peeling tape will be studied. We will use the proportional counter to measure the energy of the X-rays, with interest paid to any correlation between pressure and X-ray energy. Also, varying the voltage to the motor allows investigation into the effects of the peeling rate of the tape on the pulse rate and energies of the emitted X-rays. We also test whether the sticky tape can be rewound and used again for X-ray production, and if so how many times this recycling can occur before the glue depletes so as to not release sufficient radiation. The ultimate goal remains to construct and tune a device to produce an X-ray image of sufficient quality to demonstrate feasibility for medical applications. Perhaps the most important aspect of this experiment is determining the safety of the X-ray apparatus by calculating radiation dose from the use of the device and its effect on any human subjects. The expected outcome of this research is that decreasing the pressure will result in higher energy X-ray radiation and higher quality images. Also, increased peeling speed is expected to produce a higher flux of X-ray radiation and allow better imaging. However, increasing the energy of radiation will also increase the chance of damaging effects from radiation on human subjects. We must find the proper balance between image quality and dangerous side effects; the problem behind all medical physics. Nevertheless, we expect to safely produce images of sufficient quality to discern individual bones in a sample, for example. Economic This project utilizes materials and methods for X-ray production far less costly than those used to produce images in the medical industry today. Since X-rays are pervasive in medical, dental, and veterinary imaging, the economic benefits of a cheaper method for production of X-rays would be far-reaching. The United States spends fifteen percent of gross domestic product on health care, nearly double the average percent spent by the other nations of the Organisation for Economic Co-Operation and Development (OECD) [4]. Hopefully, research into this method for X-ray production will lower skyrocketing health care costs in this nation, and around the world. Environmental The motor used to unravel the tape and the pump used to produce the vacuum require far less energy to operate than the devices being used for X-ray production in clinical settings today, which would help lower the environmental impact of the health care industry. The principle environmental risk of this research and any possible widespread application of this effect would be the waste of used sticky tape. A key component of this research into the environmental effects will be whether the tape can be rewound and recycled to produce X-rays again, and if so how many times this can happen before the energy of the X-rays decreases below an acceptable threshold. However, it seems that an environmentally conscious method for manufacturing sticky tape exists as 3M, the world’s foremost producer of sticky tape, has received awards for environmentally responsible companies [5]. Sustainability X-ray production apparatuses produced from peeling sticky tape are more sustainable than traditional methods for X-ray production. Tape and X-ray film are inexpensive as well as easily manufactured and transported. Batteries or another power source for the peeling motor and vacuum pump would be easily obtained and sustained, even in remote locations. Manufacturability All of the components of the apparatus are already manufactured widely and cheaply. Motors, sticky tape, plastic containers, and vacuum pumps are readily available for assembly into an X-ray producing unit. In addition, several unpeeling assemblies could be combined to produce a single X-ray signal for larger images, making this apparatus modular. Ethical For this project to be ethically responsible, the final apparatus must be safe. The dose rate has to fall below an acceptable threshold to qualify as safe and an ethically responsible tool for medical imaging. Knowledge of the risks of X-ray radiation from the apparatus to potential users and subjects should be distributed with the apparatus, perhaps by warning labels which clearly specify any danger, the dose rate, and proper use. Health and Safety The primary health risk from this research comes from ionizing radiation. The dose to the experimenter and any innocent bystanders must be closely monitored so as to avoid cell mutation or any other damage from X-ray radiation. Precautions we must take include using lead shielding when necessary and always wearing a film badge in the radiation lab. As always, there is no eating or drinking in the RadLab, and hands should be washed often due to the many closed sources in the laboratory. Finally, the detector requires a high-voltage power supply, and care must be taken to avoid electric shock. Social Lower cost X-ray production could lead to lower cost healthcare, as well as increased availability to medical diagnostics. The increase in access would thus lead to improved public health. Political While X-ray imaging is expensive in the United States and other developed nations, it is available for the most part. However, developing nations and remote areas do not have access to such technology. If a cheaper unit for X-ray imaging can be successfully developed, they could be supplied to developing nations by the United States government or governments of other wealthy nations, as well as charities and non-government organizations based in developed countries. The effect on better public health in developing nations could mirror an increase in political cooperation and improved relations between the United States and the developing world. References: [1]: N.E. Harvey, “The luminescence of adhesive tape,” Science 89, 460-461 (1939) [2]: V.V. Karasev, N.A. Krotova, and B.W. Deryagin, “Study of electronic emission during the stripping of a layer of high polymer from glass in a vacuum,” Dokl. Akad. Nauk. SSR 88, 777-780 (1953) [3]: C.G. Camara, J.V. Escobar, J.R. Hird, and S.J. Putterman, “Correlation between nanosecond X-ray flashes and stick-slip friction in peeling tape,” Nature 455, 1089-1093 (23 October, 2008) [4]: OECD Health Data 2007 – Version: October 2007, Organisation for Economic Co-Operation and Development, http://www.oecd.org/document/44/0,3343,en_2649_34631_2085228_1_1_1_1,00.html (accessed 2007) [5]: 3M Headlines, 3M, http://www.3m.com/intl/FR/english/front/other.html (accessed January 28, 2009)
Relevant Literature/Texts: C.G. Camara, J.V. Escobar, J.R. Hird, and S.J. Putterman, “Correlation between nanosecond X-ray flashes and stick-slip friction in peeling tape,” Nature 455, 1089-1093 (23 October, 2008) Podgorsak, Ervin B., Radiation Physics for Medical Physicists, New York: Springer-Verlag Berlin Heidelberg, 2006 |