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How to Build a Cloud Chamber to Visualize Radiation

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How to Build a Cloud Chamber to Visualize Radiation How to Build a Cloud Chamber to Visualize Radiation John Smith, MS, DABMP Abbott NW Hospital, Minneapolis GOALS Learn the History of cloud chambers and other radiation detectors Learn some of the science behind cloud chambers Learn how to make a cloud chamber See a working cloud chamber J. Norman Collie (10 September 1859 – 1 November 1942) British Scientist, Mountaineer and explorer In 1891, James Collie was climbing the Scotish mountain Ben MacDhui when he had an unnerving experience Ben MacDhui was covered in Mists, as it often was, and Collie was near the peak when he felt a presence nearby and heard the sound of large crunching footsteps, as if from a giant “with a stride three or four times the length of my own.” Collie was unable to make out the source of the noises because of mist, and continued "... [as] the eerie crunch, crunch, sounded behind me, I was seized with terror and took to my heels, staggering blindly among the boulders for four or five miles Am Fear Liath Mòr When Collie told the story years later, the locals told him that he had run into “Am Fear Liath Mor,” the Big Grey Man of Ben MacDhui. For years many people climbing Ben MacDhui had had terrifying encounters, hearing his footsteps or seeing his large grey form in the mists. A Man named Norman Forbes was Climbing Ben MacDhui when he heard the Giant’s footsteps, but later he realized that they were actually from two deer that had been hidden in the mist. James Hogg: “….a giant blackamoor, at least thirty feet high, and equally proportioned, and very near me. I was actually struck powerless with astonishment and terror.” Until he realized that the Blackamoor was copying his gestures. He was looking at his own shadow on the mist. Brocken Spectre The Brocken Spectre is a light phenomenon when the light source is behind or above a figure casting a shadow on a mist. The shadow is often surrounded by a rainbow glow or “Glory” You may have seen this when looking out the window of an airplane seeing the airplane’s shadow on clouds below. Charles Thomson Rees Wilson 14 February 1869 – 15 November 1959 Scottish physicist and meteorologist at the Cavendish Laboratory In 1894, while working on another Scottish Mountain, Ben Nevis, C.T.R. Wilson was fascinated by his sightings of the Brocken Spectre and this inspired him to come up with a way to make and study clouds in a laboratory. Wilson’s Cloud Chamber By 1895, Wilson had come up with the idea for the “Expansion Cloud Chamber” Ideal Gas Law A reversible adiabatic process can be represented by the polytropic process equation: PVn = constant Where n = and = Cp = f+2 Cv f And also: P1‐T = constant and TV‐1 = constant ‐1 ‐1 TiVi = TfVf ‐1 Tf = Ti (Vi/Vf) where for a diatomic gas (N2, O2) = 7/5 Or you might have noticed that expanding a gas makes it cold. Wilson knew that if he could suddenly drop the temperature of humid air, he could get clouds to form at ground level Wilson is often given credit for this idea, but he was not the first scientist to make clouds in the lab. 1875 French Scientist Paul Jean Coulier made fog in a glass container in a similar way, and discovered that small particles were needed to form droplets (like tobacco smoke) 1880 John Aiken of Edinburgh rediscovered the effect and measured the number and size of “nuclei” needed to form droplets. Cloud Condensation Nuclei – CCNs (or cloud seeds) are small particles on which water condenses What do you need to make clouds? • Air saturated with water • Sudden drop in temperature to make the air “Supersaturated” • Small particles to act as “CCNs”, or Cloud Condensation Nuclei Wilson’s Cloud Chamber Wilson Conceived of the Cloud chamber as something to study meteorology, but he was at the Cavendish laboratory, one of the main centers of physics research • 1895 – Discovery of X‐rays – Wilhelm Roentgen • 1895 – Wilson makes cloud chamber • 1896 – Discovery of Radioactivity – Becquerel • 1897 – Discovery of the Electron – J.J. Thompson • 1898 – Discovery of Radium – Pierre and Marie Curie • 1899 – Discovery of Alpha and Beta radiation – Rutherford • 1899 – Discovery of Natural Background radiation • 1900 – Discovery of Gamma Radiation – Paul Villard • 1905 – Einstein describes the photon 1895 ‐ 1911 • Roentgen discovers that radiation makes air “conductive” (What we now call “ionization.”) • Wilson finds out that conductive air (ions) make good cloud condensation nuclei (CCNs) • Wilson uses radiation to form clouds in his cloud chamber • Wilson decides to photograph tracks of radiation particles Alpha Particle tracks from 1911 Alpha Particle tracks from 1911 Did the cloud chamber lead to the discovery of natural background radiation? Did the cloud chamber lead to the discovery of Cosmic Rays? Natural Background Radiation was discovered by the gold leaf electroscope (1899) Victor Hess discovered Cosmic rays in 1912 by measuring background ionization high in the air in a balloon For many years the cloud chamber was not used to make physics discoveries. Cloud chambers were built for sale, but also sold were Wilson’s photographs of particle tracks, which were referenced more often. The cloud chamber was used more for confirmation rather than original research. Carl Anderson at Cal Tech discovered the positron in 1932. A “positive electron” had been proposed by Dirac in 1928, and was actually seen but not recognized by Soviet scientist Dmitri Skobeltsyn And Caltech physicist Chung‐Yao Chao in 1929. In 1936 Carl Anderson also used a cloud chamber to discover the muon. He received the 1936 Nobel Prize in Physics along with Victor Hess who discovered cosmic radiation. Positron in Cloud Chamber One of the problems with an expansion cloud chamber is that the supersaturated condition only lasts for a moment This led to the invention, in 1936, of the “Diffusion Cloud Chamber” which we will make today The Diffusion cloud chamber was invented by Alexander Langsdorf, Jr American Physicist who worked on the Manhattan Project with Enrico Fermi in Chicago. Produced Plutonium for the Trinity bomb test Martyl Langsdorf Felt soaked WARM in alcohol Clear tank Cold Dry Ice In 1952 Don Glaser invented the Bubble Chamber In a Superheated liquid, bubbles will form when an ionizing particle travels through the liquid Bubble chambers could be used to detect more energetic particles. As with cloud chambers, magnetic and electric fields could be used to get information on the charge and mass of particles. In the 1960s and 1970s, particle physics research often used bubble chambers to study the tracks made by elementary particles Don Glaser was a musician, and the story was told that he got the idea for the bubble chamber while playing music and drinking beer at a bar. Unfortunately, he has said that this is not true. Another way to both visualize and get electronic measurement of radiation was with a spark chamber, something like a stack of Geiger Counters In 1968, Georges Charpak invented the “Multi‐Wire Proportional Chamber” (MWPC) He received the Nobel Prize in Physics for this in 1992 Particle tracks are now produced in computers from the digital data from the MWPCs In the 1950’s you could buy an “Atomic Energy Lab” with radioactive materials and a working Wilson Cloud Chamber $270 $575 The First Cloud Chamber that I made Start with a small fish tank and line the bottom with felt. I used these adhesive computer cable clips to attach the felt, But the they tend to come loose when we apply alcohol Next, I made a wooden box to fit the fish tank and the metal plate I had Line the bottom with some foam insulation. This will help insulate the bottom of the box, but also pushes up the dry ice to make contact with the metal plate. I used an aluminum plate which I painted black for the base After putting in the dry ice, place the metal plate on top of the ice, making sure there is good contact between ice and plate. Remember that the Dry Ice is very cold, and the metal plate will get very cold, so wear protection for your hands and eyes. Saturate with isopropyl alcohol Saturate with isopropyl alcohol The Fish tank goes on top of the metal plate upside down. Set up light source and dim room lights Watch for tracks to appear An Even Cheaper version with used baking sheet and styrofoam Stack the Styrofoam to make a container for the dry ice Choose a clear, tall glass for the chamber, a beer glass works well. Cut a piece of felt to fit on the bottom, and use modeling clay to secure it inside the glass Use some more clay around the base to get a good seal on metal plate Will Your Students Be Amazed? .
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