October 7, 2008

A Tradition of Experiment

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Allen Kim ’10 wound his way between the congested tables of Clark Hall’s third floor. He circumvented Ernest Rutherford’s gold foil experiment. He sidestepped past some radioactive particles. He dodged some gamma rays, and evaded the nuclear forces emanating from the magnetic resonance imaging device. After scaling the steps to the fourth floor of Clark Hall, he located his homework, a contraption of gizmos, gadgets and coils that manipulates the physical properties of light. He finished his journey, and began his homework assignment for PHYS 410/510: Advanced Experimental Physics.

[img_assist|nid=32483|title=Famous Experiments|desc=|link=node|align=left|width=|height=0]Famous Experiments“The purpose of this particular class is to not only give the theorists but also the experimentalists a true real-life experience in the research world,” explained Nick Szabo, the lab’s staff director.

These theorists and experimentalists are not professors, but physics and engineering students.

“There’s just a huge amount of history that goes along with this class. Guys who have won Nobel prizes were in this class,” said Szabo.

The class’s distinguished history began over eighty years ago, and one of its earliest “products” was Isidor Isaac Rabi, who won a Nobel Prize in 1944 for his work with Nuclear Magnetic Resonance. Rabi developed techniques to measure the momentary magnetic characteristics of atoms, emerging from the momentary distributions of negative charges around the positive nucleus. Rabi’s research provided the basis of the Magnetic Resonance Imaging, or MRI machine, now a common research tool at Clark Hall.

“It’s not like a lecture course. It’s more like research,” explained Prof. Paul McEuen, physics. “It’s not a cookbook. It’s like, ‘Over there is something. Now, go make something happen.’”

In all, the class offers over 80 experiments, ranging in subject from nuclear physics and electromagnetic radiation to aeronautics and optics.

“It’s about getting hands on experience with experiments,” Kim explained.

Kim researches the light spectrum by using various methods to filter the light. He sends the light waves through a polarizing lens and through fructose and sucrose solutions of varying concentrations. In doing so, he manipulates the wave movement and the energy of the light, altering its frequencies and wavelengths. The varying frequencies and wavelengths produce various colors of light, and display the characteristics of the light spectrum.

In 1908 at the University of Manchester, Hans Geiger and Ernest Marsden, under the direction of Ernest Rutherford, shot tiny alpha particles at a sheet of gold metal. Based on the atomic model of the time, the infamous “plum pudding model,” Rutherford expected the alpha particles to easily pass through the thin foil. However, when some of these particles were deflected, Rutherford famously described his reaction by saying that it was as if he shot a cannonball at some tissue paper, and the cannonball was reflected toward him.

From these reflections, Rutherford identified the central, rigid, positive nuclei of all atoms, creating the modern view of the atom and changing physics and chemistry forever. Many of the experiments in PHYS 410 apply Rutherford’s model to explain results, and now, 100 years after Rutherford completed his experiment., on the third floor of Clark Hall, an undergraduate students replicates Rutherford’s work by directly recreating his experiment.

Students of Physics 410 also re-investigate the foundations of physics and chemistry, checking the arithmetic of famous scientists, like Sir Isaac Newton and Albert Einstein. These investigations use traditional technologies to re-measure the speed of light, the gravitational constant, and mass numbers of the periodic elements.

For instance, even in the era of lasers, students in PHYS 410 measure the speed of light by using a simple contraption of mirrors and ordinary light. Students measure the minuscule amount of time it takes the light to travel from one side of the lab, to hit a mirror, to travel back, and hit another mirror. From this simple contraption, the students extrapolate the true speed of light.

“It’s almost trivial when you have a laser or more modern equipment,” McEuen described. “It’s kind of like an old car when you can know how all the parts work, rather than taking more modern equipment and just plugging and playing.”

Yet, modern equipment offers specific advantages in some experiments.

Sudeep Mandel grad researches Muons, tiny cosmic particles that enter the atmosphere from space, pass through most substances, and finally disappear. Muons represent the most abundant charged particle at sea level, but like all charged particles Muons lose energy due to ionization. Whenever a Muon particle interacts with another atom, it loses energy, and rapidly decays. Since the particle travels at the speed of light and interacts with many particles, its half-life is only 2.2 microseconds. Mandel researches this half-life by collecting and studying these particles. He gathers the Muons with a special collector, which is connected to a computer. Whenever a particle decays in the collector, a tiny flash of light appears, and by measuring the quantity of these flashes, Mandel extrapolates the lifetime of the short-lived particles. According to relativity, time slows down for objects moving at high speeds. By measuring the altered half-life of these relativistic muons, scientists provide one of many proofs of Einstein’s theory of Special Relativity.

Multiple teachers of PHYS 410 won Nobel prizes over the last 80 years, including Robert C. Richardson and David M. Lee, who won the prize in 1996 for their discovery of the super fluidity of helium. In the early 1970s, while teaching PHYS 410, Richardson, Lee, and their colleague, Douglas D. Osheroff of Stanford, experimented with the rare helium isotope, helium-3. The trio super-cooled the isotope to two milliKelvin, or two-thousandths of a degree above absolute zero, the coldest it could possibly be. In doing so, the trio discovered that the liquid could flow without viscosity or inner friction— if the liquid were sloshed, it would continue sloshing back and forth forever. Their discovery revolutionized the view of the electron orbital of the Helium atom.