Featured Student Stories

The same way Earth receives light from the Sun, it also receives atomic nuclei emitted from the Sun and other stars in the Universe. As they travel through space, these nuclei can get accelerated to become what we call cosmic rays. Noah Green is designing an instrument for the High Energy Light Isotope eXperiment (HELIX) that will detect cosmic rays to better understand where these cosmic rays are coming from and how far they have traveled to reach Earth. This project is a collaboration between 8 institutions, with Noah being one of 7 graduate students working on this instrument and the only one from the University of Michigan.

Noah is a 3^rd year physics graduate student in Professor Gregory Tarlé’s lab. He’s currently working out of Chicago, IL, where the instrument, specifically a mass spectrometer, is being built. Mass spectrometry is a technique in which ionized chemical species are analyzed by measuring their mass-to-charge ratio enabling the identification of analyzed species accurately. More specifically, the HELIX mass spectrometer will detect isotopes from cosmic rays that reach Earth’s atmosphere over Antarctica. The HELIX mass spectrometer will consist of four subsystems that will be able to collectively measure a particle’s energy, momentum, and charge. With these measurements and a little special relativity, the identity of the cosmic rays passing through the HELIX spectrometer can be determined.

With this instrument, they will be doing isotope analysis of cosmic rays. Isotopes are atoms of the same element that have a different number of neutrons, giving them a different mass while maintaining their chemical properties. A common example of isotope analysis is radiocarbon dating; when scientists look at the ratio between carbon-12 and carbon-14 (weakly radioactive) to determine how old something is. Isotope analysis is highly reliable because the amount of time it takes for the radioactivity of an isotope to fall to half of its original value, or their half-life, is well established. Noah will be looking at various isotopes, but he specifically mentioned beryllium-10, which has a half-life of 1.38 million years, that will let him figure out how long cosmic rays stay within our galaxy.

In addition to assisting in building the instrument, Noah’s efforts are specifically directed to designing the plumbing system that will maintain all four subsystems of the mass spectrometer functioning at the adequate pressure and temperature, designing the aerogel tiles in the ring imaging Cherenkov system (RICH), and writing the software code to analyze the data being collected. When he isn’t working on something directly related to the instrument, he is running simulations and data analysis to prepare himself to analyze the data they will collect.

The HELIX spectrometer will be mounted on a balloon and deployed in Antarctica in 2020 for 7-10 days to collect data on the cosmic rays. The spectrometer will be operating non-stop for the duration of its deployment. Therefore, extensive planning has gone into designing and building of the instrument, logistics for deployment, software design and code writing, experiment design as well as simulations to determine what data can be collected and what questions can be answered from this instrument floating over Antarctica for a week or so.

When faced with the age-old question of what to work on in grad school, Noah decided to take on this project because “[he] could contribute to it from start to finish”. He saw this as an opportunity to make a significant contribution to his field while learning how to be an experimental physicist. “You’re not here [in graduate school] to win a Nobel prize. You’re here to learn how to do research. HELIX may be small, but that means I get to be involved in everything from hardware to modeling, and see the whole experiment to completion.”

As a 6th-year PhD student with the Raithel Lab, Andira Ramos is quite familiar with the demands on one’s time as a graduate student, but was nonetheless eager to describe her work and some of what goes into it. Though experimental physics research is at times challenging, she explains that she enjoys the variety of both her field and the academic environment in general. A day might include time spent with parts in the machine shop, work with electronics, programming of computer simulations, painstakingly precise adjustment of an experimental setup, or of course actually measuring and analyzing data.

The data, in this case, are to try and better understand interactions between light and matter. While such knowledge may seem esoteric, the technologies it enables underlie many of the medical and computing advances made in recent decades. In the lab, interactions between light and matter can be used to make especially precise measurements of fundamental constants such as the Rydberg constant, a value used to describe atomic energy levels. This particular measurement is the focus of Andira’s work, motivated by what is called the “proton-radius puzzle.” This unresolved question in physics comes from separate observations of different radii for the proton. Typical measurements of the Rydberg constant, on the other hand, rely on knowing a single value for the proton radius. So Andira is measuring the Rydberg constant in a way that is not dependent on the ambiguous proton size, which first sidesteps the proton-radius puzzle but ultimately helps us understand its nature, once the new measurement is obtained. The experiments required for these investigations are themselves intricate - such precise measurements require nearly perfect control of the atoms, achieved using a magneto-optical trap, a method in which a magnetic field is aligned with laser beams that slow (i.e. cool down) and trap a cloud of atoms in a designated space for assessment. Once trapped, the atoms can be subjected to excitation, causing their electrons to change energy levels or even escape the atom entirely. Replacement instead of an electron with a muon, which has the same charge but 200 times the mass, is the source of the proton-radius puzzle, as the proton radius differs when it’s being orbited by a muon rather than an electron. The resulting difference is between about 8.42 x 10^-16 and 8.75 x 10^-16 meters, underscoring the need for precision. Zooming back to what this means at our scale, she jokes that she warns undergraduates against bumping an experimental setup - “That was three months of work!”

Familiarity and comfort with the lab didn’t come right away, though, and Andira draws a contrast between her own experience and that of colleagues who had accumulated laboratory experience in between their graduate and undergraduate studies. She came straight from her undergraduate degree at Florida International University, where she had initially been studying accounting, knowing that it would make her readily employable. An astronomy class ignited a new and different passion, and with the encouragement of her astronomy professor set her sights on the closest available course of study, majoring in physics with an astronomy minor and hoping to become a professor herself. While she confirmed that she enjoys teaching, as suggested by the eagerness and care with which she explained her experimental work, she is now looking to pursue a career in industry where she hopes to work on space probes and help advance our knowledge of the universe on a bigger scale.

In the meantime, Andira has had the opportunity to reflect on life as a graduate student, and highlights the importance of building community outside of the lab. For her, this has included both weekly department coffee gatherings and her own efforts to organize outings for swing dancing in town. She emphasized that she hopes future students will take more advantage of such opportunities, and thereby maintain a supportive environment for each others’ success.