3DEXPERIENCE Lab Contribution
When I spoke with John Leyva, a Ph.D. student who is working on the GRAMS collaboration project at Northeastern, I was fascinated by their research on the "missing mass of the universe", Dark Matter. In this experiment, they seek to build a sensor to "indirectly search for particles corresponding" to a "particularly unexplored region of the energy spectrum from ~0.1-100 MeV". (To learn more about this experiment scroll down)
I knew I wanted to help, and I noticed they were having difficulties getting parts made and tested. I offered my assistance in the design and fabrication of some of their 3D-printed parts, some of which you can see below:
Stay tuned for updates on this project.
What is the Grams Collaboration Project
In the words of John Leyva:
"This is the R&D/proof of concept detector being built by the Northeastern University team on behalf of the international GRAMS (Gamma-Ray and AntiMatter Survey) collaboration. The GRAMS experiment aims to conduct a survey of multi-messenger astrophysics phenomena by using time projection chamber technology.
Physics Background
Multi-messenger astronomy typically refers to the production of high energy cosmic particles or gravitational waves resulting from violent/exotic astrophysical processes including but not limited to supernovae, neutron star mergers, blazars, active galactic nuclei, black hole collisions, etc. Specifically, the GRAMS detector is being designed to have world-leading sensitivity to a particularly unexplored region of the energy spectrum from ~0.1-100 MeV. In addition to gaining further insight into the mechanisms behind processes that have already been confirmed to exist, the primary goal of the GRAMS experiment is to indirectly search for a particle corresponding to the famously "missing mass of the universe" referred to as dark matter. Since the first hypothesis of its existence in 1932, both theoretical and observational results have bolstered our confidence that the entire visible universe makes up a mere ~%5 of what is truly there. Although many theories have been put forth to explain this observation, the most popular points to the existence of an undiscovered particle whose detection has thus far remained out of our technological reach.
Detector Mechanisms
Time projection chambers or TPCs are a class of detectors designed to ‘catch’ high energy particles and perform a 3D reconstruction of their trajectories through space. In the case of GRAMS, the bulk of the detector consists of a volume of liquid Argon (LAr) that is placed in a strong electric field. Referring to the photos, the cubic volume that is bounded by the blue PCBs will contain the LAr, and the horizontal traces that can be seen on each face make up the field cage that produces a uniform electric field everywhere inside the vessel.
When a cosmic ray penetrates the detector and interacts with an Argon atom, a phenomenon called scintillation (quite similar to fluorescence) occurs in which an excited Argon atom releases a pulse of light (for Argon, the scintillation light is ultraviolet at ~128nm). Mounted to the bottom 3D printed frame of the TPC (seen in white), a semiconductor-based detector called a Silicon Photomultiplier (SiPM) that is sensitive to single photons waits for this signal.
In addition to this flash of light, a shower of electrons are also produced as the cosmic ray is slowed down in the detector until all of its kinetic energy is dissipated. Because these electrons find themselves in a strong electric field, they are accelerated upwards towards the green PCB seen in the photo which contains a grid of charge-sensitive pixels.
Using these two signals, it is possible to measure the energy deposited by the particle as well as reconstruct its 3D trajectory. Placing the detector in a magnetic field also allows for the identification of certain species of charged cosmic rays via the effect of the Lorentz force on their trajectory.
If the cosmic ray happens to be a high energy photon (at these energies, this would be classified as a gamma ray), another phenomenon known as Compton scattering can occur inside the detector involving an interaction between the cosmic gamma-ray and electrons in the Argon. Our collaborators in Japan (Waseda University & The University of Tokyo), have been building software relying on neural networks that can use Compton scattering data to triangulate the source of these gamma rays. Using the detector as a ‘Compton telescope’, it may be possible to answer many outstanding questions that astrophysicists have regarding stellar processes as well as unusually violent processes like that of pulsars and blazars."
