Physicists reveal new $100 ‘ghostly particle’ detector

21 Nov 2017

Physicists at MIT have designed a pocket-sized cosmic ray muon detector to track these ghostly particles. Image: MIT

To help students better understand leftover muon particles from space, a team of physicists has built a $100 detector.

Unbeknownst to many of us, muon particles are raining down on the surface of our planet, even as far as 7km down into the Earth, as a result of collisions from cosmic rays in our atmosphere.

Lasting for only a fraction of a second, the particles are slightly heavier than an electron and, because of their ability to pass through objects, they have been described as ‘ghostly’ in nature.

Now, a team of physicists from MIT is hoping to show others just how prevalent muons are in our daily lives, with help from a $100 detector built from spare parts.

In a paper published to the American Journal of Physics, the team revealed its pocket-sized device that lights up and counts each time a muon passes through.

The team estimates that an average secondary-school student should spend about four hours building a detector for the first time, and just one hour building it a second time.

When the detectors are up and running, they can be carried by students in any environment, and some have already sent them up in balloons to measure muon rates at high altitudes.

Making something useful

The detector came about after graduate student Spencer Axani attempted to create a muon detector as an addition to the IceCube particle detector in the South Pole.

The detector would be used to identify and filter out the ‘noise’ of muons from the more coveted and scientifically significant particles called neutrinos.

When he realised it would have many benefits as an outreach tool, Axani went through a pile of discarded electronics equipment at MIT and found that he could build a small, thin device to measure them, requiring very little power.

He also designed simple electronics and software components to display the number of muons passing through the detector, making it a self-contained measurement and readout instrument.

In the near future, the detectors could also be sent up on suborbital rockets at altitudes of 100,000ft.

One of the paper’s co-authors, Janet Conrad, said: “When you get up high enough, you get out of the muon production region of cosmic rays and you can start seeing the turnover, where rates of muons increase at a certain altitude and then start decreasing beyond a certain altitude.”

She added: “This [device] is a really neat example of how pretty esoteric physics can produce something which is directly useful.”

You can find out how to build your own device through the team’s CosmicWatch programme, which lists parts to purchase as well as detailed instructions on how to assemble, calibrate and run the detector.

Colm Gorey was a senior journalist with Silicon Republic