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| Neutrino Project |
 Title text: We definitely put the pool in a mine for shielding. It was absolutely not to hide it from the funding people. |
Explanation
A neutrino is a type of subatomic particle that extremely rarely interacts with matter. In nearly all cases, neutrinos pass through objects, regardless of density or composition, with no effects whatsoever unless there are so many of them. For instance, about 100 trillion neutrinos pass through your body every second to no noticeable effect.
However, there is a very small chance that a neutrino will collide with any material, including water, which has the advantage of being transparent to the light that occurs due to that interaction. Neutrinos can thus be detected by constructing a large pool of water, shielded from as many other particles and radiations as possible, and carefully monitoring it for the small flashes of light that occur when a neutrino does interact with one of the many water molecules within the pool. Photomultiplier tubes are used to assist in detecting these very faint and infrequent flashes and reveal the possible nature (and direction) of the interactions that caused them.
The comic jokes that these detectors were not constructed with this purpose in mind. Instead, Cueball and Ponytail, the organizers of this project, obtained funding for a “neutrino project” and then embezzled these funds for a pool party, likely primarily to buy the large swimming pool seen in the panel. They supposedly only then realize that the pool could be repurposed as an actual neutrino detector. (It is unclear what, exactly, they had claimed to be building with the funding they somehow obtained.)
It is unclear how large the pool in the comic really is. The Super-Kamiokande detector in Japan, one of the world’s largest and most well-known neutrino detectors, holds over 50,000 tons of water. This is approximately 20 times the water capacity of Olympic-size swimming pools. The only statement made about the water capacity in the swimming pool is “huge”, which is not a precise measurement of volume or mass.[citation needed] The pool appears to be between 10 and 20 meters in diameter. While the surface of the pool seems to be at most half as large as that of an olympic-sized pool, its depth could be approximately the same, since it seems to safely allow jumps from an approximately 1m high platform. Therefore, a regular pool of this appearance would be expected to hold less water than an olympic-sized one, and certainly much less than would be required for an effective neutrino detector. However, since the bottom of the pool is not visible, the physicists might just have built a pool with an appropriate volume by making it extremely deep. Assuming a diameter of 20m and therefore a surface area of approximately 314m², the pool would need to be approximately 1582m deep. Constructing such a pool would be even more expensive than building a neutrino detector[citation needed], thanks to the large depth. It's more likely that the pool simply isn't circular with such a small diameter.
The title text elaborates on why the pool was suitable for a neutrino detector. In real life, these detectors must be heavily shielded from all other particle interactions that might drown out neutrino interactions. This generally requires them to be deep underground (like this and this and this), so a surface-level pool would obviously be unsuitable for that purpose. Randall implies that the pool was built in a deep mine in order to prevent it from being noticed by the people responsible for funding the project, which could fulfill the shielding requirement but is a humorously excessive strategy for hiding a swimming pool from a small group of people.
Transcript
- [There is a large pool with a curved edge at the bottom of the panel, with a diving board and several stickfigures in and around it. Ponytail and Cueball are talking in the pool, two hairy Kidballs are passing a ball, a Kidball is jumping of the diving board, and a Danish and a Ponytail with a drink are walking along the outside of the pool.]
- Ponytail in pool: How much trouble do you think we'll be in when they find out we used the grant money to throw a huge pool party instead?
- Cueball: We could argue that we did build a neutrino detector.
- Cueball: There's a lot of water here. A solar neutrino will probably interact with it at some point.
- Ponytail: ...Wait. Actually, if we got some photomultiplier tubes...
- [Caption below comic:]
- How the neutrino detector was invented
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