# Neutrino catching **URL:** \ **Category:** Factual Questions\ **Created:** [March 16, 2012, 8:57pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002 "2012-03-16T20:57:39Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![SlickRoenick](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@SlickRoenick](https://boards.straightdope.com/u/SlickRoenick)\ **Post date:** [March 16, 2012, 8:57pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/1 "2012-03-16T20:57:39Z")
> **[Researchers send instant message with neutrinos](https://scienceblog.com/52770/researchers-send-wireless-message-using-elusive-particles/)** > > A group of scientists led by researchers from the University of Rochester and North Carolina State University have for the first time sent a message using If neutrinos can pass through any obstacle, regardless of mass or thickness, how are scientists able to “catch” a neutrino signal on the other end of the sender to read the data transferred? ---
**Author:** ![wheresmymind](https://avatars.discourse-cdn.com/v4/letter/w/91b2a8/32.png) [@wheresmymind](https://boards.straightdope.com/u/wheresmymind)\ **Post date:** [March 16, 2012, 9:08pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/2 "2012-03-16T21:08:43Z")
Neutrinos can’t pass through _any_ obstacle. They just have such a small mass that they have to pass through A LOT of matter before they have a decent chance of hitting something. If you have a block of lead, on the subatomic scale it’s mostly empty space, and neutrinos are small enough that MOST of them will slip right through, like a gnat flying through a chain-link fence. But if you fire a few billion or trillion of them into the block, one or two will strike something. This is why all the neutrino detectors are incredibly massive (hundreds or thousands of tons): they need a lot of mass to ensure that they catch at least one. ---
**Author:** ![Simplicio](https://avatars.discourse-cdn.com/v4/letter/s/c37758/32.png) [@Simplicio](https://boards.straightdope.com/u/Simplicio)\ **Post date:** [March 16, 2012, 9:10pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/3 "2012-03-16T21:10:01Z")
Neutrino’s have some small chance to interact with matter as they pass through, so if you have enough matter combined with enough neutrinos, you’ll see an interaction. This is why neutrino detectors in astrophysics are so huge. You need a lot of mass to have a chance to see even a few. So for example, the Kamiokande uses something like 3,000 tons of water. When SN 1987a went off something like a thousand trillion extra neutrinos went through the detector, which then actually detected a total of twelve. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [March 16, 2012, 9:47pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/4 "2012-03-16T21:47:42Z")
“Extremely rarely” does not equal “never.” Almost all neutrinos will pass through normal matter like it wasn’t there, but a very small percentage (per billionthage?) of neutrinos will interact. And while most such interactions will not result in anythimg obvious, one can set up conditions in which the results almost _have_ to be from neutrino interaction and are relatively blatant. The Homestake Mine Neutrino Detector is an example of this: a tank full of perchloroethylene dry-cleaning fluid at the lowest level of a deep mine, and therefore shut off from all EM radiation including cosmic rays. Anything which impacts is very likely a neutrino – although few of them will, that any reactions do happen is a strong indicator of a neutrino interaction having occurred. And the neutrino impacting the chlorine atom will induce a decay to argon, a noble gas, which will bubble to the top. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [March 17, 2012, 3:55am UTC](https://boards.straightdope.com/t/neutrino-catching/616002/5 "2012-03-17T03:55:58Z")
So how do these detectors work? Okay, I get that an underground lake of dry cleaning fluid will occasionally produce an argon atom which will float up. So how do you detect when THAT happens? It still sounds like watching for a needle to bubble up to the top of a haystack. In general, if you have megatons of detector in order to detect those 12 neutrinos out of the bazillions that came through – how do you detect that your detector has detected something? ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [March 17, 2012, 2:55pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/6 "2012-03-17T14:55:08Z")
Wikipedia has a [Neutrino Detector](http://en.wikipedia.org/wiki/Neutrino_detector) page. I had thought they always detected the Cherenkov radiation from the interaction, but from the [Radiochemical methods](http://en.wikipedia.org/wiki/Neutrino_detector#Radiochemical_methods) section: > [@](#): > > Chlorine detectors, based on the method suggested by Bruno Pontecorvo, consist of a tank filled with a chlorine containing fluid such as tetrachloroethylene. A neutrino converts a chlorine-37 atom into one of argon-37 via the charged current interaction. The threshold neutrino energy for this reaction is 0.814 MeV. The fluid is periodically purged with helium gas which would remove the argon. The helium is then cooled to separate out the argon, and the argon atoms are counted based on their electron capture radioactive decays. A chlorine detector in the former Homestake Mine near Lead, South Dakota, containing 520 short tons (470 metric tons) of fluid, was the first to detect the solar neutrinos, and made the first measurement of the deficit of electron neutrinos from the sun (see Solar neutrino problem). Kind of surprising to me that it apparently works. ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [March 17, 2012, 9:12pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/7 "2012-03-17T21:12:57Z")
How do they find a few atoms of argon amongst all the helium? Even if they cool it, a few atoms of argon aren’t exactly going to leave a puddle of liquid argon at the bottom of the container. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [March 17, 2012, 10:53pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/8 "2012-03-17T22:53:05Z")
> [@snailboy](#): > > How do they find a few atoms of argon amongst all the helium? Even if they cool it, a few atoms of argon aren’t exactly going to leave a puddle of liquid argon at the bottom of the container. See, that’s the basic question that I and **snailboy** and **ZenBeam** are asking. Neutrino interaction are extremely “rare” or sparse events. Whatever possibly-observable result those interactions produce must also be extremely sparse. For us clueless laypersons (well, me, anyway) it just seems mind-boggling that particle-physics researchers are able to snag and observe a few stray argon atoms or individual photons or the occasional quantum of some radioactive emission, out of 530 tons of detector fluid. That’s a lot of dry-cleaning! ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [March 17, 2012, 11:10pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/9 "2012-03-17T23:10:25Z")
Professional physicists never misplace the receipt/ticket. Thats their little secret. ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [March 17, 2012, 11:27pm UTC](https://boards.straightdope.com/t/neutrino-catching/616002/10 "2012-03-17T23:27:40Z")
> [@Senegoid](#): > > For us clueless laypersons (well, me, anyway) it just seems mind-boggling that particle-physics researchers are able to snag and observe a few stray argon atoms or individual photons or the occasional quantum of some radioactive emission, out of 530 tons of detector fluid. Especially considering the number of atoms in the fluid is probably going to be at least 30 digits long. (I just tried to calculate it precisely and came up with a 32 digit number, but I realized I forgot to divide by the molecular mass of the fluid. I don’t care to go back and recalculate it but I’m pretty sure the molecular mass of tetrachloroethylene is less than 100 so I’m just gonna say it’s in the nonillions.)