Closure of the Neutrino Detector Question

Question

The question How do you detect Coherent Elastic Neutrino-Nucleus Scattering (CEvNS)? had been closed with the "engineering" closure reason.

This question appears to be about engineering, which is the application of scientific knowledge to construct a solution to solve a specific problem. As such, it is off topic for this site, which deals with the science, whether theoretical or experimental, of how the natural world works.

The post was then reopened by the moderator @rob who encouraged discussion in meta, so here I am!

Rob left a comment on the main post, and the heart and intent is something I can understand:

I think that questions about the construction and operation of equipment whose main or only purpose is physics research, such as a neutrino detector, are more about physics than they are about engineering

I've always tried to evaluate posts based on the content of the post rather than the exact topic. For example, I can't say "projectile motion questions" are definitely on-topic or definitely off-topic; both types could exist that ask about projectile motion. More goes into closure/reopening decisions than the explicit topic.

I tried to apply the same reasoning here. Certainly "questions about the construction and operation of equipment whose main or only purpose is physics research" sounds like a topic that a good post could definitely be about.

However, ignoring the fact that there are multiple questions in the OP (which might constitute a separate closure reason), what are the questions here?

How does the COHERENT neutrino detector, neutrinos and CEvNS?

Definitely some good physics to be found here. Seems like it should be a post all on its own, really

What is used to detect CEvNS?

Seems like that would just be included in the previous question. Sure, that's fine.

Considering that we now have neutrino detectors the size of milk jugs, how might one make their own neutrino detector?

Starting to feel a little dicey, but if it's related to the physical reasoning from the other questions, fine.

What might you need if you had a large budget to make it? And what would you need if you had a limited budget?

Referring to the meta post that clarifies engineering questions: "The physics community, while often tangentially knowledgeable in these areas, is not the place to seek guidance when ease-of-use, manufacturing costs, material availabilities, etc. are also primary considerations."

It seems like this point is getting more into the engineering.

Are any of the supplies you might need to build your own neutrino detector be cheaper if you made them yourself?

What might a 'shopping list' for building your own neutrino detector look like?

See above

Why might the smallest neutrino detector work despite its incredibly small size?

This seems to be back to the physics, but it's buried under other questions that read way more like engineering.

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So, maybe the closure vote should have been for "needing more focus"? But even then, I will respectfully disagree with the decision to reopen this one, at least not before the OP edited it to be a better post. I understand not wanting to shut down discussions about the physics of neutrino detectors, but, at least in my case, that was not the reasoning behind my vote to close.

Answer 1

Thanks for starting this discussion. Just to clarify, I'm answering here as a user of the site, rather than as a moderator. I want to do what the community wants to do; but this is an issue where I would like to nudge the community a little bit.

I'm a zillion times better as a physicist because of the time I spent doing things wrong-but-eventually-right in the lab. But experimental details, especially uncertainties, imprecisions, and experimental blind spots, get more and more sidelined as physics results migrate from the lab to the public. I think there is a place for our community to counter that tendency, especially when folks come to us asking whether it's possible to demonstrate modern-physics phenomena using affordable technology.

I agree that the question is a little unfocused, but I think that's because the asker doesn't know very much about the topic yet. A classic problem in a question-and-answer context: constructing a well-formed question is much easier if you already know the answer, or most of the answer. I think that v3 of the question is better than v1. I also note that the asker has followed the only advice they got in comments, which was to add links.

To my mind, the best possible answer to the question would be something like NIST's guide to building a Kibble balance out of Legos (web page, open access: Chao et al., Am. J. Phys. 83 (2015)), except about neutrinos, and with much less expectation of detail in our online community than a publication in a journal about physics education. In fact, there is substantial overlap between the list of questions you have quoted and the section headers of the Chao et al. paper: what are the basic operating principles, what things do you give up doing it on the cheap, what parts do you need, and how much do they cost. That structural similarity says "good question" to me, even if the question could stand to be improved.

What might you need if you had a large budget to make it? And what would you need if you had a limited budget?

Are any of the supplies you might need to build your own neutrino detector be cheaper if you made them yourself?

What might a 'shopping list' for building your own neutrino detector look like?

Referring to the meta post that clarifies engineering questions: "The physics community, while often tangentially knowledgeable in these areas, is not the place to seek guidance when ease-of-use, manufacturing costs, material availabilities, etc. are also primary considerations."

To me, the question reads more as requests for general guidance, while the meta post seems to refer to more specific guidance. If I saw a question about whether the Thorlabs BSP-1234 is a better beamsplitter than the Edmunds PBS-56789, I'd vote to close it. The Chao et al. paper has a ridiculous table at the end which says you can build their Kibble balance for \$632.47 (in 2015 dollars) — but in the paragraph above that table, they say of course you can save money by swapping out some components, and give an example of a data acquisition system change that shaves off one-third of the price.

It's well known that you can build a cloud chamber particle detector with about \$10 of dry ice from the grocery store and junk that you probably already have in your kitchen. There's nifty circular-polarization experiments that you can do if you and some friends go see a three-dee movie and steal the glasses afterwards.

I read the pricing requests in this question as order-of-magnitude requests. Can you build a neutrino detector with kitchen junk and \$100 or \$1000 of stuff from the hardware store? Would a proof-of-concept detector be workable for a motivated group of physics undergraduates, who might be able to scare up a \$10k grant and/or scavenge abandoned stuff from the shelves of other laboratories in the department? Is borated plastic scintillator another name for some product that's actually easy to find? These are the questions that I hear when I read the three that I've re-quoted.

I built my first dry-ice kitchen cloud chamber in 2002 as a young adult. If I had wanted then to move on to a more sophisticated particle detector, the question I would have asked would have looked a lot like the question we're discussing. At least in part, I voted to reopen the question because I think this community is a place where 2002-rob should have felt welcomed.

Answer 2

It is certainly true that this particular question might very reasonably be closed as too broad, but if we are discussing what counts as engineering, I think the statement in the relevant meta post could use some clarification:

The physics community, while often tangentially knowledgeable in these areas, is not the place to seek guidance when ease-of-use, manufacturing costs, material availabilities, etc. are also primary considerations.

The experimental "physics community" is not just "tangentially knowledgeable" about the engineering issues, ease-of-use, costs, material availabilities, etc. of building cutting edge research experiments. We are extremely knowledgeable, and as much as we love and work closely with engineers when needed, it is physicists - not engineers - who end up being the primary experts on such issues and who are pushing the limits of technology and engineering to achieve our physics goals.

I am not sure of the source of the quoted statement that "questions about the construction and operation of equipment whose main or only purpose is physics research" are reasonable Physics SE posts, but I believe this should be added to the guidance if it is not already there.

For all aspects of this particular neutrino detector question, physicists are far more likely than engineers to be able to answer, but it is certainly true it would be best split into separate questions such as:

• What is the physics that allows small detectors such COHERENT to detect CEvNS?
• What would be the most inexpensive way to detect neutrinos? (For this, the neutrino energies and flux would need to be considered, and whether the cost of the neutrino source is included. The answer is different for a spallation neutron source, the Sun, a long-baseline neutrino facility, geoneutrinos, the $1\,\mathrm{Ci}\,\,^{90}\mathrm{Sr}$ calibration source I used to have, ….)
• How small could a neutrino detector be? (Again, this depends on the neutrino source and the physics objectives.)

Answer 3

It has always seemed there is some overlap between physics and engineering questions. If somebody wants to build a gadget to do X, I guess my take on it would be

• If the question is about the physics of X and how that plays into making a gadget, it is a physics question.
• If the question is about how to make the gadget strong enough or cheaply, it is engineering.

An engineer might ask about how to make a gadget so he can sell it. A physicist might ask the same question so he can make one for his lab and hot have to buy it. This doesn't seem relevant to whether it is about engineering or physics.

Up to a point I feel like it shouldn't matter. The question is being asked because somebody needs to know. Or wants to know. I know we don't want to focus on different grades of steel and such. But sometimes we can be helpful even if the question is semi off topic. So sometimes I err on the side of answering an engineering question. Perhaps with just a comment.

In particular, we sometimes get questions about the best optical component. I often put a link to the RP Photonics Encyclopedia, or sometimes the Buyer's Guide. Many people do not know about it. Pointing them to it can get themlooking in the right direction. It isn't necessarily helpful for the physics community that might read the question again. But it helps the OP get past being stuck.