A liquid crystal of Potassium-42 Chloride for directional neutrino detection

[Ramael]

TL;DR Summary

A liquid crystal of Potassium-42 Chloride for directional neutrino detection

I've been speculating on a method of neutrino detection that uses beta decay instead of scintillation for the detection of neutrinos and was curious about its viability. Potassium-42 can be synthesized by colliding Calcium 40 with protons. It has a half-life of 12.36 hours and decays into Calcium 42 via beta decay. If reacted with chlorine in that brief window and put under the correct pressure and temperature, potassium chloride can organize into a liquid crystal that forms smectic layers. As ambient neutrinos collide with the potassium 42, its likelihood for undergoing beta decay increases. This setup seeks to identify this increase by rotating a magnetic field and detecting differences beta emissions as this liquid crystal lattice becomes parallel vs perpendicular to a neutrino source in order to identify a magic angle where beta decay is the strongest. Unlike a scintilator that can identify THAT a neutrino has been detected, this setup aims to determine the direction of incident neutrinos in an effort to produce higher resolution neutrino images. Especially if organized into an array.

 

[mfb]

How many micrograms of K-42 can you reasonably produce?

Your decay heat is in the range of tens of megawatts per kilogram, so even if you could produce larger quantities you couldn't store them as a single object. It's also going to saturate every reasonable detector.

As ambient neutrinos collide with the potassium 42, its likelihood for undergoing beta decay increases.

Based on what?

this setup aims to determine the direction of incident neutrinos in an effort to produce higher resolution neutrino images.

You haven't provided any mechanism that would detect that direction. If you know the direction of the neutrino source then you know that direction, but that's not a feature of the supposed detector.

You can do inverse beta decay with incident neutrinos, of course. That's different from beta decays but it also produces electrons. With the short half life of K-42, what neutrino flux would you need to make that e.g. 1% of the overall events?

 

[Ramael]

> Based on what?

Potassium 42 can undergo inverse beta decay. Discussions on using tritium to detect neutrinos go all the way back to the 1960s. Also proton collisions are potentially scalable, even though we haven't really economized particle colliders for commercial use yet. I don't think that will always be the case, though.

> You haven't provided any mechanism that would detect that direction.

Yes I have. Smectic phases have distinct layers and a direction in a liquid crystal. I described rotating the liquid crystal (A diaelectric material) in a magnetic field above in order to identify a magic angle where beta decay would be highest due the mechanism listed above. I took optics and am trying to apply optical principles to the detection of neutrinos here. When the crystal lattice is parallel to the neutrino source it would behave functionally transparent to neutrinos. But like magic angle graphene, or polarized lenses, there's an angle where the the likelyhood to collide with an atom in the lattice is maximized. In polarized lenses the distance between the nanomaterial interferes with the wavelength of visible light at 90 degrees, so its not quite the same. But the idea was to design a diffractive material for neutrinos. (still likely a very weakly diffracting material)

> Your decay heat is in the range of tens of megawatts per kilogram, so even if you could produce larger quantities you couldn't store them as a single object. It's also going to saturate every reasonable detector.

I figured it would produce a lot of heat. The liquid crystal has to remain pressurized to remain a liquid crystal. So pressure would have to taken into account and heavily controlled throughout the entire decay process. The whole reaction has to maintain a constant pressure and temperature. So keeping the material at a constant temperature, aka cooling, would also have to be taken into consideration.

Exposing the sample to a strong magnetic field may also help to confine the material and keep the crystal lattice ordered.

Regarding the half life of potassium 42, I figured a shorter half life would mean more events and therefore a stronger possible signal. Of course the noise from the background decay of the sample would be greater than your signal. But in optics its still possible to reconstruct a low resolution image with low quality data. In astrophysics, image stacking is a process that involves combining multiple images of the same object or region of the sky taken over a period of time to improve the overall quality of the final image. Each individual image might suffer from noise, distortions, or imperfections due to factors like atmospheric turbulence, telescope limitations, or sensor noise. But by aligning and averaging/combining these images, the noise tends to cancel out while the signal, such as the light from distant celestial objects, remains, resulting in a clearer and higher-quality final image.

We can apply similar methods to the microscopic as we do to extremely distant objects to produce higher resolution images even despite the noise. Although you make a valid point. The signal to noise ratio may still be so impossibly low that it becomes impractical. Still, choosing a material with a longer half life would mean fewer events and a weaker signal, so if you wanted the highest resolution image possible, it would still be better to choose a material with a shorter half life and to just find ways of separating the signal from the noise.

Also, its questionable whether it will be able to form a liquid crystal while producing so much heat. Still this was mostly food for thought. Also, I forgot that inverse beta decay produces electrons rather than positrons. Which would mean that your signal would also produce an associated gamma emission from annihilating electron-positron pairs. This could futher be used to separate a signal from the noise. So thank you for reminding me about that.

 

[Vanadium 50]

A few points:

1. You need to specify the energy range of the neutrinos you are interested in. MeV neutrinos act differently than 100 GeV neutrinos.
2. Your detector is putting out 10²⁰ neutrinos per kilogram, and neutrino detectors are many, many tons. How do you see a signal over a background that is a billion trillion times bigger?
3. The internal heat will likely vaporize the detector. You can say "keep it under pressure" but you have not said how much pressure you need to keep the detector a liquid, much less a liquid crystal.
4. Nuclear decays do not "remember" the direction of the neutrino that excited the nucleus. So the directionality argument won't work.
5. The outgoing lepton in charged current events has some correlation with the parent neutrino momentum. So your proposal would replace a correlation that could be better with no correlation at all.
6. Roughly every day your detector needs to be replaced. Typically inexpensive isotopically pure materials are $3000/g or $3B/ton. How many tons do you need? And this will not be inexpensive.

 

[Ramael]

> Nuclear decays do not "remember" the direction of the neutrino that excited the nucleus. So the directionality argument won't work.

You would get a different signal strength depending on the orientation of the crystal. Determining the direction of a continuous source would be a matter of measuring how many emissions you get at varying angles and determining its peak. You can design a program that either adjusts the orientation of the liquid crystal to track those peaks or by just surveying a predetermined area. And an array of multiple detectors would be able to triangulate distances.

I am not sure what pressures and temperatures would be required for this liquid crystal but the wattage was given above so one may be able to calculate it based on the pressures and temperatures used for regular KCl liquid crystals.

> Roughly every day your detector needs to be replaced. Typically inexpensive isotopically pure materials are $3000/g or $3B/ton. How many tons do you need? And this will not be inexpensive.

And yes I am aware that these detectors will only last a day. he he. But I'm speculating on a future where linear and toroidal accelerators benefit from mass production, economies of scale and possibly better magnets. This technology is impractical by today's standards, but if cheap particle accelerators ever became a reality than experiments like this one might become more attractive. Especially if we could make use of neutrino detectors for practical purposes. Such as imaging deep inside planets and stars. Or defence systems that can detect fissile materials. And penetrate pretty much everything.

And I guess the energy range would depend on its application. All three of those scenarios I gave, studying stars/studying earth/fissile materials, have different energy neutrinos. There are different applications you could use for the sun. Imagine if we could directly image the neutrinos produced from uranium decay and other heavy isotopes in the sun and actually measure roughly how much rocky mass it really has? Or in the distant future we could measure the neutrino profile of a quark gluon plasma in neutron stars. Plus cosmic neutrino background radiation would be able to produce an even younger picture of the universe than the CMB can.

 

[Ramael]

Oh, and by the way, have they determined whether neutrinos are their own anti particle or not yet? If they aren't, then this detector should only be sensitive to anti-neutrinos. So we would know the answer to that question the first time we use it on a source that produces regular neutrinos.

 

[Vanadium 50]

You would get a different signal strength depending on the orientation of the crystal.

No you won't. Look, it's about time you stopped making these unsubstantiated assertions and show us an actual calculation (or a reference to one).

I am not sure what pressures and temperatures would be required

Then calculate it, rather than just asserting you can do this. Note that the liquid crystal phase is lower temperature phase. (And smectics tend to have a relatively low critical temperature)

But I'm speculating on a future

We have a Science Fiction section here.

Such as imaging deep inside planets and stars

We already do that. (Well, for one planet and one star)

here are different applications

Talk is cheap. Put some numbers to it.

are their own anti particle or not yet? If they aren't, then this detector

...is no better than the existing detectors.

You asked if your idea would work. You got many reasons why it won't. You have three options: agree that it won't work, show quantitatively that it will, or be judged a crackpot. Those are the choices. Note that addressing the objections by hand waving is not one of them.

 

[berkeman]

Thread is now on a short leash, pending the calculations by @Ramael

 

[mfb]

I took optics and am trying to apply optical principles to the detection of neutrinos here.

That doesn't work. There is no neutrino equivalent to optical properties of materials. Each nucleus will see the same neutrino flux no matter where your atoms are in the sample.

You would get a different signal strength depending on the orientation of the crystal.

Even if you would - and you haven't provided an argument that would work - that's still not detecting the direction of an observed neutrino. It just means the detector would be somewhat better in some directions than others.

Regarding the half life of potassium 42, I figured a shorter half life would mean more events and therefore a stronger possible signal.

Beta decays are the background, your signal is the inverse beta decay. Choosing something with a short half life increases the background, not the signal.

But in optics its still possible to reconstruct a low resolution image with low quality data.

Yes, you can stack 100 images with a signal to noise ratio of ~1 to get an image with a signal to noise ratio of 7 or so. That approach doesn't help you if your background is a trillion times your signal. And that number is optimistic.