Comment by PaulHoule | Hacker News Reader

Comment by PaulHoule | Hacker News Reader

One interesting thing about muon accelerators is that they could produce enough neutrinos to be dangerous:

https://accelconf.web.cern.ch/p99/PAPERS/WEBR6.PDF

which might be a good thing in that the neutrino mass is a "missing part of the standard model" as opposed to "possible physics beyond the standard model". The neutrino mass term could explain dark matter, dark energy and the matter-antimatter asymmetry

https://arxiv.org/abs/1303.6912

whereas a Higgs Factory or top factory seems likely to be a big disappointment because all the evidence we have is that the Higgs field is as simple as it could possibly be and a top factory might end up just verifying that complex calculations people did 40 years ago (by the time the machine comes up) were right.

Muon colliders are a possible path to a Higgs factory or top factory but the path to a muon accelerator that can revolutionize precise neutrino physics is much shorter and I think more rewarding.

Notably neutrino physics is win-win. Either the right-handed neutrino exists as a heavy particle and is very likely to be the darkon or the neutrino is a Majorana fermion (is its own antiparticle) which is certainly a weird and interesting result. Contrast that to all the other poorly motivated darkon candidates such as sparticles, axions, etc.

I remember reading a lot of papers about muon accelerators about 20 years ago, they have been a big research topic in the US and Japan because we didn't have CERN.

My initial gut reaction was that the authors were ignoring the obvious solution of simply putting the ring below ground level and setting up maintenance walkways above the ring instead of next to it.

Then I realised the the Earth is spherical and that it doesn’t matter how deep you put this thing, the beam will come out somewhere, even if it needs to go through a thousand kilometres of regolith to get there.

So there could be some random patch of grazing land somewhere in another country that’s dangerous to go near whenever the experiment is running.

PS: I solved the funding problem! Just tell the military about this new unstoppable death ray that can kill anyone even through the planet. [Disclaimer: death will be a decade from now due to cancer. Victim must remain stationary for one year. Construction work is required to retarget beam.]

>Construction work is required to retarget beam.

If you mount two of them like a gyroscope, inside a spherical opening, the planes could overlap into a target-able beam.

> they could produce enough neutrinos to be dangerous

Dangerous in the sense of "ionizing radiation" or in the sense of "this will overturn careers"? Getting killed by neutrinos sounds like a freak accident from a sci-fi story.

Read the paper. You could get a dangerous dose if you were near the plane of the accelerator.

"near" is a relative term that isn't specific enough to get an idea of how dangerous something is.

It's dangerous to be near hydrogen sulfide. It's dangerous to be near a primed hand grenade. It's dangerous to be near an artillery shell impact. It's dangerous to be near a drunk driver. It's dangerous to be near an active battlefield or even near a war.

But they are all different nears.

When you say its dangerous to be near the plane of the collision, are we talking 1m, 10m, 100m, 1000m, etc? Are there dangerous byproducts created that might kill you even after the event itself? That's useful information. A general "don't be near" isn't really helpful.

My reading is that "in the plane" literally means in the plane, +- a couple or tens of meters, depending. The paper is concerned with effects on the earth's surface, in an aircraft or orbit the duration of exposure and lack of stuff for neutrinos to run into probably means it's less of a concern. To put a number on it, they give examples of accelerators buried at 300 meters which would create a radiation hazard at a radius of 62 kilometers where the plane exits the surface (assuming earth is spherical).

As far as the danger, the paper estimates up to a few mSv/year if you hung out in the wrong place all the time. You definitely wouldn't want to have a town in the way of that, but it's not an immediate danger on an individual level. The danger would be greater/more concentrated if there were straight segments in the accelerator, or if it was closer to the surface (smaller circle of intersection).

"My reading is that "in the plane" literally means in the plane, +- a couple or tens of meters, depending."

What wad said was so vague as to be practically useless.

"...they give examples of accelerators buried at 300 meters which would create a radiation hazard at a radius of 62 kilometers"

Again, this is overly vague and unhelpful. As I replied to LegitShady, no specific mention is made about the type of radiation dangers or how long radiation would be expected to linger in soils etc.

Well said. I was annoyed by the lack of specific information for exactly the reasons you mentioned

More specific estimates of safe distances versus collider power would be helpful, same too about the nature and type of radioactive byproducts in soil (what elements would be expected to become radioactive along with their half-lifes, etc.).

Sometimes I think it ought to compulsory for scientists to study philosophy—at least its parts that deal with logic, language and semantics.

Philosophy defines near —like good— as a 'simple notion' that cannot be subdivided into simpler terms. The word needs qualifiers/quantifiers (figures, distances, amounts) for it to be useful—info that the paper was overly vague about or omitted to specify.

Next time this argument is made include references to Betelgeuse, Yellowstone, and super massive black holes.

From the paper:

> Most of the ionization energy dose deposited in a person will come from interactions in the soil and other objects in the person’s vicinity rather than from the more direct process of neutrinos interacting inside a person. At TeV energy scales, much less than one percent of the energy flux from the daughters of such interactions will be absorbed in the relatively small amount of matter contained in a person, with the rest passing beyond the person.

If you're looking to get bit by a radioactive spider, spiders living down range of such a collider might be a decent place to start.

With high-energy particles the showers made when the particles hit something can be more dangerous than the original particles.

For instance if you are building a space colony there is an optimal thickness for the biological shield: most high energy particles blast right through you and if you have too much shielding there are too many opportunities for a particle to explode a nucleus in the shield and multiply the number of radioactive particles dramatically. Off the top of the head I'd say about six feet of soil is about right, but you don't do better with 60 feet or anything reasonable until you are talking multiple kilometers (maybe of vacuum or air space) that give shower muons time to decay.

Speaking of muons, it is an easy experiment often used in physics education to measure the the lifetime of cosmic ray muons produced in showers.

https://www.physlab.org/wp-content/uploads/2016/04/Muon_cali...

If a muon gets slowed down by matter you see a pulse of radiation, then you see a pulse of radiation a few microseconds later when the particle decays. If you measure the time gap in two-pulse events you can get the half-life. It was a popular experiment in Cornell's 510 lab for grad students who weren't particularly interested in doing experiments because it was so easy.

Doctor Manhattan

Dangerous enough to cause partial meltdown if they hit fissile material.

In theory hitting nukes with energetic neutrino ray would be enough to disarm them. By melting fissile material under normal circumstances.

Here's the full version of the first paper,

https://arxiv.org/abs/physics/9908017 ("Potential Hazards from Neutrino Radiation at Muon Colliders")

wow, i would not have imagined you could possibly produce a dangerous dose of neutrinos! the numbers involved must be extremely high.

Related XKCD: "How close would you have to be to a supernova to get a lethal dose of neutrino radiation?"

https://what-if.xkcd.com/73/

Note that these neutrinos (from the collider) have much higher energy than those from a supernova.

Interestingly, that may actually make the collider-produced neutrinos less dangerous than those from a supernova. I'm not sure how it translates to other types of radiation, but at least for neutron radiation (e.g. cosmic rays) the amount of energy one would absorb peaks and then falls off at higher energies. Not harmless though, just slightly less dangerous.

Neutrino cross sections increase with energy, so these are much more dangerous than from a supernova. Note that when they do interact, much or all of the energy of the neutrino manifests in a form that can then interact further, so the more energetic neutrino also creates more secondary radiation when it does interact.

That's really interesting, thanks for the clarification

It's not their number so much as their energy. The cross section for energetic neutrinos interacting with matter scales as energy squared, if I recall correctly. These neutrinos have cross sections too low to shield, but too high to ignore.

Yes, but I'm guessing you still can't blast someone on the opposite side of Earth with a stream of neutrinos going right through the core.

> enough neutrinos to be dangerous

That would have to be a huge amount of these little things.

... and higher energy so that they have a higher interaction cross section

https://arxiv.org/pdf/1305.7513.pdf

There will be bad sci-fi movies about this.

> they could produce enough neutrinos to be dangerous

I find hard to believe that we can produce more neutrinos that the sun produces.

Doesn't the beam intensity decrease with the square of the distance?

This is fascinating. Never would have thought neutrinos could be a problem!

There was a discussion two months ago (https://news.ycombinator.com/item?id=39271472) about a paper on using neutrino beams to destroy nuclear weapons, which showed that neutrinos can be dangerous.

Reply on news.ycombinator.com