# Tag Info

1

The energy per time ("power") in the radiation due to heat ( the infra-red "light" that you see using a night vision) scales with the temperature $T$ of a body like $T^4$

2

there are many experiments that put different contraints on the neutrino masses. Here is a good collection from the particle data group.

3

A cloud chamber is a detector which can make visual the track of particles. It is based on the fact that supersaturated vapors will condense around charge centers, i.e. ions, and that charged particles going through the chamber will generate ions by multiple scattering. These make dots in the gas of the cloud chamber. [] The track trace depends on the ...

0

I don't think 0.96 $\mu$Sv/h or 365.25$\times$24$\times$0.96 = 8.5 microsieverts/year is a problem. To put this in perspective, Every year, we receive natural radiation : 2,000 microsieverts CT scan : 7,000 microsieverts Additional radiation in a life time for those living around Fukusima : 10,000 microsieverts US radiation worker in a year : 50,000 ...

3

The technical term for this force is the radiation reaction force and it is electromagnetic in nature. Maxwell's equations do not describe this phenomenon simply because they're not meant to; it's like asking the heat equation to describe the chemical reactions that happen in a fire. Maxwell's equations describe the electric and magnetic fields generated ...

4

All processes involving neutrinos are weak mediated because neutrinos have zero electromagnetic and color charge. At tree level, all processes involving a $\nu + \bar\nu$ final state without other debris involve a time-like $Z^0$ (except neutrino NC scattering) which implies the annihilation of a particle/antiparticle pair (and will be suppressed relative ...

3

I'm speculating here, basically looking at two considerations. Considering you used the term "radioactive decay" I'm going to look at this from a gross nuclear viewpoint rather than a particle/subnuclear viewpoint. If a nucleus is in it ground state, it would have no mode to lose energy without changing Z. So, in this case, no. If a nucleus is not in its ...

2

Really, your confusion is rooted in the fact that the equation you give relating temperature and particle mass assumes that the thing's whose temperature you're predicting is a gas of particular matter that obeys Newtonian mechanics. Light, and really anything in the early universe, decidedly does not obey Newtonian mechanics. There are several ways one ...

2

The way to understand this is as follows. Assume that the early-universe is radiation-dominated, and additionally assume that the early universe is of FLRW type with a single fluid that obeys a barotropic equation of state $p = w \mu$ where: $w = 1/3$ for radiation $w=0$ for dust $w=1$ for a stiff fluid, etc... Now, the Einstein field equations ...

0

One of the more important short half life isotopes which actually occurs (we strongly believe) in nature is $^8Be$ which is part of the helium burning, or tri-alpha, process of fusion in older stars. The half life is about 67 as, so after two alphas fuse, a third one must quickly interact, and apparently it does. This isn't the shortest lived Be, however. ...

-1

I think it is hyrdrogen-7 which is 4n decay, half life is 21x10^-23 seconds

0

All parties are to be congratulated for asking such 'key' question and exploring answers regarding 'conventionally' calculated 'binding energy' of H-3 and He-3 and the stability of each! I suggest (like Sears & Zemansky illustrated in their standard, much used old 'College Physics' textbook) that H-1, the neutral Bohr Atom mass, and specifically its ...

3

The IR radiation from a gas heater is dangerous, but not for the reasons you seem to think. Each year nearly 500 people die as a result of space heater radiation http://www.nfpa.org/press-room/news-releases/2010/space-heaters-involved-in-79-percent-of-fatal-home-heating-fires. Granted, in the US, space heaters are almost always electric, but I'm sure there ...

3

Solar radiation is pretty close to $1kW/m^2$. That's already borderline problematic for a human who is completely exposed. I would guestimate with a giant foam hand that $2kW/m^2$ for more than a few minutes is more than enough to give humans a bad time. You could, of course, test this experimentally with a 100W light bulb. What's the closest distance that ...

2

This is a standard particle-vortex duality transformation. The idea is there exists a "dual" description of a superfluid, in which the bosons (to be precise, the Goldstone mode) is described by a 2-form(tensor) gauge field, and the vortices are now string-like "matter" charged under the gauge field. The effective action for phase fluctuations (i.e. Goldstone ...

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