# Tag Info

15

This problem originated with passengers using electronics (they call them PED's - portable electronic devices) during flight. While all consumer electronics have to be qualified by a regulatory body (FCC, etc.) to prove they do not emit harmful interference, this doesn't mean they emit no interference especially to high gain sensitive navigation equipment. ...

14

Actually, all the atoms are identical. The time at which it is observed to decay is not an intrinsic property of a given atom, but rather an effect of quantum mechanics. For any given time bin, there is some finite amplitude for a transition to a decayed state, which in turn corresponds to a finite probability, since the particle(s) emitted will escape from ...

12

The reason why alpha particles heavily dominate as the proton-neutron mix most likely to be emitted from most (not all!) radioactive components is the extreme stability of this particular combination. That same stability is also why helium dominates after hydrogen as the most common element in the universe, and why other higher elements had to be forged in ...

10

The field of the accelerated charge cannot change instantaneously. From "Gravitation" by Misner, Wheeler, and Thorne. So it does have an electric field-but why does accelerating a field(which is in the answer below) cause light to be made? Or rather, why wouldn't a constant velocity just do it? The field of a uniformly moving charge does not ...

9

It may have something to do with the growth rate of sunflowers. During peak growing times sunflowers can grow inches in a single day, which likely results in them drawing more water out of the ground, allowing them to concentrate the radioactive materials through deposition in the plant matter at a faster rate than other plant organisms. I would suspect ...

9

To pretty much everything you stated in your question, "no". That convection requires a medium is not the main difference, it is simply the most obvious aspect of what is a fundamentally different mechanism for transfering energy. Convection is the transfer of energy by movement of a medium, whereas radiation is the transfer of energy by, well, thermal ...

9

You can get an upper limit by simply treating the case of The radioisotope structured as a point source. The whole dose still present, corrected for half-life. No shielding. A simple $\frac{\text{presented area}}{4\pi r^2}$ for the acceptance (in this case the radiation is emitted in all directions, acceptance represents the fraction that hits the target, ...

8

Short answer: no. Longer answer: No, excepting neutrinos none of the products of radioactive decay has the penetrating power to pass through the atmosphere, and neutrino detection is not something we can do from satellites. To elaborate, the immediate products of radioactive decay are (some set of, depending on the decay in question) fission fragments, ...

8

Ultra-high energy cosmic rays all come from a very, very long way away (anything with the power to create them nearby would constitute a danger to life as we know it). I think the preferred mechanism these days is dynamic acceleration in the jets formed by active galactic nuclei, but don't quote me. Anyway, ultra-relativistic though they are, that means ...

8

Pasted text of the letter in English - the link also contains the original typed German letter. Open letter to the group of radioactive people at the Gauverein meeting in Tübingen. Zürich, Dec. 4, 1930 Physics Institute of the ETH Gloriastrasse Zürich Dear Radioactive Ladies and Gentlemen, As the bearer of these ...

8

The neutron is made of two down quarks and an up quark; the proton of two up quarks and a down quark. This leads to two effects that differentiate their masses. One is that the up and down quark themselves have different masses. The other is that the proton is charged, and so quantum corrections involving virtual photons affect its mass. The details are ...

8

The simple answer is no, though as usual in Physics things are a bit more complicated than that. There are several ways in which radionucleotides decay: alpha decay, beta decay, gamma decay, and fission. These are all mediated by the weak and strong nuclear forces, though the electromagnetic force plays some part in alpha decay and nuclear fission. There is ...

8

Although none of these questions is an exact duplicate, there is a lot of overlap, and I hope we can avoid stringing this kind of stuff out indefinitely. The good news is that you're apparently being very cautious about the safety hazards of your planned matter-antimatter spaceship -- hazards that science fiction authors typically blithely ignore. Please let ...

8

You are always subjected to a low background of ionizing radiation from a number of natural and artificial sources, which include cosmic rays, trace amounts of radioactive nuclei in the air and in food, and indeed from the ground. A good place to read up on this is the corresponding Wikipedia article. The radiation from the core, however, has no chance of ...

8

In fact, an electric charge at rest on the Earth's surface is accelerated and this actually poses a challenge to the idea that uniformly accelerated charge radiates. I believe this is still an open question. For example: One of the most familiar propositions of elementary classical electrodynamics is that "an accelerating charge radiates". In fact, ...

8

How do I stay alive to be killed by neutrinos? You wouldn't. The point is being made that even the beam of neutrinos with a supernova at one astronomical unit distance would be intense enough that enough of them would interact with the matter of your body to be lethal. So even the neutrinos would get you if all the other stuff - notably $\gamma$s didn't. ...

7

It is not a matter of "falling in": all s orbitals have non-trivial probability densities at the center. It is about energy balance in the nucleus. Kr-83 is a lower energy configuration than Rb-83 by enough to make up for the neutrino and the gamma(s). Evidently Kr-85 is not a sufficiently lower energy state than Rb-85.

7

The color of a surface doesn't reliably indicate the emissivity at non-visible wavelengths. The color in the visible spectrum is more of a side effect than anything. Most thermal radiation around body temperature or room temperature happens in the infrared region, not the visible, and that's not reliably indicated by visible color: The transparent ...

7

I hear that the WC-135 Constant Phoenix has recently been deployed to monitor radiation in the air around Japan. The Vela satellites which were operational until 1984, and currently the DSP satellites, are intended to give immediate reports of nuclear bomb detonation and ICBM launches. The Vela satellites included gamma ray detectors, which accidentally ...

7

Schrödinger came up with the cat in 1935, which was relatively late in the development of quantum mechanics. Back in the 1920's there had been a lot more uncertainty. The Copenhagen school had wanted to quantize the atom while leaving the electromagnetic field classical, as formalized in the Bohr-Kramers-Slater (BKS) theory. De Broglie's 1924 thesis ...

7

There are many reasons for this situation. Power produced is non-adjustable. The battery produces power at nearly constant rate (slowly decaying with time). It cannot be increased and if not consumed (or stored) the power is lost. (Mentioned by DumpsterDoofus) low power density. ${}^{63}\text{Ni}$ for instance produces ~5 W/kg (and kg here is just mass of ...

6

Indeed, it's likely that the rice came from Japan, and if it did, it's pretty likely it came from the Fukushima region which is famous across Japan and beyond for its rice - and other products. However, it could have been harvested before the tsunami. But as discussed here, Are these radioactive particle matter and air emmissions dangerous, 2000KM from ...

6

There's certainly no problem being out in the Sun during an eclipse: There's nothing being emitted then that's not being emitted at other times. The danger is just that the relative darkness near totality may make it seem safe to look at the Sun, even when it's not. But as long as you don't look directly at the Sun, you're fine. During the time when an ...

6

There is nothing magical about lead for this purpose. The driving factor is the number of electrons per unit volume, which reduces (to a first approximation) to the mass density. You get very good (better than lead) shielding performance from gold, tungsten, mercury, etc; and quite reasonable performance from iron or copper. Question for the student: why ...

6

The bad news: Space radiation is much harsher compared to boring gamma rays from our primitive nuclear reactors. Space radiation has much higher energy levels, and you cannot completely shield it, even with 10 meters of lead (which is in fact not very effective for neutrons). The good news is that an individual gamma photon, for example, usually would not ...

6

Thermal neutrons capture on hydrogen and carbon with reasonable (i.e. not large, but significant) cross-sections (this is the delayed event detection methods of most organic liquid scintillator anti-neutrino detectors--i.e the one that don't dope their scintillator with Gadolinium). So though a "cloud"--meaning a localized diffuse gas--of neutrons can ...

6

As @dmckee says the problem is complicated. It is complicated because it is not a solution of a potential describing one force, but a balance between electromagnetic forces and the strong force that is keeping the quarks within the nucleons. (In the nucleus the strong force is like a type of Van der waals potential, a higher order interaction, overflowing ...

6

Hint :You have masses (from parent nuclei mass you can get mass of daughter nuclei by subtracting mass of $\alpha$ particle , and the Q value ie. the energy that gets liberated and $931.5 \ MeV \approx 1 amu$ and so you can see the excess mass is easily negligible ie $<0.1amu$ $^{212}Po \rightarrow \ ^{208}D + \ ^4\alpha$ momentum is zero ...

6

When people say that the decay rate depends critically on the $Q$ value, they're talking about alpha decays compared to other alpha decays. When you compare alpha decay to emission of other small clusters, the dependence on the atomic number $Z_c$ of the emitted cluster is much more prominent. The reason is as follows. In the Gamow model of beta decay, we ...

5

First, just recall that one becquerel is one radioactive decay per second. If your spinach has had 1-3 Bq/kg, then you should just completely forget about any threats - there is no danger whatsoever. The safe limits are 100-500 Bq/kg, see e.g. http://www.anarchyjapan.com/2011/04/for-now-no-changes-in-food-radiation-safety-levels/ which are 100+ times ...

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