Radiation is a process in which energetic particles or energetic waves travel through a medium or space. The particles or waves radiate (i.e., travel outward in all directions) from a source.

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Why doesn't diamond glow when hot?

In an answer to this SE question, the respondent explains that heating a perfect diamond will not cause it to glow with thermal blackbody radiation. I don't quite follow his explanation. I think it ...
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How is the Earth heated by a Full Moon?

While the moon is certainly not a good reflector of solar radiation, surely the radiation it reflects back heats the Earth (even if it is a terribly small amount). How would one go about calculating ...
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Why do $\beta$ particles not get attracted to the nucleus?

I currently have a very limited knowledge of how radiation works etc, but while sat in class the other day, one question occurred to me that even my teacher could not answer. We have been learning ...
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Interpretation of Wigner function in optics

I work in the field of synchrotron radiation sources where radiation (often x-rays) is produced from an electron beam going through magnetic fields. The quality of the resulting x-ray beam is ...
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16k views

What common materials can effectively block infrared radiation?

I have a plastic container and want to make sure that infrared radiation (specifically, in the 750-850 nanometer range) cannot pass through it. Would wrapping it in aluminum foil do the trick? If not, ...
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109 views

How did Lyman discover his series?

How did Lyman discover his series in hydrogen atom? How did he know that the final energy level is the first level and not the second or the third or etc.? Or how did the other scientists know which ...
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410 views

Do photons make the universe expand?

I have a problem understanding the ideas behind a basic assumption of cosmology. The Friedmann equations follow from Newtonian mechanics and conservation of Energy-momentum $(E_{kin}+E_{pot}=E_{tot})$ ...
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720 views

Why don't we use beta radiation for making electricity?

Why don't we use beta radiation to make our electricity? Since it is an electron being released/made, it would make sense to try and capture it. But, we obviously don't so. What am I missing in my ...
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381 views

why can't you use your cellphone on an airplane? [closed]

why airplanes are banned with use of cellphones? What were the impacts while we answer an call or make an call ,what was the physical reason behind the ban of using cellphone inside airplanes ? I ...
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532 views

Cosmic ray hazards

The Pierre Auger Observatory site mentions the detection of a 3E20 eV (48 J) cosmic ray whose energy, well above the GZK cutoff, was based on an analysis of its atmospheric shower. This was equivalent ...
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Why is an opaque body opaque?

When does a body qualify to be called an opaque body? Is it anybody which cannot let visible light through it or is there any other definition? And when and how does a body allow radiations through ...
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2 ways to generate electromagnetic wave

According to Maxwell's equations, accelerating charges emit electromagnetic radiation. According to Quantum physics, heating causes electromagnetic radiation too. These 2 radiations, are they ...
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686 views

Confusion about Length Contraction (ex in Muon decay)

I am a bit confused about the implications of length contractions; For example, in the muon decay problem, we assume that the distance between the muon and the earth is contracted only in the frame ...
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Where is radiation density in the Planck 2013 results?

I've been looking at the Planck 2013 cosmological parameters paper, trying to update my toy cosmology simulator with the most recent data. Most of the interesting values such as $H_0$, $\Omega_m$, ...
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516 views

Death by neutrinos - polonium go home

In Randall Munroe's What If? He is calculating the Lethal Neutrinos dose. If you observed a supernova from 1 AU away—and you somehow avoided being being incinerated, vaporized, and converted to ...
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Would being underwater help survive a nuclear bomb?

If I jump in my pool, on the river near my house knowing that a nuclear bomb, or atomic or H-Bomb exploded around 10 km from my house, would I survive? The way I see it is that water will protect me ...
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Do brick walls effectively protect against ionizing radiation from a nuclear explosion?

Of course it depends on the distance and the amount of radiation, so let's say its about 10,000 Rad. Now, can wall made of brick protect someone behind it from such radiation ?
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Radioactive decay - What mechanism decides when an unstable nucleus decays?

My first question on Stackexchange (if it is formatted wrong or something please tell me so I know in future) - here it is: Given an unstable nucleus (exactly which nucleus is not particularly ...
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How can blackbody radition be explained by quantization?

I don't understand why quantization makes a peak on the blackbody radiation curve (so there is no UV catastrophe) and the relationship between that peak and quantization concept. When the blackbody ...
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847 views

Why doesn't a nuclear fuel pool become irradiated?

Why doesn't the volume of water in a nuclear fuel pool become irradiated? Why wouldn't the water around the pool become radioactive and circulate around making the whole thing deadly? My question ...
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What is the temperature of the clear night sky from the surface of Earth?

Before you all jump in with 2.73 K or thereabouts, this is more of an experimental question. It will obviously depend on humidity and radiation being scattered back towards the surface of the Earth. ...
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178 views

Earth's magnetic field shields us… from what threat?

This is a nice artistic picture of the magnet field of the earth, shielding us from the solar wind. (source) Wherever you look, it is stated that without our shield, life would not be possible on ...
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228 views

Energy balance for beta decay of cobalt-60

I am confused by a simple fact about the $\beta^{-}$ decay of ${}^{60}{\rm Co}$ nucleus. According to Wikipedia, the most likely decay branch is to an excited state of ${}^{60}{\rm Ni}$, see the ...
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678 views

Radiation emission and absorption

Any object can emit and absorb radiation and the power of emission can be represented by the Stefan-Boltzmann law: $$P=A\epsilon\sigma T^4$$ In many texts the net power radiated is the difference ...
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159 views

Oort Cloud Detection

The hypothetical Oort cloud is an explaination for long period comets. It presumably is made up of icy bodies orbiting up to 50,000 AU from the Sun. If so, shouldn't the Spitzer IR telescope have ...
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Why do microwave ovens use radiation with such long wavelength?

According to Wikipedia: Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in). Typically, I put the dish inside the oven in its center. I suspect most ...
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498 views

Acceleration of electric charges and radiation

According to classical electromagnetic theory, accelerated charges should emit radiation and lose energy. The reason given in my book why atoms don't emit radiation (say, when the atom moves along a ...
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415 views

Is there a direct relationship between an isotope's neutron count and radioactivity?

In my textbook, it lists isotopes of Carbon: C-12, C-13, and C-14. It noted that C-14 is radioactive (C-12 and C-13 are not). Is there a direct relationship between the number of neutrons and an ...
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168 views

Radiation exposure to a child who was briefly in the presence of an adult who had received a 18FDG PET scan

I am a physician who thought she was good at math, but apparently am not as I cannot figure out this mathematical/physics question. (My background is obviously NOT nuclear medicine!) A family friend ...
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2answers
362 views

Why is the excited state of 116 Indium more stable than ground state?

Why is the excited state of 116 Indium more stable than ground state? Both undergo beta decay, but the ground state has a half-life of 14 seconds, while the excited state has a half-life of 54 ...
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439 views

Optically thick media

What does "optically thick media" mean? Does this property depend on the length of an enclosure? Why is the diffusion approximation for the radiative transfer equation applied to optically thick ...
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2k views

Maximum electron momentum in $\beta^-$-decay

This should be easy, but I think I have a mind-block... For $\beta^-$-decay, what is the maximum possible momentum for the electron? The two equations I can use are conservation of energy and ...
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What is the required thickness of concrete needed to entomb a leaking reactors emissions?

What is the minimum thickness of an aggregate concrete membrane to prevent radioactive particles from escaping a broken reactor? I am interested in calculating the amount of concrete required to ...
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1k views

Can extra-solar gamma rays reach the Earth's surface?

Can gamma rays of high enough energy entering our planet's atmosphere reach the surface (50% probability)? Or, in other words, is there a window for extremely high-energy gamma rays like for the ...
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678 views

Where does the excess energy emitted by a microwave go?

If there is nothing in the microwave, where does the excess radiation go? Why doesn't the radiation accumulate and blow it up? Should I cook two pieces of Canadian Bacon twice as long as I cook one?
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Without a reactor vessel breach, how does radiation build-up in containment buildings of troubled nuclear reactors?

It seems that at Three Mile Island and in Fukushima, there was a build-up of radioactive gasses, and other gasses like hydrogen in the containment buildings. Wikipedia says: The containment ...
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The role of W bosons in the weak nuclear force and beta decay

I am a beginner Physics student and I am studying the weak nuclear force and how particle interactions work. Now, from my book and the Feynman diagram, I learned that a neutron can change into a ...
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148 views

Can Half Lives (hypothetically) be Measured by Wave-functions?

I understand that half-lives are measured over several days/months/years of observing a certain amount of an element and seeing how long it takes to decay a certain amount, but I'm curious as to ...
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279 views

How to block neutrons

What is a good way to block neutrons and what is the mechanism that allows this? It's my understanding that polyethylene is somewhat effective. Why?
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227 views

Does any lower frequency electromagnetic radiation naturally reach us from the Sun?

I am not sure whether the sun originally emits everything in the electromagnetic spectrum, (whatever the relative strengths of each portion might be), but I do read that many waves, including gamma / ...
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What is the difference between Radiation and Electromagnetic Radiation

Are the two equivalent or is Electromagnetic Radiation a subset of Radiation. I am further confused by the fact that electromagnetic radiation includes both ionizing and non ionizing types of ...
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How does quantization solve the ultraviolet catastrophe?

I understand how classical physics leads to the UV catastrophe. But I cannot understand how quantization solves it. How can quantization prevent the body from radiating a lot of energy? I know ...
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643 views

One way insulation?

I know from basic physics lessons that a box painted black will absorb heat better than a box covered in tin foil. However a box covered in tin foil will lose heat slower than a black box. So what ...
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Why does positronium decay into 2 photons more often than into 3 photons?

I cannot find the answer to the above question. I know that para-positronium is created with a probability of $25\%$ and decays into 2 photons, while ortho-positronium is created with a probability ...
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97 views

$\alpha$ decay to more than one nuclear state

I do not understand how $\alpha$ decay can be a probabilistic process such that there are multiple products from the decay. For example: $^{241}\mathrm{Cm}$ decays to the excited states of ...
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80 views

What produces this 477 keV spectral line?

Question about a specific line on a gamma spectrum, here. Below is a background gamma spectrum observed by a Ge[li] detector. I've been able to identify all the lines with mostly certainty, apart ...
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Temperature effects on lead against radiation

I would like to know if bringing lead to near absolute zero temperatures would have any affects on how resistive it is against gamma radiation. It takes 40 centimeters of lead to reduce gamma ...
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2answers
182 views

What is the connection between the non-reversibility of the decay of unstable nuclei (as Uranium, Plutonium) and the 2nd principle of thermodynamics?

The 2nd principle of the thermodynamics says that if a system (e.g. an ideal gas) is left undisturbed, its number of microscopic states only increases. This is a statement of irreversibility of the ...
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Soft Bremsstrahlung: why $\hat{k}\cdot\mathbf{v}= \mathbf{v}'\cdot\mathbf{v}$?

On page 181 in Peskin & Schroeder they say that we consider the integral (intensity) $$\tag{1}\mathcal{I}(\mathbf{v},\mathbf{v}') = ...
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569 views

Transverse current equivalence in Coulomb gauge

I have a question concerning transverse (solenoidal) current in the Coulomb gauge. This current is the one that enables the radiation, since we have a wave equation for the vector potential: ...