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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Neutron decay and electron anti neutrino $n\to p + e + \bar{\nu}_e$

Why do we need neutrino to explain neutron decay? Is there any evidence regarding existence neutrinos in the context of $n\to p + e + \bar{\nu}_e$?
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189 views

$\Omega_{r}$ from WMAP results?

To do some Friedmann-Lemaître cosmology calculations, I would like to know an estimation of $\Omega_{r_0}$ ($\Omega$ radiation today). WMAP 7 give estimation of $\Omega_{b}$, $\Omega_{c}$ and ...
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1answer
136 views

Radiative transfer equation solution

The solution of the radiative transfer equation for spherical ionized blob : \begin{equation} \frac{dI_{\nu}}{ds} = j_{\nu}-\alpha I_{\nu} \end{equation} and solution is (Ref: ...
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147 views

How do gravitational waves sustain and propagate large scale spacetime curvature?

I understand that gravity in GR is a manifestation spacetime curvature dictated by the field equations by the principle that objects follow the geodesic path in spacetime. And, I get how ...
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268 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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Possibility for radiation in dark matter that is not interactive with regular matter?

Definition: Radiation in this case does not refer to electromagnetic radiation. It refers to any kind of emission of energy, even energy that does not interact with regular matter. Just like dark ...
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623 views

Transient radiation--heating a slab

Hey guys I really need help on this problem. A ceramic slab of dimentions 5cm x 10 cm x .25 cm has to be heated to $177\,^{\circ}{\rm C}$. The ceramic slab travels on a conveyor belt traveling at ...
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Why are alpha particles made of 2 protons and neutrons?

When experiencing alpha decay, atoms shed alpha particles made of 2 protons and 2 neutrons. Why can't we have other types of particles made of more or less protons?
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How to calculate gamma radiation shielding?

A device emits 0.2 μSv/h of gamma rays. How thick does an aluminum sheet need to be to completely stop radiation from coming out ? What equation is to be used to calculate this ?
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2answers
389 views

Has Bose-Einstein theory been considered for dark matter?

Has Bose-Einstein theory been considered for dark matter? The theory would explain why no measurable radiation is emitted due to zero temperature--its lack of interaction with other matter and its ...
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What exactly is the difference between radiation and convection?

Okay, so everywhere I've read, I hear the main difference is the requirement of a medium. But for example, if you take the case of heat 'radiating' from a red-hot iron, isn't that actually convection ...
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Finding electric power generated using heat transfer

I'm working through an example I have been given to study. Suppose I have a 2m X 4m photovoltaic panel on my roof that is irradiated with a solar flux of $G_s = 700W/m^2$. Given: $\alpha_s = 0.83$ ...
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Why does a microwave oven affect other electronic devices

When I turn my microwave oven over the stove on, it will cause a motion sensor light in the hallway next to the kitchen to got off and on. This affect can be reproduced anytime. I did notice that ...
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“Dear radioactive ladies and gentlemen” - Letter by Wolfgang Pauli

In 1930, Wolfgang Pauli wrote a letter to Lise Meitner for a convention in Tübingen, considering the problem of beta decay. Does anybody know, where to find the original letter online ?
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50 views

Problem on nuclear physics radioactivity [duplicate]

Possible Duplicate: How do we know that C14 decay is exponential and not linear? Please help me solving this problem. Find the half life period of uranium-238,if one gram of it emits ...
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1answer
3k views

Why are umbrellas black?

Why are umbrellas specifically in black? Of course we do have colored ones, but black is the majority. Is there any scientific reason behind it?
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2answers
318 views

Can x-ray radiation be compared to background radiation?

I've been trying to learn about the possible effects of x-ray radiation from dental x-rays and most of the resources I come across compare the exposure to that of natural background radiation. ...
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1answer
433 views

Steady State Temperature of an Object Orbiting the Earth

This may be irrelevant or stupid to ask but I couldn't come up with a good answer. At least, we could not agree on with my friend the other day. I would like an estimate of the temperature of a human ...
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2answers
246 views

Reconstruction of information stored in an evaporating black hole from the emission spectrum?

For simple setups, where the radiation field deviates not too far from thermodynamic equilibrium (< 10 %), corrections to the Planckian thermal emission spectrum can be calculated (and measured) ...
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1answer
548 views

Absorption / Control / Reduction of EMF radiation using passive antennae & matched load

Wanted to understand the physics behind usage of passive antennae and matched load combination, to absorb, control and reduce the Electromagnetic-Field (s.a. due to microwave radiation from cellular ...
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1answer
347 views

Does neutron radiation form clouds?

I've heard a couple of scary stories from experienced accellerator physiscists about something called neutron clouds. Apparently, if you have an experiment like a fixed-target experiment that produces ...
6
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4answers
511 views

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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3answers
826 views

Can two spaceships go fast enough to pass straight through each other?

Probability of interaction between two particles tends to wane with increasing energy. Technically, the cross section of most interactions falls off with increasing velocity. $$\sigma(v) \propto ...
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61 views

Light vs. X-ray interactions with Phosphor

Looking for some information on how light and xrays interact with phosphorous, or what might cause the following: Scenario A focus beam of light is directed at a phosphor plate at the same time as ...
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0answers
220 views

How is the “negative dispersion” derived?

I'm looking at Kopfermann H., Ladenburg R., Nature, 122, 338-339 (1928) and it appears Ladenburg in Ladenburg R., Z.Physik, 4, 451-468 (1921) was the first to discover the phenomenon of "negative ...
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2answers
203 views

Does magnetic geometry determine the scaling of a Polywell fusor?

Does magnetic geometry determine the scaling of a Polywell fusor? Forgive imprecise terminology here - by "magnetic geometry" I mean the configuration of the magnets, the configuration that creates ...
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4answers
822 views

Why do electron-positron pair annihilate upon contact?

I'll a appreciate a layman's explanation, if there exists one, to this question that arose when reading an popular-science level article on Einstein and the $E=MC^2$ equation. What I mean is that, ...
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2answers
431 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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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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1answer
149 views

Radiation dosage problem [closed]

A large room is filled with air polluted with Caesium-137 at an average density of 1 Cs-137 particle per $\text{cm}^3$. A human is sitting inside the room for duration of $T$. What is the total energy ...
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5answers
440 views

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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2answers
187 views

Is there a reason for photodynamic therapy to not cause cancer if mobile phones might?

I don't want to open a debate about whether cell phones can cause cancer, I read the thread: Could cell-phone radiation cause cancer? For the sake of this question let's assume there's a chance for ...
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748 views

Sunflowers and radioactivity

I read yesterday that sunflowers were used and to cleanup radioactivity at Chernobyl and the Atomic Bomb sites in Japan and may be used as part of a campaign to clean up the Fukushima area. But my ...
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46 views

radioactive decay in molecular constituents [duplicate]

Possible Duplicate: What happens to chemical compunds that include radioactive nuclei, when those decay? Suppose a radioactive atom, which is incorporated in a molecule, decays? What ...
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Decay of massless particles

We don't normally consider the possibility that massless particles could undergo radioactive decay. There are elementary arguments that make it sound implausible. (A bunch of the following is ...
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1answer
370 views

Laptops in space

I was reading an article regarding the Shuttle's GPCs and how they stack up against commercially-made hardware on http://www.nasa.gov/mission_pages/shuttle/flyout/flyfeature_shuttlecomputers.html and ...
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3answers
2k views

What other shielding material than lead is effective against gamma rays?

As the question in the title states I am wondering what material can be effectively used to shield gamma rays apart from lead? I believe concrete is often used, but it is nowhere near as effective as ...
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Are dangerous rays emitted during Solar Eclipse?

It is said one should avoid staring at Sun as it can damage the eyes, but it is also said that one should not come out in sun during eclipse as it emits dangerous rays. Is that true? If yes, why?
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406 views

Nuclear decay rate affected by sun and quantum randomness

If nuclear decay rate were affected by sun, then emission probabilities would be subject to sun state and its influence, so quantum randomness would depend on it, Would it still be truly random? One ...
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1answer
398 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: ...
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2k views

Tunneling of alpha particles

Consider this explanation of the alpha decay: It says The Coulomb barrier faced by an alpha particle with this energy is about 26 MeV, so by classical physics it cannot escape at all. ...
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1answer
704 views

Wien's fifth power Law and Stephan Boltzmann's fourth power laws of emissive power

Wien's fifth power law says that emissive power is proportional to the temperature raised to the fifth power. On the other hand, the Stefan–Boltzmann law says emissive power is proportional to the ...
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2answers
341 views

Do and can phone signals come inside AC car which is glass-packed

Can phone signals penetrate glass, so can I expect phone signals to come if I am sitting inside a closed AC car. Thanks,
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416 views

Is there a way to decrease the rate of nuclear Beta decay?

In that question and its answers it was mentioned that you could trigger radioactive decay by bombarding atoms with gamma rays of the right energy level (there may be other solutions I do not know ...
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2answers
301 views

What is the risk from radiation on imported food from Japan

I'm currently resident in Hong Kong a country which appars to import heavily from Japan. Last saturday 7th May I went to a restaurant: http://www.openrice.com/english/restaurant/sr2.htm?shopid=39760 ...
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1answer
193 views

The most stable metal for radioactive environment

Could you suggest which metal/alloy shows the least activation & better long-term stability for space (LEO, inside Van allen belts, deep space) applications? Or stability of construction ...
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1answer
154 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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3answers
767 views

Are these radioactive particle matter and air emmissions dangerous, 2000KM from Fukushima?

I have 2 questions, as a expat and new parent residing in Shanghai (2000km from Fukushima) where we are now experiencing radioactive fallout from the Fukushima Nuclear Plant (Japan), we can not get ...
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1answer
118 views

Solar Cycle UV Variation

The average energy we receive from the Sun is 1,366 w/m^2, and this only varies by 0.1% from the activity peak to trough of its 11 year cycle. About 9% of the energy comes from wavelengths less than ...
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959 views

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 ...