Questions tagged [radiation]

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 does light not propagate backward in dense media?

It is easy to see how light propagating in a dense medium destructively interferes laterally and constructively interferes in the forward direction. This is why light will travel forward in such a ...
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On the right-angled fork track of alpha particles

In high school we were told that the idea "alpha particles are actually helium nuclei" came from observing the right-angled fork track, produced by placing an alpha source in a diffusion cloud chamber ...
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Why bulk of HPGe detectors is doped?

When I am looking at schematic diagrams of HPGe gamma spectrometer detectors (like this Ortec GLP one), it is often mentioned that bulk of Ge is doped. In this example - P-type doped. Is there a ...
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"Single-shot" Heat engine efficiency limits

The sun is 5778K and Earth is ~290K. Using the sun as the hot reservoir and earth as a cold reservoir we get 95% Carnot efficiency. However, the solar power efficiency limit is only 86%, see: http://...
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Shield gamma/X-ray/ultraviolet radiation without blocking radio waves

I was theoretically considering building an airtight enclosure that shielded the insides from gamma/X-ray/ultraviolet radiation but did not block radio waves (so that communication would not be ...
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Frequency spectrum of bremsstrahlung

I have tried to find a method to derive the spectrum of the emitted radiation of accelerated relativistic charged particles but I've never found such a method in any books. Does anyone know a method ...
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Do Solar Cells Regenerate After Exposure to Ionising Radiation?

In the past, plenty of research has been done on the effects of ionising radiation on solar cells. This is due to the importance of high efficiency solar cells for electric spacecraft propulsion. Such ...
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Interaction with Gravitational Radiation

I have a question about hypothetical gravitational radiation. To put it simply, is there any sort of material or field or other force which can interact with it? I'm thinking about lenses and mirrors ...
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Equivalent Dose absorption from Na22 source

No idea what exactly the rules are or how I should ask this question, but here's the verbatim quesiton: "A Na$^{22}$ source has an activity of 100 $ \mu $C. If you handle the source, how big is the ...
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Trouble justifying calculation of force on a sphere due to radiation pressure

I am attempting to calculate the force on a sphere in a plane wave of light where the light has intensity $I$. My calculations have concluded that, regardless of whether or not the sphere absorbs or ...
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Surface UV exposure with cooler star

If the sun's surface was ~ 4000K (and earth closer to compensate), the UV component of the radiation would be less. However, UV makes ozone via photolysis of oxygen. Also, the stratosphere would ...
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Effect of Background Radiation on a Transmitted Signal

I'm coding a basic simulation of using error correcting codes to transmit data from a satellite back to earth. I'm not sure what to set the "noise level" to. Let's say a satellite orbiting Mars ...
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A problem concerning the change of temperature and spectrum of a filament

The spectrum of a filament has been given before, the left one having the lowest temperature, the middle with a medium temperature and the right one with the highest. My question is this: Why does the ...
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Are scalars starting at around 1300 MeV analogous to some kind of sound in the vacuum glue?

Are scalars starting at around 1300 MeV analogous to some kind of sound in the vacuum glue? Background: There are scalars starting at around 1300 MeV which are probably some combination of glue-...
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Does accelerated charged particles violate the conservation of energy?

While trying to understand the Wheeler–Feynman absorber theory, I read that the motivation of the theory was to explain why accelerated charged particles doesn't violate the conservation of energy by ...
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Confusion over Feynman’s description of the Wu experiment for parity violation

In his lecture on symmetry in physical law, Feynman said: Using a very strong magnet at a very low temperature, it turns out that a certain isotope of cobalt, which disintegrates by emitting an ...
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Work done by radiation on an electron

I'm studying quantum mechanics (already done with relativity) and I'm trying to understand the matter-radiation interactions. It's said everywhere that matter emits or absorbs photons but nowhere it's ...
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$Q$-value in Beta decay

I was reading about the mass defect or $Q$-value in Beta Decay and the book that I was following said this, It iscalled beta minus decay as negatively charged beta particles are emitted. The rest mass ...
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Radiations in static fields by poynting Vector

Why is the Poynting vector $\vec S=\frac{1}{\mu_0}(\vec E\times \vec B)$ not able to produce radiation when fields are static?
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How much potential energy is in a tritium glowstick?

I have a small tritium key chain light I got for my birthday. It will glow for decades, so I thought it would be fun to try to figure out how bright it is in lumens, and how much energy is stored in ...
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What will eventually happen to a coin spinning in space?

There were some answer comments at Is it possible to make the Sun spin a coin in space? that could be a question in their own right, so here it is. Posit that we have a coin in space, on both faces ...
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Why gravitational waves can only be generated by a time-varying quadrupole moment of the mass distribution?

The (rather old) source I dispose of "Sexl, Urbantke : Gravitation and Cosmology" describes the radiation of gravitational waves only rather sketchy. So why gravitational waves are only generated by ...
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Is this the correct interpretation of specific intensity?

I've always been taught to define specific intensity as the following quantity: if I have a detector here next to me with an area element $dA$ and I detect a power element $dP$ from a source of solid ...
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Does a fusor emit dangerous radiation?

I noticed some online videos where people have built these things in their house or garage. Is it dangerous to do so? The high voltage appears to be a potential hazard, but what about radiation -- ...
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Polarization of radiation emitted by a rotating charge

Why is the radiation emitted by a rotating charge circularly polarized?
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How do you calibrate a proton-recoil scintillation fast neutron detector?

I have a proton recoil scintillator, but gamma sources like Cs-137, Co-60 don't seem to have linear calibration for the device. Are there other ways of calibrating this device? I'm trying to detect ...
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How long until the Tesla Roadster in space turns white?

The car launched into space by the Falcon Heavy rocket is painted red. But it's not in any kind of protective container so it'll be exposed to direct and unfiltered sunlight for a really long time. ...
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Positive frequency modes and lightlike coordinates

My question is about defining positive frequency modes of radiation in a generic (static) spacetime. I mean, take a black hole and Eddington-Finkelstein null coordinates; $u$ and $v$ are Killing ...
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How to decide between sizes of particles for maximum light intensity for scintillation?

Are nanoparticles or microparticles or quantum dots better suited as scintillation materials as far as light yield intensity is concerned? I was unable to find literature that compares micro vs ...
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Help with the Bethe-Bloch formula?

I need some help with the Bethe-Bloch formula for the energy loss of a heavy charged particle in a solid. I'm trying to write a short paper on the detection of alpha particles with a Si detector and ...
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How does dark matter distribution help to identify it's composition

A question regarding this recently released data, and the paper https://arxiv.org/abs/1708.01538 that details it's distribution: Abstract: We use 26 million galaxies from the Dark Energy Survey (...
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Why can Beta decay be treated like a four-point interaction?

Consider the standard formula for beta decay $n\rightarrow W^{*-}\rightarrow p+e^-+\nu_e$ a standard question that I have seen come up is why can this be treated as a four-point decay. Now intuitively ...
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What force causes light to reflect off a surface?

Since $\vec F=d\vec p/dt$ and light consists of photons which experience a change in their momentum when they are reflected off a surface it follows that some force must act on those photons at the ...
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What is the general form for the cross section and rate for orbital electron capture?

I want to derive the basic equations for the rate of electron capture, taking into account the relativistic kinematics explicitly $$p^{+}+e^{-}\rightarrow n^{0}+\nu_{e}$$ The idea is to treat ...
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How to calculate exposure of beta and alpha decay

Is there a way to calculate exposure in roentgen from activity of from q-values? I currently have the activity of a beta decay in mCi over a certain amount of time and the total amount of energy, ...
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World's Largest Radio Telesope : How accurately does it need to be figured?

In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ...
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Bremsstrahlung in body tissue

As far as I know, the intensity of the produced radiation from bremsstrahlung is proportional to: $$I \propto \frac{Z^2}{m^2},$$ where $Z$ is the atomic number, and $m$ is the mass of the particle. ...
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Pearmeability of various materials by EM-waves of cell-phones

Is there any way I can show (even if approximately) that one needs x cm of glass, y cm of brick, z cm of reinforced concrete, etc. to block cell-phone signal of a certain frequency and strength? I ...
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Lens-Mirror systems and conservation of specific intensity

This came out of a discussion I started yesterday and a related discussion I found. I'll recap the problem quickly: Consider two blackbodies, with surface areas $A_1$ and $A_2$ and temperatures $T_1$ ...
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How to calculate material depth at which penetrating radiation direction becomes randomized?

Consider a very light particle impinging on a material composed of atoms which are effectively infinitely heavy (e.g., because they are bound together and stiff). If the scattering with nuclei is ...
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How do experimental physicists know the decay path of transuranium elements ahead of time?

I have been watching (and enjoying) Dr. Poliakoff's YouTube videos on the synthesis of transuranium elements like Roentgenium and Copernicium, which decay so quickly that they are identified (if I ...
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How do we 'watch ' atomic interactions?

I'm relatively new to objective physics and it's measuring and imaging abilities.. Specifically I don't know if we can 'watch' inter/or intra molecular exchanges like the photonic and electronic. I ...
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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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How to solve the Fukushima incident?

I am trying to find out if it is somehow possible to take all this nuclear material, put it in some type of gamma chamber or blast it with neutrons to change the uranium isotopes into something ...
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2 votes
1 answer
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What happens when a lower energy photon strikes a higher energy atom?

I understand that when a higher energy photon hits an atom it could elevate an electron and add energy to the atom, but what happens if a lower energy photon strikes a higher energy atom? If it doesn'...
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Hawking radiation question

A stationary observer near the black hole horizon will detect Hawking radiation proportional to their local acceleration. If we call $\alpha=\frac{GM}{r^{2}}\frac{1}{\sqrt{1-\frac{2GM}{r}}}$ the ...
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Radiation Pressure derivation

Radiation pressures mathematical expression according to Wikipedia is, $\frac{1}{\mu_0 c}\vec{E} × \vec{B}$ "Radiation pressure is the mechanical pressure(force/area) exerted upon any surface due ...
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Microwave Oven Radiation

I read that microwave ovens are allowed by FDA to emit max 5mW/cm2 electromagnetic radiation at about 5 cm from the surface: https://www.fda.gov/radiation-emitting-products/resources-you-radiation-...
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Magnet spindown in a vacuum

How long will it take for a strong neodymium magnet with a mass of 1kg to spindown in free space (vacuum) due to the radiation energy loss and hence the loss of angular momentum?
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Nuclear Physics - Meaning of Terms in Beta Decay Hamiltonian

I am new to nuclear and particle physics, but am familiar with the concept of a Hamiltonian and nonrelativistic quantum physics. In this paper by Yang and Lee on parity conservation in weak ...
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