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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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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How to see alpha radiation

Hello I am looking to replicate the double-slit experiment using alpha radiation from a sample of Polonium-210. Keep in mind that I would need to put it in a vacuum so cloud chambers would not work. I ...
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Finding the geometric efficiency of a cylindrical Marinelli beaker

I want to find the geometric efficiency of a cylindrical marinelli beaker filled with soil to perform gamma spectroscopy, so essentially the ratio of rays that pass through the detector to the overall ...
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337 views

What is the amplitude of the electric field in a laser?

I'm looking for reliable informations about the amplitude (not the intensity), in volt/meter, of the electric field in a typical laser. Or in other words : what are the typical amplitudes of the ...
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32 views

DNA breaks with particles or photons (Radiation therapy)

When protons (or other particles) or photons are used in radiation therapy to treat cancer patients, the main effect is for it to make DNA breaks that hopefully will make the cancer cell die ...
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37 views

Black Body radiation (intensity in certain distance)

i need some help with this task: I have a black body radiator which is spherical and it has radius $r=0.56m$. It radiates with intensity $1.5\frac{kW}{m^2}$. I would like to know the intensity in ...
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53 views

Emissivity and Final Temperature of a Black and White object

Objects can be categorized as blackbodies (emissivity $\epsilon = 1$), grey bodies (emissivity $\epsilon < 1$) and white bodies (emissivity $\epsilon = 0$). If we placed two objects (identical ...
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53 views

Carnot Engine- Cold Reservoir is a black body [closed]

My question: A satellite powered by a Carnot engine uses heat from a nuclear reactor at a fixed temperature T0. Heat is released into outer space via thermal radiation emitted by a set of fins at ...
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What common materials absorb most infrared light?

I'm competing in a simple robotics competition where most of the participants use reflected infrared light to detect their opponent. I'd like to make my own robot as difficult to see as possible. What ...
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68 views

In a waveguide, where does the energy in attenuated waves go?

In an electromagnetic waveguide, there is generally a "cutoff frequency." Electromagnetic waves with a frequency that is lower than this cutoff frequency will not propagate at all -- i.e., they will ...
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88 views

Understanding Vaidya metric and pure radiation stress-energy tensor

I am following Vaidya metric and how it is related to pure radiation from Wikipedia. But when it reaches the line where stress-energy tensor is equated to product of two four-vectors, I cannot follow ...
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58 views

Charge moved across a potential difference; where does the energy for emitted radiation come from?

Let's use an electron and a 1V potential difference as a mode. In school I learned that if the electron is at the negative end of the electric field, its potential energy is equal to the work that ...
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64 views

What is radiative width?

I am trying to understand gamma radiation and trying to figure out how to calculate radiative width. Is the radiative width how far the atom can be from another one and the probability of it then ...
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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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1answer
26 views

Illuminance on the vertical façade from the ground

I am trying to understand the illuminance on a vertical façade from the light reflected from the ground. And am reading this through Daylighting and Architecture book. On page 41 it makes use of two ...
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1answer
38 views

Lead shielding very close to the Sun

I understand that eventually lead would melt when it nears the sun. In a liquid state how effective would lead be in blocking radiation? Would it still be as effective as solid state of lead? What ...
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27 views

Alpha Radiation - Charges [duplicate]

Has the radiating material that emits only alpha radiation a negative charge? I am just wondering, because alpha radiation is a positive charged helium ion - so where are the electrons going?
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In non-metallic solids w/ just atoms or ions (no molecules), are bonds (vibrations) and electronic transitions the sole cause of blackbody radiation?

Since there wouldn't be a conduction band filled with any electrons in a non-metallic solid made of just atoms or ions (no molecules), it's hard to imagine any other type of movement and dipole moment ...
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56 views

Can you concencrate paralel laser beams?

I've seen some videos of laser toys but they all seem to use either one laser or lens with some specific range of focus. What I was thinking is this: But it seems like it might violate the 2nd law ...
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61 views

Radioactive decay-Why does it depend on numbers left

As textbooks describe the rate law for radioactive decay as a first order reaction dN/dt=kN,why is it so(mine does not give the reason)? How is the radioactive decay of one atom depeendent on the ...
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60 views

Probability of photon to photon collision

2 photons having sufficient energy can collide and form an electron positron pair (which then annihilate and form a new photon pair - with lower energy?). I assume this means that they can't collide (...
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78 views

Why does lead have a higher attenuation coefficient for 5.0 MeV than for 10.0 MeV?

I was doing some calculations on radiation, and I noticed that lead has a higher attenuation coefficient for 5.0 MeV than for 10.0 MeV, namely $1.44 \, \mathrm{cm}^{-1}$ for the former and $1.23 \, \...
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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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113 views

How does the discrete energies of alpha and gamma rays prove the existence of nuclear energy levels

I was reading up about Nuclear Energy Levels and came up with the aforementioned question. To me, there seems to be no direct connection between the two statements and therefore, I would like to know ...
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24 views

The angular diameter distance for a radiation dominated universe

I'm attempting to work out the angular diameter distance for a radiation dominated universe, with $k=0$ and $\Lambda=0$. I have gotten myself to this point: $$ D_{A}=\frac{1}{H_{0}(1+z)}\int^{z}_{0}...
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28 views

Calculating solar irradiance of Earth [closed]

The mean solar radiation flux absorbed per unit area of Earth’s surface, neglecting the atmosphere, is calculated as FS(1-A)/4, where FS is the solar constant and A is albedo. I can see how this would ...
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39 views

Definition of emissivity?

A have come across a definition of emissivity which is along the following lines: Emissivity is the power emitted per solid angle per frequency per surface area. This definition, however seems ...
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19 views

Using ion radiation to make electricity? [duplicate]

Is it possible to capture the ion radiation from a nuclear source and make electricity from it? I always thought it was possible, but never looked into it? Is this what a beta voltaic battery does?
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How to integrate to find the view factor of two parallel disks of different radii? [closed]

You have two parallel coaxial disks of different radii. I have tables that give me the value as $$F_{ij} = \tfrac{1}{2} [S - \sqrt{S^2 - 4(r_j/r_i)^2}]$$ where $$S = 1 + \frac{1 + R_j^2}{R_i^2}$$ ...
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18 views

Protonic emissions

In a beta emission a neutron decays,into a proton and an electron, and an electron randomly gets ejected from the nucleus due to the phenomenon of barrier tunnelling(correct me if am wrong).But why is ...
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19 views

How much power is being actually delivered by an electric heater to a cooking pan?

I've been doing experiments on an electric heater heating a cooking pan filled with 2 litres of water, from 20°C to 70°C; now I'm trying to draw a theoretical heat transfer model thath should match ...
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1answer
29 views

In solids, is it phonons, or is it the oscillations of electrons in bands, that emit most of the blackbody radiation?

In solids (most any object we see), which tends to emit most of the blackbody radiation: phonons (atomic, or molecular dipole, lattice vibrations) or oscillating electrons in their energy bands?
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32 views

Is an “underwater” submarine affected by a nuclear bomb exploding above the water? [duplicate]

I've just read Would being underwater help survive a nuclear bomb?. Submarines are way more armored and far from the surface than a human body (https://en.wikipedia.org/wiki/Submarine_depth_ratings), ...
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Why photoluminescene spectrum is not identical to electroluminescence spectrum?

Electroluminescence (EL) and photoluminescence (PL) spectra are not identical: there's a small red-shift of the PL spectrum relative to the EL spectrum. Why is this happening if both EL and PL are ...
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Can we enhance a thermal gradient by combining a dark surface and a shiny surface with an external glass layer?

I refer to the article at this site: http://solarcooking.wikia.com/wiki/Solar_Kettle-Thermos_Flask As we know, dark surfaces absorb radiation (eg. solar water heater), while shiny surfaces reflect ...
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67 views

Why is there only alpha and beta (and gamma) decay?

Why is it that we mostly speak of alpha and beta decay (when looking at emitted particles with rest mass)? Why don't we speak of decays that emit something like $2n3p$, $3n2p$ and so on? Do they occur ...
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Why does natural counting with a gamma spectrometer differ from Neutron activation analysis?

As stated in the title, why are the data from natural counting using s gamma spectrometer different than the data from neutron activation analysis using the same samples?
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How is the stellar flux for exoplanets calculated?

I have noticed that in many Wikipedia articles, the stellar flux received by each planet is stated. I tried to calculate this stellar flux from the given data, but the results didn't seem to be ...
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30 views

Half- life of Radon

If there is increase in the pressure of a container with radon in it , what will happen to the half life of radon?
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22 views

What is the Best Electron Tube for creating X-Rays?

This is a question of Experimental Physics. I have seen that you can create X-Rays with a High Voltage Circuit using Electron Tubes. http://www.dangerouslaboratories.org/xray1.html. My question is, ...
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Gamma Spectrum: What is causing this behavior?

In my radiation detection lab we're identifying a unknown source, based on the gamma spectrum it's an activated gold foil. You can clearly see 4 peaks: 411.78 keV (Au-198), 675.93 keV (Au-198), 823.51 ...
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solar energy on a specific location

How to find the amount of solar wattage in any specific place on earh in a monthly manner? by solar wattage I mean the energy recieved from the sun in a squared meters.
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Solar radiation conversion check [closed]

I'm analysing some solar radiation data, which is the calculated as the daily sum of PAR in MJ per m$^2$ per day. Assuming that PAR makes 42% from total irradiance, how can I convert this to solar ...
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Why is the intensity of an alpha ray constant along a material?

I'm taking a course in radiation physics and I've come across the following problem: A thin beam of alpha particles of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity ...
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67 views

Can electrons within a positive ion absorb and reflect light?

I understand that in a crystalline metallic structure, such as one making up a bar of gold, there are one, or more, valance electrons of each atom that have left their outer shell (became free ...
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4answers
845 views

Detecting radiation from tritium keychain

I am measuring radiation from 6 tritium glow keychains. Usual gamma detector does not detect anything (this is expected), but on beta detector with thin window I am getting about 5 counts per second. ...
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How many photons are there in free space on average

Estimates of the amount of for example "dark matter" are of interest to the cosmologists. However, I have never seen an estimate of how many "free" photons could be speeding about in the known ...
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Fermi's theory of beta decay - Does Fermi's Hamiltonian have the wrong transformation properties?

I'm studying the theory of beta decays as proposed by Fermi in the 30's, and I found an inconsistency between the transformation properties that he claims for his Hamiltonian and the transformation ...
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How do electrons jump orbitals?

My question isn't how they receive the energy to jump, but why. When someone views an element's emission spectrum, we see a line spectrum which proves that they don't exist outside of their orbitals (...
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415 views

How can heat turn into light

I am confused about how hot surfaces can radiate light to their surroundings. When I shine a light on a surface the light turns to heat spontaneously, and when I leave that hot surface it radiates ...