# Tag Info

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Planck's law of black-body radiation can be stated in many different ways, depending on whether one is interested in the spectral energy density per volume or per area. It can also be expressed in terms of radiation wavelength or frequency. The energy of a photon is $$\epsilon = h\nu = \frac{hc}{\lambda}$$ I will not derive Planck's law here. It can be ...

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The rest mass of the intermediate particle is not relevant. Even if the W boson was real and not only a virtual particle, the energy-momentum is conserved during beta decay and the whole energy-momentum couples to the gravitational field in the Einstein equations $$G_{\mu\nu}=\frac{8\pi G}{c^4}T_{\mu\nu}$$ where $T_{\mu\nu}$ is the energy-momentum tensor. ...

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All high bias detectors experience electronics noise which rises roughly exponentially toward low energy. Add to that the (single, double, ...) Compton edges from the lines you are trying to sample and you can expect a lot of background down there without needing there to be any actual x-rays flying around in those energies. Most of the Ortec devices run ...

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It is, perhaps easier to catalog the non-photon sources and leave the addition and unit conversion to you. The cosmic background is almost entirely muons. If you spend times in building with non-trivial radon level, that does it largely alpha. Most (but not all) of the natural radiation background is gamma, but it runs a wide range of energies for a few ...

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For those curious I was able to find an answer. IT stands for Isomeric Transition. A metastable state emits a photon to decay to a lower energy List of decay modes: http://ie.lbl.gov/education/decmode.html

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The CMB was emitted from everywhere, in all directions. The CMB emitted at the point where you are standing right now, has now been dispersed to a distance $d_\mathrm{CMB}$ equal to the distance that light can travel in the almost 13.8 billion years that have passed since it was emitted*. (note that $d_\mathrm{CMB}$ is much larger than 13.8 billion ...

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Cosmology models the data for the creation of the universe with the Big Bang model.. The BB has a beginning as a singularity, and in the early times there was no "flatness". The model is a four dimensional model in space time. All (x,y,z) points in our three dimensional neighborhood were in the original singularity; thus all points are at the center of the ...

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I wonder if a bunch of microwave questions that appeared here recently is related to an enlightening (as usual) recent what if by xkcd. The radiation used in microwave ovens is not resonant for water molecules and industrial microwave ovens use 915 MHz (probably, because larger cavities can produce more power). The frequency of 2.45 GHz is chosen because it ...

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The wavelengths that microwaves use allows the waves to resonate with the water to heat it up, with the added value that they are easily blocked to prevent damage to objects outside of the machine.

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The dose that kills a tumor is deliberately aimed at that tumor. If, instead of using a collimated beam, you put a person in a wide beam for radio "therapy", you would be treating their entire body as a tumor and kill them. The dose in RT is computed locally - "this" part of the body (these grams of tissue) absorbed (were exposed to) "this many" Joules of ...

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That is the lethal does to stop human bodily function if radiated into a vital organ or the entire body. Cells die at a much lower level of grays, so a lethal does of gray's is not necessary to kill a tumor.

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You might be interested in the extensive Wikipedia article on U/Pb dating. Your equations are a little too simplistic; what's really happened is: at time $t=0$, we had some amounts $N_{\text{Pb}}(0)$ and $N_{\text{U}}(0)$; but due to the $\text{U}\rightarrow\text{Pb}$ decay mode this has changed to:  N_{\text U}(t) = N_{\text U}(0) \exp(-t/\tau_{\text ...

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It initially contains no lead, so $N_{0(Pb)} = 0$. Lead is an eventual byproduct of uranium. The statement "The half lives of all the decays leading to Lead are many orders of magnitude smaller than the half life of the initial alpha decay of U." is there to mean that you can assume for practical purposes that Uranium decays into lead, even though it ...

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Related: What's the reason behind calling cathode rays tube by the name cathode? Short answer: the voltages accelerate the electrons away from the cathode so that they hit the screen (anode). You actually have two anodes, one a tiny bit behind the cathode where the electrons come out. This one has a hole where the electrons can fly through. A second ...

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It's basically just an electrical circuit. The interesting part is that a portion of the circuit has no wire, but is a bare electron flying through the CRT. It lands in a particular spot and collectively, many such electrons can form a picture, due to the retained glow from the phosphorus screen.

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