# Tag Info

4

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 ...

3

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

3

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 ...

3

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 ...

2

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. ...

1

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 ...

1

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 ...

1

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 ...

Only top voted, non community-wiki answers of a minimum length are eligible