Tag Info

New answers tagged

0

The Stefan-Boltzmann law for net power radiated pertains to the object. That is, we're simply asking, how much radiation leaves this object (this depends on the object's emissivity), and how much radiation is absorbed by this object (this depends on the objects absorptivity). The emissivity and absorptivity in the equation you present thus pertain to the ...


1

The two existing answers have noted that EM radiation (X-rays, gamma) is effectively stopped by electrons. There are at least 4 other types common types of radiation: Alpha particles (2 protons, 2 neutrons - essentially He4 2+) Beta particles (single electron) Neutrons Ions (other than alpha particles) The first thee are commonly generated by nuclear ...


6

Radiation can be several things, but since you specifically mentioned lead shielding, let's look at X-rays - a lot of what you learn applies to other radiation as well. To stop radiation it needs to interact with "something" that makes it give up its energy and momentum. This is how you get the radiation to stop going in the direction it was going. Now ...


7

There are several different things labeled "radiation". Gamma rays are electromagnetic radiation, similar to visible light but at a higher frequency. X- rays are also electromagnetic radiation. For electromagnetic radiation, elements with heavy nuclei are good shielding. See this Wikipedia article on protection against electromagnetic radiation. Also called ...


7

For the first question, yes. Because the surface of the sun is close to a blackbody emitter, it radiates at all wavelengths below the peak. So radio waves are included. However, the longer the wavelength, the less the power that is put into that portion of the spectrum. Radio is so far from visible light on the EM spectrum that the solar radiation in ...


4

The diffusion approximation is one solution to the radiative transfer equation. In general, the choice of applying this particular solution depends on the optical limit, as you say. For an optically thin medium, radiation will travel and may interact along the way. This is not characterized as a diffusive process, because the beam can interact with the ...


3

An optically thick medium is one for which the mean free path of a photon is low. This means that a photon won't be able to travel very far before it interacts with the matter than makes up the medium. The measure of optical thickness, optical depth, does depend on the volume of material in the medium. For example, for a material with a fixed density, ...


-1

Well, I would say that you are confused about the quantization idea. For quantization to be taken into account, physics of particles should be examined. For a simple example, particle in a box problem given in the beginning of quantum mechanics courses. So, quantization does not mean only atom, it can be examined for many situations in the real life. ...


7

This link gives a clear account of the difference between the classical and the need for the quantum mechanical formulation . Blackbody radiation" or "cavity radiation" refers to an object or system which absorbs all radiation incident upon it and re-radiates energy which is characteristic of this radiating system only, not dependent upon the type of ...


5

At first, consider two particles decay: $A\rightarrow B + e^-$ Where A is initially rest. So $\vec{p_B}+\vec{p_{e^-}}=0$ now \begin{align} \frac{p_B^2}{2m_B}+\sqrt{p_{e^-}^2+m_{e^-}^2}&=E_{released} \\ \frac{p_{e^-}^2}{2m_B}+\sqrt{p_{e^-}^2+m_{e^-}^2}&=E_{released} \tag{1} \end{align} see here you have uncoupled equation (equ.1) for $p_{e^-}$ ...


1

You're correct: the unique thing about beta decay is that there's a three-body final state. In the reference frame where the decay takes place at rest, the daughter nucleus, beta particle, and neutrino share the momentum roughly equally, and because of the mass scales the beta and the neutrino take the bulk of the energy. It's pretty straightforward to show ...


0

There, in fact, is such a way to convert heat produced from radioactive decay into electrical energy. Many systems doing just this have already been designed and used. The most straightforward device is a Radioisotope Thermoelectric Generator, which does exactly what you are asking. However, in principle, almost any system could be implemented that uses ...


1

The gray model results from starting with the assumption that we have a plane-parallel slab: The light ray from the source (i.e., the star's atmosphere) travels at some angle, $\theta$, from normal, $z=0$. Since the light is coming from an angle, we need to account for that by modifying the radiative transfer equation to have a vertical optical depth, ...


0

Radiation is only damaging to DNA when it is ionising (contains enough energy to remove electrons from atoms). This occurs in frequencies higher than visible light (UV, x-rays, gamma rays). Anything below that, such as radio waves that RC toys use, won't cause any harm with that little power.


2

The remote car toy radiation are radio waves. So it's as dangerous as using a radio... The power of thoses emitter are not enought to be dangerous. So it's safe for your kids.


0

The cross section $\sigma$ is related to the absorption coefficient $\alpha$ by: $$ \sigma = \frac{\alpha}{N} $$ where $N$ is the number density of the scattering medium i.e. the number of particles per unit volume. This is described in more detail in the Wikipedia article on the absorption cross section. If you want $\alpha$ in units of cm$^{-1}$ you ...


0

If you're in the pool the pressure wave could crush you depending on strength of blast. Water can't compress. So there's a two fold issue to entertain your idea, heat and pressure. Radiation will be your next concern if you survive the initial blast.


2

I am wondering if one could properly define the temperature of conducting electrons by noting the equivalent noise temperature of a semiconductor amplifier at least in the majority carrier case, such as FETs (not BJTs). For example, if the noise figure were say 2(3dB) then that would imply that the equivalent temperature is just the ambient reference ...


5

Heat is a thermodynamic quantity defined in the framework of thermodynamics. Heat, in the strict use in physics, is characteristic only of a process, i.e. it is absorbed or produced as an energy exchange, always as a result of a temperature difference. Heat is thermal energy in the process of transfer or conversion across a boundary of one region of ...


2

It's very unlikely, but not impossible, that the metal stock your magnets were made from was contaminated with a radioactive isotope. I mention this because I once encountered radioactive re-bar - it was only noticed because it was brought into a lab with radiation detectors at the door. Eventually it was traced back to contamination (radioactive cobalt) and ...


1

As we're discussing above, it seems that the detector you're using seems to be functioning properly when used with verifiable radioactive material. The extra clicks are being caused by current induced in the counter by magnetic flux when you may be moving the detector. In order to get around this, it seems that you should use, in addition to the crinkled ...


0

If the temperature inside clothing is the same as outside, the wear will not do anything. This is because white surface worse adsorbes light but also it worse emits infrared radiation. Conversely, dark surface better adsorbs, but also better emits. In the case the outside temperature higher than inside, such wear will help to be cooler, but even better ...


1

As far as I am aware, mass (and subsequently size) is the primary reason such interactions are more or less penetrating. An $\alpha$ particle is one of the higher-mass cases of ionizing radiation and as such is stopped very easily. A photon ($\gamma$ radiation) is comparatively much more difficult to stop because of its physical properties - high energy, 0 ...


1

Direct sunlight falling on people walking in the desert calls for white or light colors. The coolest sun shades are white, also sun umbrellas. Coolest clothing, black versus white, is light colored. The reason is that in direct sunlight the energy of the sun, could be 1200 watts/metersquare all falls on the cloth. White reflects the visible light, which ...


0

Is it conjecture that the electron must penetrate the nucleus in order for internal conversion to occur, or is this a straightforward result? 1) it is an experimental result that K etc electrons are ejected from atoms that have radioactive nuclei 2)The probabilities of the electrons to overlap with the nucleus are given by the atomic solutions of the ...



Top 50 recent answers are included