# Tagged Questions

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.

143 views

### The logarithmic decay of WIFI

I have been told that Wi-Fi, LTE etc signal strength fall of as $$\propto \frac1{\log(r)}$$ where $r$ is the distance. I am wondering why this is. I better explain what I mean with this question. ...
176 views

### “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://...
44 views

### Water + metal + fan = convection cooling?

I'm playing around with the notion of a swamp fan, but I live in a humid climate and have no interest in putting more humidity in my bedroom. Supposing I submerged a rod of metal into a mostly sealed ...
16 views

### 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 ...
107 views

### 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 ...
36 views

### 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 ...
59 views

### 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 ...
71 views

### 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 ...
70 views

### 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-...
14 views

### 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 ...
88 views

### 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 ...
52 views

### How deep would a moonbase have to be dug for radiation protection?

The atmosphere of the earth protects us from cosmic rays and other kinds of space radiation. On the moon there is little to no atmosphere so anyone on the surface of the moon is directly exposed to ...
49 views

### Is there an orbit decay associated with synchrotron radiation of a relativistic particle?

I had a question about a particle (say a proton) with relativistic energies interacts with a magnetic field (in the z direction). As it is accelerates the particle emits synchrotron radiation. ...
29 views

### 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 $T_1$ ...
35 views

### 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 ...
49 views

### 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 ...
39 views

### 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 ...
56 views

### Is deep-space radiation greater in the Sun, or in the shadow of Earth?

http://space.stackexchange.com/questions/604/is-it-possible-to-get-pregnant-through-natural-means-in-space indicates cosmonauts are at risk of irradiation whilst in space. What little I know about ...
243 views

### 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 ...
15 views

### 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, ...
75 views

### 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 ...
31 views

### 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. ...
12 views

### 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 ...
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}...
40 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 ...
33 views

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

### 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.
38 views

### Electron energy from beta decay

I read in my IB-physics book that the average energy for an electron in the beta decay of Potassium-40 is 0.44 MeV. However this would imply the electron have a velocity of 3.9E8 m/s, i.e. faster than ...
32 views

The following question is from General Problems on Physics by I.E Irodov 6.220. Find the decay constant and the mean lifetime of $^{55}\operatorname{Co}$ radionuclide if its activity is known to ...
37 views

### Question on decay constant

I have a model of the radioactivity of a target which is undergoing Neutron Spallation. The Protons are incident upon the target for approximately 200 hours. Within the model, over the course of ...
68 views

### signal from uniformly moving charge

As a charge moves, its field changes, and this change can only be propagated outward at the speed of light. Thus the field lines will be curves that keep changing apparent source point and direction. ...
19 views

### Why spurious pulses are likely in partial discharges?

My notes The gas multiplication in the proportional counters is based on the secondary ionization created in collisions between electrons and neutral gas molecules, resulting in some visible ...
59 views

### To what altitudes does cosmic radiation penetrate?

How far does high energy (Cosmic) radiation penetrate(km above sea level) into the planet earth? And at what rate(/m^2/s)? (limited set of rates here) (The Aurora is low energy protons that stop at 90 ...
80 views

### What is the strongest material transparent to alpha radiation?

Is there a material which is transparent to alpha radiation while being able to hold up under atmospheric pressure on one side and ultra high vacuum on the other? Put simply, what material is thin ...
74 views

### Klein-Nishina for estimating X-ray cross section

I'm looking at interaction probability for X-rays with water and DNA, and recently have starting reading up on the Klein-Nishina identities for differential cross section. When integrated over all ...
27 views

### Proton energy distribution after Si layer

I've been using SRIM to get an approximation of the energy distribution that a beam of monoenergetic incident ions will have after a thin layer of silicon. However, for my purposes it would be better ...
51 views

### Analogy for Rayleigh scattering

This morning's eclipse has me looking into Rayleigh scattering. I'm trying to think of a good analogy to explain it to somebody without getting too in-depth into electromagnetism and other subjects... ...
63 views

### Energy Equation

I am reading a book on radiation and the author, while developing the equation of radiation transfer provides two forms of the equation, the second incidentally being more general and useful that the ...
97 views

### How do I build an alpha emitter?

I would like to build an alpha emitter. I suppose I had some vague idea of knocking the electrons off of some helium. But upon further examination the idea does strike me as...naive? My question is ...
92 views

312 views

### How do I calculate the Radiation length of a Molecule

I want to calculate the Radiation length in a Molecule with the Formula given on wikipedia. How do I calculate Z and A for a molecule to put it into the Formula?
73 views

### Light vs. X-ray interactions with Phosphor

Looking for some information on how light and xrays interact with phosphorous, or what might cause the following: Scenario A focus beam of light is directed at a phosphor plate at the same time as ...
18 views

### What is meant by Hydrogen dilution in Plasma?

I was going through the paper of methanol masers and it says that for a strong maser the geometrical dilution factor of HII emission should have low values. What is the meaning geometrical dilution ...
82 views

### Trapped in a room with Cobalt 60 - what is the best position to minimize dose?

Been thinking of an old TV series I once saw that involved a man being trapped in a room with a Co60 source of (presumably) high activity. So, assuming no escape and nowhere to throw or hide the Co60, ...
16 views

### Difference between PIN photodiode and silicon surface barrier in beta spectography

In a physics undergraduate lab we performed an experiment in spectography of beta decay. We used two detectors to measure the energy spectrum of Bi207: PIN photodiode Silicon surface barrier ...
20 views

### Do alpha particles add to the mass of the matter they are interacting with?

If a large number of alpha particles are fired into a target material, they presumably interact with the matter by ionisation and eventually lose energy, and are 'absorbed' by the target. Do they ...
38 views

### Does elementary particle decay simply swap mass for speed?

I'm looking at different decays of elementary particles. And I am wondering about the masses (in energy) not matching up. For example, W and Z bosons are far more massive than the particles that decay ...