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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4answers
204 views
Modeling incoming solar radiation
I want to write a model for estimating incoming solar radiation for a specific latitude on earth but I am struggling to find an appropriate source which shows the required equations for doing so. ...
2
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1answer
134 views
Does an object's color change its rate of cooling?
The motivation for this question comes directly from this thread. The proposition is that the color of something changes how fast it cools (note: specifically the rate of cooling, not taking into ...
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2answers
344 views
Why does a microwave oven affect other electronic devices
When I turn my microwave oven over the stove on, it will cause a motion sensor light in the hallway next to the kitchen to got off and on. This affect can be reproduced anytime. I did notice that ...
2
votes
1answer
241 views
Steady State Temperature of an Object Orbiting the Earth
This may be irrelevant or stupid to ask but I couldn't come up with a good answer. At least, we could not agree on with my friend the other day.
I would like an estimate of the temperature of a human ...
2
votes
2answers
161 views
Is there a reason for photodynamic therapy to not cause cancer if mobile phones might?
I don't want to open a debate about whether cell phones can cause cancer,
I read the thread: Could cell-phone radiation cause cancer?
For the sake of this question let's assume there's a chance for ...
2
votes
1answer
83 views
Alpha-stable isotopes
Why some isotopes with positive alpha-decay energy are stable? For example, alpha-decay energy of stable 194Pt is about 1.5 MeV.
But there is no stable isotopes with positive beta-decay energy.
...
2
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2answers
910 views
How to calculate gamma radiation shielding?
A device emits 0.2 μSv/h of gamma rays. How thick does an aluminum sheet need to be to completely stop radiation from coming out ? What equation is to be used to calculate this ?
2
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2answers
286 views
Has Bose-Einstein theory been considered for dark matter?
Has Bose-Einstein theory been considered for dark matter?
The theory would explain why no measurable radiation is emitted due to zero temperature--its lack of interaction with other matter and its ...
2
votes
1answer
98 views
Solar Cycle UV Variation
The average energy we receive from the Sun is 1,366 w/m^2, and this only varies by 0.1% from the activity peak to trough of its 11 year cycle. About 9% of the energy comes from wavelengths less than ...
2
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1answer
60 views
The equal opposite reaction of radiation pressure
If the photons of a laser would produce a radiation pressure upon whatever it shown upon wouldn't it be accurate to say that the laser would be propelled in the opposite direction of its beam?
2
votes
1answer
78 views
Question on Radiance equation
The radiance equation is
$$
L = \frac{d}{dA} \frac{2(\phi)}{dW cos(\theta)} (watt/srm^2)
$$
where $\phi$ is the flux.
I am thinking, should not be the cosine term on the numerator instead of the ...
2
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0answers
24 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 ...
2
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0answers
42 views
A problem concerning the change of temperature and spectrum of a filament
http://www.flickr.com/photos/83373487@N04/7636968446/in/photostream
The spectrum of a filament is given before, the left one have the lowest tempreture, the middle has the medium and the right one ...
2
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0answers
53 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 ...
2
votes
0answers
186 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 ...
2
votes
1answer
111 views
Does magnetic geometry determine the scaling of a Polywell fusor?
Does magnetic geometry determine the scaling of a Polywell fusor?
Forgive imprecise terminology here - by "magnetic geometry" I mean the configuration of the magnets, the configuration that creates ...
1
vote
4answers
820 views
Why is Neutron Heavier than Proton?
This is Neutron decay:
$$n^o \to p^+ + e^- + \overline {\nu_e}.$$
and this is proton one:
$$p^+ \to n^o + e^+ + \nu_e$$
so when the $e^+ =e^-$ and $\nu_e=\overline {\nu_e}$ why $n \not= p$?
my ...
1
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3answers
167 views
Neutron decay and electron anti neutrino $n\to p + e + \bar{\nu}_e$
Why do we need neutrino to explain neutron decay?
Is there any evidence regarding existence neutrinos in the context of
$n\to p + e + \bar{\nu}_e$?
1
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3answers
640 views
Are dangerous rays emitted during Solar Eclipse?
It is said one should avoid staring at Sun as it can damage the eyes, but it is also said that one should not come out in sun during eclipse as it emits dangerous rays. Is that true? If yes, why?
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2answers
317 views
Nuclear decay rate affected by sun and quantum randomness
If nuclear decay rate were affected by sun,
then emission probabilities would be subject to sun state and its influence,
so quantum randomness would depend on it,
Would it still be truly random?
One ...
1
vote
2answers
111 views
How to detect radiation on the metal (coin)?
I've got metal coin : http://www.worldpeacecoin.org/
Ruble/dollar, a coin of disarmament with certificate. But, I am very spleeny person, I fear of it's radiance level and I don't know if I can trust ...
1
vote
3answers
132 views
How to detect Iodine 131?
I 131--->β 333.8kev(7.27%)--->γ 636.989kev(7.17%)
I 131--->β 606.3kev(89.9%)--->γ 364.489kev(81.7%)
(you can also check the them here:
...
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2answers
217 views
Creation of the Electromagnetic Spectrum [closed]
After seeing this image:
http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg
And reading this:
"The long wavelength limit is the size of the universe itself, while it is thought that the ...
1
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2answers
210 views
Antimatter bomb
I stumbled upon this wikipedia article on antimatter weaponry.
Being greatly appalled by the sad fact that large sums of money are being wasted on this, I could not stop myself from thinking for a ...
1
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2answers
194 views
A hot object exposed to low temperature in a vacuum doesn't lose heat?
I heard somewhere that if the human body were exposed to outer space where the temperature is extremely low, the human won't actually feel cold because in a vacuum, the heat energy doesn't have ...
1
vote
1answer
420 views
Wein's fifth power Law and Stephan Boltzmann's fourth power laws of emissive power
Wien's fifth power law says that emissive
power is proportional to
temperature to the fifth power.
But the Stefan–Boltzmann
law says emissive power is
proportional to temperature to the fourth power.
...
1
vote
1answer
23 views
What type of Radiation hits Europa
I was recently reading the Wikipedia Page for Europa as I am interested in terra-formation. In one of the sentences, it says that:
The radiation level at the surface of Europa is equivalent to a ...
1
vote
2answers
64 views
Alpha particle and helium nucleus
The symbol for the alpha particle is α or $α^{2+}$, it can be written as $He^{2+}$.
What I want to know is that, are they same? I mean alpha particle and helium nucleus are same or any subtle ...
1
vote
1answer
34 views
Nuclear transition notation
I have a question which asks me to determine what x is for the following nuclear transition
$$^{29}Si(\alpha, n)X$$
But I don't have any idea what this notation implies.
Another example:
...
1
vote
2answers
72 views
$\Omega_{r}$ from WMAP results?
To do some Friedmann-Lemaître cosmology calculations, I would like to know an estimation of $\Omega_{r_0}$ ($\Omega$ radiation today). WMAP 7 give estimation of $\Omega_{b}$, $\Omega_{c}$ and ...
1
vote
2answers
230 views
$\alpha$ and $\beta$-decay, why don't they neutralize each other?
$\alpha$ radiation consist of positive charged helium nuclei, $\beta$ radiation of negative charged electrons. So why don't the $\alpha$ particles take those electrons to get neutral?
1
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1answer
88 views
When should angles be expressed in degrees vs. radians?
I am trying to calculate the albedo of a given latitude by following the methods of Brutsaert (1982), I have copied the formula below:
3.6 Shortwave and long-wave radiative fluxes
Albedo ...
1
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1answer
49 views
What was the first ionization radiation?
While trying to make somewhat of a timeline of the history of ionizatig radiation, i am wondering about the following questions:
The first photoelectrical effect was found 1839 by Alexandre ...
1
vote
2answers
82 views
Quantum yield and spontaneous decay
I'm trying to figure out how many atoms are decaying spontaneously in a span of 2 seconds. Let's say that the quantum yield is 0.45, and that the lifetime "τ" (tau) is 10 microseconds.
Then I found ...
1
vote
1answer
104 views
Specific electron energy gap values $E_{i+1}-E_i$ vs. photons with arbitrary energy $\hbar \omega$
The energy levels of electrons in an atom are quantized $E_i$. A photon of a specific momentum $\vec p$ and energy $$\omega=(E_{i+1}-E_i)/\hbar$$ hits an atom and gets absorbed. Okay now say the ...
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1answer
69 views
Does the strong (nuclear) force ever contribute to decay?
Does the strong (nuclear) force ever contribute to decay ?
Or is the weak nuclear force the only decaying force ?
1
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2answers
170 views
Where does the “borrowed energy” come from in Alpha decay?
I was also thinking about the uncertainty principle in regards with energy & time. The question of something like:
Alpha tunneling out of the nucleus is where this can be invoked, but having an ...
1
vote
1answer
52 views
References for nuclear masses, mass deficits, decay rates and modes
Where can I find the base data for computing the energy release of nuclear decays and the spectra of the decay products?
My immediate need is to find the energy release by the beta decay of Thorium ...
1
vote
1answer
106 views
How do gravitational waves sustain and propagate large scale spacetime curvature?
I understand that gravity in GR is a manifestation spacetime curvature dictated by the field equations by the principle that objects follow the geodesic path in spacetime.
And, I get how ...
1
vote
1answer
225 views
Absorption / Control / Reduction of EMF radiation using passive antennae & matched load
Wanted to understand the physics behind usage of passive antennae and matched load combination, to absorb, control and reduce the Electromagnetic-Field (s.a. due to microwave radiation from cellular ...
1
vote
0answers
32 views
When (Exactly) Does Bremsstrahlung Radiation Occur?
Regarding the Bremsstrahlung Radiation emitted when a charged particle curves inside a uniform magnetic field; Is there a way of calculating the angle through which the charged particle will precess ...
1
vote
0answers
24 views
Effective amplitude in Neutrinoless double beta decay
Can someone give me the value of the effective amplitude($A$) of $\bar{\nu_\mu}\rightarrow\nu_\mu$ oscillation of Neutrinoless double beta decay? The expression is like this:
...
1
vote
0answers
32 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 ...
1
vote
0answers
28 views
Half-Life Question [duplicate]
Possible Duplicate:
How do we know that some radioactive materials have a half life of millions or even billions of years?
I understand how to calculate decay, but it seems to me that the ...
1
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0answers
93 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?
1
vote
1answer
452 views
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:
$\alpha_s = 0.83$
...
1
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0answers
47 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 ...
0
votes
3answers
275 views
How can there be heat in a vacuum?
I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc.
If heat is caused by thermal energy being radiated from particles ...
0
votes
2answers
89 views
How can we detect a black hole? [duplicate]
If black holes are phenomena of very high density (gravitational singularities) which don't emit radiation how can we detect them so far away from us where so much other radiation can hide the black ...
0
votes
2answers
264 views
