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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109 views

Why the CMB has not been dispersed so far?

Imagine you have a box of black body radiation. What happens if you open the box for a long time? It becomes dispersed and no radiation remains in the box. Now, apply this example to the Cosmic ...
2
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2answers
217 views

Why do microwave ovens use radiation with such long wavelength?

According to Wikipedia: Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in). Typically, I put the dish inside the oven in its center. I suspect most ...
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2answers
51 views

Lethal dose of Gy's (Grays)

The unit Gray has the dimensions $\text{J/kg}$. I've read, that a dose of about 3-5 Gy's could kill a person within a few weeks - or at least that's usually the case. But I'm not really understanding ...
2
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0answers
41 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 ...
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2answers
30 views

Radiometric dating calculation [closed]

If a sample of zircon initially contains no Lead, find an expression for the ratio $$\frac{N_U}{N_{Pb}}$$ as a function of time? How do I do simplifications from this? Do I just go: ...
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2answers
33 views

Is the screen in CRT connected with a positive pole?

I don't understand this passage would you clarify it? "These electrons are then freed (liberated) from the metal and are then picked up by the screen, which is connected to a positive pole called the ...
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1answer
47 views

Working out the penetration of radioactive decay products

From my understanding of the products of radioactive decay (alpha particles, beta particles, and gamma are all I know of), the particles (or energy I guess?) are stopped by a medium according to it's ...
0
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0answers
34 views

Continuum Wave Function for the electron

I'm trying to understand certain processes like the photoelectric effect and Bremsstrahlung. In Bremsstrahlung I need to use the wave function of an electron coming from the continuum, and there is ...
7
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3answers
2k views

How does radiation shielding using absorbing materials work?

I understand that, for example, a thick enough sheet of lead can absorb gamma radiation, but I want to understand what actually happens at the molecular/atomic/subatomic level. Also, can the same ...
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1answer
39 views

Spin and parity transition levels gamma radiation

Just a quick question regarding spin and parity. I am studying nuclear physics and I am just a tad confused with a concept about gamma radiation. Say I have ${^{20}_{10}Ne}$ And the lowest electric ...
0
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2answers
66 views

Where does the “Illumination Formula” come from?

I've been studying for the pGRE for the past couple of weeks (what a load of... nevermind), and one of the questions requires the use of what is apparently deemed the illumination formula, used to ...
0
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0answers
36 views

thresholds for Cherenkov radiation visible to the human eye

In pool-type fission reactors, the beautiful Cherenkov radiation from the beta decay of intermediate products seems to be a well-understood phenomenon. I am wondering what some ballpark figures are ...
2
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0answers
65 views

Why does a damped quantum harmonic oscillator have the same decay rate as the equivalent classical system?

$\newcommand{ket}[1]{|#1\rangle} \newcommand{bbraket}[3]{\langle #1 | #2 | #3 \rangle}$ Why does the decay rate for a damped quantum harmonic oscillator exactly match the classical limit? Background ...
2
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3answers
103 views

Why do neutrons decay after 6 minutes?

If I understand correctly, Beta decay only occurs when an atom (or in this case subatomic particle) is unstable. Are neutrons consider unstable? If so why? And if they are not unstable is there is ...
2
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1answer
63 views

Would the blue glow of Cherenkov radiation be visible when diffused across ice, such as in the IceCube neutrino experiment?

The blue glow characteristic of Cherenkov radiation is visible emanating from underwater reactors. Is it also visible through ice, at the IceCube neutrino experiment (not that anyone is physically ...
0
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1answer
99 views

Emissivity of vacuum for radiation heat

What is the heat radiation emissivity of vacuum? For air as well? What is the difference? I understand that the vacuum has reflectivity of 0, So what is the other two values are in $$ reflectivity + ...
3
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3answers
145 views

How to block neutrons

What is a good way to block neutrons and what is the mechanism that allows this? It's my understanding that polyethylene is somewhat effective. Why?
2
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1answer
95 views

How would the explosion from a Pure Fusion Bomb differ from the explosion from a Fission Nuclear Bomb?

Suppose we have the technology to create high enough temperatures and pressures inside a confined space to fuse together deuterium and tritium, and create a Pure Fusion Bomb. How would the explosion ...
2
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1answer
47 views

pGRE question on natural line width

The lifetime for the $2p \rightarrow 1s$ transition in hydrogen is $1.6 \times 10^{-9}$ s. The natural line width for the radiation emitted during the transition is approximately... Their solution: ...
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1answer
474 views

Deriving Gamow factor for potential with effective centrifugal potential term

I am looking at deriving an expression for the Gamow factor for $\alpha$-decay. I understand that the potential is the sum of the nuclear, electric and effective potentials: $$V(r) = V_N(r)+V_c(r) ...
0
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1answer
57 views

Reactive near field for Wireless Power Transfer (WPT)

In literature it is stated that in reactive near field using high-Q coils in resonance the efficiency does not depend on coupling (ie. distance) and that coupling only has influence on rate of energy ...
25
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6answers
3k views

Is a suit that hides a soldier's heat signature fundamentally possible?

I recently played "Crysis", a game where the protagonist wears a suit that allows the player to hide both himself and his heat signature. Then I watched Iron Man 3, where a kid suggests that Tony ...
0
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0answers
27 views

What is a high brilliance X-Ray and how is one created

I just found this term being used in a Stanford Engineering year in review 2013-2014 "X-rays illuminate path to more efficient fuel cells" that cited this work. Never heard the term before and I came ...
0
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4answers
384 views

Can there be energy with no force or energy with no power?

I think that both force (number of newtons) and power (p=ui(?)) implies that there is energy so we can't have force without energy and we can't have power without energy(?) But can there be energy ...
3
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2answers
126 views

Does positron-electron annihilation preserve enough info to reverse exactly

An electron-positron annihilation can produce a pair of gamma rays. In the reverse process, known as pair production, can the gamma rays carry enough information to determine the resulting ...
3
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3answers
266 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 ...
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3answers
90 views

We don't know when a nucleus will decay. Then how can find its half life? [duplicate]

I mean how can we say that in 5730 years, 1/2 the no. of C14 nucleus will decay because in reality we don't know when a particular nucleus will decay
4
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1answer
290 views

What is the temperature of the clear night sky from the surface of Earth?

Before you all jump in with 2.73 K or thereabouts, this is more of an experimental question. It will obviously depend on humidity and radiation being scattered back towards the surface of the Earth. ...
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1answer
63 views

Highest background gamma ray energy?

What is the highest naturally occurring gamma ray energy that you would see in background? And what is it is source?
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1answer
82 views

how safe is using the remote car toy from radiation [closed]

how safe is using the remote car toy from radiation, especially for kids, The manufacturers claiming that it will be safe, but is that 100 % safe over kids.
0
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1answer
79 views

Energy of resultant photons from meson decay

I am a little unsure how to answer the following question, Find the energies of two photons emitted in opposite directions along the pion's original line of motion if the pion has a r.m.e of 500MEV ...
2
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2answers
158 views

Solar spectrum units

Why is intensity $I$ on a graph of the solar spectrum always showed in units of $[\mathrm{W/m^2/nm}]$ instead of simply $[\mathrm{W/m^2}]$? (The y-axis on the graph.) It is apparently shown as ...
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0answers
31 views

Are the Van Allen belts important to life? [closed]

Is it significant for life on Earth? Mars doesn't have this. Why do experts think there may be life on it? What kind of life form could live on Mars? This article I just read got me wondering. A ...
0
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0answers
18 views

What are the principle factors that limit $\beta$ decay to elements with atomic number, Z 100 or less?

I learned for the first time in Eric Scerri's new book A Tale of 7 Elements that $\beta$ decay does not occur for elements with atomic number, Z > 100. I did some further web research on this subject ...
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2answers
2k views

Would a laser with four possible energy levels be better than three?

I'm wondering about achieving population inversion for a laser. I learned that without an active medium, it's not possible to create a laser with only two energy levels, but it would be possible with ...
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0answers
25 views

Can the half-life of a free neutron be calculated or is it just empirical? [duplicate]

Everyone keeps telling me its just 10.3 minutes and no one knows how to get that number form theory. Any idea?
3
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1answer
1k views

Radiation: Inverse square law

Gamma radiation follows the inverse square law, I understand this as "double the distance, quarter the intensity" So if you have a gamma source, at the source (distance = 0), the Intensity is $I_0$, ...
8
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2answers
424 views

What exactly is the composition of radiation in interplanetary space?

The articles I found on radiation in the solar system mostly dealt with solar wind, I wonder about other types. Is there a breakdown that tells me, withhin an order of magnitude, at least what ...
16
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3answers
2k views

Decay of massless particles

We don't normally consider the possibility that massless particles could undergo radioactive decay. There are elementary arguments that make it sound implausible. (A bunch of the following is ...
0
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3answers
122 views

Why is signal bad in a tunnel?

Consider this: you are driving through a tunnel listening to your AM radio and a GPS, all of the sudden AM radio has nothing but statics and your GPS says "reconnecting - please hold". You say to ...
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0answers
20 views

Determine the number of grays absorbed by human emitted by Uranium 238

I want to count the estimated value of gamma radiation (in Grays) absorbed by human emitted by Uranium 238. Weight of it's ore is about 20 grams. The human weight is about 70 kilograms, he was about 5 ...
0
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1answer
37 views

Can you heat something in AL foil using IR?

Is it possible to heat up, let's say, a blob of mud, golf ball size, covered in AL foil, with IR? Also, how efficient would that be? Is there an IR wavelength that would get absorbed far better than ...
1
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1answer
43 views

Why is 0 $\nu \beta\beta$ decay often written with electron emission and not positron?

According to http://www.cobra-experiment.org/double_beta_decay/ I can see that double $\beta$+ decay is possible, but I often find neutrinoless double beta sources with the double $\beta$- decay ...
4
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5answers
372 views

Confusion about Length Contraction (ex in Muon decay)

I am a bit confused about the implications of length contractions; For example, in the muon decay problem, we assume that the distance between the muon and the earth is contracted only in the frame ...
6
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4answers
298 views

Do photons make the universe expand?

I have a problem understanding the ideas behind a basic assumption of cosmology. The Friedmann equations follow from Newtonian mechanics and conservation of Energy-momentum $(E_{kin}+E_{pot}=E_{tot})$ ...
3
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2answers
177 views

Can a free hydrogen atom constitute ionizing radiation?

Radiation is basically just particles flying around, right? Are free hydrogen atoms just typically not moving fast enough to be considered "radiation"?
0
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1answer
44 views

Problems with calculating Strontium-90 leakage due to Fukushima accident

Not long ago there was a spill of radioactive water at the Fukushima plants. Here are the data: $230 \times 10^6 \,\,\mathrm{Bq}$ of beta radiation are found in a liter of water. $t_{1/2} = 28.79 ...
2
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4answers
167 views

What does the exponential decay constant depend on?

We know the law of radioactivity: $$N=N_0e^{-\lambda t}$$ where $\lambda$ is the exponential decay constant. My question is: This constant depends of what?
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0answers
55 views

Definition of mass gap [duplicate]

Why do we say that a system with mass gap has correlation function which decays exponentially and one without a mass gap has a slower power law decay?
1
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1answer
39 views

$\beta^+$ decay question

I read that all baryons apart from the proton itself decay into protons (why though?) and that mesons do not decay into protons due to having less mass than protons. Thus it makes sense for the ...