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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Can I get hit positions in a plate from a normal distribution of a radiation does at that plane? [on hold]

I know this might sound confusing, but I was wondering if I had a distribution that defines the radiation does at a plane at a certain position (lets say $z=783~\mathrm{cm}$) here are the images of ...
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24 views

Fermi's theory of beta decay - density of states?

I am following through these MIT OCW notes on Fermi's theory of beta decay. On page 11 (103 as on page) they wrote the expression: $$\rho(p_e)dp_e = dN_e \frac{dN_{\nu}}{dT_\nu}$$ for the density of ...
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1answer
142 views

A “figure-8” EM field created by a dipole antenna

This question pertains to the EM field of a Pulse W5017 dipole antenna. The data sheet of this antenna can be found here (which contains information regarding the radiation patterns). There are TWO ...
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16 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, ...
5
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1answer
3k views

Where is radiation density in the Planck 2013 results?

I've been looking at the Planck 2013 cosmological parameters paper, trying to update my toy cosmology simulator with the most recent data. Most of the interesting values such as $H_0$, $\Omega_m$, ...
16
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2answers
267 views

In the Iranian nuclear deal, how can IAEA detect nuclear activity after 24 days?

This is a question related to current events, but I want to ask about the physics, which are not explained in any news article that I can find. Ernest Moniz and John Kerry wrote an op-ed in the ...
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2answers
330 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?
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2answers
53 views

Is energy only transmitted through electromagnetic and particle radiations? [closed]

Which are the other ways of transmission if any? If energy does not require any medium for transmission(as for sunlight reaching earth, the heat too), is it transmitted in quanta in particle radiation ...
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1answer
50 views

Why alpha decay usually leads to ground state while beta decay usually leads to excited state?

When alpha decay happens the daughter nucleus is usually in ground state. When beta decay happens the daughter nucleus is usually in excited state which is then de-excited by emitting gamma photon. ...
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1answer
113 views

Relativistic explanation of Radiation

I ask this question again in a simpler, shorter form. Maxwell's equations can be derived with Special relativity starting from the Coulomb's law. Therefore all the phenomena of classical ...
3
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1answer
139 views

Purcell's approach to Larmor's formula, assumption?

In 'Electricity and Magnetism' By E.M.Purcell, a derivation is given of Larmor formula (a version of which can be found here). I will give a brief overview here: A particle is considered at ...
3
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45 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 ...
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3answers
66 views

Why conductors don't scatter light?

Air molecules can be oscillated by E field and re-radiate EM waves in different directions. However, if light is shined to a conductor the E field oscillate the free charges but the effect is to ...
3
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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 ...
4
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2answers
137 views

How many photons are there in free space on average

Estimates of the amount of for example "dark matter" are of interest to the cosmologists. However, I have never seen an estimate of how many "free" photons could be speeding about in the known ...
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3answers
113 views

Deflection Effects on a Spinning Solar Sail

Suppose I have a solar-sail-powered starship flying directly away from a star. The sail is flat and perpendicular to the direction of travel. Now, in order to make the trajectory more stable (we think)...
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1answer
35 views

Multipole expansion of the electromagnetic field

In Jackson's Classical Electrodynamics, section 9.7, he develops the multipole expansion of the electromagnetic fields in terms of the vector spherical harmonics and the spherical Bessel and Hankel ...
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19 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 ...
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3answers
10k views

Would being underwater help survive a nuclear bomb?

If I jump in my pool, on the river near my house knowing that a nuclear bomb, or atomic or H-Bomb exploded around 10 km from my house, would I survive? The way I see it is that water will protect me ...
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60 views

How do you calculate the heat build-up inside a building or container as a result of the sun?

I need to calculate how much heat builds up in a closed environment eg a building or a Chromadek container. One of the factors I need to take into account is the sun. I know there are various ...
4
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2answers
39 views

How to calculate absorbed dosage

Lets say you have some unstable isotope which decays via beta decay. For example, lets say you want to calculate the amount of beta radiation that is emitted from the decay of $^{87}\textrm{Kr}\to ^{...
4
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2answers
774 views

What causes Potassium to decay into Argon the way it does

From evolutionwiki: "Potassium 40 decays into argon 40 through a process known as electron capture. In electron capture, an electron from the innermost electron shell "falls" into the nucleus, ...
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1answer
37 views

How is the amount of radiation calculated from a decay?

Lets say you have some unstable isotope which decays via beta decay. For example, lets say you want to calculate the amount of beta radiation that is emitted from the decay of $^{87}\textrm{Kr}\to ^{...
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1answer
46 views

Stopping power of charged particles in matter

So I have this diagram of how the stopping power of muons changes with energy: Depending on energy different equations are used to describe the stopping power variation. Now, currently I'm reading ...
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2answers
2k views

Nuclear bomb power - myth?

I'm not experienced in physics yet (if it helps I've covered as much as acceleration, momentum and energy transfer/chemistry ionic and covalent bonding) but I've heard that the way people compare ...
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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, ...
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1answer
40 views

Why does a CfBe neutron source not exist?

Sources such as AmBe take advantage of Beryllium's $(\alpha,n)$ process to produce high energy neutrons. Sources such as Cf utilize spontaneous fission. Why not combine the two? Such a source would ...
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5answers
4k 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 ...
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2answers
49 views

Does radiation emission depends upon absorption?

Is it possible that we stop the absorption of radiation completely? if so, will we stop emission from our own body? Does the radiation emission depends upon absorption?
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3answers
4k 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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1answer
41 views

Why is lead used for X-ray cladding equipment?

I've done some research and can see that the distance travelled by an x-ray through lead is far less than through other materials, but is there a more "full" explanation that I'm missing out on to do ...
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1answer
42 views

How does radiative cooling between the earth and space work?

On a chilly (but above freezing) temperatures on a clear night, you can freeze water outside because of radiative cooling. By what mechanism do warm bodies on earth actually lose heat to space? ...
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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 ...
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2k views

What is happening over the 15 minutes it takes a neutron to decay?

I've read that free neutrons decay into a proton, electron and neutrino with an average lifespan of about 15 minutes. Is there anything physically different about a neutron that has existed for 14 ...
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16 views

Is the decay of nuclei also depending on the 'age' of nuclei or whether they are created or not? [duplicate]

Usually the decay is said to be randomly but the average period of decay of certain atoms are stable. So if you randomly take a bunch of the same atoms the average time before the decay will fe be 5 ...
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1answer
24 views

Dependence of atomic mass number in the Bragg Kleeman rule

I have just staring learning about radioactivity, more or less about alpha particles and how there range can be approximated by the Bragg Kleeman rule, $\displaystyle{R \varpropto \frac{\sqrt{A}}{\rho}...
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2answers
4k views

Tunneling of alpha particles

Consider this explanation of the alpha decay: It says The Coulomb barrier faced by an alpha particle with this energy is about 26 MeV, so by classical physics it cannot escape at all. ...
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969 views

Do human bodies give off a consistent but unique radiation/electromagnetic/energy signature?

Is there any facet of the energy emitted by a human body that is consistent and unique - like a fingerprint, but a signal that could be detected by a remote device?
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2answers
122 views

Where are the photons coming from?

Particles and Antiparticles can annihilate, and they are completely destroyed in the process, which creates photons. From wikipedia: ...
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1answer
83 views

Inverse beta decay; energy of anti-neutrino

Assuming that the target protons are at rest, calculate the minimum energy of the anti-neutrino for this reaction to take place: $$\bar{\nu}_e+p\rightarrow e^++n$$ I know the answer is given by $E_{\...
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2k views

What temperature can you attain with a solar furnace?

A solar furnace is a device that concentrates the sun's light on a small point to heat it up to high temperature. One can imagine that in the limit of being completely surrounded by mirrors, your ...
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3answers
2k views

Does brightness of the light remains constant with the variation of the distance with respect to the source in vaccum?

I have this question going in my mind from many days, i.e why brightness of light emitted from any light source around us decreases with distance? The brightness of light from tube light, streetlight, ...
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1answer
25 views

Radiation-Glossy Black vs Matte White

Well, studying the chapter Heat I know that a matte black body radiates heat more than a glossy white one but can anyone give me an answer about what happens when its a glossy black body and a dull ...
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1answer
53 views

Would 10 metres of liquid air be as effective against cosmic radiation as Earth's atmosphere? [closed]

Assuming ballpark figures which give a depth of 10m if the Earth's atmosphere was liquefied, would that be as effective a protection against ionizing radiation from space as the gaseous atmosphere is?
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99 views

What is beyond Gamma Rays and Radiowaves in the Electromagnetic Spectrum?

The electromagnetic spectrum is commonly refered to as consisting of; Radio-waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma Rays - of increasing frequency from left to right. ...
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1answer
61 views

Do all solid objects emit visible light?

Are there solid objects that do not emit visible light? To my limited and humble knowledge, creating such an object would require us to "only" shift the spectrum of emitted radiation. Is it possible? ...
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4answers
3k 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 ...
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17 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 ...
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41 views

Why build so big sarcophagus in Chernobyl instead another alternative? [closed]

As title, why build so big sarcophagus in Chernobyl? The new sarcophagus is really tall, large and expensive and it should cover the old one. But there is already a sarcophagus build over another ...
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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. ...