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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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: $$ ...
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26 views

Calculating solar irradiance of Earth [closed]

The mean solar radiation flux absorbed per unit area of Earth’s surface, neglecting the atmosphere, is calculated as FS(1-A)/4, where FS is the solar constant and A is albedo. I can see how this would ...
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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 ...
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19 views

Using ion radiation to make electricity? [duplicate]

Is it possible to capture the ion radiation from a nuclear source and make electricity from it? I always thought it was possible, but never looked into it? Is this what a beta voltaic battery does?
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32 views

How to integrate to find the view factor of two parallel disks of different radii? [closed]

You have two parallel coaxial disks of different radii. I have tables that give me the value as $$F_{ij} = \tfrac{1}{2} [S - \sqrt{S^2 - 4(r_j/r_i)^2}]$$ where $$S = 1 + \frac{1 + R_j^2}{R_i^2}$$ ...
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Protonic emissions

In a beta emission a neutron decays,into a proton and an electron, and an electron randomly gets ejected from the nucleus due to the phenomenon of barrier tunnelling(correct me if am wrong).But why is ...
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19 views

How much power is being actually delivered by an electric heater to a cooking pan?

I've been doing experiments on an electric heater heating a cooking pan filled with 2 litres of water, from 20°C to 70°C; now I'm trying to draw a theoretical heat transfer model thath should match ...
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27 views

In solids, is it phonons, or is it the oscillations of electrons in bands, that emit most of the blackbody radiation?

In solids (most any object we see), which tends to emit most of the blackbody radiation: phonons (atomic, or molecular dipole, lattice vibrations) or oscillating electrons in their energy bands?
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32 views

Is an “underwater” submarine affected by a nuclear bomb exploding above the water? [duplicate]

I've just read Would being underwater help survive a nuclear bomb?. Submarines are way more armored and far from the surface than a human body (https://en.wikipedia.org/wiki/Submarine_depth_ratings), ...
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35 views

Why photoluminescene spectrum is not identical to electroluminescence spectrum?

Electroluminescence (EL) and photoluminescence (PL) spectra are not identical: there's a small red-shift of the PL spectrum relative to the EL spectrum. Why is this happening if both EL and PL are ...
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31 views

Can we enhance a thermal gradient by combining a dark surface and a shiny surface with an external glass layer?

I refer to the article at this site: http://solarcooking.wikia.com/wiki/Solar_Kettle-Thermos_Flask As we know, dark surfaces absorb radiation (eg. solar water heater), while shiny surfaces reflect ...
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56 views

Why is there only alpha and beta (and gamma) decay?

Why is it that we mostly speak of alpha and beta decay (when looking at emitted particles with rest mass)? Why don't we speak of decays that emit something like $2n3p$, $3n2p$ and so on? Do they occur ...
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14 views

Why does natural counting with a gamma spectrometer differ from Neutron activation analysis?

As stated in the title, why are the data from natural counting using s gamma spectrometer different than the data from neutron activation analysis using the same samples?
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1answer
29 views

How is the stellar flux for exoplanets calculated?

I have noticed that in many Wikipedia articles, the stellar flux received by each planet is stated. I tried to calculate this stellar flux from the given data, but the results didn't seem to be ...
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25 views

Half- life of Radon

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

What is the Best Electron Tube for creating X-Rays?

This is a question of Experimental Physics. I have seen that you can create X-Rays with a High Voltage Circuit using Electron Tubes. http://www.dangerouslaboratories.org/xray1.html. My question is, ...
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174 views

Gamma Spectrum: What is causing this behavior?

In my radiation detection lab we're identifying a unknown source, based on the gamma spectrum it's an activated gold foil. You can clearly see 4 peaks: 411.78 keV (Au-198), 675.93 keV (Au-198), 823.51 ...
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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.
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1answer
15 views

Solar radiation conversion check [closed]

I'm analysing some solar radiation data, which is the calculated as the daily sum of PAR in MJ per m$^2$ per day. Assuming that PAR makes 42% from total irradiance, how can I convert this to solar ...
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41 views

Why is the intensity of an alpha ray constant along a material?

I'm taking a course in radiation physics and I've come across the following problem: A thin beam of alpha particles of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity ...
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61 views

Can electrons within a positive ion absorb and reflect light?

I understand that in a crystalline metallic structure, such as one making up a bar of gold, there are one, or more, valance electrons of each atom that have left their outer shell (became free ...
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4answers
792 views

Detecting radiation from tritium keychain

I am measuring radiation from 6 tritium glow keychains. Usual gamma detector does not detect anything (this is expected), but on beta detector with thin window I am getting about 5 counts per second. ...
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77 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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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 ...
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How do electrons jump orbitals?

My question isn't how they receive the energy to jump, but why. When someone views an element's emission spectrum, we see a line spectrum which proves that they don't exist outside of their orbitals ...
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341 views

How can heat turn into light

I am confused about how hot surfaces can radiate light to their surroundings. When I shine a light on a surface the light turns to heat spontaneously, and when I leave that hot surface it radiates ...
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65 views

Cesium-137 From Fukushima Meltdown

I've been reading up on the Fukushima nuclear meltdown and its effects it had on the environment. The iodine-131 initially released from the incident decayed after 8 days, but other isotopes such as ...
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45 views

Are the leptons in $\beta^-$ decay already present in the nucleus in some form?

In beta minus decay, beta-minus particle and anti-neutrino are ejected, leaving behind daughter nucleus. $\beta^-$ and anti-neutrino both are leptons. Were the leptons already present in the ...
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5k views

How to calculate incident solar energy on earth in a given day with a spectral filter

The daily solar radiation irradiation is often quoted as being between $3.2 \text{ kW hours}/\text{m}^2$ and $7 \text{kW hours}/\text{m}^2$ per day . If you filter out a range of wavelengths, how can ...
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714 views

How can we detect cosmic background radiation?

From what I understand, CMB is the left over radiation from the Big Bang. As all matter, including the Earth, was made during the Big Bang and then as the universe expanded that matter/energy got ...
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1answer
75 views

Long distance radiation detection, David Hahn and the clock

The strange character David Hahn, obsessed with creating a nuclear reactor since a young age, was reportedly wandering around his neighborhood with a Geiger counter and by this means he located a ...
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1answer
45 views

Have cosmic rays and the CMB affected Earth's history?

Do cosmic rays and the cosmic microwave background carry with them enough energy to have a macroscopic effect on events on Earth? The most obvious example I can think of is by giving animals cancer. ...
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Does an atom become positively charged as a result of Beta decay? [duplicate]

Since a neutron breaks down into an electron and a proton, and the electron is emitted as beta particles, the atom has an extra proton (protons>electrons). So, the atom becomes positively charged. But ...
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49 views

Can neutrinos cause $^{14}\rm C\to\,^{14} N$ beta-decay?

I half-heard in a lecture that radiocarbon beta-decay is caused by neutrinos passing close to the nuclei & weakly interacting with one of the carbon neutrons, flipping it to a proton and producing ...
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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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91 views

Does a conducting wire give off measurable radiation?

In the Drude model (semi-classical, but should still apply here I think), the conducting electrons are in a constant electric field, and, in between collisions with the lattice ions (that happen, on ...
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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 ...
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28 views

Can we have Bremsstrahlung emission of particles which are heavier than the initial radiating particle?

Lets consider a light particle in a high-energy process. Can this light particle radiate "Bremsstrahlung particles" which are heavier than the initial light particle? In this context I don't refer ...
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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 ...
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22 views

What is the meaning of the magnitudes on the axes of this spectrum?

I'm taking a course on radiation physics and I've been given an spectrum by my professor (concretely it is a spectrum of $\left.^{22} Na \right.$). This is the first time that I come across this kind ...
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The problem of self-force on point charges

Allow me to preface this by stating that I am a high school student interested in physics and self-studying using a variety of resources, both on- and off-line, primarily GSU's HyperPhysics website, ...
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Other methods of X-ray production

Long running debate, I would like to find a definitive answer. In a long glass tube (borosilicate or other common glass) with high frequency AC excitation at one end, 50-60kV, with high evacuation, I ...
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2k 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 $H_0$, $\Omega_m$, ...
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Could the $\gamma$ ray “weaken law” be used in the air?

I'd better write it down. I do not know if it is called "weaken law" in English. $$N=N_0e^{-\mu d}$$ $N$ is the initial number of photons. $N_0$ is the amount measured after passing through an ...
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Direction of the radiation reaction force (vs. velocity)

The radiation reaction force is proportional to $\dot{\mathbf{a}}$, and can be derived from the the Larmor power using the concept of the conservation of energy. Looks like the radiation reaction ...
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2k views

How does heat energy travel in space?

How does the heat energy from the Sun reach us on the Earth? Since the kinetic energy of an atom is the amount of heat energy and there is no matter in space, how does heat from the Sun reach us?
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Question about Cavendish experiment

I got a question. In Cavendish experiment was used lead in both of spheres. Can we repeat that experiment with balls made from stone or anything else. Because lead could be a byproduct of radioactive ...
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Meaning of mean free path expressed as kg/m^2?

In the paper "The Question of Pure Fusion Explosions under the CTBT" at reference 12, the equation for the neutron dose from the fusion of a small amount of DT gas is given, with a term of $90 ...
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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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30 views

Radiation weighting factor photons

I'm wondering about the equivalent dose and the radiation weighting factor of photons (according to ICRP 103). Why is the weighting factor independent from the energy of the photons?