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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Understanding view-/formfactor for radiation with a specific example

There is radiation coming from a point source (black body). How much of the total emitted energy (from the point source) hits a spherical surface given by $\phi = 0 - \pi $ and $\theta = 0 - \pi/2 $? ...
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40 views

Alternatives to the neutrino in the beta spectrum?

It is well known that the neutrino appeared to explain the power distribution in the beta decay spectrum. (see PSE) What other explanations candidates were available? It is stated that the ...
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Question from radiation physic, photons per second [on hold]

A beam of red light, wavelength 700nm, has 3X10^6 photons per second and when incident on a thermophile is able to maintain an increase in temperature of 0.2K. How many photons per second is required ...
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24 views

Polarisation states in 1d?

I am working through a derivation of the spectral energy density in a 1d cavity. The derivation says that the number of modes (per unit volume) in a frequency interval $dv$ is given by: $$g(\nu)d\nu ...
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1answer
27 views

Can someone explain the radioactive decay of that would happen over time to a 1 cubic decimeter block of plutonium? [closed]

I just saw an article talking about naturally occurring plutonium on Earth and it said that some [or many or some other purposefully ambiguous statement] people think this element could [another good ...
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3answers
397 views

How do particles “know” when to decay?

So, as I understand it, in a substance that is made of radioactive elements, the half-life tells us how long until the half of those atoms decay into their next atom [is there a name for that: the ...
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1answer
17 views

Measured temperature (thermometre set to emissivity of 1) of smooth surface too high or to low?

We want to measure the temperature of a smooth flat surface with a thermometre based on absorption of thermal rays. The emissivity setting of the thermometre is set to 1 (same as a black surface), ...
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3answers
67 views

Is heat from a stovetop, transfered through convection, radiation or conduction?

It doesn't appear to be convection, as there are no moving objects (or are there); probably not radiation (?), so it is conduction? I really don't know much about heat transfer and thermodynamics, ...
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7 views

Annual Dose Equivalent Rate Formula

I know the main formula of dose equivalent rate (H) is: H= D * Q H (dot over) = H/t Dose Equivalent Rate (DER) The question is, if we already have DER in a unit (μSv/hour), and we want to find for ...
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3answers
707 views

How do we know that the cesium-beam frequency used in atomic clocks is always the same?

Atomic clocks use cesium-beam frequency to determine the length of a second. This has shown that the period of orbit of the earth is decreasing. But what experiment showed that cesium-beam's period ...
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2answers
3k views

Why doesn't the evening/morning sun feel much hotter on your face?

I understand that places on the Earth's surface get hotter in summer, and in the middle of the day rather than morning or evening, because the surface of the Earth is presented 'face-on' to the Sun at ...
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2answers
174 views

By what maximum amount can we concentrate sunlight?

This refers to a previous question re: Solar Cell Systems and as part of the answer the statement: If we concentrated sunlight to [the] maximum amount 42600× was given. My questions are: By what ...
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1answer
168 views

Increasing the efficiency of solar cell systems

As far as I know, there are currently two main approaches to utilising solar radiation for maximum energy conversion to electricity. These are either direct conversion to electricity, using ...
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37 views

In an all-out nuclear war, how long should remain sheltered? [migrated]

Fairly common in sci-fi literature is the scenario where the Earth is destroyed by an all out nuclear war. Typically, the protagonist have survived by remaining in underground shelters for decades ...
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1answer
85 views

What is the difference between zero background radiation and field background radiation in Nuclear Physics measurements?

Can someone please explain the difference between these two terms (Zero Background Radiation and Field Background Radiation) used in radiometric prospecting measurements?
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1answer
28 views

Carbon 14 disintegration

When $\beta^-$ disintegration happens to a Carbon 14 atom, a neutron "turns into" a proton, and an electron is emitted. Therefore the result of the disintegration is a Nitrogen atom plus an electron ...
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1answer
47 views

What is the energy threshhold to produce Cherenkov radiation?

I am in a nuclear course right now and am getting some misleading information from different sources. I am trying to figure out what the minimum total energy is that a proton must have in order to ...
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2answers
41 views

How does “contamination” through (radioactive) radiation work?

Physically, what does it mean when people or objects are contaminated with radiation? Is it because they actually carrying heavy metal particles?
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1answer
37 views

Surfaces that reflect UV rays

I've been trying to research what surfaces reflect UV rays for the past day but it's been difficult coming up with definitive answers. So far what I've found is that surfaces that reflect visible ...
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1answer
25 views

Does the W boson in beta decay affect the gravity generated by the system?

During beta decay we now know a heavy W boson gets involved temporarily. Would this potentially impact the gravitational field generated by the system as a whole? It doesn't seem like it should. Just ...
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1answer
87 views

Relationship between temperature and wavelength?

I am investigating the relationship between wavelength and temperature. As seen the figure below of Planks law What is the relationship between the lambda(max) and Temperature? or in simpler ...
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0answers
28 views

beta minus decay: expression for maximum electron energy

I'm having some trouble finding an expression for the maximum electron energy in beta minus decay. In the frame where the neutron is initially at rest, conservation of momentum reads: ...
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1answer
37 views

X-ray background radiation

I'm running an experiment in gamma-ray imaging (although the main emission from the decay of Am-241 is ~60keV, so much more in the range of x-rays). I'm curious as to the sort of sources that would ...
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1answer
26 views

Background gamma radiation

There are plenty of lists of sources of general background radiation, but can anyone reduce that list to the major contributing sources purely for background gamma radiation (specifically low energy, ...
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1answer
33 views

What process happens in an IT nuclear decay?

I've been researching medical isotopes and alot of them decay by an IT path. Does anyone know what IT stands for? And what physical process is happening? Example: ...
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2answers
108 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 ...
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2answers
181 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
46 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 ...
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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
27 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
46 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 ...
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0answers
30 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 ...
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1answer
34 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 ...
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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 ...
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2answers
55 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 ...
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53 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 ...
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3answers
101 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 ...
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1answer
61 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 ...
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1answer
87 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 + ...
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1answer
87 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 ...
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1answer
100 views

How hot is Plutonium-238 in Radioisotope Thermoelectric Generators (RTGs)?

As I understand it, Plutonium-238 is used to provide power through heat generation in radioisotope thermoelectric generators. My question is... how hot is a pellet of Plutonium-238? Does the heat ...
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1answer
163 views

Does tin foil keep heat out?

For example, if i were mailing a box of chocolates and lined the inside of the box with foil, then wrapped the chocolate in bubble wrap and placed it inside the foil lined box, would the box heat up ...
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1answer
45 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
54 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 ...
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1answer
452 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) ...
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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 ...
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3answers
86 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
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250 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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61 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?