What is Radiation: Definition and 1000 Discussions

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:

electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ)
particle radiation, such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation (particles of non-zero rest energy)
acoustic radiation, such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium)
gravitational radiation, radiation that takes the form of gravitational waves, or ripples in the curvature of spacetimeRadiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules and break chemical bonds. This is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively. Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere.
Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. The word "ionize" refers to the breaking of one or more electrons away from an atom, an action that requires the relatively high energies that these electromagnetic waves supply. Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds which form molecules, thereby breaking down molecules rather than atoms; a good example of this is sunburn caused by long-wavelength solar ultraviolet. The waves of longer wavelength than UV in visible light, infrared and microwave frequencies cannot break bonds but can cause vibrations in the bonds which are sensed as heat. Radio wavelengths and below generally are not regarded as harmful to biological systems. These are not sharp delineations of the energies; there is some overlap in the effects of specific frequencies.The word radiation arises from the phenomenon of waves radiating (i.e., traveling outward in all directions) from a source. This aspect leads to a system of measurements and physical units that are applicable to all types of radiation. Because such radiation expands as it passes through space, and as its energy is conserved (in vacuum), the intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source. Like any ideal law, the inverse-square law approximates a measured radiation intensity to the extent that the source approximates a geometric point.

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  1. Graham87

    Radiation/Medical Physics Problem -- Scattered and Transmitted photons at detector

    I managed to calculate the fluence of the scattered photons. However, not the transferred photons. In the solution sheet the fluence rate has an l22 in the numerator in the end of the solution sheet. Where does that come from?
  2. ErikSwan

    B Can alpha radiation make other materials radioactive?

    Most general sources that describe the basics of ionizing radiation assert that the only type of radiation that can directly make other materials radioactive is neutron radiation (via "neutron activation"). Googling "does radiation make things radioactive?" produces a few examples, for...
  3. S

    Dose recording on Pocket dosimeter -- Is it accurate for a person's whole body?

    Pocket dosimeter consists of a small ionization chamber, if a person having pocket dosimeter moving in a radiation environment, how the dose received by the man is equivalent to the dose showing on pocket dosimeter although the exposed area of a man is quite larger than the dosimeter ?
  4. Deric Xavier

    B Detection of transuranic elements in astronomical events

    Is it possible to detect transuranic elements that may eventually occur during big astronomical events? I know that transuranic elements are radioactive, so we could maybe measure the radiation that is being emited, but how could we separate the radiation that comes from the transuranic elements...
  5. cemtu

    A Why KE of Annihilation Electrons Differs?

    We know that when a high energy gamma ray(E >= 1022 keV because the total energy of 1 electron at rest and 1 positron at rest is 511 keV) passes near a high Z(atomic weight) atomic nucleus interacts with the electrical field of the nucleus and there is a probability that this high energetic...
  6. P

    Medical Skin exposure with 35S Methionine?

    I ran a gel on electrophoresis that had proteins that were radio-labeled with 35s methionine, and in the process of imaging the gel (after 36 hr exposure on phosphor screen) I accidentally grabbed it with my bare hand. I'm getting very mixed messages regarding whether this is okay or not. Thoughts?
  7. kyphysics

    Does Radiation from X-Rays/CT Stay in Body Forever (Risks)?

    I'm slightly confused by what medical professionals/scientists say when they say to limit exposure to x-rays/CT/PET, etc. scans if possible, due to radiation. I'm also confused as to why we're often told to leave the room when a relative is getting such a scan, given that medical staff that...
  8. P

    I Colorless Compounds and electromagnetic radiation

    I was trying to understand why some compounds appear colorless (transparent) and tried to give an explanation. I take benzene as an example: it is a chromophore group in which there is π-conjugation, so a certain energy gap is generated between HOMO and LUMO. This energy gap is such that in...
  9. eneacasucci

    I Understanding Scattered Radiation in Photon Beams

    Consider a source emitting a beam of photons. These photons pass through x thickness of material. The attenuation coefficient of the beam \mu is known. We can write this formula If I'm not wrong, this formula tells us the number of photons that passed through the material of thickness x...
  10. Graham87

    Troubleshooting Nuclear Reactions: Decay, Gamma Rays & More

    The problem comes with solutions. However, I dont get the 3 steps in the solutions. Why do they calculate decay for 120min in step 3? And why is only the daughter nuclide relevant and no granddaughter? There might be something lacking in my knowledge about nuclear reactions. Also, I don't know...
  11. Engineer_Kosyakova

    Engineering COMSOL plot of thermal radiation from heated surfaces -- Help please

    There is heating of the surface of the material using an electron beam. It is necessary to calculate how much heat will be released and build a graph of dependence. Please tell me how this can be done, which modules in COMSOL can be used?Thank you!
  12. C

    B EMF Radiation detected from TV

    Hello. I have a quick question in regards to EMF radiation. In particular, I would like to know what quantity of microteslas a smart TV would emit. In particular, would it be unusual for a smart TV to emit in excess of 1000 microteslas even when turned off? Thanks.
  13. G

    A Radiation Friction: Solving Abraham-Lorentz Eq for Non-Physical Solutions

    There is a well-known Abraham-Lorentz equation describing radiative friction. Suppose a particle moves in an electromagnetic field. ma(t)=q(E+vxB) + m(tau)a’(t) By solving this equation numerically, I get non-physical solutions(runaway solutions) Although, it would seem that an electron in an...
  14. H

    A Radiation back reaction in classical electrodynamics

    I've been doing some research on the topic of radiation reaction force/self force in classical electrodynamics and although there are some discussions on the internet I would like direct answers to these following questions: Is there a rigorous and universally accepted treatment of radiation...
  15. F

    Evaluate the outgoing radiation from an optical fiber on a surface

    The geometric configuration that I am adopting is the following, I hope you understand. The optical fiber is positioned relative to the bottom surface at a height ##a## and an angle ##\alpha## with respect to the y-axis in the yz-plane with x = 0. ##b## is the distance between the origin and...
  16. J

    I Interaction of EM radiation with Glass

    Hi, I wanted some clarification on the mechanism for how EM radiation interacts with standard glass, namely IR, visible and high energy (UV and X-ray). Looking online most sources seem to say the band gap is around 10eV. Since visible light is about 1-3eV visible light will be transmitted. IR...
  17. C

    Measuring wavelength of microwave radiation using double slits

    For this problem, The solution is, However, when they found the angle, they did not account for the uncertainty. I guess this is allowed still since the sine of the angle will still be greater than 1, correct? Many thanks!
  18. .Scott

    I Why is Cherenkov radiation blue? And what about refractive index?

    I got this question from my son last night. If you Google "Why is Cherenkov radiation blue", you get this: Somewhat more substantial is the Wiki article on the Frank-Tamm formula. That formula ties the Cherenkov radiation wavelengths to the transmission characteristics at any specified...
  19. Graham87

    Radiation Physics - Decay Diagram

    In the solution below it says 22% goes to 0.0309keV. From the diagram above I interpret 22% goes to 0.1298keV with EC(L)/EC(K)=3.0 and not 4.4. Why is that wrong ? Thanks alot!
  20. S

    Does Jimmy Carter's long life prove some exposure to radiation is OK?

    Former USA President Jimmy Carter seems to be near the end of his 98 years, and was one of the original US Navy nuclear engineers. Over 70 years ago, he led a team that extracted out the world's first melted down core out of a Canadian reactor, himself going 90 seconds into the "dead zone" -...
  21. eneacasucci

    I Gamma radiation decay intensity (IAEA nuclide chart)

    I was looking at the gamma radiation data from IAEA's website: (https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html) and was confused by the absolute intensity listed in the page. I Googled it and it seems to be the probability of emission but why it doesn't add up to 100%? For example...
  22. P

    B Cherenkov Radiation -- How does this not break causality?

    Hi, I want to try to solve this puzzle in my head. They say that faster than c travel would break causality. And yet particles can travel through a medium faster than light can in that medium. But surely if that can happen then a particle can arrive at a place faster than information about the...
  23. T

    I Microwave background radiation - temperature at recombination

    The commonly called value of the temperature at recombination is 3000 K. According to this reference the process of recombination can be described by the Saha equation: 3.1. Recombination and the formation of the CMB Recombination happens quickly (i.e., in much less than a Hubble time t ~...
  24. M

    Lorentzian line profile of emitted radiation

    First of all i tried to follow the textbook. Here they start of by modelling the atom as an harmonic oscilator: Then they find the solution as: They neglect the second term as omega_0 >> gamma which also makes good sense so they end up with: So far so good. After this they state the...
  25. V

    Heat Radiation question (skin's reaction to UV versus IR radiation)

    I am not sure of the answer. But I am guessing that infra-red rays carry more heat radiation than ultra-violet rays, and the heat is instantly felt on our skin when exposed to both these rays. So what we feel is the heat sensation from infra-red rays and that sensation is missing when it's...
  26. emilmammadzada

    Why do I always get 0 values in the radiation part? (MCNP5)

    MCNP Output: energy stopping power range radiation beta**2 density rad/col drange dyield n collision radiation total yield corr mev mev cm2/g mev cm2/g...
  27. Strato Incendus

    Wall thickness of ring habitats for radiation shielding

    This is a topic that will be relevant for anyone who plans to use "realistic" artificial gravity (of the centrifugal kind, rather than the "acceleration-based" kind) in their stories - be it on spaceships or space stations: How much of the ring walls has to be dedicated to radiation shielding...
  28. Strato Incendus

    What can realistically go wrong on an interstellar journey?

    Alright, since I’m still stuck on my sci-fi story because I can’t exactly outline the mid-point plot twist with a realistic catastrophe on board an interstellar spaceship, I thought I’d widen the scope a little — towards full-on open brainstorming: What, if anything, can realistically go wrong...
  29. M

    I Hawking Radiation Extrapolation: A Conjecture

    The intense gravity near the event horizon causes complementary particles to pop into existence spontaneously. As local space-time is continuous through the EV, the same would be happening just inside the EV, only more so as the gravity field and gradient is greater. So near the singularity...
  30. M

    I  Hawking Radiation: Can Particles Appear with Relativistic Velocities?

    The Hawking radiation comes from a pair of complementary particles, an electron and a positron for example, coming into existence spontaneously near the event horizon as a result of the intense gravitational field. One particle gets captured by the Black Hole while the other escapes, taking a...
  31. B

    I Emission of light from incandescence of metals

    a. We know metals emit EM radiation upon heating or electric current. I'd like to understand more fundamentally how this phenomenon takes place, on the basis of the basis of band structure, and which electrons are involved ? b. Classically, charges emit radiation when accelarating or...
  32. JCR103

    Does "Reference Man" promote a gender bias in radiation protection?

    I came across an academic article by Mary Olson entitled "Disproportionate Impact of Radiation and Radiation Regulation" (https://www.tandfonline.com/doi/abs/10.1080/03080188.2019.1603864). Based on data in BEIR VII, she illustrates that women are more sensitive to ionizing radiation than men...
  33. Quotidian

    A Radiation Shock Too Powerful to Examine (EMP)

    Hi all - I'm not a physics grad, my knowledge is limited to whatever I can glean from popular science publications. Anyway, I'm crafting a hard sci-fi story - 'hard' because it's written to seem kind of plausible, or at least not outrageously surreal - no shape-shifting or anti-gravity or...
  34. P

    Radiation emitted by a decelerated particle

    Honestly, folks, I don't even know how to start. I included in the Relevant Equations section the relativistic generalization of the Larmor formula according to Jackson, because that's the equation for the power emitted by an accelerated particle, but I don't see how that gets me very far. The...
  35. FEAnalyst

    Triangular cavity thermal radiation simulation

    Hi, I'm trying to solve a problem involving radiation in a triangular cavity: As you can see, lengths and emissivities of all surfaces are given. For two of them, the heat flux is known and the temperature has to be found while for the remaining surface it's the other way around. I have the...
  36. hilbert2

    Medical Natural compounds for radiation protection

    The "sleep hormone" melatonin, sold at health supplement stores, has been found to prevent radiation sickness from ionizing radiation: https://pubmed.ncbi.nlm.nih.gov/30073934/ There are also some other references for this findable with a Google search. But you don't want to be on melatonin...
  37. J

    I Cosmic Inflation Explained: Constant Velocity of Electromagnetic Radiation

    C = sqrt(E/M)...this would suppose the ratio of the amount of energy vs. the amount of mass in the universe. If not, why not. If there is no mass, just energy, or much less mass at the moment of the hypothetical Big Bang, then, there C would be significantly higher, thus explaining cosmic...
  38. S

    I How visible is ionizing radiation?

    Eye adapted to darkness is fairly sensitive to small numbers of photons. See for example the derivation here: Polaris, bright for a star, is estimated to send 100 000 visible photons per second into a dark adapted pupil. The rear wheels of Little Dipper are about 15 times dimmer, so about 6000...
  39. Strato Incendus

    Writing: Input Wanted A dangerous space mission that requires a lot of helping hands

    As I've mentioned in a few previous threads, at the midpoint of my sci-fi story on a generation ship, I need a disaster that wipes out about a third of the (male half of) the crew. Several people have suggested things like "a virus that disproportionately affects men", but that didn't quite cut...
  40. B

    A Displaying the dimensionless Radiation Transport Equation

    Hallo, I would like to display the RTE (Radiation Transport Equation) dimensionless. In the picture, the RTE is shown. I would like to have the Planck number (or N) inside at the end. Additionally, the Prandtl number and the Rayleigh number can be inside. I have already many attempts behind me...
  41. Buzz Bloom

    Medical An Odd Description of Skin Cancer Cause from UV Radiation

    Scientific American June 2, 2022 Vol 32 Number 6 Page 62 Title: Skin Cancer around the World Two Quotes: “The main cause of skin cancer is the exposure to the sun’s ultraviolet rays…” “UV radiation is about 40% stronger in New Zealand than it is at corresponding latitudes in the Northern...
  42. P

    B Can Particles Escape a Black Hole? The Hawking Radiation Improbability

    How can a particle created just outside the event horizon with no velocity (?) escape a black hole, never to return, when black holes gravity is so strong that they can pull matter away from stars many kilometers distant?
  43. LCSphysicist

    Radiation of a rotating bar

    Ok. I was writing a big text about it, but i will summarize it. We know that $$P = \frac{\mu \ddot{m}^2 w^4}{12 \pi c^3}$$ We know, as well, that $$\nabla \times M = 0$$. Also, $$\vec K = M \times \hat \rho = M \hat \phi$$ Total current, I = $K l = M l$. Magnetic moment, so, $$M l \pi r^2...
  44. PainterGuy

    I Some questions about Cosmic Microwave Background radiation

    Hi, I have some questions about cosmic microwave background radiation, CMB, and I thought it's better to ask them together. I have combined all related content for each question to make the question clearer, understandable, and to provide proper context for any person like who stumbles upon...
  45. PainterGuy

    I Blackbody radiation and the cosmic microwave background

    Hi, The following is my basic understanding of blackbody radiation spectrum. The important sections are in boldface. Source: https://en.wikipedia.org/wiki/Black-body_radiation#Spectrum Question 1: The quote above says that at room temperature (let's say 20 C or 293 K) the emission is in the...
  46. samy4408

    I Question about X-ray power emitted by the Coolidge tube

    hello i found this equation in a course about x rays , and i couldn't find it anywhere else they said that it is the theoretical expression of the energy spectrum , and dφ/dE is variation of the power emitted by the Coolidge tube as a function of the energy of the x ray. but i didn't understand...
  47. A

    Procedure to express radiation intensity of an LED in watts/cm^2

    I am calculating Responsivity of a pn junction photodiode (a.k.a the target) by irradiating radiation from LED sources. For this purpose, i have two LEDs, one UV and another green LED. Note that LEDs are placed close to the target. UV LED : Manufacturer has given total radiant power to be...
  48. A

    I Radiate Single Charged Particle: Free Fall in Black Hole?

    Does a single charged particle in free fall into a black hole radiate?
  49. shivajikobardan

    Engineering What is difference between solar radiation and global radiation?

    Solar radiation-: it is em radiation emitted by son. it is short wave radiation. it comes in many forms. 1) visible light 2) radio waves 3) infrared 4) x rays 5) uv rays Global radiation-: it is sum of direct and diffuse radiation arriving at a ground. What are the differences between these two?
  50. LCSphysicist

    Black body radiation and gas

    The image above is the solution posted by the book. I can follow the reasoning that has been used, but i have a trouble particularly at the first equation itself. Why should $$n = 2 \rho / m_{H} $$ instead of $$n = \rho / (2m_{H})$$, since the mass os a molecule of hydrogen is two times the...