53
votes
Why does a mirror reflect visible light but not gamma rays?
Look at the electromagnetic spectrum:
Visible frequencies have wavelengths of microns, $10^{-6}$ meters.
Gamma rays have a wavelength of $10^{-12}$ meters, picometers.
In physics, there are two ...
- 235k
49
votes
Why did the gamma ray burst from GW170817 lag two seconds behind the gravitational wave?
This is addressed in section 4.1 "Speed of Gravity" of one of the GW170817 companion papers: Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A. General ...
- 7,225
48
votes
Accepted
Do nuclei emit photons?
Nuclei emit gamma rays, which are high energy photons. The photons emitted when electron in an atom changes its energy state are usually in optical spectrum, which are more frequently encountered in ...
- 65k
31
votes
Do nuclei emit photons?
Yes, excited nuclei emit photons in the form of the highly energetic $\gamma$-rays.
That these emissions are much more energetic than the VIS photons emanating from excited electron clouds can be ...
- 35.5k
25
votes
Why did the gamma ray burst from GW170817 lag two seconds behind the gravitational wave?
The delay is real. It is the delay between the merger event = the end of the GW signal, and the GRB event = a peak in gamma photons. See this video.
As mentioned in this article, such a delay is ...
- 401
24
votes
Why does a mirror reflect visible light but not gamma rays?
The reason why is based in something called the plasma frequency of the metal of a mirror. A metal, as you may know, is composed of a series of atom (ion, effectively) cores - nuclei, together with ...
- 20.8k
24
votes
Accepted
What's the difference between Hard X-rays and Gamma-rays?
It can be a little confusing because there are two conventions.
The modern convention is to distinguish x-rays from gamma rays by how they are produced. X-rays are produced by electron energy ...
- 13k
22
votes
Why does a mirror reflect visible light but not gamma rays?
Reflection is caused by electrons reacting to the electromagnetic field by oscillating at the same frequency. When they do this they emit radiation of the same frequency as the incoming light and this ...
- 26.6k
18
votes
Why did the gamma ray burst from GW170817 lag two seconds behind the gravitational wave?
Gravitational waves are produced at ever increasing amplitudes as the NS come closer together, until they are disrupted by the tidal gravity---which determines the time the "chirp" ends. The ...
- 14.3k
13
votes
Do nuclei emit photons?
When nuclei are in an excited state and decay, they often release photons (almost always in the gamma/X-ray energies). A good example of this is the decay of metastable nuclear isomers.
For instance, ...
- 231
9
votes
What makes the thorium-229 nuclear transition special?
Looks like world’s second-lowest-energy isomer is uranium-235m, its energy is currently known as 76.8 ± 0.5 eV (https://ldrd-annual.llnl.gov/ldrd-annual-2015/nuclear/lowest).
EDIT (09/01/2018): ...
- 27.5k
6
votes
"gamma rays can only be detected when they interact with matter"
The quote is wrong.
“Any photons can only be detected when they interact with matter”. It is how they are detected that changes with the wavelength of light.
Radio and microwaves are usually ...
- 6,665
6
votes
Accepted
If gamma radiation is harmful to humans, why isn't natural light fatal?
The name of the frequency spectrum of electromagnetic radiation is important in showing the energy carried by the individual photons. Note in this table gamma rays are the highest energy rays, the ...
- 235k
6
votes
Do nuclei emit photons?
The simple answer is yes. Here is a real life example where this is important.
To produce 'signal', the MRI scanner interacts with protons in the body. Randomly orientated protons become aligned with ...
- 235
6
votes
How can a gamma ray conserve its momentum while travelling from the center towards the sun's surface?
A gamma ray photon does not travel from the core of the Sun to the photosphere. The mean free path of a gamma ray photon in the core of the Sun is of order 1 mm. The energy of the photon is absorbed ...
- 137k
6
votes
Accepted
Reflection of Gamma Rays
Yes. Kind of.
Total internal reflection is not a thing at these energies, the wavelengths of these gammas are way too small. The dominant interaction at these energies is via Compton scattering - that ...
- 6,495
6
votes
Accepted
Where are the Gamma rays in Beryllium-7 decay coming from?
${}^7\mathrm{Be}$ decays exclusively by electron capture to form ${}^7\mathrm{Li}$, but it can decay into the first excited state of lithium, and the excited lithium nucleus then decays by emission of ...
- 363k
6
votes
Could a single gamma ray photon break the Schwinger limit? If so, at what energy?
Consider an electorn-positron collision, and the subsequent production if photons. It is known that there must be at least two photons produced. This is because momentum must be conserved. In the ...
- 956
5
votes
Accepted
In the Pound Rebka Experiment, how were the gamma rays generated?
The photons in question were not atomic photons derived from relaxing an excitation of the electronic states of the atom. They were nuclear photons derived relaxing an excited nuclear states. The ...
5
votes
Health issues concerning December 27, 2004 gamma ray burst
Any health effects were too small to be noticed.
According to this NASA article, the gamma ray burst lasted a few minutes with a peak that lasted 0.1 seconds. That peak was huge, containing all the ...
- 45.7k
5
votes
Accepted
How can gamma rays affect a human body if they can move through atoms without colliding with them?
Based on your question: Yes, it is extremely unlikely that a gamma ray will hit an atom; however, Avogadro's number ($N_A$) is large: there are many atoms in your body, so it is likely it will ...
- 39.6k
5
votes
Accepted
What is the lowest energy gamma ray?
In addition to Ben Crowell's answer:
Thorium 229 has a nuclear isomer Thorium 229m that has an energy 8.28±0.17 eV above the ground state. When it decays it does so via an UV wavelength photon (which ...
- 33.4k
4
votes
Why we don't use gamma rays, x-rays or ultraviolet to transmit data?
Actually, NASA and others are considering the use of X-rays as a communication medium. The difficulty comes in the modulation, and in the fact that X-rays can't be transmitted via wires or fiber. But ...
4
votes
Accepted
EM waves with frequency much higher than gamma rays penetrate a planet like Earth?
For an electro-magnetic wave, the ability to penetrate matter goes as $1/{\sqrt{f}}$.
So as you increase the frequency, the penetration gets worse. By the time you get to gamma-rays, the energy is so ...
- 4,503
4
votes
What's the difference between Hard X-rays and Gamma-rays?
As your links say: gamma rays are produced in nuclei whereas X rays are produced by atoms.
Typical gamma rays have more energy than typical X rays. But there is an overlap region. And apart from their ...
- 10.2k
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