More electromagnetic radiation Q's

[Crash]

The smallest wavelength detected so far is 10^-11, for gamma radiation.

According to my reading that is so how is this detected and why arent they trying to detect smaller wavelengths? Is there a theoritical and pratical limit to these things?

 

BTW i didnt know which forum this should go under thats why its here, prob shoulda been in physics-theoritical

[AntiMagicMan]

If you remember that frequency is inversely proportional to wavelength by the formula f = c/lambda and that the energy of a photon is given by E=hf then you can see that as wavelengths get smaller, energies get higher.

 

The highest energy photons we have access to come from cosmic rays, these can have energies up to 1TeV which would give you a wavelength of 1.24*10^-18 m, quite a few orders of magnitude smaller than that gamma radiation.

 

I am not sure if there is a theoretical limit, you simply need to collide two particles (ideally a particle and it's antiparticle) at a very high energy to create high energy photons. But there is probally a practical limit in how much energy you can get into the original particles.

 

Hope that sorts things out for you.

[Dave]

Moved here because it's a more appropriate home.

[Crash]

So what is the smallest wavelength possible for a practical limits?

How are cosmic rays detected?

Also whats the largest? would there be a limit to the size?

[AntiMagicMan]

Do you mean the smallest we can produce? If you want really small, then you need large particle accelerators, but do you want to know the smallest we can produce with big accelerators, or with more "everyday" equipment.

 

Cosmic rays are not detected directly, their effects are detected in particle showers debris found in cloud chambers and other particle detectors. Basically the cosmic ray hits the atmosphere and a lot of energy is released in the form of electrons, pions, neutrinos and the like, and they come tumbling down to earth.

 

The largest wavelength, requires the smallest energy, I am not sure if there really is a limit as to the largest wavelength. I'll have a look around and see what I can find out.

[Crash]

Yea, i want to know more just the theoritical side, so EM rad smaller than cosmic rays does exist then?

[AntiMagicMan]

I advise you speak in terms of frequency. Scientists like to use frequency because it is directly proportional to energy.

 

Obviously you can see the upper limit on frequency is how much energy you are able to get into one place and convert into photons. Same with the smallest frequency, it depends on how little energy you can convert into a photon.

 

Theoretically I'm sure it is possible to create frequencies larger than cosmic rays, but you have to realise these photons come from supernovas and supernovas are brighter than entire galaxies when they are exploding. I don't reckon we will be able to harness energy on that scale any time soon.

[Crash]

So if we observe the effects of a hypernova, what will we see?

[AntiMagicMan]

A supernova? I don't know what a hypernova is.

 

Well if you are lucky enough to see one, you will observe over the course of a few days that a small insignificant star brightens until it becomes the brightest object in the night sky, and then becomes dim again.

[Radical Edward]

There are no upper limits in any current theories, at least none I am aware of. The highest energy photons recorded come from cosmic rays with 10^20 eV. However as photons get to a higher and higher energy, there are increasingly more things that they can transform into (i.e. an electron positron pair) and this makes these photons less likely to occur.

[Dave]

A supernova? I don't know what a hypernova is.

 

Well if you are lucky enough to see one' date=' you will observe over the course of a few days that a small insignificant star brightens until it becomes the brightest object in the night sky, and then becomes dim again.[/quote']

 

supernovae are usually detected by a lot of neutrinos being detected quite suddenly. I don't think we've managed to catch more than one though.

[AntiMagicMan]

Computerised star surveys pick them up regularly (using regularly in the sense that before computers we'd be lucky if we found 1 every 100 years ) just by scanning the sky and taking pictures and then comparing them with the previous ones.

 

I'm not sure if we detect them using neutrinos, I would have thought neutrinos are far too weekly interacting to be able to use them to detect supernovae. Do you have a source for that, i'd be quite interested.

[Radical Edward]

SN1987A was detected after a neutrino burst. It might be the only one though, and probably the one dave refers to. SN1987A was rathe close though, in the large magellanic cloud.

 

the neutrino burst, by the way consisted of a whopping 19 anti electron neutrinos

[AntiMagicMan]

Ah ok. Quite an impressive feat to detect a supernovae from 19 neutrinos!

[swansont]

SN1987A was detected after a neutrino burst. It might be the only one though' date=' and probably the one dave refers to. SN1987A was rathe close though, in the large magellanic cloud.

 

the neutrino burst, by the way consisted of a whopping 19 anti electron neutrinos [/quote']

 

It's not like we would have missed it if the neutrino detectors weren't there. The neutrinos preceded the light by a few hours, and it was in the LMC, as you note.

[AntiMagicMan]

Preceded?

 

Really, that is suprising, was that because of the refraction index of the nebula? I would have always expected the light to reach us before...

[Radical Edward]

well the neutrinos get a head start since they are emitted in the last stages of fusion of some pretty heavy elements (like silicon and stuff I think, I don't have the fusion tables to hand) before the actual star gives up and collapses (the bounce causes the SN) The final stages of fusion occur at an absolutely incredible rate.

[swansont]

Preceded?

 

Really' date=' that is suprising, was that because of the refraction index of the nebula? I would have always expected the light to reach us before...[/quote']

 

I think it's a combination of this and what RadicalEdward said. There is mention of how long the shock wave took to move through the star as it collapsed. High density if the star would be an effect on both light and neutrinos, but I think it affects the light more. I have a vague recollection of neutrino pressure being one of the mechanisms that helps blow the star apart.

[Dave]

To be fair, I'm not a physicist, I don't really know - to be quite frank I'm not that intelligent. I'm just saying what I've been told tbh.

 

I think I should stop posting on the physics forums

[Crash]

Back to the general discussion forum????

 

[edit] disregard this.........