1. Nov 7, 2014

### JonW.24

I have no concept of how the smashing of atoms plays out having never seen actual video, (would there even be a visible flash?), but my question is I guess is why is collecting the broken pieces of atoms difficult? Could the collision not occur in a magnetic field strong enough to contain the resulting sub-particles for further study? Is the problem that the matter evaporates in to energies rather than just actual physical particles?

2. Nov 8, 2014

### Staff: Mentor

Cameras and eyes would see something from high-energetic particles directly hitting the detector/retina, but that is not the regular way a camera works (in particular, you would see the same with closed lid).

What do you mean with "collect"? The only instances where something is "collected" are antiproton and positron production for various experiments using those particles.
Usually the experiments just want to detect them. It is not hard to see something - it is hard to identify which particle type went from where to where at what energy.

The interesting particles all decay way too fast to store them. And storing their decay products is not useful - the detector would just get even more crowded with particles.

High-energy physics experiments all use magnetic fields, but for a different reason: the field bends the path of charged particles, and from the curvature it is possible to calculate the momentum of the particle.

What does that mean?

3. Nov 8, 2014

### ChrisVer

How would someone see anything from particles colliding? In order to see something with the eye, it needs to radiate really low energetic photons (visible light) ~$\mathcal{O}(1eV)$...

4. Nov 8, 2014

### Staff: Mentor

The same way astronauts see cosmic rays, or most particle detectors see them - ionization and light emission inside the eye. It is called "ionizing radiation" for this reason.

5. Nov 8, 2014

### ZapperZ

Staff Emeritus
Just for future reference, you are not talking about "accelerators" but rather "particle COLLIDERS".

Accelerators are electromagnetic structures that accelerate charged particles. The majority of accelerators have nothing to do with colliders or high energy physics.

Zz.

6. Nov 8, 2014

### ChrisVer

Well then that was a confusion of words for me.

(Then you are seeing the ionization and not the actual particle collision.
A very primitive example is the Thompson's experiment (for a visualization: , @0:13). Are you seeing electrons? or the electrons' traces through an ionized gas?)

7. Nov 8, 2014

### JonW.24

"The interesting particles all decay way too fast to store them." - do you happen to know why or how it actually decays? And into what exactly, if not a proton/neutron? You would think smashing any atom would leave you with nothing but hydrogen at the end(single protons), but I assume the protons are destroyed as this hasn't happened yet.
"What does that mean?" - I assumed that if after smashing atoms you find no broken pieces of matter, that it must have converted to energy, or something like that right?

I'm curious as to why particles decay, as if the space outside of the atom is corrosive or is it, for lack of a better word, "burned" away?

I appreciate your time and patience, thanks

8. Nov 8, 2014

### JonW.24

"Just for future reference, you are not talking about "accelerators" but rather "particle COLLIDERS"."
- So accelerators do nothing but accelerate atoms or particles? Just to see how fast? I will have to research it later, thank you for the clarification.

9. Nov 8, 2014

### ChrisVer

Well I will get what you write as atoms literally... and I won't think you mean elementary particles or hadrons.
smassing atoms together, will not give you anything interesting (by that I mean unstable elementary particles- of course there are researches in which they colide nuclei to find out different properties of nuclear forces which can be interesting)...
If you collide two atoms with low energies, then you will get nothing but maybe ionization or just radiation. If the atoms have large energies, then they get totally ionized so you collide nuclei. What you can get then is other daughter nuclei and maybe some fleeing protons,neutrons and electrons/positrons with radiation.

For particles, make a distinction between writing "atoms" and "particles"...the atom is a composite system containing a nuclei and several electrons. With particles I can understand hadrons (like protons or neutrons for experimental point of view) and leptons (electrons).

10. Nov 8, 2014

### ChrisVer

As for how fast... the answer is "it depends"... it depends on the accelerator and the object it accelerates.

Also excuse me but I don't see the difference between accelerators and colliders... you accelerate particles for some reason, to send them hit a target [moving or not]

11. Nov 8, 2014

### ZapperZ

Staff Emeritus
12. Nov 8, 2014

### Staff: Mentor

Sure. You see tracks of high-energetic particles going through your eye because of the photon emission along those tracks.

Physics cannot answer "why" or "how" questions on a fundamental level. It is just an observation that they do. Our models can predict lifetimes and decay products with a very good accuracy, however.
Various other particles, most of them are again unstable and decay again.
Without interactions with the material of the detector, everything would decay to protons, antiprotons, electrons, positrons, photons and neutrinos (and very few heavier nuclei like deuterium nuclei) after a while, as those are the only stable particles. Some particles are so long-living that they rarely decay inside the detector, so in addition to those stable particles we can also see neutrons, muons, pions and kaons going through detectors.
That does not make sense. You cannot "convert particles to energy" in the same way you cannot "convert a banana to yellowness". A banana has a color, and a particle has energy. The collisions often produce new particles, and often destroy the initial protons (or whatever gets collided), but that does not happen in every collision.
No.
Accelerators can be used in colliders, but also in other experiments, in the semiconductor industry, for medical applications and for various other things.

13. Nov 8, 2014

### Astronuc

Staff Emeritus
As others have explained, one cannot 'see' atoms, or protons or electrons, but we can detect their presence, either by light emitted, or by the influence of their charge and motion in matter. And of course, we don't see subatomic particles. We take about 'detection'.

Even if we had power microscopes, we cannot directly 'see' atoms, but only the influence of the electric field or light emitted from the atoms.

It is not clear what one means by 'broken pieces of atoms'. An atom refers to a structure composed of a nucleus, which contains protons and neutrons, and a 'cloud' of electrons. Atoms tend to be neutral, i.e., the number of electrons = number of protons in the nucleus. We can temporarily ionize an atom by removing one or more electrons, but then any nearby electron will try to recombine with a + charged ion. We can also form negatively charged ions (anions), but they will readily give up their extra electrons to a positively charged ion (cation).

There are different ways to 'smash' atoms. One can accelerate protons, or other atoms, and direct he beam at a target, or collide with another beam. In order to accelerate a proton or atom, a proton or nucleus must be separated from the electron, since we use electric potentials to accelerate charged particles. Electrons can be accelerated and directed at atoms or nuclei as well.

Often, we need to accelerate particles, e.g., protons or nuclei, to high energies to effect collisions with other particles or nuclei. The energy imparted to particles or nuclei depends on what reaction one wishes to study or achieve.

Following some nuclear or particle interaction, the products are 'detected' by interaction with other matter in various detectors. It is by virtue of the light emitted from the detector matter that we 'see' the presence of the particle, but not the particle itself.

Nuclear interactions involve energies in the keV or MeV or even GeV range depending. X-rays (and low energy gamma rays) are in the keV range, and gammas are typically in the 10's of keV to high MeV range. Compare these energies to visible light in the eV range or ultraviolet light, which is on the order of 10 eV.

Our eyes and chemical systems operate in the low eV/atom range.

14. Nov 8, 2014

### Astronuc

Staff Emeritus
There are at least two themes here - one has to do with atoms, which are comprised of nuclei (containing protons and neutrons) and electrons, and the other has to do with subatomic particles, the "interesting particles", such as mesons or hyperons, which are unstable.

If one collides atoms, they may reform into different atoms. Often we might collide a proton, deuteron, or other light nucleus with a heavier atom. The light nucleus may interact with the large nucleus and may cause changes in one or both nuclei depending on the energy of the light nucleus. In fusion, we combine light nuclei and they reform into different nuclear configurations. We can also high Be-9 nuclei with alpha particles (nucleus of He atom) and this will cause the formation of an excited 13C atom, which decays quickly to 12C + n.

I don't know if this would be helpful, but it contains an overview of particle physics.
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/parcon.html

Here is a simpler overview of nuclear reactions
http://en.wikipedia.org/wiki/Nuclear_reaction

Particles do not evaporate, but other than protons and electrons (an neutrinos), most particles are unstable and will decay to lower energy (more stable) protons or electrons. Neutrons are only stable in nuclei of atoms.

15. Nov 8, 2014

### JonW.24

16. Nov 9, 2014

### kurros

Well you shouldn't really think of it as "smashing" atoms. This is just PR "fluff" that isn't a very good analogy to what is happening. First, particle colliders usually collide protons or electrons, not whole atoms. Second, the in-going particles don't "smash", rather the energy of the collision transforms them into other particles/produces other particles out of the vacuum. So it is the interactions between particles that is being studied, rather than their "contents" as such.

The more fundamental question is why some particles *don't* decay, since particles decaying is the more normal thing. It is all about energy; if a lower energy state can be reached by a particle decaying, then it will, sooner or later. E.g. muons will decay to electrons (and some other junk) since the total rest-mass (energy) of the decay products is less than the original muon. If there is nothing to decay into, i.e. no way for the particles to lower their rest-energy any further, then they won't, and the final state is stable. This is why the stable particles in our universe are the light ones, and the new particles produced at colliders are heavier ones.

This picture is a little hand-wavy but I think it gets the gist across.

17. Nov 9, 2014

### JonW.24

I actually think I understand the concept; and you're right, the extent of my knowledge in any real science is mostly 80% PR articles. It's only recently that I've picked up a text book again. Thank you guys for putting so much time in to my questions. Really.

How similar are electrons and photons? I've read that photons are just packets of energy, but what are electrons in transit, meaning once it's been separated from it's atom?

18. Nov 9, 2014

### e.bar.goum

Not very similar at all. Electrons are particles with (negative) electric charge, they have a mass, and have quantum mechanical spin =1/2, so two electrons can't have exactly the same properties of location/energy/spin all at once. Photons on the other hand, have no charge, have no mass, and have spin = 1, so you can have as many photons in once spot as you like.

You can say they're similar in that electrons can interact with the electromagnetic force, and photons carry the electromagnetic force, and that they are both part of the Standard Model of Particle Physics.

Electrons in transit, ones that aren't associated with atoms are still electrons - they have the same properties.

One thing that hasn't been mentioned in this thread: There are actually a few scenarios where we do gather up the results of nuclear reactions to study them. At GSI in Germany, they have an ion storage ring, where they study the outcomes of nuclear reactions by storing them in a ring, and measuring their mass/energy very very precisely.

19. Nov 9, 2014

### Astronuc

Staff Emeritus
Photons are electro-magnetic radiation and they are massless. Electrons are negatively charged particles with mass. The charge on an electron is equal and opposite that of the proton.

Photons - http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html#c5

Electrons - http://hyperphysics.phy-astr.gsu.edu/hbase/particles/lepton.html#c2 are leptons
http://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html

Proton - http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nucuni.html

20. Nov 10, 2014

### Staff: Mentor

Usually we accelerate the particles so that we can then do something useful with them.

In the case of CERN's Large Hadron Collider, protons are accelerated in several stages, the last of which is in the collider itself:
• a linear accelerator, to 50 MeV
• the Proton Synchrotron Booster, to 1.4 GeV
• the Proton Synchrotron, to 26 GeV
• the Super Proton Synchrotron, to 450 GeV
• in the LHC main ring itself, to 4 TeV.
The final stage of acceleration takes 20 minutes, and then the protons "coast" at constant energy for 10 to 24 hours while the detectors at the collision points accumulate data.