# I In PET scanners, why is a cyclotron used to make positrons?

1. Dec 20, 2017

Why could you not use a non-linear accelerator, like the LHC (but obviously nowhere as big)? Would it non be able to produce positrons more quickly because it can obtain larger fractions of the speed of light in a smaller period of time?

2. Dec 20, 2017

### phyzguy

I don't understand your question. A cyclotron is a non-linear accelerator, like the LHC but much smaller. The particles travel in a spiral path.

3. Dec 20, 2017

### ZapperZ

Staff Emeritus
Not only the confusing question brought up by @phyzguy, but cyclotrons are not used in a PET scan to "make positrons". Positrons are produced by tracers (radioactive nuclei) that are injector or digested. These positrons do not come from cyclotrons.

So that first post is full of unicorns.

Zz.

4. Dec 22, 2017

### Orodruin

Staff Emeritus
However, it should be mentioned that the tracers often are relatively short-lived and need to be produced on-site (such as fluorine-18 with a half-life of just below 2 hours). The usual way of doing so is to use a cyclotron so, in a sense, the cyclotron is used indirectly to "make positrons" by creating the positron emitters.

Clearly it would not be viable to have a LHC-size accelerator near every hospital as would be required (again, due to the short half-lives involved). A smaller cyclotron works perfectly well for the purpose.

5. Dec 22, 2017

### ZapperZ

Staff Emeritus
The TRACERS may be produced in an accelerator, but not the POSITRONS for PET scans, which is the premise of the OP in the title.

Zz.

6. Dec 22, 2017

### Orodruin

Staff Emeritus
Which is just what I said. I was essentially tracing down where the OP may have gotten the idea.