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

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Discussion Overview

The discussion centers on the use of cyclotrons in the production of positrons for PET scanners, exploring the mechanisms of positron generation and the role of radioactive tracers. Participants examine the feasibility of alternative accelerators, such as non-linear accelerators, in this context.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question whether a non-linear accelerator, like the LHC, could produce positrons more quickly due to achieving larger fractions of the speed of light in a smaller period of time.
  • Others clarify that a cyclotron is also a type of non-linear accelerator, but it is much smaller than the LHC and operates by having particles travel in a spiral path.
  • One participant asserts that positrons are not produced by cyclotrons but rather by tracers (radioactive nuclei) that are injected or digested, challenging the premise of the original question.
  • Another participant acknowledges that while positrons are produced by tracers, cyclotrons are used to create these tracers, which are often short-lived and need to be produced on-site, such as fluorine-18.
  • There is a reiteration that while tracers may be produced in an accelerator, the positrons for PET scans do not come directly from cyclotrons, emphasizing the distinction between tracer production and positron generation.

Areas of Agreement / Disagreement

Participants express disagreement regarding the role of cyclotrons in positron production, with some asserting that cyclotrons are indirectly involved through tracer production, while others maintain that positrons themselves do not originate from cyclotrons.

Contextual Notes

The discussion highlights the complexity of the relationship between cyclotrons, tracers, and positron production, with participants pointing out the limitations of the original question and the need for clarity regarding definitions and processes involved.

Giada
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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?
 
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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.
 
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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.
 
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ZapperZ said:
Positrons are produced by tracers (radioactive nuclei) that are injector or digested. These positrons do not come from cyclotrons.
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.
 
Orodruin said:
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.

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

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