At the Heart of the Atom


How is antimatter used in medicine?

In Dan Brown’s novel Angels and Demons physicists at CERN use the LHC, the Large Hadron Collider, to produce 1/4 gram of antimatter. The material was stolen in order to destroy the Vatican. It is true that if 1/4 gram of antimatter were to completely annihilate with 1/4 gram of matter the amount of energy produced would equal that of the bomb that destroyed Hiroshima. But, in over ten years of experimental production only 10 million antiprotons have been trapped and stored for times ranging from seconds to months. One-quarter gram is 1016 times as many antiprotons! Further, the antiprotons must be stored in extremely cold, totally evacuated “bottles” that are large pieces of apparatus. Finally, the LHC is not used to produce antiprotons.

A three-dimensional image that shows biological activity in a person can be made using PET, or Positron Emission Tomography. PET uses a short-lived positron-emitting isotope, typically 11C, 13N, 15O, or 18F. The isotope is chemically attached to a molecule that is involved in the activity that is to be studied. Fluid containing that molecule is injected into the person and after enough time passes for the molecule to reach its target, the person is put into the PET machine. The positron that is emitted by the decaying nucleus strikes an electron and decays into two gammas that are simultaneously emitted back-to-back, that is, 180° apart. Detectors record the arrival of the two gammas, and computers extrapolate them back to the location of the gamma emission. When a sufficient number of events are recorded a three-dimensional image of the region where the biologically-active molecule accumulated can be made. PET scans can be combined with CT or MRI scans to pair information on the anatomy with biological activity for diagnostic purposes.


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