carbon-11
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| carbon-11 | |
|---|---|
| Background | #c0c0ff |
| Decay product | boron-11 |
| Mass number | 11 |
| Halflife | 20.364(14) min |
| Decay mode1 | Positron emission |
| Decay energy1 | 0.960 MeV |
| Parent | ¹¹N |
| Parent2 | ¹¹B |
| Parent3 | ¹¹Be |
| Parent decay3 | β⁻ |
| Spin | 3/2⁻ |
| Excess energy | 10.650(4) MeV |
| Binding energy | 73.440(4) MeV |
carbon-11 is a radioactive isotope of carbon with a half-life of approximately 20.4 minutes. It decays almost exclusively via positron emission to the stable nuclide boron-11. This short-lived radionuclide is a crucial tool in nuclear medicine, particularly for positron emission tomography imaging, due to its favorable physical and chemical properties.
Properties
Carbon-11 is a proton-rich isotope with five neutrons and six protons in its atomic nucleus. It has a nuclear spin of 3/2⁻ and a relatively high positron emission energy of 0.960 MeV. The positron range in tissue is moderate, which contributes to good spatial resolution in imaging applications. Its short half-life necessitates rapid radiochemistry and synthesis of radiopharmaceuticals, but minimizes radiation dose to patients. The decay product, boron-11, is stable and non-radioactive.
Production
Carbon-11 is primarily produced in cyclotrons using charged particle nuclear reactions on lighter target materials. The most common production route is the proton irradiation of nitrogen-14 gas via the 14N(p,α)11C reaction, often using a gas target system. Alternative methods include irradiating boron-10 with deuterons or using beryllium-10 targets. Facilities like the TRIUMF laboratory and the Brookhaven National Laboratory have developed specialized infrastructure for its reliable generation. Post-irradiation, the produced carbon-11, typically as carbon-11 dioxide or carbon-11 methane, is rapidly transferred to a hot cell for radiosynthesis.
Decay
Carbon-11 decays 99.79% by positron emission (β⁺ decay) to the ground state of boron-11. A minor branch (0.21%) involves electron capture, also yielding boron-11. The emitted positron travels a short distance in matter before annihilating with an electron, producing two coincident 511 keV gamma rays emitted in opposite directions. This annihilation radiation is the detectable signal used in PET scanning. The decay scheme was precisely characterized through experiments at institutions like the Lawrence Berkeley National Laboratory.
Applications
The principal application of carbon-11 is in the synthesis of radiopharmaceuticals for positron emission tomography in medical research and oncology. Tracers like carbon-11 raclopride for dopamine receptor imaging, carbon-11 Pittsburgh compound B for amyloid plaque detection in Alzheimer's disease, and carbon-11 acetate for myocardial metabolism are widely used. It is also employed in basic science research, including plant physiology studies to trace photosynthesis and in chemistry for reaction mechanism investigations. Leading centers for its application include the Karolinska Institutet and the University of Pittsburgh.
History
Carbon-11 was first discovered in 1934 by Martin Kamen and Samuel Ruben using the cyclotron at the University of California, Berkeley, while investigating photosynthesis with radioactive tracers. Its potential for medical imaging was recognized in the 1970s with the development of PET scan technology by scientists such as Michael Phelps and Edward Hoffman. Pioneering work in radiochemistry at the Massachusetts General Hospital and the Hamamatsu Photonics research group enabled the practical synthesis of complex carbon-11-labeled compounds. Its use has since become a cornerstone of molecular imaging.
Category:Isotopes of carbon Category:Positron emission tomography