cooled and recirculated to pass through the same target thousands of times. It has the disadvantage of being typically limited to exotic nuclei with half-lives on the order tenths of seconds or more.
Superconducting driver accelerator: A high-power primary accelerator or linac employed for the production of rare isotopes. In a superconducting linac, the acceleration of the particles is provided by electric fields in a series of superconducting resonant cavities. In a superconducting cyclotron, the magnetic field keeping the particles in circular orbits is generated by a superconducting magnet, but the accelerating fields are created by room-temperature structures.
Surrogate method: In cases in which it is difficult to measure a desired cross section directly because the target has too short a lifetime or otherwise cannot be obtained, it is sometimes possible to infer the cross section from a surrogate reaction that exploits different initial particles but shares a common intermediate product nucleus with the desired reaction. As a point example of the surrogate method, consider the partial cross section for n + 155Gd → 156Gd** → 156Gd* + γ. One can infer the cross section from the “inverse” neutron removal reaction 3He + 157Gd → 156Gd* + α + γ, under the assumption that the common intermediate excited nucleus, 156Gd** equilibrates (the Weisskopf-Ewing approximation). Recently, the surrogate method has been experimentally and theoretically revisited to successfully measure the energy-dependent fission cross section for 235mU. Furthermore, the equilibration and angular momentum constraint assumptions that underlie the surrogate method have been the subject of experimental tests.
Two-step method: A production method for exotic nuclei in which the primary beam impacts a first target, which produces secondary projectiles that produce exotic nuclei in a secondary target. The most frequent case refers to a primary deuteron beam impinging on a target nucleus to produce an intense beam of neutrons, which bombards a heavy target such as uranium to produce exotic neutron-rich nuclei. This technique has the advantage of separating the area of intense beam heating (the first target) from the exotic-nucleus production target.