Beam component identification via X-rays
One method of determining the various isobaric beam components present in
a typical radioactive ion beam is to pass the beam through a thin foil.
The resultant disruption to the ion's electrons causes vacancies in the
electron shells and X-rays are produced as these vacancies are filled.
Reasonably often, the vacancy occurs in the lower shell and the so-called
K X-ray is emitted. Since these X-rays are unique to a given isotope,
the various components can be continuously sampled. Note that at present,
this method is not suitable for event-by-event data but is able to
monitor changes in beam comonents over time. X-ray production is
enhanced when the foil and the beam have similar Z. We typically use
a foil with slightly lower Z than the beam so that the X-rays produced
from the foil atoms do not interfere with the detection of the higher
energy X-rays from the beam. A thin kapton window is used to minimize
absorption in the walls of the vacuum chamber.
A sketch of the experimental setup and the data taken in a recent experiment using a beam of A=128 comprised primarily of Sn, Sb, and Te isotopes. The ions passed through a 4 mg/cm2 Mo foil and the resulting X-rays were detected in a single, large-area LEPS (Low-energy photon spectrometer).
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This file last modified Monday July 25, 2005