Explanation
Charged particles, such as protons and heavy ions, lose energy when passing through material primarily through ionization. The Bethe-Bloch equation describes that energy loss. The Bragg Curve is a graph of the energy loss rate, or linear energy transfer (LET) as a function of the distance through a stopping medium.
The energy loss is characterized primarily by the square of the nuclear charge, Z, and the inverse square of the projectile velocity, β. This gives the Bragg Curve its familiar shape, peaking at very low energies, just before the projectile stops.
The Bragg Curve falls with increasing energy until a minimum is reached near a velocity of β = 0.9, about 2.2 GeV for protons. LET increases slowly, rising logarithmically for energies above the minimum.
The kinetic energy of the NSRL Beam is measured using the Bragg Peak. Polyethylene, most often from one of the binary filters, is used to slow down and stop the beam particles.
The LET is measured with a pair of ion chambers, one upstream and one downstream of the binary filter. The plot of the ratio, downstream over upstream, shows how the relative LET changes as a function of the amount of material in the beam.
SEE Library Bragg Data
Bismuth
Gold
Tantalum
Terbium
Silver
Niobium
Iron
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