degrader

A degrader is a device or material that reduces the energy or intensity of a beam, particle, or signal through interaction with matter. In experimental physics, degraders are used to tune the energy of particle beams or to calibrate detectors. A typical degrader is a slab of material placed in the beam path; its thickness and composition determine how much energy is lost as the particles pass through. The energy loss is described by stopping power and involves processes such as ionization and radiation losses. The passage also introduces angular deflections due to multiple scattering, which can broaden and diverge the beam, affecting focusing and resolution.

In accelerator and beamline contexts, energy degraders allow researchers to select lower energies without changing the accelerator settings. In medical physics, range shifters or degraders are used in proton or ion therapy to adjust the depth of tissue penetration, enabling treatment of tumors at varying depths. These devices may be fixed-thickness or dynamically controlled, and they require careful thermomechanical management and calibration to minimize dose inhomogeneity and secondary radiation.

Materials are chosen based on density, atomic number, radiation hardness, and ease of fabrication; common options include polyethylene, graphite, and aluminum. Precision in thickness and uniformity is essential, as small variations translate into energy and dose errors.

Degraders function as energy attenuators, and while simple in concept, their design involves consideration of energy loss, scattering, activation, and heat generation. They play a practical role in experiments, measurements, and clinical therapy.