Bragg peak

It is named after William Henry Bragg, who discovered it in 1903 using alpha particles from radium,[1][2] and wrote the first empirical formula for ionization energy loss per distance with Richard Kleeman.

[3] When a fast charged particle moves through matter, it ionizes atoms of the material and deposits a dose along its path.

In the lower figure, it is the narrow peak of the "native" proton beam curve which is produced by a particle accelerator of 250 MeV.

The plateau created by modifying the proton beam is referred to as the spread out Bragg Peak, or SOBP, which allows the treatment to conform to not only larger tumors, but to more specific 3D shapes.

[8] Momentum cooling in cyclotron-based proton therapy facilities enables a sharper distal fall-off of the Bragg peak and the attainment of high dose rates.

The Bragg curve of 5.49 MeV alphas in air has its peak to the right and is skewed to the left, unlike the x-ray beam below.
The dose produced by a native and by a modified proton beam in passing through tissue, compared to the absorption of a photon or x-ray beam