| 摘要 |
The present invention is related to an energy degrader for particle beams comprising at least two successive slabs of matter through which the beam passes in succession with focusing means located before the first slab and located between the successive slabs to concentrate the beam successively onto a small spot inside or close to each slab. The energy degrader is preferably positioned between an accelerator and a principal beam transport system, which guides the beam to its destination. The slabs may be made of diamond, boron carbide, beryllium and/or graphite. The beam is focused and refocused by 3 or more quadrupole lenses to a small spot at the centre of each slab. By dividing the degrader in this way into several separate slabs with refocusing lenses between the slabs the increase of beam emittance due to lateral scattering is minimised. The invention is also related to the use of such a degrader for proton therapy purposes.
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