<p num="114">FIELD: physics.</p> <p num="115">SUBSTANCE: invention relates to the neutron beam chopper. Chopper contains three synchronously rotating disks, in which windows are made. Disks are mounted on the shaft in such a way that they can be turned out for the given angle. Third disk is configured to change the windows width. To do this, the shutters on this disk can be made or this disk can be made consisting of two identical parts, which can be turned out on the shaft relative to each other, which will allow the windows width changing. On the disks the neutron absorbing material plates are fixed. Plates and the third disk form those incident on the sample neutrons from the beam removal system, whose wavelengths exceed the required maximum wavelength.</p> <p num="116">EFFECT: technical result is the design simplification, recycling elimination, increase in luminosity, possibility of the spectrum arbitrary width formation and in the given wavelength range.</p> <p num="117">5 cl, 5 dwg</p>