Wikiadmin: Wikiadmin moved page Problem: Neutron velocity selector to Problem:Neutron velocity selector

2020-09-20T15:30:21Z

Wikiadmin moved page Problem: Neutron velocity selector to Problem:Neutron velocity selector

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2020-02-18T22:15:11Z

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ucph>Tommy: Created page with "A neutron velocity selector is a drum that spins around an axis parallel to the beam. This axis lies below the guide. From the drum, a series of absorbing neutron blades stick..."

2019-07-14T21:27:29Z

Created page with "A neutron velocity selector is a drum that spins around an axis parallel to the beam. This axis lies below the guide. From the drum, a series of absorbing neutron blades stick..."

New page

A neutron velocity selector is a drum that spins around an axis parallel to the beam. This axis lies below the guide. From the drum, a series of absorbing neutron blades sticks out radially. The ends of the drum are twisted with respect to each other. A principal sketch is shown in [[Instrumentation#label-fig:velocityselector|velocity selector figure]] on the [[Instrumentation]] page.

This effect of the selector is that only neutrons around a certain velocity (or wavelength) can pass through it.

Assume a selector length of \(L=0.25\) m, \(n=68\) blades, and a twisting angle, \(\phi = 48.3^\circ\), as for the selector at the SANS-2 instrument at PSI. Calculate the rotation speed you should use to select 10 Å neutrons.

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Consider how long time it will take the neutron to travel through the velocity selector.
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What should the angular velocity \(\omega\) be, when twisting \(48.3^\circ\) during the same period of time it takes the neutron to travel through the velocity selector?
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The velocity, \(v\), of neutron with \(\lambda=10\)Å is

:\(v=\frac{h}{m_n \lambda}\),

and the time it takes the neutron to travel through the drum of the velocity selector, is

:\(\Delta t = \frac{L}{v}=6.34*10^{-4}\).

Thereby the angular velocity, \(\omega\), is

:\(\omega = \frac{\phi v}{L} =1333.9 \frac{\text{rad}}{\text{s}} = 12738 \, \text{rpm}\)

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Problem:Neutron velocity selector - Revision history

Wikiadmin: Wikiadmin moved page Problem: Neutron velocity selector to Problem:Neutron velocity selector

Wikiadmin: 1 revision imported

ucph>Tommy: Created page with "A neutron velocity selector is a drum that spins around an axis parallel to the beam. This axis lies below the guide. From the drum, a series of absorbing neutron blades stick..."