Time of flight modulation of intensity by zero effort on Larmor

Abstract

A time of flight Modulation of Intensity by Zero Effort spectrometer mode has been developed for the Larmor instrument at the ISIS pulsed neutron source. The instrument utilizes resonant neutron spin flippers which employ electromagnets with pole shoes, allowing the flippers to operate at frequencies of up to 3 MHz. Tests were conducted at modulation frequencies of 103 kHz, 413 kHz, 826 kHz and 1.03 MHz, resulting in a Fourier time range of ~0.1 ns to 30 ns using a wavelength band of 4 Å to 11 Å.

Time-of-flight modulated intensity small-angle neutron scattering measurement of the self-diffusion constant of water

“…The direct advantages of a continuous source are an easier determination of the q value at various points on the detector and, usually, an overall higher neutron flux. However, a pulsed source can use the modulation in the wavelength spread as a way of tuning the length L focus (Geerits et al, 2019). Additionally, the detector simultaneously measures a wide range of Fourier times and q ranges, leading to an efficient use of the different neutron wavelengths.…”

“…We have implemented this technique on an existing polarized SANS instrument using the coils that were developed for Larmor labelling (Geerits et al, 2019), and despite the good agreement of the diffusion constant with other measurements, several areas for improvement remain. First, the detector causes a significant loss in the intensity modulation signal, as the tubes are 0.8 cm diameter.…”

“…The RF flippers in this experiment were tuned to /2 mode in order to simplify the setup of the instrument. In a traditional MI-SANS experiment, the RF flippers perform a flip, meaning that the initial and final neutron polarization directions must be reoriented with a v-coil (Geerits et al, 2019). In /2 mode, the v-coil is not required, which saves approximately 1 day of setup time but reduces the accessible Fourier time by a factor of two.…”

“…FF ' B FF , where B FF is the focusing field strength. This term will also include any stray field from the RF flippers (Geerits et al, 2019). When the detector is placed at L focus , it will measure an oscillating intensity due to the interference between the energy states (Keller et al, 2002).…”

“…In this paper, we present the methodology of using a highresolution neutron scattering technique to measure the intermediate scattering function and diffusion constant, and apply it to the important case of bulk water at $300 K. The modulated intensity by zero effort small-angle neutron scattering (MI-SANS, also called MIEZE-SANS) technique is a variant of neutron (resonance) spin echo (Mezei, 1972) (NSE/ NRSE) (Golub & Gä hler, 1987;Gä hler et al, 1992;Hank et al, 1997). Both are very high resolution neutron scattering measurements of dynamics in the picosecond to nanosecond time regime Lebedev & Torok, 1999;Bleuel et al, 2006Bleuel et al, , 2009.…”