The J-NSE spectrometer at the FRM II

Quick links:

 JCNS proposal submission web page

 Next deadline for JCNS proposals

 Instrument responsibles: O. Holderer and M. Zamponi

Neutron Spin Echo Spectroscopy

The spin echo spectrometer NSE is especially suited for the investigation of slow (~ 101 ns) relaxation processes. Problems from the fields of "soft matter" and glass tran- sition are preferentially tackled.

Scheme of NSE
Upper part: spin motion, spin history leading to the formation of the spin-echo. Longitudinally polarized neutrons enter from the left.
Lower part: J-NSE set-up, π/2-flipper between associated current rings, primary main precession solenoid VL with symmetry scan windings in the middle and stray-field compensating loops at both ends, π-flipper near the sample S, symmetric arrangement on the secondary side followed by analyzer and detector. The arrows indicate the strength of the longitudinal field.

Description of the Instrument

The neutron spin echo technique uses the neutron spin as an indicator of the individual velocity change the neutron suffered when scattered by the sample. Due to this trick the instrument accepts a broad wavelength band and at the same time is sensitive to velocity changes down to 10-5. However the information carried by the spins can only be retrieved as the modulo of any integer number of spin precessions as intensity modulation proportional to the cosine of a precession angle difference. The measured signal is the cosine transform I(Q,τ) of the scattering function S(Q, τ). All spin manipulations only serve to establish this special type of velocity analysis. For details see "Neutron Spin Echo", ed. F. Mezei, Lecture Notes in Physics, Vol. 128, Springer Verlag, Heidelberg, 1980.

Due to the intrinsic Fourier transform property of the NSE instrument it is especially suited for the investigation of relaxation-type motions that contribute at least several percent to the entire scattering intensity at the momen- tum transfer of interest. In those cases the Fourier trans- form property yields the desired relaxation function directly without numerical transformation and tedious resolution deconvolution. The resolution of the NSE may be corrected by a simple division.

For a given wavelength the Fourier time range is limited to short times (about 1 ps for the FRM II-setup) by spin depolarization due to vanishing guide field and to long times by the maximum achievable field integral J. The time is proportional to J x λ³. The J-NSE may achieve a J = 0.5 Tm corresponding to τ= 48 ns at λ = 8 Å.

The instrument itself (see schema 1) consists mainly of two large water-cooled copper solenoids that generate the precession field. The precession tracks are limited by the π/2-flippers and the π-flipper near the sample position. The embedding fields for the flippers are generated by Helmholtz-type coil pairs around the flipper locations. After leaving the last flipper the neutrons enter an analyzer containing 60 (30 x 30 cm2) CoTi supermirrors located in a solenoid set. These mirrors reflect only neutrons of one spin direction into the multidetector. By the addition of compensating loops the main coils and the analyzer coil are designed such that the mutual influence of the different spectrometer components is minimized.

Examples for Experiments

Echo at λ = 5 Å and τ = 0.24 ns

Echo obtained in the direct beam at λ = 5 Å and a Fourier time of τ = 0.24 ns showing nicely the echo group whose width corresponds to the 9.3 percent FWHM wavelength distribution. The maximum amplitude of the oscillation compared to the average contains the desired information on the time dependence of I(Q, τ). The residual intensity at the minimum is caused by the imperfection of the polarizes, general background and - rather for higher τ's - by magnetic path integral in homogeneities.

Some literature about NSE related experiments:

Biology:

Bu ZM, Biehl R, Monkenbusch M, et al.

"Coupled protein domain motion in Taq polymerase revealed by neutron spin-echo spectroscopy"

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 102 (49): 17646-17651 DEC 6 2005

Polymer Dynamics:

Wischnewski A, Richter D,

"Polymer Dynamics in Melts",

in "Soft Matter Volume 1", edited by G. Gompper, M. Schick

Microemulsions:

Holderer O, Frielinghaus H, Byelov D, et al.,

"Dynamic properties of microemulsions modified with homopolymers and diblock copolymers: The determination of bending moduli and renormalization effects"

JOURNAL OF CHEMICAL PHYSICS 122 (9): Art. No. 094908 MAR 1 2005

Glass dynamics:

Richter D, Monkenbusch M, Arbe A, et al.

"Neutron spin echo in polymer systems"

ADVANCES IN POLYMER SCIENCE 174: 1-221 2005

J-NSE related instrumentation papers

M. Monkenbusch, R. Schätzler and D. Richter
The Jülich neutron spin-echo spectrometer - Design and performance
Nuclear Instruments and Methods in Physics Research Section A, Volume 399, Issues 2-3, 11 November 1997, Pages 301-323 | Abstract

O. Holderer, M. Monkenbusch, G. Borchert, C. Breunig and K. Zeitelhack
Layout and performance of the polarizing guide system for the J-NSE spectrometer at the FRM II
Nuclear Instruments and Methods in Physics Research Section A, Volume 586, Issue 1, 11 February 2008, Pages 90-94 | Abstract

O Holderer, M Monkenbusch, R Schätzler, H Kleines, W Westerhausen and D Richter
The JCNS neutron spin-echo spectrometer J-NSE at the FRM II
Measurement Science and Technology, Volume 19, Issue 3, March 2008, Pages 034022 1-6 | Abstract

Proposers Page

Instrument parameters

Internal pages (only accessible within FZJ and JCNS)

Internal pages

Links

• jcns.info
• FZ Jülich
• Wiki NSE