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QENS - Quasielastic Neutron Spectrometer

Instrument Scientist - Nicolas de Souza
Scientific Assistant - Ray Ziegler
Post Docs -

Beam Tube	H2
Initial Flight Path	8.0 m

**QENS Analyzer Arm Data**
Bank	2-theta	Bragg Angle	final distance (m)	002 (Å)	Q (Å^-1)
1	16.5	46.96	2.184	4.87	0.369
2	23.5	47.29	1.941	4.90	0.520
3	30.5	47.66	1.725	4.93	0.668
4	37.5	48.08	1.530	4.96	0.810
5	44.5	48.53	1.353	5.00	0.946
6	51.5	49.02	1.194	5.04	1.080
7	58.5	49.57	1.051	5.08	1.204
8	65.5	50.22	0.922	5.13	1.321
9	72.5	51.03	0.806	5.19	1.427
10	79.5	52.13	0.703	5.26	1.520
11	86.5	53.69	0.610	5.37	1.595
12	93.5	53.69	0.610	5.37	1.696
13	100.5	52.13	0.703	5.26	1.827
14	107.5	51.03	0.806	5.19	1.946
15	114.5	50.22	0.922	5.13	2.053
16	121.5	49.57	1.051	5.08	2.150
17	128.5	49.02	1.194	5.04	2.238
18	135.5	48.53	1.353	5.00	2.317
19	142.5	48.08	1.530	4.96	2.387
20	149.5	47.66	1.725	4.93	2.448
21	156.5	47.29	1.941	4.90	2.499
22	163.5	46.96	2.184	4.87	2.540

QENS is a "crystal-analyzer" or "inverse-geometry" spectrometer that accepts a white beam from the solid methane moderator onto the sample. Compared to the old QENS instrument the new QENS significantly increases the data rate (by about one order of magnitude) for both quasielastic and inelastic neutron scattering measurements on all the available energy transfer range from -2.5 to 200 meV. The original 3 analyzer arms mounted on a rotating table have been replaced by twenty-two stationary analyzer arms. Data are now simultaneously collected over the whole available Q range, from 0.3 up to 2.6 Å^-1, with a energy resolution of 90 µ eV. Moreover, compared to more classical instruments, this new design makes it possible to override the slab sample shadow problem, that usually dramatically reduces the scattered intensity onto the detectors placed in the sample plane.

Additionally, two banks of detectors have been placed for diffraction measurements at high and low Q, covering a global Q range from 0.05 to 25.0 Å^-1.

QENS is used primarily for chemical spectroscopy at low energies and for quasi-elastic scattering to study diffusive motions. Because of its efficient use of neutrons, QENS is used extensively for dynamical studies when the amount of sample in the beam is necessarily very small. This includes studies of chemical samples which cannot be made in large quantities, and studies of the dynamics of small molecules adsorbed in systems such as zeolites, clays, and intercalated graphite.

April 5, 2007

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