Spectrometer of polarized neutrons

 

1 - Moderator
2 - Double Disk Background Chopper
3 - Collimators
4 - Cross-type Collimator
5 - Small-Angle Scattering Mode Polarizer
6 - Adjustable Platforms
7 - Spin-Flipper
8 - Variable Diaphragms
9 - Sample Position
10 - Electromagnet
11 - Fan Polarization Analyzer
12 - Position-Sensitive Detector
13 - Control and operative visualization/analysis
14 - Data Acquisition
15 - Data Transfer

 

Responsible for the instrument:
Petrenko Alexander

Moscow Region, Dubna, Joliot Curie, 6
phone: +7 (49621) 6-31-19 
e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

 

Zhaketov Vladimir
Moscow Region, Dubna, Joliot Curie, 6
phone: +7 (49621) 6-28-75
e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

 

Group Staff

 

Main research fields:

1. layered magnetic and superconducting thin films;
2. three-dimensional nanostructures;
3. colloidal solutions;
4. ferromagnetic fluids.

 

Description of REMUR

 Description of the spectrometr of polarized neutrons given in works [1-3]. The REMUR reflectometer is designed to study properties of thin films, interfaces in multilayer structures, various types of ordering, self-organization in biological systems, etc. by the method of specular and off-specular neutron reflection from the surface of films. A polarized neutron beam is formed by a neutron-optical system consisting of a set of mirrors and diaphragms that specify necessary collimation and polarization of the beam. In the reflectometer the so-called slit geometry is used, in which a narrow neutron beam 0.1-1 mm wide is collimated by slits in the vertical direction. Neutron scattering occurs in the horizontal plane. Highly efficient adiabatic radio-frequency flippers [4] are used to reverse the neutron spin direction in a wide range of neutron wavelengths (0.9-10 Å). The analysis of polarization of the reflected beam is performed using wide-aperture fan mirror analyzer [5, 6]. The reflected beam is detected by two-coordinate gas 3He detectors with spatial resolution of about 2.5 mm.

 

Basic Parameters

 

Reflectometer

 

Sample plane vertical.
Scattering plane horizontal.
Neutron wavelength 0.9 - 15 Å.
Wavelength resolution δλ = 0.015 Å.
Scattering angle range 1 - 100 mrad.
Sample-detector distance 0.7 - 4.9 m.
Detector spatial resolution 2.5 mm.
Flux at sample for two polarization modes:
two polarizers PR1 + PR2
second polarizer PR2

104 n/(s·cm2)
3·104 n/(s·cm2)

 

Grazing incidence small-angle mode

 

Neutron wavelength 0.9 - 15 Å
Flux at sample  103 n/(s·cm2)
Sample-detector distance 0.7 - 4.9 m

 

Sample environment

 

 

Three-circle goniometer with an electromagnet mounted on top of it and generating external magnetic field in the range 0-20 kOe and making it possible to change the field direction with respect to the sample plane in the range of ± 90°.

 

 

There is a set of removable poles with cross sections: 40 × 20 mm2, 110 × 70 mm2 and 60 × 40 mm2.

The maximum magnetic field with a pole gap of 15 mm is 20 kOe for small poles with cross section of 40 × 20 mm2 and 10 kOe for large poles of 110 × 70 mm2.

Cryostat with a vertical magnetic field of up to 3 Tesla and T=1.45-600 K. The maximum sample size is 40x40 mm2.

 

Detectors

 

2D PSD

 

Gas mixture 3Не (2 atm) + CF4 (1.2 atm)
Working area 23 × 23 mm2
Spatial resolution (FWHM) 2.3 mm along the X axis and 2.7 mm along the Y axis

 

 

Characteristics of polarizers and polarization analyzer

 

Reflectometry polarizers PR1 and PR2

 

Substrate sizes 28 × 100 × 800 mm3
Polarized beam cross section 0.24 ÷ 0.8 mm
Beam glancing angle 1 ÷ 3.3 mrad
Critical wavelength 0.86 ÷ 2.84 Å

 

 

Reflectometry fan analyzer

 

Number of mirrors 94
Substrate sizes 250 × 60 × 0.3 mm3
Channel cross section  
– at the entrance 1.0 × 40 mm2
– at the exit 0.93 × 40 mm2
Beam capture angle in horizontal plane 27.3 mrad
Focal distance: 4400 mm
Flow area (vertical × horizontal) 40 × 120 mm2
“Geometrical” transmission 0.66
Coating on both sides FeCoV/TiZr
Critical wavelength 1.3 Å

 

Fan polarization analyzer

 

The analyzer mirrors are arranged in the form of a fan with a focus on a sample at a distance of 4.45 m (Fig. 1). The neutron beam is reflected from a sample and comes to the analyzer. In this configuration the angle a between the scattered neutron beam and the analyzer mirrors remains constant for all beams reflected from the sample and the polarization efficiency of the analyzer does not depend on the angle of neutron scattering by the sample.

 

 

Fig. 1. Scheme of fan polarization analyzer (top view).

 

 

Fig. 2. Fan polarization analyzer (93 mirrors are arranged vertically).

 

 

Fig. 3. Polarization efficiency of polarizers and the fan analyzer.

 

Adiabatic radiofrequency spin-flippers

 

Spin-flippers comprise two pairs of constant magnetic field coils and a radiofrequency coil with an alternating magnetic field frequency of 76 kHz. The amplitudes of constant and alternating magnetic fields of the spin-flipper show a sine-cosine dependence in the range of 10-40 Oe. To calculate the parameters of spin-flippers, the imposed requirement is that the neutron spin-flip probability be f(λ = 1 Å) ≥ 0.99. The experimental value of the neutron spin-flip probability f (λ) for a neutron wavelength interval of 1.4-10 Å is equal to unity within the limits of statistical errors. The length of spin-flippers along the beam is 800 mm, the neutron beam cross section is 150 mm.

 

 

Adiabatic radiofrequency spin-flipper

 

 

 

 

Publications

 

[1] V.L. Aksenov, K.N. Jernenkov, S.V. Kozhevnikov, H. Lauter, V. Lauter-Pasyuk, Yu.V. Nikitenko, A.V. Petrenko, The polarized neutron spectrometer REMUR at the pulsed reactor IBR-2, JINR Communications D13-2004-47 (2004) (in Russian and English).

[2] V. L. Aksenov, V. V. Lauter-Pasyuk, H. Lauter, Yu. V. Nikitenko and A. V. Petrenko, Polarized neutrons at pulsed sources in Dubna, Physica B 335 (2003) 147-152.

[3] V. L. Aksenov, Yu. V. Nikitenko, Polarized Neutron Reflectometry at IBR-2, Neutron News 16 (2005) 19-23.

[4] S.V. Grigoriev, A.I. Okorokov, V.V. Runov, Peculiarities of the Construction and Application of Broadband Adiabatic Flipper of Cold Neutrons, Nucl. Instr. Meth. A 384 (1997) 451.

[5] Yu.V. Nikitenko, V.A. Ul'yanov, V.M. Pusenkov, S.V. Kozhevnikov, K.N. Jernenkov, N.K. Pleshanov, B.G. Peskov, A.V. Petrenko, V.V. Proglyado, V.G. Syromyatnikov, A.F. Schebetov, Fan analyzer of neutron beam polarization on REMUR spectrometer at IBR-2 pulsed reactor, Nuclear Instruments and Methods in Physics Research A 564 (2006) 395-399.

[6] V. A. Ul'yanov, Yu. V. Nikitenko, V. M. Pusenkov, S. V. Kozhevnikov, K. N. Jernenkov, N. K. Pleshanov, B. G. Peskov, A.V. Petrenko, V. V. Proglyado, V. G. Syromyatnikov, A. F. Schebetov, A fan analyzer of neutron beam polarization of the spectrometer REMUR at the pulsed reactor IBR-2, JINR Communications E-13-2004-161 (2004).

[7] O.V. Fateev, G.A. Cheremukhina, S.P. Chernenko, Yu.V. Zanevsky, H. Lauter, V.V. Lauter, S.V. Kozhevnikov, Yu.V. Nikitenko, A.V. Petrenko, A Position-Sensitive Detector for the Polarized-Neutron Spectrometer. Pribory i Tekhnika Eksperimenta 2 (2001) 5-12 (in Russian). Instruments and Experimental Techniques, 44 (2001) 137-143 (in English).