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PANTHER

Thermal neutron time-of-flight spectrometer

 Reactor hall, thermal beam H12


Beam tube 100 mm diameter

Monochromator  
FaceEi (meV)Flux (10^5 n/cm2/s)
Graphite7.5-112 5.105 at Ei=20 meV
Cu(220)   55-130 
Choppers  
Fermi choppermax 30000 rpm      1.5 degrees slit package
Background choppersmax  10000 rpm6 slits of width 105 mm
Energy resolution
5-6% of Ei
Beam size at sample 
Width20 mm                                                                    
Height40 mm
Detector coverage 
Horizontal5 to 136 degrees                                          
Vertical-13 to +30 degrees

INSTRUMENT DESCRIPTION

Panther is installed on the H12 thermal beam tube in the reactor hall.

The incoming energy is determined by a double focusing pyrolytic graphite monochromator, using Bragg reflection in first (002), second (004), and possibly third (006) order. The take-off angle can be varied between 36 and 62 degrees. A double focusing copper monochromator using the (220) reflection is also available for higher incoming energies.

Both monochromators consist of 11 rows and 15 columns of crystals of dimension 20 by 20 mm.  Both the horizontal and vertical focusing can be varied, in order to maximize the flux on the sample position or to produce a less divergent beam for single-crystal measurements. A straight slit Fermi chopper produces short neutron pulses with a high pulse-repetition rate, and is normally operated in time-focusing mode to optimize the energy resolution.

Background is reduced by an optional sapphire filter and five background choppers. The choppers operate like a discrete velocity selector with variable pitch, obtained by spinning them in the same direction at the same speed but with different phases. This removes also higher- and lower-order contamination from the monochromators. The discs have a diameter of 750 mm and a thickness of 100 mm along the beam. They are made from epoxy-loaded carbon fibre coated with 10B4C. The maximum speed is 10000 rpm, and to match the maximum speed of the Fermi chopper they have six windows of width 105 mm.

A large sample chamber of diameter 800 mm allows to host various sample environments, in particular an orange cryostat specifically designed for Panther. An oscillating radial collimator is installed between the sample space and the detectors.

Position-sensitive detectors (PSD) of diameter 22 mm and height 2 m are arranged in nine banks, each comprising 32 tubes. The tubes are separated by Cd spacers to reduce cross-talk and the banks are separated by space of 22 mm, where Cd vanes are placed to reduce parasitic scattering. The detector tubes are mounted vertically inside a vacuum chamber at a distance of 2.5 m from the sample. The 3He pressure is 10 bars and the total solid angle covered by the detectors is 2 steradians.