Main characteristics of FlatCone

active pixel width

1.3 deg.

no. of pixels


angular coverage

75 deg.

SA distance

765 & 1000 mm

analyzer crystals

Si 111

cold neutrons

kf = 1.4 Å-1
ΔE = 0 - 10 meV

thermal neutrons

kf = 3 Å-1
ΔE = 0 - 40 meV

scan modes

ΔE = const.
Q = const.


≈ 1/3 of TAS

transverse resolution

ΔQ ≈ 1/2 TAS

background (FlatCone & IN20 Si111, July 2006)
P= 58.3 MW, H13 & OS closed
EN = 15 meV, empty Orange
EN = 15 meV, CuGeO3 in Orange

3 cts/channel/6000 sec
14 cts/channel/100sec
50 cts/channel/100 sec

host instruments

IN8, IN14, IN20


polarization analysis insert

3He filter

vacuum sample chamber




FlatCone can be used either in the horizontal mode to collect data from the equatorial reciprocal plane or in the tilted mode (see figure below) to collect data from reciprocal planes above the equatorial plane using the flatcone geometry.

Thanks to the absence of second order reflections the silicon analyzers provide a signal free of higher harmonic contamination when working with thermal neutrons (kf = 3Å-1). With cold neutrons the choice of kf = 1.4 Å-1 permits to access a window of energy transfers of up to 1 meV while working with a Be-filter in the incident beam. The work at higher energy transfers with an unfiltered beam on IN14 needs some experience and caution.

A valuable tool when using FlatCone is the application vTAS which offers a FlatCone option.
In the simulation mode one can modify all instrument parameters and then play with the measurement parameters by interactively moving either the Q,ki,kf triangle (reciprocal space) or the instrument parts (direct space).