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4F1 : Polarized neutrons on a triple axis set on the cold neutron source

Polarized neutrons with a polarization analysis are available for incident wavevectors k_i<2.662 Å^-1. The spin polarization of the incident beam is performed by a bender with a transmission T=0.5 at
k_i=2.662 Å^-1, increasing to T=0.6 for k_i<1.55 Å^-1.
The analysis of the spin polarization is performed by an horizontally focussing analyser (Heusler alloy) made of 5 single crystals with 5 cm heigh and 10 cm of full width. The transmission is 0.5. The horizontal curvature (focussing), is fully computer controlled.
Two spin flippers can be used along the neutron path. One consists of two coils ( Mezei type), the other is a superconducting foil set in a cryogenerator (cryoflipper).

6T1 : High temperature furnace for crystallographic texture measurements

A new furnace has been devised to equip the 4-circles spectrometer 6T1 dedicated to crystallographic texture measurements.
On this spectrometer, the high intensity of the incident beam allows to follow the "in situ" evolution of the crystallographic texture during annealing with a characteristic time of the order of a minute.
Furthermore, it will permit to characterise the texture of high temperatures phases (interest : understand the texture evolution during a phase transformation process, predict the material behaviour with temperature…).

The body of the furnace is a sphere (diameter : 160mm, 1mm thick) manufactured from aluminium and water cooled. The heating elements are tungsten resistors put 3 cm under and above the sample, allowing to reach a temperature up to 1000°C. The typical time for heating up to 500°C is
4 minutes. 3 Vanadium screens are used to enhance the efficiency of the device. In general cylindrical or cubic samples with a volume between 0.1 to 2 cm³ (depending on the chemical composition) can be studied either under vacuum (< 10^-4 Torr) or under several atmospheres of gas pressure at any temperature from room temperature to 1000°C. The sample temperature is measured by a thermocouple placed in contact with the top of the sample and monitored by a standard furnace controller. Due to the furnace configuration, complete pole figures could be obtained for
10° < 2q < 80° .

Guide smashing

Since our last information letter, we have experienced problems with the neutron guides. A guide is made of several elements (1.25m long) jointed together. Each element is a rectangular tube (internal section 25 * 150 mm²) the walls of which are 4 thick glass plates coated on one side with the reflecting layer. As neutrons must propagate in vacuum and, if like ours, the guides are not inside a housing, in steady state conditions the glass plates are permanently under an absolute pressure of
1 atm.

In the past we have already suffered few failures and we always managed to have some spare elements and to be able to repare immediately. This year, within a period of 6 months, we had 5 elements breaking on three different guides. The result is that some guides, and consequently the corresponding spectrometers has been out of work for a certa in period.

Although the origin of these failures are not well understood, we planed to replace, as soon as possible, the elements which have been the most hardly irradiated insofar as they are probably those which have been the most weakened.