Upgrade of the time-of-flight diffractometer EPSILON

At beam line 7A of the pulsed reactor IBR-2 (JINR Dubna) the strain diffractometer EPSILON has been working for several years. Due to a flight path of 102m a good resolution (Deltad/d < 3 x 10(-3)) was achieved. Nevertheless, further improvements of the instrument were required because of intended studies on geological samples. The modernisation of EPSILON is a renewal of the whole recording system, including collimators and detectors. The two previously used Soller collimators are replaced by nine radial collimators. Each collimator consists of 48 gadolinium oxide coated mylar foils with an angular distance of about 20' of arc to each other and therefore covers a range of nearly 16degrees for 2Theta. In the other direction a range of about 18degrees is covered. Three collimators in each case are grouped into a unit covering 66degrees in the plane perpendicular to the incident beam. Single He-3 counter tubes with a diameter of 10mm, and an active length of 120mm are used. Each collimator/detector block is mounted on a ring carrier with its surface perpendicular to the incident neutron beam. All blocks have the possibility of adjustment in three directions. The transparency of the collimators is about 90%-95%.