The detector consists of 42 BaF2 crystals of 15 cm length.
Covering the full solid angle without any gaps requires two different crystal
shapes, which can be seen in the figure. The shapes of the crystals are
optimized in a way that they all cover the same solid angle, although they
have different shapes.
Figure: The detector is composed of 12 crystals of type A (red), 30 crystals of type B (green).
Table: Dimensions of the different crystal shapes for
a 4 array of unit radius.
See figure before for definitions of the linesegments.
12 0.4329 0.3178
23 0.4329 0.3178
34 0.4329 0.4298
45 0.4329 0.3178
56 0.4329 0.3178
61 - 0.4298
10 0.3682 0.3453
20 0.3682 0.3820
30 0.3682 0.3453
40 0.3682 0.3453
50 0.3682 0.3820
60 - 0.3453
The volumes described above can be arranged to form a closed sphere with an inner radius of 10 cm and an outer radius of 25 cm. In the present situation, however, the crystals were moved outwards by 0.335 cm and the resulting gaps of 2 mm between the crystals were filled 0.1 mm aluminum foil, 0.5 mm Teflon and 0.4 mm air surrounding. These materials are used to reflect the scintillation light at the surfaces and to isolate each crystal from its neighbors. The front of the crystal is also covered with aluminum and Teflon. The following picture shows the detector with all crystals in an opened position.
The neutrons reach the sample, centered in the BaF2 crystal
ball, after 80 cm flight path. The crystal nearest to the Lithium target
(neutron production) is replaced by lead in order to absorb -
rays as well collimate the neutrons. The opposite crystal contains a clyndrical
whole of 5 cm diameter.
For any kind of comments or suggestions please contact