Neues
Termine
Konferenzen
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SANS-Workshop 21./22. Juni
21. Juni - 22. Juni
Seminare
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Commissioning of the CASCADE detector at MIRA
04. Juni 14:45 - 15:45
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Structural and dynamic study of several magnetic systems by means of Neutron Resonant Spin Echo techniques
11. Juni 14:45 - 15:45
- “ZETA” is a Neutron Resonant Spin Echo (NRSE) option which is currently installed on the thermal...
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Macromolecular crystallography at the European Spallation Source
18. Juni 14:45 - 15:45
- The structure determination of biological macromolecules by X-ray crystallography is a key...
Detector Unit
Description
The detector unit is used to detect the radiation diffracted from the sample. The unit is mounted on the detector holder of the diffractometer. The detector shielding is used to let only those neutrons to the detector, which are diffracted by the sample. An integrated slit system defines the cross section of the entrance window.
Detection of neutrons in the ³He counter happens by a reaction between the neutrons with the ³He gas. The detection probability of this process decreases with shorter wavelengths. Therefore, because of the very short wavelengths in our experiment, an extra long ³He proportional counter was manufactured.
A 2D detector (a.k.a. multidetector or area counter) is capable to detect incoming neutrons position sensitive in contrast to a single counter. This yields advantages especially for the background correction and reflex centering to determine the lattice parameters.
Single Counter
- Shielding
- Shielding made of boronized PE,
- compartment for a single detector and a multidetector,
- capsulation with an aluminum box,
- mounting on combined rotational and translational mechanik to add an analyser unit. ³He single counter
- Eurisys 73NH17/5X end window counter,
- 50 mm entrance window,
- 5 bar ³He pressure and 170 mm active length for high detection probability (>90% at 0.8 Å),
- separation of γ radiation by puls height discrimination,
Area counter
In comparison to a single detector the specification profile of a 2D detector is quite complex. The following overview show the relevant specifications of several multidetector types.
| Requirements | image plate | ³He -detector | position sensitive multiplier | |
| Diameter/Length [mm] | min. 100 | up to 300 | up to 300 | up to 125 |
| Resolution [mm] | 2 | 100 µm | 1 (4 bar CF4) | 1.0-1.5 |
| max. cps/area | 50.000 | >100.000 | 50.000 | 100.000, depends on counter electronic |
| Detection- probability [%] | >50% (1 Å) | not available (see below) | 65% (1.1 Å) 25% (0.3 Å) 10 bar full pressure | 65% (1.1 Å) 25% (0.3 Å) 1mm Li glass |
| n0/γ-separation | yes | no (foil material) | yes, puls height spectrum | yes, puls height spectrum |
Further information:
Image plate foil material:
Gd2O3/BaFBr Problems concerning absorption length: <0.07 mm (λ =1.1 Å), 4 mm (λ =0.5 Å)
Position sensitive multiplier
Szintillator: 6Li glass, (95% enrichment)
| Thickness [mm] | 1 | 2 |
| Resolution [mm] | 1-1.5 | 2-3 |
| Detection probability | 65% (1.1 Å)-25% (0.3 Å) | 85% (1.1 Å)-45% (0.3 Å) |
³He gas counter
| CF4 pressure [bar] | 1.5-2 | 4 |
| Resolution [mm] | 2 | 1 |
| ³He pressure [bar] | 4 | 6 | 8 | 10 |
| detection probability (λ=0.3 Å) [%] | 17 | 25 | 32 | 38 |
| detection probability (λ=1.1 Å) [%] | 50 | 65 | 75 | 85 |
