GCR Rotating X-Ray CT Scanner (RXCT)
Documentation Under Development
Instrument overview
The GeoTEK RXCT scanner consists of two arms- an X-arm and a Y-arm attached to the right and left-hand sides of a central cabinet. During each measurement, the core is held in place by the self-centralizing core cones (labelled 3 in the schematic diagram below) passes from the X-arm cabinet through the central cabinet and finally to the Y-arm cabinet, till the required length of core is scanned. Within the central cabinet, the X-ray source and detector (1 and 5 in the schematic ) sit on a gantry which rotates to around the sample images it from various angles. The core sample itself remains stationary during the imaging process. In the RXCT system, the samples are also referred to as panel or camera). The source and detector can also move independently or synchronously along the gantry. Movement of the source or the detector inwards (towards the sample) or outwards (away from the sample) leads to changes in the scanning magnification.
Safety features
All cabinets are lined with lead to prevent X-rays from leaving the interior of the instrument. As an additional safety measure, the X-ray source only fires when all the cabinets are closed, and the Interlock system is engaged. The instrument also has an emergency stop button which immediately stops the X-ray as well as the motors that are used to move the X and Y arms.
The RXCT scanner can be used to scan whole round and section half cores of varying diameters, lengths of up to ~150cm and maximum weights of 30kg.
Sample holders compatible with a range of core diameters are available at GCR:
Sample holder size | Core diameter (cm) |
|---|---|
BQ | 3.64 |
NQ | 4.64 |
HQ | 6.35 |
PQ | 8.5 |
3” | 7.62 |
4” | 10.16 |
5.25” | 12.7 |
The instrument start-up procedures and scanning workflow are described in the following sections:
RXCT Start-up Procedure
RXCT Scan Setup Procedures
The following types of scans can be obtained from the GEOTEK RXCT:
i) Radiography- Consist of the projection of the entire core onto the detector panel
ii) Laminography- Similar to radiography and needs about the same scan time. However, cross core depth information can be obtained. This can target certain depths in the core and provides better depth information and accentuates features slightly.
iii) CT scans- Source and detector revolve around the sample to collect multiple cross-sectional slices which are then reconstructed. Much more depth is resolved than radiography or laminographiy. Higher contrast between materials of varying densities allows the identification of internal features of a sediment core, e.g., voids /matrix (medium density) and clasts (high density). There are two types of CT scans:
a. Circular- The source and detector move in a circular fashion with respect to the core, scanning a discrete portion of it with each 360deg rotation, during which the core stays stationary. Then, the core moves so that a new, unscanned portion comes under the source-detector system and is scanned.
b. Helical- The source and detector rotate while the core translates between them, creating a helical scanning path.
The RXCT software can bin pixels on the detector while generating the image. Larger bin size reduces the data volume and leads to the loss of resolution. However, data with larger bin sizes have higher sensitivity (more photons/unit area) and have good signal/noise ratio.
Mode 0: 1x1 Mode 1: 2x2 Mode 3: 4x4
Scan times:
The measurement time depends on the type of scan being run and the scanning parameters. Linear scans take the least amount of time, followed by helical and circular CT scans. Usually, scanning time increases with smaller pixel binning at the detector, larger core diameters, higher resolution, higher level of detail, smaller angular steps, lower frame rate, lesser averaging over radiographs and longer cores. All scanning times are given in min/m.
Scan type | Details | Scanning time* (mins) per meter *Laminography data is saved | ||
|---|---|---|---|---|
1x1 | 2x2 | 4x4 | ||
Linear Scan
| Ultrafine |
|
|
|
Fine | 56 | 15 | 8 | |
Standard | 27 | 11 | 6 | |
Coarse | 12.5 | 5 | 3 | |
Very Coarse | 9 | 4 | 2 | |
Scan type | Mode | Resolution (µm) | Angular step (o) | Scan time (mins) per meter | Individual file size |
|---|---|---|---|---|---|
Helical CT | 1x1 | ~22.8 | 0.2 | 50 | ~4MB |
2x2 | ~45 | 0.2 | 35 | 1.28 MB | |
4X4 | ~105 | 0.2 | 35 | 328 KB | |
Circular CT | 1x1 | ~24 | 0.2 |
| ~4MB |
2x2 | ~45 | 0.2 |
| 1.28 MB | |
4X4 | ~105 | 0.2 | 80 | 328 KB |
Data processing:
The raw data obtained through Radiography, Laminography and Helical/Circular scanning need to be processed before they can be used. The data processing workflows are linked below: