Drill Core Analysis by Neutron Activation (Drill Core Analyzer “CorA”)

Conventional geochemical laboratory analyses provide a high sensitivity, yet examine small masses. In order to provide these small individual samples for the analyses, portions of the drill core must be extracted, prepared by digestion, homogenized and divided. This can be considered as unfavorable, since the extracted portion of the drill core might not be a representative sample. Moreover, the sample cannot be recovered, and is not available as evidence or for further examination and processing tests. The system for the analysis of drill cores (see Figure 1) which is to be developed in the project CorA could obtain information from the samples in an efficient and non-destructive manner.

Several non-destructive methods for analyses of drill cores already exist. Hyperspectral imaging, for example, is capable of retrieving structural and mineralogical information from drill cores by the evaluation of emitted shortwave, visible and near-infrared radiation. The measurement time for this analysis is comparably short (about 50 s per 1.5 m core) [01]. However, this surface analysis does not provide any information about the core´s inner composition. The Neutron Activation Analysis (NAA) poses an advantage in comparison to existing analytical methods. It could gain information for high level use of resources integrally and non-destructively. NAA is generally divided into PGNAA (Prompt Gamma Neutron Activation Analysis) and DGNAA (Delayed Gamma NAA), depending on the measurement time (see Figure 2).

The PGNAA is an analysis method, which detects element-specific signatures quasi-instantaneously emitted by neutron-induced nuclear reactions. The elemental composition of a whole sample can be determined by these signatures. As uncharged particles neutrons have a high penetrability and are able to pass through a massive sample. In the case of drill core analysis, the whole core is examined.

The objective of the project CorA is the development of a system that utilizes PGNAA in order to determine the elemental composition of a drill core non-destructively. For this purpose, PGNAA is not yet a commercially available technology. For the proposed analysis method, a drill core placed in a PTFE (polytetrafluoroethylene) tray would be transported through the measurement system and analyzed segmentally in sections of 10 cm each. PTFE offers the advantage that it consists almost only of carbon and fluorine, which has little influence on the analysis. The PTFE trays would be designed in such a way that they can be filled with samples (drill cores, cuttings or even sludge) on the drilling site. This would abolish further drill core handling or alteration prior to an analysis by the proposed system.

The system to be developed is compact, such that it can be mounted and operated in a standardized container. Provided that all relevant standards for transportation and radiation protection are met, the system could be hauled by a conventional truck or all-terrain vehicle and moved to sites of ongoing drilling operation.