INAA

Samples analyzed by Instrumental Neutron Activation Analysis (INAA) are encapsulated and irradiated in a nuclear reactor. After a suitable decay, samples are measured for the emitted gamma ray fingerprint.

Major mineral applications by INAA include rocks, soils, sediments (both stream and lake bottom) humus, vegetation and heavy minerals. The INAA technique allows for multiple elements to be determined simultaneously and a small sample size can be used. A major advantage of INAA analysis is the fact that the sample does not have to be put into solution, particularly beneficial for some geological matrices where complete dissolution is difficult to effect. This method is quite sensitive, accurate and precise, and is used to analyze for minor and select trace elements in low concentrations. INAA is very good for Au, Co, As, Sb, W, Ta, U, Th, Cs, In, Re, Cl and lower levels of most LREE.

Determining rock types, alteration patterns and levels of pathfinder elements are key for the geologist to assess exploration potential. Actlabs’ “Au+34” (1D) is a cost effective multi-element approach to Au, PGE and base metal exploration. 1D Enhanced, with enhanced detection limits, is also available.

The cost for this type of analysis is comparable to other single element analytical techniques for Au and is quite cost effective when determining a full suite of elements. Refractory elements are very difficult to put into solution easily and even elements such as Au can be extremely difficult to put into solution completely where INAA is a major advantage

INAA (Instrumental Neutron Activation Analysis) is an analytical technique dependent on measuring gamma radiation induced in the sample by irradiation with neutrons. The primary source of neutrons for irradiation is usually a nuclear reactor. Each activated element emits a “fingerprint” of gamma radiation which can be measured and quantified. Routine multi-element analyses by INAA are performed on practically any material from the smallest sample which can be weighed accurately to very large samples.

A 30g aliquot, if available, is encapsulated in a polyethylene vial and irradiated along with flux wires at a thermal neutron flux of 7 x 10 12 ncm-2 s-1. After a 7-day period to allow Na-24 to decay the samples are counted on a high purity Ge detector with resolution of better than 1.7 KeV for the 1332 KeV Co-60 photopeak. Using the flux wires and control standards, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. For values exceeding the upper limits, assays are recommended. One standard is run for every 11 samples. One blank is analyzed per work order. Duplicates are analyzed when sample material is available.

1D (Au+34) Elements and Detection Limits (ppm)

1D Enhanced (Au+34) Elements and Detection Limits (ppm)

Reference:
Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.

An aliquot is encapsulated in a polyethylene vial and irradiated along with flux wires at a thermal neutron flux of 7 x 10 12 ncm-2 s-1. After a 7-day period to allow Na-24 to decay the samples are counted on a high purity Ge detector with resolution of better than 1.7 KeV for the 1332 KeV Co-60 photopeak. Using the flux wires and control standards, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. For values exceeding the upper limits, assays are recommended. One standard is run for every 11 samples. One blank is analyzed per work order. Duplicates are analyzed when sample material is available. For all analytes except Au, a 1g aliquot is used. For Au a 30g size, if available, is used.

One standard is run for every 11 samples. One blank is analyzed per work order. Duplicates are analyzed when samples are provided.

Code 5A Basic Elements and Detection Limits (ppm)

Code 5B Other Elements and Detection Limits (ppm)

Reference:
Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.

1g samples are weighed into medium poly vials and are irradiated at a thermal flux of 7 x 1012 n cm-2s-1 in a computer controlled rabbit system, which sends the INAA vials directly to the source of irradiation then back to the fume hood in the lab for analysis. After appropriate decay times to allow aluminum and other very short lived isotopes to decay, the samples are counted sequentially for the analyte(s) of interest. Values are corrected for decay and compared to a standard calibration. Two standards are analyzed with every work order. Duplicates are analyzed when samples are provided.

Elements and Detection Limits (ppm)

Reference:
Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.

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