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)

Element Detection LimitUpper Limit
Ag5100,000
As210,000
Au5 ppb30,000 ppb
Ba100500,000
Br11,000
Ca1%50%
Ce310,000
Co55,000
Cr10100,000
Cs210,000
Eu0.22,000
Fe0.02%75%
Element Detection LimitUpper Limit
Hf1500
Hg11,000
Ir5 ppb10,000 ppb
La110,000
Lu0.051,000
Mo510,000
Na0.05%10%
Nd510,000
Ni5010,000
Rb3010,000
Sb0.210,000
Sc0.1200
Element Detection LimitUpper Limit
Se510,000
Sm0.110,000
Sn0.05%10%
Sr0.1%40%
Ta110,000
Tb0.51,000
Th0.510,000
U0.510,000
W410,000
Yb0.21,000
Zn50100,000

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

Element Detection LimitUpper Limit
Ag5100,000
As0.510,000
Au2 ppb30,000 ppb
Ba50500,000
Br0.51,000
Ca1%50%
Ce310,000
Co15,000
Cr5100,000
Cs110,000
Eu0.22,000
Fe0.01%75%
Element Detection LimitUpper Limit
Hf1500
Hg11,000
Ir5 ppb10,000 ppb
La0.510,000
Lu0.051,000
Mo110,000
Na0.01%10%
Nd510,000
Ni2010,000
Rb1510,000
Sb0.110,000
Sc0.1200
Element Detection LimitUpper Limit
Se310,000
Sm0.110,000
Sn0.02%10%
Sr0.05%40%
Ta0.510,000
Tb0.51000
Th0.210,000
U0.510,000
W110,000
Yb0.21,000
Zn50100,000

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)

Element Detection LimitUpper Limit
As210,000
Au5 ppb30,000 ppb
Ba200100,000
Br21000
Ce510,000
Co210,000
Cr10100,000
Cs210,000
Eu0.22000
Element Detection LimitUpper Limit
Fe0.02%75%
Hf15000
La110,000
Lu0.11000
Mo510,000
Na500100,000
Nd1010,000
Rb5010,000
Sb0.210,000
Element Detection LimitUpper Limit
Sc0.5200
Se510,000
Sm0.110,000
Ta210,000
Th110,000
U210,000
W510,000
Yb0.51000

Code 5B Other Elements and Detection Limits (ppm)

Element Detection LimitUpper Limit
As110,000
Au5 ppb30,000 ppb
Ba100100,000
Br0.51000
Ce310,000
Co0.510,000
Cr1100,000
Cs0.510,000
Eu0.22000
Element Detection LimitUpper Limit
Fe0.01%75%
Hf0.5500
La0.110,000
Lu0.051000
Mo210,000
Na100100,000
Nd510,000
Rb2010,000
Sb0.110,000
Element Detection LimitUpper Limit
Sc0.1200
Se210,000
Sm0.0110,000
Ta0.510,000
Th0.210,000
U0.110,000
W210,000
Yb0.21000

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)

Element Detection LimitUpper Limit
Al1100,000
Br510,000
Cl100100,000
Cu52,500
Dy0.55,000
Ga510,000
I0.55,000
In0.15,000
Mg0.05%50%
Mn0.110,000
Na50200,000
Re15,000
Ti50100,000
V0.110,000

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

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