4A - Exploration - INAA
A 1 g aliquot is encapsulated in a polyethylene vial and irradiated with flux wires and an internal standard (1 for 11 samples) at a thermal neutron flux of 7 x 10
12
n cm
-2
s
-1
. After a 7-day decay 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, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. The standard present is only a check on accuracy and is not used for calibration purposes. From 10-30% of the samples are rechecked by re-measurement. 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 samples are provided.
Gamma-ray energies are listed in Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.
Code 4A-Exploration
Elements and Detection Limits (ppm)
|
Element
|
Detection Limit
|
Upper Limit
|
|
Element
|
Detection Limit
|
Upper Limit
|
|
Element
|
Detection Limit
|
Upper Limit
|
|
Ag
|
5
|
100,000
|
|
Ir
|
5 ppb
|
-
|
|
Zn
|
40
|
100,000
|
|
As
|
2
|
-
|
|
Mo
|
5
|
10,000
|
|
La
|
0.2
|
10,000
|
|
Au
|
5 ppb
|
30,000 ppb
|
|
Na
|
0.01%
|
10%
|
|
Ce
|
3
|
10,000
|
|
Ba
|
100
|
-
|
|
Ni
|
50
|
10,000
|
|
Nd
|
5
|
10,000
|
|
Br
|
1
|
-
|
|
Rb
|
20
|
-
|
|
Sm
|
0.1
|
10,000
|
|
Ca
|
0.5%
|
-
|
|
Sb
|
0.2
|
10,000
|
|
Eu
|
0.1
|
-
|
|
Co
|
1
|
10,000
|
|
Sc
|
0.1
|
-
|
|
Tb
|
0.5
|
-
|
|
Cr
|
2
|
100,000
|
|
Se
|
3
|
-
|
|
Yb
|
0.1
|
-
|
|
Cs
|
0.5
|
-
|
|
Sr
|
500
|
-
|
|
Lu
|
0.05
|
-
|
|
Fe
|
0.02%
|
-
|
|
Ta
|
1
|
10,000
|
|
U
|
0.5
|
10,000
|
|
Hf
|
0.5
|
-
|
|
W
|
3
|
10,000
|
|
Th
|
0.5
|
10,000
|
Note: Assays are recommended for values which exceed the upper limits.
|