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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 1012 n cm-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, 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. Selected duplicates are analyzed when enough material is submitted.  

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

Fe

0.02%

75%

Sc

0.1

1000

As

2

100,000

Hf

0.5

-

Se

3

10,000

Au

5 ppb

30,000 ppb

Ir

5 ppb

10,000

Sm

0.1

10,000

Ba

100

100,000

La

0.2

10,000

Sr

500

-

Br

1

-

Lu

0.05

1000

Ta

1

10,000

Ca

0.5%

-

Mo

5

10,000

Tb

0.5

1000

Ce

3

10,000

Na

0.01%

10%

Th

0.5

10,000

Co

1

10,000

Nd

5

10,000

U

0.5

10,000

Cr

2

100,000

Ni

50

10,000

W

3

10,000

Cs

0.5

-

Rb

20

10,000

Yb 

0.1

-

Eu

0.1

-

Sb

0.2

10,000

Zn

40

100,000

 

Notes:     

Assays are recommended for values which exceed the upper limits.

 

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

 


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