F.B Johnson's Paper

[Qiaozhi]

More food for thought:

A 1mm diameter pure gold ball has a of 1.3us. An equivalent lead ball would need to be 3mm in diameter for the same .

Likewise:
2mm gold ball: = 5.2us, lead ball = 6mm
5mm gold ball: = 32us, lead ball = 14.9mm

The lead ball diameter approximates to 3x the diameter of the gold ball.

So (at first sight) it seems to contradict the fact that small gold nuggets are difficult to detect, given that the conductivity of gold has 9x the conductivity of lead. However, this is for pure gold, and gold found in the field [presumably] has a much lower conductivity due to impurities. Plus the gold is not all in one chunk, which restricts the flow of eddy currents to a reduced area, this weakening the return signal.

Question for Green - Have you charted the decay constant for any real gold nuggets?

[green]

[QUOTE=Qiaozhi;208427]More food for thought:

A 1mm diameter pure gold ball has a of 1.3us. An equivalent lead ball would need to be 3mm in diameter for the same .

Likewise:
2mm gold ball: = 5.2us, lead ball = 6mm
5mm gold ball: = 32us, lead ball = 14.9mm

The lead ball diameter approximates to 3x the diameter of the gold ball.

So (at first sight) it seems to contradict the fact that small gold nuggets are difficult to detect, given that the conductivity of gold has 9x the conductivity of lead. However, this is for pure gold, and gold found in the field [presumably] has a much lower conductivity due to impurities. Plus the gold is not all in one chunk, which restricts the flow of eddy currents to a reduced area, this weakening the return signal.

Question for Green - Have you charted the decay constant for any real gold nuggets?[/QUOT

http://www.geotech1.com/forums/showt...620#post199620

[Qiaozhi]

http://www.geotech1.com/forums/showt...620#post199620

Thanks.

This is interesting, because target 9 (which is the largest gold nugget) has a shorter than target 8.
Which seems to confirm the theory that using the conductivity value for pure gold just doesn't work out correctly for gold nuggets.

Working the supplied values backwards, to derive the diameter of an equivalent ball of pure gold, gives:

Target 7: diameter = 1.5 mm
Target 8 : diameter = 2.2 mm
Target 9: diameter = 2 mm

Which is clearly nonsense.
It appears that the larger the gold nugget, the less accurate the calculation. It also demonstrates why gold nuggets are so hard to detect in the field.

[green]

Thanks.

This is interesting, because target 9 (which is the largest gold nugget) has a shorter than target 8.
Which seems to confirm the theory that using the conductivity value for pure gold just doesn't work out correctly for gold nuggets.

Working the supplied values backwards, to derive the diameter of an equivalent ball of pure gold, gives:

Target 7: diameter = 1.5 mm
Target 8 : diameter = 2.2 mm
Target 9: diameter = 2 mm

Which is clearly nonsense.
It appears that the larger the gold nugget, the less accurate the calculation. It also demonstrates why gold nuggets are so hard to detect in the field.

It's been awhile, not sure if I'm remembering right. Targets made of lead, gold and aluminum had the same signal strength at short delay times if they were the same size and shape. TC wasn't the same. I think the larger nugget had a shorter TC because it was thinner. http://www.geotech1.com/forums/showt...579#post187579 shows an example of TC change with shape using the same target.