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sgarn t1_j2cqvwm wrote

>is it because gold is so malleable but so is lead and lead is much more dense

Gold is much more dense than lead, at 19.3 vs 11.3 g/cm³, but the density of the metal isn't really a direct factor in Rutherford scattering in contrast to the atomic mass (more directly the atomic number, but this was prior to the discovery of the neutron) and atomic density. With gold being very close in atomic number to lead, and gold being more malleable and non-reactive than lead, and with gold foil more ubiquitous than lead foil, and with gold being more atomically dense than lead, there wouldn't have been an advantage to using lead over gold.

From Geiger's 1910 paper on the early experiments:

"Gold appeared to be the most suitable substance for such comparative measurements, since it can be obtained in very thin and uniform foils, and in addition its scattering power is higher than that of any other material available."

"Since thin and uniform sheets could only be obtained for gold, tin, silver, copper, and aluminium, the experiments were confined to these metals."

These and later experiments by Geiger and Marsden under the supervision of Rutherford ultimately showed that scattering per atom was proportional to the square of the atomic weight. That is, other materials were observed, but since gold was far more suitable and lead was very close in atomic weight to gold, it would not have yielded much more insight compared to lighter and more malleable materials. It's important to note that thin sheets and uniform thickness were important because the scattering was also observed as a function of the number of sheets used.

In fact, it appears that [lead was used in the early experiments] ( but it was less effective than gold - this was speculated to be due to impurities in the lead but I believe atomic density would have played a role here, possibly also the relative difficulties in producing thin sheets of lead.


BelowDeck t1_j2evaij wrote

That's incredible. There has to be an industrialized process for that by now, and I wonder how the products would compare.


Mountebank t1_j2flzjf wrote

I can’t believe how they’re using their bare hands when moving the stack of gold foil in that jackhammer press. Does Japan not have an equivalent to OSHA? Or does that not apply to small businesses like the one in the video?

For comparison, my workplace has a similar machine, but you need to press two buttons with both hands to start it and there’s a screen of lasers between the user and the press that shuts the machine down if the lasers are blocked.


Revanish t1_j2dfz24 wrote

I've always kinda assumed it had to do with availability but never saw it confirmed. Thank you so much very interesting.


enderjaca t1_j2emudj wrote

>with gold foil more ubiquitous than lead foil

Just to clarify, that doesn't necessarily mean that gold is found more commonly than lead, it's that gold foil was relatively easy to make compared to lead foil? Is that still true today?

I recall selling and using adhesive lead foil for adjusting the weight and balance of tennis racquets, for example. Most modern commercial uses of gold foil I've noticed seem to be related to artistic projects or embellishing food at fancy restaurants.


a_wild_redditor t1_j2eojab wrote

Gold leaf is readily available very thin, it can be well under 1μm. The lead sheet or foil I'm familiar with is much thicker since common uses require its density (counterweighting as you mentioned), its radiation shielding properties, and/or its easy formability by hand while holding its shape afterwards.


LittleLostDoll t1_j2f3ufs wrote

if yoiu up lead baloon on youtube adam savage talks about when they wanted to see if they could get a lead baloon to float they were having trouble getting the lead thin enough, and two companies broke their machines even try

this ws about 15-20 years ago but id think even today it isnt much thinner than they were able to get back then


Kraz_I t1_j2f8byk wrote

Gold is the most ductile and malleable of all pure metals (and probably alloys too, since they tend to be harder and more brittle). This is why it's used in computers and advanced electronics, even though silver and copper are more conductive. A very small amount goes a long way, it can still hold together at under 1 micron thickness.

If you tried to hammer lead into a foil that thin at ambient temperature, (which is the traditional way gold foil is made), it would crumble to bits.

Even in antiquity, artisans knew how to make very thin gold foil by hammering it thin, then folding it with paper between the layers to prevent cold welding, and continuing the process, with the number of layers doubling each time.