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> its unstable lead-210 isotope would have largely decayed away over the centuries into stable lead-206 I know very little about radiation or metallurgy. Why a

> its unstable lead-210 isotope would have largely decayed away over the centuries into stable lead-206 I know very little about radiation or metallurgy. Why are the few centuries the lead was underwater relevant compared to the thousands or millions of years it existed in the ground prior to being mined? Compared to the timescale that the lead exists on, 100 years either way seems like it should be irrelevant.

saagarjha 7y ago
If it occurs naturally, it's because it's constantly being replenished by something higher up in the decay chain (apparently, this happens to be Polonium 214 and Thallium 210: https://upload.wikimedia.org/wikipedia/commons/a/a1/Decay_chain%284n%2B2%2C_Uranium_series%29.PNG https://upload.wikimedia.org/wikipedia/commons/a/a1/Decay_ch...).
ISL 7y ago
What is special is that it was chemically refined as lead in ancient times. Lead-210 is in the natural Uranium decay chain: https://en.wikipedia.org/wiki/Decay_chain#Uranium_series https://en.wikipedia.org/wiki/Decay_chain#Uranium_series The uranium that feeds the chain has a half-life of ~4.5 billion years, so a handful of good 'ol dirt generally has the entire chain's worth of isotopes present. Refining the lead out of ore concentrates almost-pure lead (with all of its isotopes). Lead-210 has a 22-year half-life, so the lead-210 in Roman lead has almost entirely decayed away at the present day. Being underwater is also special. Cosmic rays strike nuclei on Earth's surface all the time, sometimes transmuting them into other, potentially-radioactive isotopes. They aren't of safety concern, but they are readily observed in low-background physics experiments. "Cosmogenic activation" is a serious problem -- the best facilities these days re-refine copper, from which the experiments are built, deep underground in order to remove cosmogenics. Similarly, detectors are transported by boat in order to prevent the activation that happens via air travel. Ancient Roman lead avoids both problems. It is old, removing the 210Pb, and has low cosmogenic activation.
- garmaine 7y ago
  Also, nuclear bombs. Iron from old (pre-1945) sunken ships is valued for its lack of trace radioactive isotopes in making sensitive detection equipment.
  - kpU8efre7r 7y ago
    https://en.wikipedia.org/wiki/Low-background_steel?wprov=sfla1 https://en.wikipedia.org/wiki/Low-background_steel?wprov=sfl...
- kingbirdy 7y ago
  That makes sense. Thanks!

saagarjha 7y ago

If it occurs naturally, it's because it's constantly being replenished by something higher up in the decay chain (apparently, this happens to be Polonium 214 and Thallium 210: https://upload.wikimedia.org/wikipedia/commons/a/a1/Decay_chain%284n%2B2%2C_Uranium_series%29.PNG https://upload.wikimedia.org/wikipedia/commons/a/a1/Decay_ch...).

ISL 7y ago

What is special is that it was chemically refined as lead in ancient times. Lead-210 is in the natural Uranium decay chain: https://en.wikipedia.org/wiki/Decay_chain#Uranium_series https://en.wikipedia.org/wiki/Decay_chain#Uranium_series The uranium that feeds the chain has a half-life of ~4.5 billion years, so a handful of good 'ol dirt generally has the entire chain's worth of isotopes present. Refining the lead out of ore concentrates almost-pure lead (with all of its isotopes). Lead-210 has a 22-year half-life, so the lead-210 in Roman lead has almost entirely decayed away at the present day. Being underwater is also special. Cosmic rays strike nuclei on Earth's surface all the time, sometimes transmuting them into other, potentially-radioactive isotopes. They aren't of safety concern, but they are readily observed in low-background physics experiments. "Cosmogenic activation" is a serious problem -- the best facilities these days re-refine copper, from which the experiments are built, deep underground in order to remove cosmogenics. Similarly, detectors are transported by boat in order to prevent the activation that happens via air travel. Ancient Roman lead avoids both problems. It is old, removing the 210Pb, and has low cosmogenic activation.

garmaine 7y ago
Also, nuclear bombs. Iron from old (pre-1945) sunken ships is valued for its lack of trace radioactive isotopes in making sensitive detection equipment.
- kpU8efre7r 7y ago
  https://en.wikipedia.org/wiki/Low-background_steel?wprov=sfla1 https://en.wikipedia.org/wiki/Low-background_steel?wprov=sfl...
kingbirdy 7y ago
That makes sense. Thanks!