FilterHN

10 months ago

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For context, the 0.1 rem yearly dose to the patient is about 1/6th of the average background dose we all get every year.

This Pu-238 is the same stuff that's powering the Voyager probes and a few Mars rovers.

Note that it's not Pu-239, which is fissile nuclear fuel for chain reactions (power plants, bombs, etc.)

10 months ago

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> For context, the 0.1 rem yearly dose to the patient is about 1/6th of the average background dose we all get every year.

Wouldn't you be more concerned about dose rates in tissues near the device though, rather than whole body dose? At the surface of the pacemaker it would be about 90 rem / year.

BurningFrog

10 months ago

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Since it's a device that saves the life of the patient, you can accept a lot of patient risk as a tradeoff.

10 months ago

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Obviously. That doesn't address my question though, the dose of concern is surely the nearby tissue rather than one calculated over the whole body. If the pacemaker is resting against my lungs, I'm not going to be concerned about foot cancer.

I'm not implying the risk was miscalculated in the medical approval process, I'm sure it's safe enough. I'm just questioning OP's statement about radiation dose, yes it's strictly true but seems to underplay the importance of the nature of the dose.

SoftTalker

10 months ago

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Pu-238 decays mainly by alpha decay which would be easily contained by the titanium casing.

cyberax

10 months ago

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It also spontaneously fissions, with daughter products often being gamma/beta active. And it always contains some contaminants

10 months ago

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Thanks. Presumably we're talking about "Dose rates at the surface of the pacemaker are approximately 5 to 15 mrem per hour from the emitted gamma rays and neutrons" though.

SoftTalker

10 months ago

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Yeah ideally I would not want that in or close to my body but if the choice is literally life or death I guess I'll take it.

How do modern pacemakers work? Can they be recharged inductively or is surgery required to replace batteries periodically?

kondro

10 months ago

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REM is already an adjusted measure for absorption, not an general quantity of radiation.

10 months ago

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This doesn't address my question. OP was talking about the whole-body dose, I'm asking about the surface and nearby dose.

jmb99

10 months ago

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If I die without a pacemaker, or maybe have an increased risk of certain cancers with a pacemaker but get to live, I’d choose the pacemaker.

10 months ago

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Duly noted.

_kb

10 months ago

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Or approximately 100 bananas, for scale.

10 months ago

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Banana equivalent dose is 0.01 mrem, so 0.1 rem = 100 mrem = 10,000 bananas.

ChuckMcM

10 months ago

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Yeah but their spouse :-) 75x larger dose.

10 months ago

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No it's less! They switched from rem to millirem for the spouse.

ChuckMcM

10 months ago

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Dang! Me and my misreading of the units. That makes more sense too.

jandrewrogers

10 months ago

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> Dose rates at the surface of the pacemaker are approximately 5 to 15 mrem per hour from the emitted gamma rays and neutrons.

Where are these gamma rays and neutrons coming from? The decay chain for Pu-238 is via alpha emission (Pu-238 -> U-234 -> Th-230 -> ...) which won't penetrate the casing.

10 months ago

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Not sure about neutrons. Gammas, or x-rays at least, could come from bremmstrahlung.

pfdietz

10 months ago

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Alpha particles will produce secondary radiation occasionally when they hit light nuclei. The oxygen in the Pu oxide is almost entirely O-16 to minimize neutron production.

Horffupolde

10 months ago

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Possibly Pu-239 or other impurities.

cyberax

10 months ago

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All U and Pu isotopes undergo spontaneous fission, producing neutrons and random daughter products.

bobmcnamara

10 months ago

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Some very small portion of Pu-238 will eventually pass through Tl-210 -> Pb-209.

sanarothe

10 months ago

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For similar / further reading on historical pacemakers, check out https://www.implantable-device.com/category/implantable-comp... where David Prutchi has amassed what I think is a comprehensive history of pacemakers / neurostimulators ranging from these early atomic designs up through current day devices / companies.

xattt

10 months ago

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More interesting to me is how this tech was programmed. There would have been some external unit to set parameters.

userbinator

10 months ago

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Since it's from 1974, my guess is a few trimpots behind a sealed cover.