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.)
stinkbeetle · 10h ago
> 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 · 9h ago
Since it's a device that saves the life of the patient, you can accept a lot of patient risk as a tradeoff.
stinkbeetle · 7h ago
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 · 10h ago
Pu-238 decays mainly by alpha decay which would be easily contained by the titanium casing.
stinkbeetle · 7h ago
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.
cyberax · 5h ago
It also spontaneously fissions, with daughter products often being gamma/beta active. And it always contains some contaminants
kondro · 10h ago
REM is already an adjusted measure for absorption, not an general quantity of radiation.
stinkbeetle · 7h ago
This doesn't address my question. OP was talking about the whole-body dose, I'm asking about the surface and nearby dose.
jmb99 · 8h ago
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.
stinkbeetle · 2h ago
Duly noted.
_kb · 9h ago
Or approximately 100 bananas, for scale.
acidburnNSA · 8h ago
Banana equivalent dose is 0.01 mrem, so 0.1 rem = 100 mrem = 10,000 bananas.
ChuckMcM · 9h ago
Yeah but their spouse :-) 75x larger dose.
acidburnNSA · 9h ago
No it's less! They switched from rem to millirem for the spouse.
ChuckMcM · 9h ago
Dang! Me and my misreading of the units. That makes more sense too.
sanarothe · 4h ago
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.
jandrewrogers · 9h ago
> 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.
acidburnNSA · 9h ago
Not sure about neutrons. Gammas, or x-rays at least, could come from bremmstrahlung.
Horffupolde · 9h ago
Possibly Pu-239 or other impurities.
bobmcnamara · 9h ago
Some very small portion of Pu-238 will eventually pass through Tl-210 -> Pb-209.
pfdietz · 9h ago
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.
cyberax · 5h ago
All U and Pu isotopes undergo spontaneous fission, producing neutrons and random daughter products.
anovikov · 1h ago
Pu-238 in this thing would cost $14K in today's prices!
xattt · 10h ago
More interesting to me is how this tech was programmed. There would have been some external unit to set parameters.
userbinator · 9h ago
Since it's from 1974, my guess is a few trimpots behind a sealed cover.
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.)
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.
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.
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.