The nuclear-physics infrastructure behind PET scans | Hacker News Reader

The nuclear-physics infrastructure behind PET scans

lanl.gov

60 pointsLAsteNERD4 comments

> Isotopes of a given element have the same number of protons (92 for uranium), but different numbers of neutrons (143 for U-235 and 146 for U-238), meaning they behave the same chemically but differ in mass or radiation emissions.

A fun but off-topic note: "behave the same chemically" is only approximately true. For heavy atoms like the ones discussed in the article, it's basically true. But for hydrogen, adding one neutron doubles its mass and you can get real effects on chemical reaction rates.

https://en.wikipedia.org/wiki/Kinetic_isotope_effect

And of course, an obligatory "In The Pipeline" link on how it's used in drug discovery: https://www.science.org/content/blog-post/isotopes-get-your-...

The chemical differences are how deuterium isotope separation is performed. This used to be the Girdler sulfide process, now it's catalytic exchange stacks using the exchange of hydrogen isotopes between molecular hydrogen and water.

hydrogen and deuterium also count as different groups when accounting for optical activity

carbon forms 4 bonds , if the 4 things bound to carbon are different then the molecule can be assembled in two ways ( mirror images like your left and right hand , similar but distinct as no rotation of your left hand can make it a right hand) and the two different arrangements rotate the polarized light in different ways . so if you have say CHDClF (carbon bonded to hydrogen , deuterium , chlorine and flourine) it is optically active

it was interesting to learn this , i thought it was a purely electromagnetic phenomena and the mass of the nucleus would not be relevant

but iodine 127 and iodine 131 do not have enough of a difference to show detectable optical activity

Nice; we need more of these sort of scientific articles on HN.

There is so much the general public is unaware of when it comes to the use of Atomic/Nuclear Physics in our modern societies.

Here is a fun fact: Americans Will Do Anything to Get Indian Mangoes - https://archive.ph/xVqfl#selection-2157.0-2157.48

But due to USDA requirements, Indian Mangoes actually have to undergo gamma irradiation treatment using Cobalt-60 (https://en.wikipedia.org/wiki/Cobalt-60#Applications) before they can be exported. So some of the top atomic research centers in India have a special facility just to phytosanitize mangoes!

There are even research papers on how to do the above more efficiently for example; Improving phytosanitary irradiation treatment of mangoes using Monte Carlo simulation - https://www.sciencedirect.com/science/article/abs/pii/S02608...

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