+Avogadro's number changed (and AMU with that)

[timbrisc]

Issue migrated from trac ticket # 5775

component: unit definitions | priority: major

2020-09-16 17:48:55: gschadow@pragmaticdata.com created the issue

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Originally from Lynch, Paul (NIH/NLM/LHC) [E] plynch@mail.nih.gov for Clem McDonald:

A needed change to a couple of UCUM constants:

In 2019 the definition of “mole” was revised (https://en.wikipedia.org/wiki/2019_redefinition_of_the_SI_base_units#Mole) to be exactly 6.02214076×10^23^ (instead of being experimentally determined), but UCUM has an older value of 6.0221367×10^23^.

Also, the conversion of an atomic mass unit to g (experimentally determined) needs an update. Per the 2018 CODATA recommendations (https://physics.nist.gov/cuu/pdf/wallet_2018.pdf) the recommended value is now 1.660 539 066 60(50) × 10^−24^ g. UCUM has 1.6605402 × 10^-24^. Note that the “(50)” is the uncertainty on the previous two digits and should not be included in the value.

The re-definition of a mole as a number affects how conversions between mass and moles are done, because now molecular weight is no longer exactly equal numerically (modulo units) to molar weight, though the difference is very slight (about the 7th significant digit). However, I don’t think that affects any part of the text in the specification, as far as I can tell.

So, there is the definition of the two constants to change (“Table 4: SI units”, and “Table 5: Other units…”), and also there are several units in “Table 26: Example Unit Terms by Term” which involve “mol” whose “canonical form value” will need to be revised.

I don’t know how updates to constants have been handled in the past, but perhaps it is worth considering incrementing the version number of the standard from 2.1 to 2.1.1.

[timbrisc]

2020-09-16 17:57:29: gschadow@pragmaticdata.com edited the issue description

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2020-09-16 18:07:33: gschadow@pragmaticdata.com commented

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[443] - tentative update of Avogadro's number and definition value of AMU, needs some more checking of text and also needs more commentary to describe the update history and the new official status of the mol."

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2021-01-15 03:58:20: simon.cox@csiro.au commented

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Table 3. in ​​https://iopscience.iop.org/article/10.1088/1681-7575/aa950a/pdf

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2021-01-15 23:12:30: mitchbre@regenstrief.org changed status from new to assigned

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2021-01-15 23:12:30: mitchbre@regenstrief.org set owner to cjmcdonald

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2021-02-17 17:40:23: mitchbre@regenstrief.org commented

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note from Clem: we should fix these. Believe it NLM may have changed it in their ucum converter

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2021-02-17 18:53:29: gschadow@pragmaticdata.com commented

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This I had already applied in a joint session with the Regenstrief people. [443]

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2021-02-17 19:14:16: simon.cox@csiro.au commented

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I didn't see it in the ucum-essence.xml file. But now I understand that 'essence' is not the normative artefact. That was perhaps a misunderstanding on my part.

However, I think it also exposes a problem with UCUM - the normative definitions should be available in a machine-processable form, not just a table embedded in an HTML spec. At the least a machine-processable artefact should be automatically synced from the spec.

[timbrisc]

2021-03-16 15:45:39: mitchbre@regenstrief.org changed status from assigned to accepted

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2021-03-16 15:45:39: mitchbre@regenstrief.org changed owner from cjmcdonald to mitchbre

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2021-03-16 15:45:39: mitchbre@regenstrief.org commented

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Decision from 17 February 2021 Board Meeting was to update all constants.

[timbrisc]

2021-11-02 19:06:54: mitchbre@regenstrief.org changed title from Avogadro's number changed (and AMU with that) to +Avogadro's number changed (and AMU with that)

[dr-shorthair]

The Avogadro constant (definition of mole) was already updated to the 2018 value in ucum-source.xml and in ucum.xml. However, ucum-essence.xml and ucum.html still have the older value and the latter is what is most visible on the website.

[timbrisc]

Need to adjust various mole-based values, e.g. picomole.

[timbrisc]

Included in v2.2 release