I was browsing the book Isotopes: Principles and Applications by Faure and Mensing and I would like to know what is the history of the use of the word daughter for a decay product. It seems to me that the book gives no explanation about the terminology so I think it is a well established convention for a long time.

A quick search gives me this Historical perspective:

A radionuclide generator is a concept defined as an effective radiochemical separation of decaying parent and daughter radionuclides such that the daughter is obtained in a pure radionuclidic and radiochemical form. Radionuclide generators were historically called ‘cows’ since the daughter radioactivity was ‘milked’ (i.e. removed) from its precursor and the parent then generated a fresh supply of the daughter.1

but even if I understand the cow and milk metaphor I do not understand the use of the word daughter, contrasted for example with the word son; moreover, I do not get the asymmetry between daughter, which has a specific gender, and parent, which it seems to me gender neutral.

I know that maybe this question is more suitable for https://english.stackexchange.com/ but I am interested in the context of physics: maybe someone received an explanation about the terminology during a formal nuclear physics university lesson.

In my bookshelf, an Italian author2 uses the word discendente (descendant) that I would consider almost gender neutral; another Italian author3, translating from the English, uses the word figlio (son).

1Radionuclide Generators. In : Handbook of Nuclear Chemistry. Boston, MA : Springer US, 2004. p. 1379–1415. ISBN 978-0-387-30682-7. Available from: https://doi.org/10.1007/0-387-30682-X_32

2Paolo Chiorboli, Fondamenti di Chimica, UTET, Torino, 1975 (II edizione, 1980).

3Cornelis Klein, Anthony R. Philpotts Mineralogia e petrografia Prima edizione italiana condotta sulla seconda edizione inglese A cura di Giorgio Gasparotto, Roberto Braga. Zanichelli, Bologna, 2018.

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    $\begingroup$ Just a thought: around 1915, the decay chains of uranium and thorium were explored (by Rutherford and Soddy). As a decay chain contains different element names, someone might have thought it resembled a female ancestral line in genealogy. $\endgroup$
    – jkien
    Mar 20, 2021 at 23:29
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    $\begingroup$ G. v. Hevesy and F. Paneth, "Lehrbuch der Radioaktivität." Leipzig: J. A. Barth 1923, p. 74 (my emphasis): "Ein Radioelement befindet sich mit seinem Zerfallprodukt im radioaktiven Gleichgewicht, wenn in der Zeiteinheit ebenso viele Atome der Tochtersubstanz zerfallen, wie entstehen" $\endgroup$
    – njuffa
    Mar 22, 2021 at 4:57
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    $\begingroup$ A German source from 1910 speaks of "mother substances" and "daughter substances" and that there is a "genetic connection" between radioactive elements: "Da die radioaktiven Elemente gruppenweise in einem genetischen Zusammenhang stehen, derart, daß jedes einzelne Radioelement die Tochtersubstanz eines anderen und selbst wieder die Muttersubstanz eines dritten Radioelementes ..." Unfortunately I can't tease out the name of the actual paper from Google Books. $\endgroup$
    – njuffa
    Mar 22, 2021 at 5:15
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    $\begingroup$ It's a report of a talk at a meeting. "7 . Herr E . EBLER - Heidelberg : Über die Radioaktivität der Mineralquellen" ,on "pages" 292ff of the Hathi Trust version, babel.hathitrust.org/cgi/… $\endgroup$ Mar 22, 2021 at 12:02
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    $\begingroup$ @AlessandroJacopson In German the grammatical gender of substance is also female: die Substanz. $\endgroup$
    – njuffa
    Mar 22, 2021 at 18:05

1 Answer 1


According to Wikipedia, a decay product is also referred to as a daughter product, a daughter isotope, radio-daughter or daughter nuclide.

The term possibly arose from cell biology where it is common to call the cells after division daughter cells, possibly because they too can go on to divide. In fact, it is documented that the term fission was borrowed from cell biology:

In 1938, Lise Meitner spent Christmas at the home of her friend Eva von Bahr and whilst there, she received a letter from Otto Hahn describing his chemical proof that some of the products of the bombardment of uranium with neutrons were barium. No previous known method of radioactive decay could account for such a large product and she wrote back to Hahn to say:

At the moment, the assumption of such a thoroughgoing breakup seems very difficult to me, but in nuclear physics we have experienced so many surprises, that one cannot unconditionally say: "it is impossible".

Later, after a walk in the woods with her nephew Otto Frisch, in fact in the midst of one, Meitner & Frisch correctly interpreted Hahn's results as the splitting of the uranium atom. Frisch decided that he needed a name for this new process and spoke to William Arnold, an American biologist and asked him what biologists called the process by which living cells divided into two cells. Arnold informed him that the term was fission and Frisch duly used the term in his joint paper with Meitner submitted to Nature describing the phenomenon of uranium fission. As the term fission was new, he used it in quotes. However, it was the first and last time that the term fission was used in quotes as the term was quickly assimilated into the vocabulary of nuclear physics.


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