# Should Copper 65 and Copper 63 isotopes have a larger density than a copper 29 atom?

I was looking at the first page of a paper (see https://aip.scitation.org/doi/10.1063/1.1735598#Metrics-content for details) and I ran across something odd. According to the paper, Copper isotopes 63 and 65 had much lower densities than the stable copper 29 atom. Moreover, Copper 65 had a density of 7.17 while copper 63 had a density of 7.93. Unfortunately, since I do not have a membership to the website I was only able to read the first page, which prevented me from finding out whether the source of this anomaly was human error or nature. I was wondering how this is possible since according to current atomic theory these isotopes should have a much larger nucleus than Copper 29.

• What do you mean by copper 29? That would indicate copper with 29 protons and no neutrons, which doesn't exist as an isotope. – David Z Jul 30 '18 at 21:13
• Out of curiosity, why were you looking up data for copper isotope densities? Is it related to your research? – wcc Jul 30 '18 at 21:13
• David- 29 is the copper's atomic number. But since I did use 65 and 63 to describe the copper isotopes, I should have probably used copper 58 to describe normal copper. – Anthony Ducharme Jul 30 '18 at 21:38
• Perhaps take a look here en.wikipedia.org/wiki/Isotopes_of_copper 58Cu is unstable with a half life of 3.204(7) seconds. For heavy atoms an excess of neutrons over protons is required for stability. – my2cts Jul 30 '18 at 21:47
• I took a look at that my2cts, and that helped a lot. Also IAmAStudent, the reason why I was looking at the densities is that I was looking into gravitational anomalies with radioactivity. – Anthony Ducharme Jul 30 '18 at 22:15

The discrepancy between the isotopically enriched samples and the cited value for natural copper [$8.93\, g/\text{cm}^3$] was thought to be due to trapped gases. Consequently, some of each sample was vacuum melted in an effort to reduce this trapping.
After taking measures to reduce the gas trapping, and taking account of chemical and isotope impurities, the paper reports $8.83\pm 0.05\, g/\text{cm}^3$ for Cu-63 and $9.12\pm 0.05\, g/\text{cm}^3$ for Cu-65, in Table I of the paper. These corrected values are in excellent agreement with densities calculated (not measured) using crystallography and isotopic data.