Editing Group 5 element (section)

=== Dubnium ===

The last element of the group, [[dubnium]], does not occur naturally and so must be synthesized in a laboratory. The first reported detection was by a team at the [[Joint Institute for Nuclear Research]] (JINR), which in 1968 had produced the new element by bombarding an [[americium]]-243 target with a beam of [[neon]]-22 ions, and reported 9.4&nbsp;MeV (with a half-life of 0.1–3 seconds) and 9.7&nbsp;MeV (''t''<sub>1/2</sub>&nbsp;>&nbsp;0.05&nbsp;s) [[alpha decay|alpha activities]] followed by alpha activities similar to those of either <sup>256</sup>103 or <sup>257</sup>103. Based on prior theoretical predictions, the two activity lines were assigned to <sup>261</sup>105 and <sup>260</sup>105, respectively.<ref name="1993 report">{{Cite journal|year=1993|title=Discovery of the Transfermium elements|url=http://s3.documentcloud.org/documents/562229/iupac1.pdf|journal=Pure and Applied Chemistry|volume=65|issue=8|pages=1757|doi=10.1351/pac199365081757|access-date=September 7, 2016|last1=Barber|first1=R. C.|last2=Greenwood|first2=N. N.|author-link2=Norman Greenwood|last3=Hrynkiewicz|first3=A. Z.|display-authors=3|last4=Jeannin|first4=Y. P|last5=Lefort|first5=M|last6=Sakai|first6=M|last7=Ulehla|first7=I|last8=Wapstra|first8=A. H|last9=Wilkinson|first9=D. H|s2cid=195819585}}</ref>

After observing the alpha decays of element 105, the researchers aimed to observe the [[spontaneous fission]] (SF) of the element and study the resulting fission fragments. They published a paper in February 1970, reporting multiple examples of two such activities, with half-lives of 14&nbsp;ms and {{val|2.2|0.5|u=s}}. They assigned the former activity to <sup>242mf</sup>Am{{efn|This notation signifies that the nucleus is a [[nuclear isomer]] that decays via spontaneous fission.}} and ascribed the latter activity to an isotope of element 105. They suggested that it was unlikely that this activity could come from a transfer reaction instead of element 105, because the yield ratio for this reaction was significantly lower than that of the <sup>242mf</sup>Am-producing transfer reaction, in accordance with theoretical predictions. To establish that this activity was not from a (<sup>22</sup>Ne,''x''n) reaction, the researchers bombarded a <sup>243</sup>Am target with <sup>18</sup>O ions; reactions producing <sup>256</sup>103 and <sup>257</sup>103 showed very little SF activity (matching the established data), and the reaction producing heavier <sup>258</sup>103 and <sup>259</sup>103 produced no SF activity at all, in line with theoretical data. The researchers concluded that the activities observed came from SF of element 105.<ref name="1993 report" />

JINR then attempted an experiment to create element 105, published in a report in May 1970. They claimed that they had synthesized more nuclei of element 105 and that the experiment confirmed their previous work. According to the paper, the isotope produced by JINR was probably <sup>261</sup>105, or possibly <sup>260</sup>105.<ref name="1993 report" /> This report included an initial chemical examination: the thermal gradient version of the gas-chromatography method was applied to demonstrate that the chloride of what had formed from the SF activity nearly matched that of [[Niobium(V) chloride|niobium pentachloride]], rather than [[hafnium tetrachloride]]. The team identified a 2.2-second SF activity in a volatile chloride portraying eka-tantalum properties, and inferred that the source of the SF activity must have been element 105.<ref name="1993 report" />

In June 1970, JINR made improvements on their first experiment, using a purer target and reducing the intensity of transfer reactions by installing a [[collimator]] before the catcher. This time, they were able to find 9.1&nbsp;MeV alpha activities with daughter isotopes identifiable as either <sup>256</sup>103 or <sup>257</sup>103, implying that the original isotope was either <sup>260</sup>105 or <sup>261</sup>105.<ref name="1993 report" />

{{multiple image
| footer = Danish nuclear physicist [[Niels Bohr]] and German nuclear chemist [[Otto Hahn]], both proposed as possible namesakes for element 105
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| image1 = Niels Bohr.jpg
| alt1 = Photo of Niels Bohr
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| image2 = Otto Hahn (Nobel).jpg
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A [[Transfermium Wars|controversy]] erupted on who had discovered the element, which each group suggesting its own name: the Dubna group named the element ''nielsbohrium'' after [[Niels Bohr]], while the Berkeley group named it ''hahnium'' after [[Otto Hahn]].<ref name=transuranium>{{cite book |last1=Hoffman |first1=D. C. |last2=Ghiorso |first2=A. |last3=Seaborg |first3=G. T. |title=The Transuranium People: The Inside Story |year=2000 |pages=369–399 |publisher=Imperial College Press |isbn=978-1-86094-087-3}}</ref> Eventually a joint working party of [[IUPAC]] and [[IUPAP]], the Transfermium Working Group, decided that credit for the discovery should be shared. After various compromises were attempted, where element 105 was called ''kurchatovium'', ''joliotium'' and ''hahnium'', in 1997 IUPAC officially named the element dubnium after Dubna,<ref name=97IUPAC>{{cite journal |doi =10.1351/pac199769122471 |title =Names and symbols of transfermium elements (IUPAC Recommendations 1997) |date =1997 |journal =Pure and Applied Chemistry |volume =69 |issue = 12 |pages =2471–2474|doi-access =free }}</ref><ref name="Emsley" /> and ''nielsbohrium'' was eventually simplified to ''bohrium'' and used for [[bohrium|element 107]].<ref>{{cite journal |last1=Ghiorso |first1=A. |last2=Seaborg |first2=G. T. |last3=Organessian |first3=Yu. Ts. |last4=Zvara |first4=I. |last5=Armbruster |first5=P. |last6=Hessberger |first6=F. P. |last7=Hofmann |first7=S. |last8=Leino |first8=M. |last9=Munzenberg |first9=G. |last10=Reisdorf |first10=W. |last11=Schmidt |first11=K.-H. |year=1993 |title=Responses on 'Discovery of the transfermium elements' by Lawrence Berkeley Laboratory, California; Joint Institute for Nuclear Research, Dubna; and Gesellschaft fur Schwerionenforschung, Darmstadt followed by reply to responses by the Transfermium Working Group |journal=Pure and Applied Chemistry |volume=65 |issue=8 |pages=1815–1824 |doi=10.1351/pac199365081815 |doi-access=free}}</ref><ref name="IUPAC97">{{Cite journal |author=Commission on Nomenclature of Inorganic Chemistry |date=1997 |title=Names and symbols of transfermium elements (IUPAC Recommendations 1997) |url=http://publications.iupac.org/pac/pdf/1997/pdf/6912x2471.pdf |url-status=live |journal=Pure and Applied Chemistry |volume=69 |issue=12 |pages=2471–2474 |doi=10.1351/pac199769122471 |archive-url=https://web.archive.org/web/20211011132719/http://publications.iupac.org/pac/pdf/1997/pdf/6912x2471.pdf |archive-date=2021-10-11 |access-date=2023-07-11}}</ref>