Editing Group 7 element (section)

=== Bohrium ===

Two groups claimed [[Timeline of chemical element discoveries|discovery of the element bohrium]]. Evidence of bohrium was first reported in 1976 by a Soviet research team led by [[Yuri Oganessian]], in which targets of [[bismuth-209]] and [[lead]]-208 were bombarded with accelerated nuclei of [[chromium]]-54 and [[manganese]]-55 respectively.<ref>{{cite journal|doi=10.1016/0375-9474(76)90607-2|title= On spontaneous fission of neutron-deficient isotopes of elements | volume=273|year=1976|journal=Nuclear Physics A|pages=505–522  | last1 = Yu | last2 = Demin | first2 = A.G. | last3 = Danilov | first3 = N.A. | last4 = Flerov | first4 = G.N. | last5 = Ivanov | first5 = M.P. | last6 = Iljinov | first6 = A.S. | last7 = Kolesnikov | first7 = N.N. | last8 = Markov | first8 = B.N. | last9 = Plotko | first9 = V.M. | last10 = Tretyakova | first10 = S.P.}}</ref> Two activities, one with a half-life of one to two milliseconds, and the other with an approximately five-second half-life, were seen. Since the ratio of the intensities of these two activities was constant throughout the experiment, it was proposed that the first was from the [[isotope]] bohrium-261 and that the second was from its daughter [[dubnium]]-257. Later, the dubnium isotope was corrected to dubnium-258, which indeed has a five-second half-life (dubnium-257 has a one-second half-life); however, the half-life observed for its parent is much shorter than the half-lives later observed in the definitive discovery of bohrium at [[Darmstadt]] in 1981. The [[International Union of Pure and Applied Chemistry|IUPAC]]/IUPAP Transfermium Working Group (TWG) concluded that while dubnium-258 was probably seen in this experiment, the evidence for the production of its parent bohrium-262 was not convincing enough.<ref name="93TWG" />

In 1981, a German research team led by [[Peter Armbruster]] and [[Gottfried Münzenberg]] at the [[GSI Helmholtz Centre for Heavy Ion Research]] (GSI Helmholtzzentrum für Schwerionenforschung) in Darmstadt bombarded a target of bismuth-209 with accelerated nuclei of chromium-54 to produce five atoms of the isotope bohrium-262:<ref name="262Bh">{{cite journal |last1=Münzenberg |first1=G. |last2=Hofmann |first2=S. |last3=Heßberger |first3=F. P. |last4=Reisdorf |first4=W. |last5=Schmidt |first5=K. H. |last6=Schneider |first6=J. H. R. |last7=Armbruster |first7=P. |last8=Sahm |first8=C. C. |last9=Thuma |first9=B. |year=1981 |title=Identification of element 107 by α correlation chains |journal=Zeitschrift für Physik A |volume=300 |issue=1 |pages=107–8 |doi=10.1007/BF01412623 |bibcode = 1981ZPhyA.300..107M |s2cid=118312056 |url=https://www.researchgate.net/publication/238901044 |access-date=24 December 2016 }}</ref>

:{{nuclide|link=yes|bismuth|209}} + {{nuclide|link=yes|chromium|54}} → {{nuclide|link=yes|bohrium|262}} + {{SubatomicParticle|link=yes|neutron}}

This discovery was further substantiated by their detailed measurements of the alpha decay chain of the produced bohrium atoms to previously known isotopes of [[fermium]] and [[californium]]. The [[International Union of Pure and Applied Chemistry|IUPAC]]/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report.<ref name="93TWG">{{Cite journal |doi=10.1351/pac199365081757 |title=Discovery of the transfermium elements. Part II: Introduction to discovery profiles. Part III: Discovery profiles of the transfermium elements |year=1993 |author=Barber, R. C. |journal=Pure and Applied Chemistry |volume=65 |pages=1757 |last2=Greenwood |first2=N. N. |last3=Hrynkiewicz |first3=A. Z. |last4=Jeannin |first4=Y. P. |last5=Lefort |first5=M. |last6=Sakai |first6=M. |last7=Ulehla |first7=I. |last8=Wapstra |first8=A. P. |last9=Wilkinson |first9=D. H. |issue=8|s2cid=195819585 |doi-access=free
}}</ref>