Rutherfordium (104Rf) is asynthetic element and thus has nostable isotopes. Astandard atomic weight cannot be given. The firstisotope to be synthesized was either259Rf in 1966 or257Rf in 1969. There are 17 knownradioisotopes from252Rf to270Rf (three of which,266Rf,268Rf, and270Rf, are unconfirmed) and severalisomers. The longest-lived isotope is267Rf with ahalf-life of 48 minutes, and the longest-lived isomer is263mRf with a half-life of 8 seconds.
^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
^abc# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
Super-heavy elements such as rutherfordium are produced by bombarding lighter elements inparticle accelerators that inducesfusion reactions. Whereas most of the isotopes of rutherfordium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higheratomic numbers.[31]
Depending on the energies involved, the former are separated into "hot" and "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets (actinides), giving rise to compound nuclei at high excitation energy (~40–50 MeV) that may either fission or evaporate several (3 to 5) neutrons.[31] In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to theground state, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products.[32] The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (seecold fusion).[33]
The synthesis of rutherfordium was first attempted in 1964 by the team at Dubna using the hot fusion reaction ofneon-22 projectiles withplutonium-242 targets:
The first study produced evidence for aspontaneous fission with a 0.3 secondhalf-life and another one at 8 seconds. While the former observation was eventually retracted, the latter eventually became associated with the259Rf isotope.[34] In 1966, the Soviet team repeated the experiment using a chemical study of volatile chloride products. They identified a volatile chloride with eka-hafnium properties that decayed fast through spontaneous fission. This gave strong evidence for the formation of RfCl4, and although a half-life was not accurately measured, later evidence suggested that the product was most likely259Rf. The team repeated the experiment several times over the next few years, and in 1971, they revised the spontaneous fission half-life for the isotope at 4.5 seconds.[34]
In 1969, researchers at theUniversity of California led byAlbert Ghiorso, tried to confirm the original results reported at Dubna. In a reaction ofcurium-248 withoxygen-16, they were unable to confirm the result of the Soviet team, but managed to observe the spontaneous fission of260Rf with a very short half-life of 10–30 ms:
In 1970, the American team also studied the same reaction withoxygen-18 and identified261Rf with a half-life of 65 seconds (later refined to 75 seconds).[35][36] Later experiments at theLawrence Berkeley National Laboratory in California also revealed the formation of a short-lived isomer of262Rf (which undergoes spontaneous fission with a half-life of 47 ms),[37] and spontaneous fission activities with long lifetimes tentatively assigned to263Rf.[38]
Diagram of the experimental set-up used in the discovery of isotopes257Rf and259Rf
The reaction ofcalifornium-249 withcarbon-13 was also investigated by the Ghiorso team, which indicated the formation of the short-lived258Rf (which undergoes spontaneous fission in 11 ms):[39]
In trying to confirm these results by usingcarbon-12 instead, they also observed the firstalpha decays from257Rf.[39]
The reaction ofberkelium-249 withnitrogen-14 was first studied in Dubna in 1977, and in 1985, researchers there confirmed the formation of the260Rf isotope which quickly undergoes spontaneous fission in 28 ms:[34]
The team determined a half-life of 2.1 seconds, in contrast to earlier reports of 47 ms and suggested that the two half-lives might be due to different isomeric states of262Rf.[40] Studies on the same reaction by a team at Dubna, lead to the observation in 2000 of alpha decays from261Rf and spontaneous fissions of261mRf.[41]
The hot fusion reaction using a uranium target was first reported at Dubna in 2000:
238 92U +26 12Mg →264−x 104Rf + x n (x = 3, 4, 5, 6).
They observed decays from260Rf and259Rf, and later for259Rf. In 2006, as part of their program on the study of uranium targets in hot fusion reactions, the team at LBNL also observed261Rf.[41][42][43]
The first cold fusion experiments involving element 104 were done in 1974 at Dubna, by using lighttitanium-50 nuclei aimed at lead-208 isotope targets:
The measurement of a spontaneous fission activity was assigned to256Rf,[44] while later studies done at theGesellschaft für Schwerionenforschung Institute (GSI), also measured decay properties for the isotopes257Rf, and255Rf.[45][46]
In 1974 researchers at Dubna investigated the reaction oflead-207 with titanium-50 to produce the isotope255Rf.[47] In a 1994 study at GSI using the lead-206 isotope,255Rf as well as254Rf were detected.253Rf was similarly detected that year when lead-204 was used instead.[46]
Most isotopes with anatomic mass below 262 have also observed as decay products of elements with a higheratomic number, allowing for refinement of their previously measured properties. Heavier isotopes of rutherfordium have only been observed as decay products. For example, a few alpha decay events terminating in267Rf were observed in the decay chain ofdarmstadtium-279 since 2004:
This further underwent spontaneous fission with a half-life of about 1.3 h.[48][49][50]
Investigations on the synthesis of thedubnium-263 isotope in 1999 at theUniversity of Bern revealed events consistent withelectron capture to form263Rf. A rutherfordium fraction was separated, and several spontaneous fission events with long half-lives of about 15 minutes were observed, as well as alpha decays with half-lives of about 10 minutes.[38] Reports on the decay chain offlerovium-285 in 2010 showed five sequential alpha decays that terminate in265Rf, which further undergoes spontaneous fission with a half-life of 152 seconds.[51]
Some experimental evidence was obtained in 2004 for a heavier isotope,268Rf, in the decay chain of an isotope ofmoscovium:
However, the last step in this chain was uncertain. After observing the five alpha decay events that generatedubnium-268, spontaneous fission events were observed with a long half-life. It is unclear whether these events were due to direct spontaneous fission of268Db, or268Db producedelectron capture events with long half-lives to generate268Rf. If the latter is produced and decays with a short half-life, the two possibilities cannot be distinguished.[52] Given that theelectron capture of268Db cannot be detected, these spontaneous fission events may be due to268Rf, in which case the half-life of this isotope cannot be extracted.[28][53] A similar mechanism is proposed for the formation of the even heavier isotope270Rf as a short-lived daughter of270Db (in the decay chain of294Ts, first synthesized in 2010) which then undergoes spontaneous fission:[29]
According to a 2007 report on the synthesis ofnihonium, the isotope282Nh was twice observed to undergo a similar decay to form266Db. In one case this underwent spontaneous fission with a half-life of 22 minutes. Given that the electron capture of266Db cannot be detected, these spontaneous fission events may be due to266Rf, in which case the half-life of this isotope cannot be extracted. In the other case, no spontaneous fission event was observed; it could have been missed, or266Db might have undergone two more alpha decays to long-lived258Md, with a half-life (51.5 d) longer than the total time of the experiment.[26][54]
Currently suggested decay level scheme for257Rfg,m from the studies reported in 2007 by Hessbergeret al. at GSI[63]
Several early studies on the synthesis of263Rf have indicated that this nuclide decays primarily by spontaneous fission with a half-life of 10–20 minutes. More recently, a study ofhassium isotopes allowed the synthesis of atoms of263Rf decaying with a shorter half-life of 8 seconds. These two different decay modes must be associated with two isomeric states, but specific assignments are difficult due to the low number of observed events.[38]
During research on the synthesis of rutherfordium isotopes utilizing the244Pu(22Ne,5n)261Rf reaction, the product was found to undergo exclusive 8.28 MeV alpha decay with a half-life of 78 seconds. Later studies atGSI on the synthesis ofcopernicium and hassium isotopes produced conflicting data, as261Rf produced in the decay chain was found to undergo 8.52 MeV alpha decay with a half-life of 4 seconds. Later results indicated a predominant fission branch. These contradictions led to some doubt on the discovery of copernicium. The first isomer is currently denoted261aRf (or simply261Rf) whilst the second is denoted261bRf (or261mRf). However, it is thought that the first nucleus belongs to a high-spin ground state and the latter to a low-spin metastable state.[56]The discovery and confirmation of261bRf provided proof for the discovery of copernicium in 1996.[64]
A detailed spectroscopic study of the production of257Rf nuclei using the reaction208Pb(50Ti,n)257Rf allowed the identification of an isomeric level in257Rf. The work confirmed that257gRf has a complex spectrum with 15 alpha lines. A level structure diagram was calculated for both isomers.[65] Similar isomers were reported for256Rf also.[66]
The table below provides cross-sections and excitation energies for cold fusion reactions producing rutherfordium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.
The table below provides cross-sections and excitation energies for hot fusion reactions producing rutherfordium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.
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