rutherfordium

lawrencium ← rutherfordium → dubnium Hf ↑ Rf ↓ (Upq) 104Rf Periodic table
Appearance
unknown
General properties
Name, symbol, number	rutherfordium, Rf, 104
Element category	transition metal
Group, period, block	4, 7, d
Standard atomic weight	[267] g·mol−1
Electron configuration	[Rn] 5f14 6d2 7s2 (predicted)
Electrons per shell	2, 8, 18, 32, 32, 10, 2 (predicted) (Image)
Physical properties
Phase	Unknown
Atomic properties
Oxidation states	4
Miscellanea
CAS registry number	53850-36-5
Most stable isotopes
Main article: Isotopes of rutherfordium
iso NA half-life DM DE (MeV) DP 267Rf syn 1.3 h SF 263aRf? syn ~15 m SF α 7.90 ? 263bRf syn 8 s SF 262Rf syn 210 ms SF 261aRf syn 1.1 m α 8.28 257No 261bRf syn 3.0 s 91% SF 9% α 8.51 257No 260Rf syn 22.2 ms SF 259Rf syn 2.5 s ~85% α 8.87,8.77 255No ~15% EC (SF?) 259Lr 258Rf syn 14.7 ms 31% α 9.05,8.96 254No 69% SF 257mRf syn 4.0 s α 9.02,8.97 253No 257gRf syn 3.5 s 89% α 8.90,8.78,8.52,8.28 253No 11% ε 257Lr 256gRf syn 6.2 ms 99.7% SF 0.3% α 8.79 252No 256m1Rf syn 25 µs γ 256gRf 256m2Rf syn 17 µs γ 256m1Rf 256m3Rf syn 27 µs γ 256m2Rf 255Rf syn 1.8 s ~50% α 8.81,8.77,8.74,8.71 251No ~50% SF 254Rf syn 22 µs SF 253Rf syn 48 µs SF
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Rutherfordium (pronounced /ˌrʌðərˈfɔrdiəm/ RUDH-ər-FOR-dee-əm) is a chemical element with the symbol Rf and atomic number 104. This is a radioactive synthetic element whose most stable known isotope is ²⁶⁷Rf with a half-life of approximately 1.3 hours. Chemistry experiments have confirmed that rutherfordium behaves as the heavier homologue to hafnium in group 4 (see below).

History

Discovery

Element 104 was reportedly first detected in 1966 at the Joint Institute of Nuclear Research at Dubna (then in U.S.S.R.). Researchers there bombarded ²⁴²Pu with accelerated ²²Ne ions and separated the reaction products by gradient thermochromatography after conversion to chlorides by interaction with ZrCl₄. The team identified a spontaneous fission activity contained within a volatile chloride portraying eka-hafnium properties. Although a half-life was not accurately determined, later calculations indicated that the product was most likely ²⁵⁹Rf:^[1]

24294Pu + 2210Ne → 264-x104Rf → 264-x104RfCl₄

In 1969 researchers at the University of California, Berkeley conclusively synthesized the element by bombarding a californium-249 target with carbon-12 ions and measured the alpha decay of ²⁵⁷104, correlated with the daughter decay of ²⁵³102. ^[2]

24998Cf + 126C → 257104Rf + 4 n

The American synthesis was independently confirmed in 1973 and secured the identification of element 104 as the parent by the observation of K X-rays in the elemental signature of the daughter ²⁵³No. ^[3]

Naming controversy

	Rutherfordium Common English pronunciation of rutherfordium
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The Russian scientists proposed the name Kurchatovium for the new element. The American scientists proposed the name Rutherfordium for the new element.

In 1992 the IUPAC/IUPAP Transfermium Working Group (TWG) assessed the claims of discovery and concluded that both teams provided contemporaneous evidence to the synthesis of element 104 and that credit should be shared between the two groups.^[1]

The American group wrote a scathing response to the findings of the TWG, stating that they had given too much emphasis on the results from the Dubna group. In particular they pointed out that the Russian group had altered the details of their claims several times over a period of 20 years, a fact which the Russian team do not deny. They also stressed that the TWG had given too much credence to the chemistry experiments performed by the Russians and accused the TWG of not having appropriately qualified personnel on the committee. The TWG responded by saying that this was not the case and having assessed each point raised by the American group said that they found no reason to alter their conclusion regarding priority of discovery. ^[4] It should be said that IUPAC finally used the name suggested by the American team (rutherfordium) which may in some way reflect a change of opinion.^[5]

As a consequence of the initial competing claims of discovery, an element naming controversy arose. Since the Soviets claimed to have first detected the new element they suggested the name kurchatovium, Ku, in honor of Igor Vasilevich Kurchatov (1903-1960), former head of Soviet nuclear research. This name had been used in books of the Soviet Bloc as the official name of the element. The Americans, however, proposed rutherfordium (Rf) for the new element to honor Ernest Rutherford, who is known as the "father" of nuclear physics. The International Union of Pure and Applied Chemistry (IUPAC) adopted unnilquadium , Unq, as a temporary, systematic element name, derived from the Latin names for digits 1, 0, and 4. In 1994, IUPAC suggested the name dubnium to be used since rutherfordium was suggested for element 106 and IUPAC felt that the Dubna team should be rightly recognised for their contributions. However, there was still a dispute over the names of elements 104-107. However in 1997 the teams involved resolved the dispute and adopted the current name rutherfordium.^[5]

Future experiments

The team at GSI are planning to perform first detailed spectroscopic studies on the isotope ²⁵⁹Rf. It will be produced in the new reaction:

23892U + 2412Mg → 259104Rf + 3 n

Isotopes and nuclear properties

Nucleosynthesis

Cold fusion

²⁰⁸Pb(⁵⁰Ti,xn)^258-xRf (x=1,2,3)

This reaction was first studied in 1974 by the team at Dubna. They measured a spontaneous fission activity assigned to ²⁵⁶Rf. ^[6] The reaction was further studied in 1985 by the GSI team who measured the decay properties of the isotopes ²⁵⁷Rf and ²⁵⁶Rf. The team were able to determine some initial spectroscopic properties of ²⁵⁷Rf and found that the alpha decay pattern was very complicated. ^[7]

After an upgrade of their facilities, they repeated the reaction in 1994 with much higher sensitivity and detected some 1100 atoms of ²⁵⁷Rf and 1900 atoms of ²⁵⁶Rf along with ²⁵⁵Rf in the measurement of the 1n,2n and 3n excitation functions. The large amount of decay data for ²⁵⁷Rf allowed the detection of an isomeric level and the construction of a partial decay level structure which confirmed the very complicated alpha decay pattern. They also found evidence for an isomeric level in ²⁵⁵Rf. ^[8] The GSI team continued in 2001 with the measurement of the 3n excitation function. In 2002, scientists at the Argonne University in Illinois began their first studies of translawrencium elements with the synthesis and alpha-gamma spectroscopy of ²⁵⁷Rf.^[9] In 2004, the GSI began their spectroscopic studies of the ²⁵⁷Rf isotope. In 2007, the LBNL studied the 2n product, ²⁵⁶Rf, in a search for K-isomers and discovered three such isomers.^[10]

Currently suggested decay level scheme for ²⁵⁵Rf from the study reported in 2007 by Hessberger et al. at GSI^{[citation needed]}

²⁰⁷Pb(⁵⁰Ti,xn)^257-xRf (x=2)

This reaction was first studied in 1974 by the team at Dubna. They measured a spontaneous fission activity assigned to ²⁵⁵Rf. The reaction was further studied in 1985 by the GSI team who measured the decay properties of the isotope ²⁵⁵Rf. A further spectroscopic study was reported in 2000 which led to a first decay level scheme for the isotope.^[11] The isomeric level proposed in 1994 was not found. In 2006, the spectroscopy was continued and the decay scheme was confirmed and improved. ^[12]

²⁰⁶Pb(⁵⁰Ti,xn)^256-xRf (x=1,2)

The team at GSI first studied this reaction in 1994 in an effort to study neutron deficient isotopes of rutherfordium. They were able to detect ²⁵⁵Rf and 144 atoms of the new isotope ²⁵⁴Rf, which decayed by spontaneous fission.^[8]

²⁰⁴Pb(⁵⁰Ti,xn)^254-xRf (x=1)

The team at GSI first studied this reaction in 1994 in an effort to study neutron deficient isotopes of rutherfordium. They were able to detect 14 atoms of the new isotope ²⁵³Rf, which decayed by spontaneous fission.^[8]

²⁰⁸Pb(⁴⁸Ti,xn)^256-xRf (x=1)

In 2006, as part of a program looking at the effect of isospin on the mechanism of cold fusion, the team at LBNL studied this reaction. They measured the 1n excitation function and determined that the change of a Ti-50 projectile to a Ti-48 one significantly reduced the yield, in agreement with predictions. ^[13]

¹²⁴Sn(¹³⁶Xe,xn)^260-xRf

In an important study, in May 2004, the team at GSI attempted the symmetric synthesis of rutherfordium by attempting to fuse two fission fragments. Theory suggests that there may be an enhancement of the yield. No product atoms were detected and a limit of 1000 pb was calculated.

Hot fusion

²³⁸U(²⁶Mg,xn)^264-xRf (x=3,4,5,6)

The hot fusion reaction using a uranium target was first reported in 2000 by Yuri Lazarev and the team at the Flerov Laboratory of Nuclear Reactions (FLNR). They were able to observe decays from ²⁶⁰Rf and ²⁵⁹Rf in the 4n and 5n channels. ^[14] They measured yields of 240 pb in the 4n channel and 1.1 nb in the 5n channel. In 2006, as part of their program on the study of uranium targets in hot fusion reactions, the team at LBNL measured the 4n,5n and 6n excitation functions for this reaction and observed ²⁶¹Rf in the 3n exit channel.^[15][16]

²⁴⁴Pu(²²Ne,xn)^266-xRf (x=4,5)

This reaction was reported in 1996 at LBNL in an attempt to study the fission characteristics of ²⁶²Rf. The team were able to detect the spontaneous fission (SF) of ²⁶²Rf and determine its half-life as 2.1 s, in contrast to earlier reports of a 47 ms activity. It was suggested that the two half-lives may be related to different isomeric states. ^[17] The reaction was further studied in 2000 by Yuri Lazarev and the team at Dubna. They were able to observe 69 alpha decays from ²⁶¹Rf and spontaneous fission of ²⁶²Rf. ^[18] Later work on hassium has allowed a reassignment of the 5n product to ^261mRf.

²⁴²Pu(²²Ne,xn)^264-xRf (x=3,4?,5?)

The synthesis of element 104 was first attempted in 1964 by the team at Dubna using this reaction. The first study produced evidence for a 0.3 s SF activity tentatively assigned to ²⁶⁰104 or ²⁵⁹104 and an unidentified 8 s SF activity. The former activity was later retracted and the latter activity associated with the now-known ²⁵⁹104.^[1] In 1966, in their discovery experiment, the team repeated the reaction using a chemical study of volatile chloride products. The group was able to identify a volatile chloride decaying by short spontaneous fission with eka-hafnium properties. This gave strong evidence for the formation of [104]Cl₄ and the team suggested the name kurchatovium. Although a half-life was not accurately measured, later evidence suggested that the product was most likely ²⁵⁹104. ^[1] In 1968, the team searched for alpha decay from ²⁶⁰104 but were unable to detect such activity. In 1970, the team repeated the reaction once again and confirmed the ~0.2 s SF activity. They also repeated the chemistry experiment and obtained identical results to their 1966 experiment and calculated a likely half-life of ~0.5 seconds for the SF activity. In 1971, the reaction was repeated again and 0.1 s and 4.5 s SF activities were found. The 4.5 s activity was correctly assigned to ²⁵⁹104.^[1] A chemistry experiment in the same year reaffirmed the formation of a 0.3 SF activity for an eka-hafnium product.^[1] Later, the 0.1-0.3 s SF activity was retracted as belonging to a kurchatovium isotope but the observation of eka-hafnium reactivity remained and was the basis of their successful claim to discovery.^[1] The reaction was further studied in 2000 by Yuri Lazarev at Dubna. They were able to observe ²⁶¹Rf in the 3n channel, later reassigned to ^261mRf.

²⁴²Pu(²⁰Ne,xn)^262-xRf

This reaction was first studied in 1964 to assist in the assignments using the analogous reaction with a Ne-22 beam. The Dubna team were unable to detect any 0.3 s spontaneous fission activities.^[1] The reaction was later studied in 2003 at the Paul Scherrer Institute (PSI) in Bern, Switzerland. They detected some spontaneous fission activities but were unable to confirm the formation of ²⁵⁹Rf.^[19]

²⁴⁸Cm(²²Ne,αxn)^266-xRf (x=3?)

This reaction was studied in 1999 at the University of Bern, Switzerland in order to search for the new isotope ²⁶³Rf. A rutherfordium fraction was separated and several SF events with long lifetimes and alpha decays with energy 7.8 MeV and 7.9 MeV were observed. A second experiment using a study of the fluoride of rutherfordium products also produced 7.9 MeV alpha decays.^[20]

²⁴⁸Cm(¹⁸O,xn)^266-xRf (x=3?,5)

This reaction was first studied in 1970 by Albert Ghiorso at the Lawrence Berkeley National Laboratory (LBNL). The team identified ²⁶¹Rf in the 5n channel using the method of correlation of genetic parent-daughter decays. A half-life of 65 s was determined. ^[21] A repeat later that year using cation exchange chromatography indicated that the product did not form a +2 or +3 cation and behaved as eka-hafnium. A study of the properties of rutherfordium isotopes was performed in 1981 at the LBNL. In a series of reactions, a 1.5 s SF activity was identified and assigned to a fermium descendant although later evidence indicates a possible assignment to ²⁶²Rf. In contrast, in a subsequent review of isotope properties by Somerville et al. at LBNL in 1985, a 47 ms SF activity was assigned to ²⁶²Rf. This assignment has not been verified. ^[22] The reaction was further studied in 1991 by Czerwinski et al. at the LBNL. In this experiment, spontaneous fission activities with long lifetimes were observed in rutherfordium fractions and tentatively assigned to ²⁶³Rf. In 1996, chemical studies on the chloride of rutherfordium was published by the LBNL. In this experiment, the half-life was improved to 78 s. A repeat of the experiment in 2000 assessing the volatility of the bromide further refined the half-life to 75 s.

²⁴⁸Cm(¹⁶O,xn)^264-xRf (x=4)

This reaction was studied in 1969 by Albert Ghiorso at the University of California. The aim was to detect the 0.1-0.3 s SF activity reported at Dubna, assigned to ²⁶⁰104. They were unable to do so, only observing a 10-30 ms SF activity, correctly assigned to ²⁶⁰104. The failure to observe the 0.3 s SF activity identified by Dubna gave the Americans the incentive to name this element rutherfordium.^[1]

²⁴⁶Cm(¹⁸O,xn)^264-xRf

In an attempt to unravel the properties of spontaneous fission activities in the formation of rutherfordium isotopes, this reaction was performed in 1976 by the FLNR. They observed an 80 ms SF activity. Subsequent work led to the complete retraction of the 0.3s - 0.1s - 80 ms SF activities observed by the Dubna team and associated with background signals.^[1]

²⁴⁹Bk(¹⁵N,xn)^264-xRf (x=4)

This reaction was studied in 1977 by the team in Dubna. They were able to confirm the detection of a 76 ms SF activity. The assignment to rutherfordium isotopes was later retracted. The LBNL re-studied the reaction in 1980 and in 1981 they reported that they were unable to confirm the ~80 ms SF activity. The Dubna team were able to measure a 28 ms SF activity in 1985 and assigned the isotope correctly to ²⁶⁰104.^[1]

²⁴⁹Cf(¹³C,xn)^262-xRf (x=4)

This use of californium-249 as a target was first studied by Albert Ghiorso and the team at the University of California in 1969. They were able to observe a 11 ms SF activity which they correctly assigned to ²⁵⁸104.^[2]

Currently suggested decay level scheme for ²⁵⁷Rf^g,m from the study performed in 2004 by Hessberger et al. at GSI^{[citation needed]}

²⁴⁹Cf(¹²C,xn)^261-xRf (x=3,4)

In their 1969 discovery experiments, the team at University of California also used a C-12 beam to irradiate a Cf-249 target. They were able to confirm the 11 ms SF activity found with a C-13 beam and again correctly assigned to ²⁵⁸104. The actual discovery experiment was the observation of alpha decays genetically linked to ²⁵³102 and therefore positively identified as ²⁵⁷104.^[2] In 1973, Bemis and his team at Oak Ridge confirmed the discovery by measuring coincident X-rays from the daughter ²⁵³102.^[3]

As decay product

Isotopes of rutherfordium have also been identified in the decay of heavier elements. Observations to date are summarised in the table below:

Chronology of Isotope Discovery

Unconfirmed and retracted isotopes

²⁶⁸Rf

In the synthesis of ununpentium, the isotope ²⁸⁸115 has been observed to decay to ²⁶⁸Db which undergoes spontaneous fission with a half life of 29 hours. Given that the electron capture of ²⁶⁸Db cannot be detected, these SF events may in fact be due to the SF of ²⁶⁸Rf, in which case the half-life of this isotope cannot be extracted. ^[26]

²⁶⁶Rf

In the synthesis of ununtrium, the isotope ²⁸²113 has been observed to decay to ²⁶⁶Db which undergoes spontaneous fission with a half life of 22 minutes. Given that the electron capture of ²⁶⁶Db cannot be detected, these SF events may in fact be due to the SF of ²⁶⁶Rf, in which case the half-life of this isotope cannot be extracted. ^[25]

²⁶⁵Rf

In 1999, American scientists at the University of California, Berkeley, announced that they has succeeded in synthesizing three atoms of ²⁹³118. These parent nuclei successively emitted seven alpha particles to form ²⁶⁵Rf nuclei. Their claim was retracted in 2001. As such, this rutherfordium isotope is unconfirmed or unknown.^[27]

^255mRf

A detailed spectroscopic study of the production of ²⁵⁵Rf nuclei using the reaction ²⁰⁶Pb(⁵⁰Ti,n)²⁵⁵Rf allowed the tentative identification of an isomeric level in ²⁵⁵Rf. A more detailed study later confirmed that this was not the case.

Nuclear isomerism

^263a,bRf

Initial work on the synthesis of rutherfordium isotopes by hot fusion pathways focussed on the synthesis of ²⁶³Rf. Several studies have indicated that this nuclide decays primarily by spontaneous fission with a long half-life of 10–20 minutes. Alpha particles with energy 7.8-7.9 MeV have also been associated with this nucleus. More recently, a study of hassium isotopes allowed the synthesis of an atom of ²⁶³Rf decaying by spontaneous fission with a short half-life of 8 seconds. These two different decay modes must be associated with two isomeric states. Specific assignments are difficult due to the low number of observed events. Further studies are required to allow definite assignments.

^261a,bRf

Early research on the synthesis of rutherfordium isotopes utilised the ²⁴⁴Pu(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 by the GSI team on the synthesis of element 112 and hassium isotopes produced conflicting data. In this case, ²⁶¹Rf was found to undergo 8.52 MeV alpha decay with a short half-life of 4 seconds. Later results indicated a predominant fission branch. These contradictions led to some doubt on the discovery of element 112. The first isomer is currently denoted ^261aRf whilst the second is denoted ^261bRf. However, it is thought that the first nucleus belongs to a high-spin ground state and the latter to a low-spin metastable state. ^[28] The discovery and confirmation of ^261bRf provided proof for the discovery of ununbium in 1996.

²⁵⁷Rf

A detailed spectroscopic study of the production of ²⁵⁷Rf nuclei using the reaction ²⁰⁸Pb(⁵⁰Ti,n)²⁵⁷Rf allowed the identification of an isomeric level in ²⁵⁷Rf. The work confirmed that ^257gRf has a very complicated spectrum with as many as 15 alpha lines. A level structure diagram was calculated for both isomers.

Chemical yields of isotopes

Cold fusion

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.

Hot fusion

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.

Chemical properties

Electronic structure

Rutherfordium is element 104 in the Periodic Table. The two forms of the projected electronic structure are:

Extrapolated properties

Oxidation states

Element 104 is projected to be the first member of the 6d series of transition metals and the heaviest member of group IV in the Periodic Table, below titanium, zirconium and hafnium. It may also be named eka-hafnium or dvi-zirconium and some of its properties may be extrapolated from the group trends of elements. The IV oxidation state is the only stable state for the latter two elements and therefore rutherfordium should also portray a stable +4 state.

Chemistry

In an analogous manner to zirconium and hafnium, rutherfordium is projected to form a very stable, high melting point oxide, RfO₂. It should also react with halogens to form tetrahalides, RfX₄, which hydrolyse on contact with water to form oxyhalides RfOX₂. The tetrahalides should be volatile solids existing as monomeric tetrahedral molecules in the vapour phase.

In the aqueous phase, the Rf⁴⁺ ion should hydrolyse less than titanium(IV) and to a similar extent to zirconium and hafnium, thus leading to the rutherfordyl oxyion, RfO₂²⁺. Treatment of the halides with halide ions promotes the formation of complex ions. The use of chloride and bromide ion should form the hexahalide complexes RfCl₆^2- and RfBr₆^2-. For the fluoride complexes, zirconium and hafnium tend to form hepta- and octa- complexes. Thus, for the larger rutherfordium ion, the complexes RfF₆^2-, RfF₇^3- and RfF₈^4- are possible.

Experimental chemistry

Gas phase

The tetrahedral molecule RfCl₄

Early work on the study of the chemistry of rutherfordium focused on gas thermochromatography and measurement of relative deposition temperature adsorption curves. The initial work was carried out at Dubna in an attempt to reaffirm their discovery of the element. Recent work is more reliable regarding the identification of the parent rutherfordium radioisotopes. The isotope ^261mRf has been used for these studies. The experiments relied on the expectation that rutherfordium would begin the new 6d series of elements and should therefore from a volatile tetrachloride due to the tetrahedral nature of the molecule.

As series of experiments have confirmed that rutherfordium behaves as a typical member of group 4 forming a tetravalent chloride (RfCl₄) and bromide (RfBr₄) as well as an oxychloride (RfOCl₂).^[29]

Aqueous phase

Rutherfordium is expected to have the electron configuration [Rn]5f¹⁴ 6d² 7s² and therefore behave as the heavier homologue of hafnium in group 4 of the Periodic Table. It should therefore readily form a hydrated Rf⁴⁺ ion in strong acid solution and should readily form complexes in hydrochloric acid, hydrobromic or hydrofluoric acid solutions.

The most conclusive aqueous chemistry studies of rutherfordium have been performed by the Japanese team at JAERI using the radioisotope ^261mRf. Extraction experiments from hydrochloric acid solutions using isotopes of rutherfordium, hafnium, zirconium and thorium have proved a non-actinide behaviour. A comparison with its lighter homologues placed rutherfordium firmly in group 4 and indicated the formation of a hexachlororutherfordate complex in chloride solutions, in a manner similar to hafnium and zirconium. ^[30]

^261mRf⁴⁺ + 6 Cl^- → [^261mRfCl₆]^2-

Very similar results were observed in hydrofluoric acid solutions. Differences in the extraction curves were interpreted as a weaker affinity for fluoride ion and the formation of the hexafluororutherfordate ion, whereas hafnium and zirconium ions complex seven or eight fluoride ions at the concentrations used:

^261mRf⁴⁺ + 6 F^- → [^261mRfF₆]^2-

References

External links

• WebElements.com - Rutherfordium