Definitions

# rutherfordium

[ruhth-er-fawr-dee-uhm, -fohr-]
rutherfordium, artificially produced radioactive chemical element; symbol Rf; at. no. 104; mass number of most stable isotope 261; m.p., b.p., and sp. gr. unknown; valence +4. It is the first transuranium element beyond the actinide series, thus being the first of the transactinide elements. Situated in Group 4 of the periodic table, it has properties similar to those of hafnium and zirconium.

In 1964 a Soviet team led by G. N. Flerov at the Joint Institute for Nuclear Research at Dubna announced the discovery of element 104. They claimed to have isolated an isotope with mass number 260 and a half-life of 0.3 sec by bombarding plutonium-242 atoms with neon-22 ions. Subsequently, they suggested that element 104 be named kurchatovium (symbol Ku) to honor Igor Kurchatov, a Soviet pioneer in nuclear physics. In 1969, an American research team led by A. Ghiorso at the Lawrence Berkeley National Laboratory announced that, while they had been unable to confirm the Dubna group's results, they had identified at least two isotopes of element 104 different from the one identified by the Soviet scientists. They bombarded californium-249 atoms with carbon-12 and carbon-13 ions to creates isotopes with mass numbers 257 (half-life of 4.8 sec), 259 (half-life of 3 sec), and possibly 258 (half-life of 13 msec). Disputing the Soviet claim of discovery, the Americans suggested the name rutherfordium to honor the British physicist Lord Ernest Rutherford. An international committee set up to resolve such disputes decided in 1992 that the Berkeley and Dubna laboratories should share credit for the discovery. The syntheses of at least 10 isotopes of rutherfordium, with half-lives ranging from 0.5 msec (Rf-254) to 65 sec (Rf-261), have been confirmed.

In 1994 a committee of the International Union of Pure and Applied Chemistry (IUPAC), convened to resolve naming disputes for the transactinide elements, recommended that element 104 be named dubnium in recognition of the work done at the Dubna laboratory. The committee also recommended that element 106, which had been called seaborgium by the American team that discovered it, be called rutherfordium. In 1997, however, the name rutherfordium for element 104 was recognized internationally.

Rutherfordium is a chemical element in the periodic table that has 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).

## Official discovery

Element 104 was reportedly first detected in 1966 at the Joint Institute of Nuclear Research at Dubna (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:

$, ^\left\{242\right\}_\left\{94\right\}mathrm\left\{Pu\right\} + , ^\left\{22\right\}_\left\{10\right\}mathrm\left\{Ne\right\} to , ^\left\{264-x\right\}_\left\{104\right\}mathrm\left\{Rf\right\}to ,^\left\{264-x\right\}_\left\{104\right\}mathrm\left\{RfCl\right\}_\left\{4\right\}$

The Russian scientists proposed the name Kurchatovium for the new element.

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

$,^\left\{249\right\}_\left\{98\right\}mathrm\left\{Cf\right\} + ,^\left\{12\right\}_\left\{6\right\}mathrm\left\{C\right\}to ,^\left\{257\right\}_\left\{104\right\}mathrm\left\{Rf\right\} + 4 ,^\left\{1\right\}_\left\{0\right\}mathrm\left\{n\right\}$

The American scientists proposed the name Rutherfordium for the new element.

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.

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.

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. 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.

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 (pronounced /ˌjuːnɪlˈkwɒdiəm/ or /ˌʌnɪlˈkwɒdiəm/, 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.

## Electronic structure

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

Bohr model: 2, 8, 18, 32, 32, 10, 2

Quantum mechanical model: 1s22s22p63s23p64s23d10 4p65s24d105p66s24f145d10 6p67s25f146d2

## Extrapolated chemical properties of eka-hafnium/dvi-zirconium

### 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. 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 RfCl62- and RfBr62-. For the fluoride complexes, zirconium and hafnium tend to form hepta- and octa- complexes. Thus, for the larger rutherfordium ion, the complexes RfF62-, RfF73- and RfF84- are possible.

## Experimental chemistry

### Gas phase chemistry

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).

### Aqueous phase chemistry

Rutherfordium is expected to have the electron configuration [Rf]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 tean 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.

$,^\left\{261m\right\}mathrm\left\{Rf\right\} + 6mathrm\left\{Cl\right\}^\left\{-\right\}, to \left[,^\left\{261m\right\}mathrm\left\{RfCl\right\}_\left\{6\right\}\right]^\left\{2-\right\}$

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:

$,^\left\{261m\right\}mathrm\left\{Rf\right\} + 6mathrm\left\{F\right\}^\left\{-\right\}, to \left[,^\left\{261m\right\}mathrm\left\{RfF\right\}_\left\{6\right\}\right]^\left\{2-\right\}$

### Summary of compounds and complex ions

Formula Names(s)
RfCl4 rutherfordium tetrachloride ; rutherfordium(IV) chloride
RfBr4 rutherfordium tetrabromide ; rutherfordium(IV) bromide
RfOCl2 rutherfordium oxychloride ; rutherfordium(IV) dichloride oxide ; rutherfordyl(IV) chloride
[RfCl6]2- hexachlororutherfordate(VI)
[RfF6]2- hexafluororutherfordate(VI)
K2[RfCl6] potassium hexachlororutherfordate(VI)

## History of synthesis of isotopes by 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. 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.

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. 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. In 2004, the GSI began their spectroscopic studies of the 257Rf isotope.

### 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. The isomeric level proposed in 1994 was not found. In 2006, the spectroscopy was continued and the decay scheme was confirmed and improved.

### 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.

### 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.

### 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.

### 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.

## History of synthesis of isotopes by 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. 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.

### 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 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.

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. 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 spontaneous fission (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. 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.

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. A chemistry experiment in the same year reaffirmed the formation of a 0.3 SF activity for an eka-hafnium product. 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. 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. 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.

### 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.

### 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.

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. 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.

### 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.

### 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.

### 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.

### 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. In 1973, Bemis and his team at Oak Ridge confirmed the discovery by measuring coincident X-rays from the daughter 253102.

## Synthesis of isotopes as decay products

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

Evaporation Residue Observed Rf isotope
288115 268Rf (possible EC of 268Db)
291116 , 287114 , 283112 267Rf
282113 266Rf (EC of 266Db)
271Hs 263gRf
263Db 263mRf (EC of 263Db)
266Sg (possibly 266mSg) 262Rf (possibly 262mRf)
277112 , 273Ds , 269Hs , 265Sg 261mRf , 261Rf
271Ds , 267Hs , 263Sg 259Rf
269Ds , 265Hs , 261Sg 257Rf
264Hs , 260Sg 256Rf
259Sg 255Rf

## Chronology of isotope discovery

Isotope Year discovered discovery reaction
253Rf 1994 204Pb(50Ti,n)
254Rf 1994 206Pb(50Ti,2n)
255Rf 1974? 1985 207Pb(50Ti,2n)
256Rf 1974? 1985 208Pb(50Ti,2n)
257Rfg,m 1969 249Cf(12C,4n)
258Rf 1969 249Cf(13C,4n)
259Rf 1969 249Cf(13C,3n)
260Rf 1969 248Cm(16O,4n)
261Rfm 1970 248Cm(18O,5n)
261Rfg 1996 208Pb(70Zn,n)
262Rf 1996 244Pu(22Ne,4n)
263Rfm 1990? 248Cm(18O,3n)
263Rfg 2004 248Cm(26Mg,3n)
264Rf unknown
265Rf unknown
266Rf 2006? 237Np(48Ca,3n)
267Rf 2003/2004 238U(48Ca,3n)
268Rf 2003? 243Am(48Ca,3n)

## Isomerism in rutherfordium nuclides

### 263Rf

Initial work on the synthesis of rutherfordium isotopes by hot fusion pathways focused 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. It is reasonable to tentatively assign the long life to a meta-stable state, namely 263mRf, and the shorter life to the ground state, namely 263gRf. Further studies are required to allow a definite assignment.

### 261Rf

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. However, it is now understood that the first nucleus belongs to an isomeric meta-stable state, namely 261mRf and the latter to the ground state isomer, namely 261gRf. The discovery and confirmation of 261gRf 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.

## Unconfirmed 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.

### 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.

## Retracted isotopes

### 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.

### 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.

## 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.

Projectile Target CN 1n 2n 3n
50Ti 208Pb 258Rf 38.0 nb , 17.0 MeV 12.3 nb , 21.5 MeV 660 pb , 29.0 MeV
50Ti 207Pb 257Rf 4.8 nb
50Ti 206Pb 256Rf 800 pb , 21.5 MeV 2.4 nb , 21.5 MeV
50Ti 204Pb 254Rf 190 pb , 15.6 MeV
48Ti 208Pb 256Rf 380 pb , 17.0 MeV

### 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.

Projectile Target CN 3n 4n 5n
26Mg 238U 264Rf 240 pb 1.1 nb
22Ne 244Pu 266Rf + 4.0 nb
18O 248Cm 266Rf + 13.0 nb

## 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:

$,^\left\{238\right\}_\left\{92\right\}mathrm\left\{U\right\} + ,^\left\{24\right\}_\left\{12\right\}mathrm\left\{Mg\right\}to ,^\left\{259\right\}_\left\{104\right\}mathrm\left\{Rf\right\} + 3 ,^\left\{1\right\}_\left\{0\right\}mathrm\left\{n\right\}$