Rutherfordium-261

Properties and data of the isotope ²⁶¹Rf.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Rutherfordium-261 is a radioisotope of the chemical element rutherfordium, which has 157 neutrons in its atomic nucleus in addition to the element-specific 104 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 261. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²⁶¹Rf is exclusively for academic purposes.

The first observation of ²⁶¹Rf was reported in 1970: A curium-248 target was bombarded with a 90–100 MeV beam of oxygen-18 ions, producing rutherfordium-261 in a fusion-evaporation reaction [1].

Two long-lived states of the isotope rutherfordium-261 are known, with half-lives of about 2.1 s and 74 s, both produced by the same nuclear reaction:

²⁴⁸Cm(¹⁸O,5n)²⁶¹Rf.

Both activities have been unambiguously identified by characteristic α-decays and correlations with the daughter nuclide ²⁵⁷No. The assignment of these two states to the ground and isomeric states, respectively, is not yet definitively established. Older studies assigned the 68s state to the ground state, while current evaluations (e.g., NUBASE 2020) list the 2s state as the ground state. This decision is based on systematic trends in the spins and excitation energies of neighboring Rf and No isotopes, but not on a direct experimental determination of the energy level order.

The experimental assignment of the ground and isomeric states for rutherfordium-261 is therefore not definitively established.

See also: List of individual Rutherfordium isotopes (and general data sources).

General data

Name of the isotope:Rutherfordium-261; Rf-261Symbol:²⁶¹Rf or 261104RfMass number A:261 (= number of nucleons)Atomic number Z:104 (= number of protons)Neutrons N:157Isotopic mass:261.108770(70) u (atomic weight of Rutherfordium-261)Nuclide mass:261.0517266 u (calculated nuclear mass without electrons)Mass excess:101.3186 MeVMass defect:2.06542514 u (per nucleus)Nuclear binding energy:1923.93112536 MeV (per nucleus)
7.37138362 MeV (average binding energy per nucleon)Separation energy:S_N = 5.901(211) MeV (first neutron)
S_P = 4.247(141) MeV (first proton)Half-life:2.1(2) sDecay constant λ:0.33007008598093 s^-1Specific activity α:7.615818204707 × 10⁺²⁰ Bq g^-1
20583292445.155 Ci g^-1Spin and parity:
(nuclear angular momentum)(3/2+)Year of discovery:1970

Radioactive Decay

Half-life T_½ = 2.1(2) s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁵⁷No	18(4) %	8.646(65) MeV
SZ	div	82(4) %

Starting nuclides and radioactive decay of rutherfordium-261

Parent Nuclides

Direct parent isotope is: ²⁶⁵Sg.

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^261mRf	234+x keV	1.9(4) s

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 157) and isobaric (same nucleon number A = 261) with Rutherfordium-261. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 157	Isobar A = 261
97	²⁵⁴Bk
98	²⁵⁵Cf
99	²⁵⁶Es
100	²⁵⁷Fm
101	²⁵⁸Md
102	²⁵⁹No	²⁶¹No
103	²⁶⁰Lr	²⁶¹Lr
104	²⁶¹Rf	²⁶¹Rf
105	²⁶²Db	²⁶¹Db
106	²⁶³Sg	²⁶¹Sg
107	²⁶⁴Bh	²⁶¹Bh
108	²⁶⁵Hs
109	²⁶⁶Mt
110	²⁶⁷Ds

External data and identifiers

Adopted Levels, Gammas:NuDat 261Rf

Literature and References

[1] - A. Ghiorso, M. Nurmia, K. Eskola, P. Eskola:
²⁶¹Rf; new isotope of element 104.
In: Physics Letters B, (1970), DOI 10.1016/0370-2693(70)90595-2.

[2] - Hiromitsu Haba:
Superheavy element chemistry at GARIS.
In: EPJ Web of Conferences 131, 07006, (2006), DOI 10.1051/epjconf/201613107006.