Isotopes of darmstadtium

Darmstadtium (110Ds) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 269Ds in 1994. There are 9 known radioisotopes from 267Ds to 281Ds (with many gaps) and 2 or 3 known isomers. The longest-lived isotope is 281Ds with a half-life of 9.6 seconds.

Main isotopes of darmstadtium (110Ds)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
279Ds syn 0.2 s 10% α 275Hs
90% SF
281Ds syn 14 s 94% SF
6% α 277Hs

List of isotopes
Nuclide
[n 1]		 Z N Isotopic mass (Da)
[n 2][n 3]		 Half-life
 Decay
mode
[n 4]		 Daughter
isotope
 Spin and
parity
[n 5][n 6]
Excitation energy
267Ds[n 7] 110 157 267.14377(15)# 3(+6−2) µs α ? 263Hs ? 9/2+#
269Ds 110 159 269.14475(3) 230(110) µs
[179(+245−66) µs]		 α 265Hs 3/2+#
270Ds 110 160 270.14458(5) 160(100) µs
[0.10(+14−4) ms]		 α 266Hs 0+
270mDs 1140(70) keV 10(6) ms
[6.0(+82−22) ms]		 α 266Hs (10)(−#)
271Ds 110 161 271.14595(10)# 210(170) ms α 267Hs 11/2−#
271mDs 29(29) keV 1.3(5) ms α 267Hs 9/2+#
273Ds 110 163 273.14856(14)# 0.17(+17−6) ms α 269Hs 13/2−#
277Ds[n 8] 110 167 277.15591(41)# 3.5 ms[1] α 273Hs 11/2+#
279Ds[n 9] 110 169 279.16010(64)# 0.18(+5−3) s SF (90%) (various)
α (10%) 275Hs
280Ds[n 10] 110 170 280.16131(89)# 6.7 ms[2][3] SF (various) 0+
281Ds[n 11] 110 171 281.16451(59)# 9.6 s SF (94%) (various) 3/2+#
α (6%) 277Hs
  1. mDs – Excited nuclear isomer.
  2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. Modes of decay:
    SF:Spontaneous fission
  5. ( ) spin value – Indicates spin with weak assignment arguments.
  6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. Unconfirmed isotope
  8. Not directly synthesized, occurs in decay chain of 285Fl
  9. Not directly synthesized, occurs as decay product of 283Cn
  10. Not directly synthesized, occurs in decay chains of 288Mc and 292Lv; unconfirmed
  11. Not directly synthesized, occurs in decay chain of 289Fl

Isotopes and nuclear properties

Nucleosynthesis

Super-heavy elements such as darmstadtium are produced by bombarding lighter elements in particle accelerators that induce fusion reactions. Whereas most of the isotopes of darmstadtium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic numbers.[4]

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.[5] 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 the ground state, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products.[4] The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion).[6]

The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=110.

TargetProjectileCNAttempt result
208Pb 62Ni270DsSuccessful reaction
207Pb 64Ni271DsSuccessful reaction
208Pb 64Ni272DsSuccessful reaction
209Bi 59Co268DsSuccessful reaction
232Th 48Ca280DsFailure to date
235U 40Ar275DsFailure to date
238U 40Ar278DsReaction yet to be attempted
244Pu 34S278DsSuccessful reaction
244Pu 36S280DsReaction yet to be attempted
248Cm 30Si278DsReaction yet to be attempted
250Cm 30Si280DsReaction yet to be attempted

Cold fusion

Before the first successful synthesis of darmstadtium in 1994 by the GSI team, scientists at GSI also tried to synthesize darmstadtium by bombarding lead-208 with nickel-64 in 1985. No darmstadtium atoms were identified. After an upgrade of their facilities, the team at GSI successfully detected 9 atoms of 271Ds in two runs of their discovery experiment in 1994.[7] This reaction was successfully repeated in 2000 by GSI (4 atoms), in 2000[8][9] and 2004[10] by the Lawrence Berkeley National Laboratory (LBNL) (9 atoms in total) and in 2002 by RIKEN (14 atoms).[11] The GSI team studied the analogous reaction with nickel-62 instead of nickel-64 in 1994 as part of their discovery experiment. Three atoms of 269Ds were detected.[7] A fourth decay chain was measured but was subsequently retracted.[12]

In addition to the official discovery reactions, in October–November 2000, the team at GSI also studied the analogous reaction using a lead-207 target in order to synthesize the new isotope 270Ds. They succeeded in synthesising 8 atoms of 270Ds, relating to a ground state isomer, 270Ds, and a high-spin metastable state, 270mDs.[13]

In 1986, a team at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, studied the reaction:

209
83Bi + 59
27Co → 267
110Ds + 1
0n

They were unable to detect any darmstadtium atoms. In 1995, the team at LBNL reported that they had succeeded in detecting a single atom of 267Ds using this reaction. However, several decays were not measured and further research is required to confirm this discovery.[14]

Hot fusion

In 1986, the GSI team attempted to synthesise element 110 by bombarding a uranium-235 target with accelerated argon-40 ions. No atoms were detected.[15]

In September 1994, the team at Dubna detected a single atom of 273Ds by bombarding a plutonium-244 target with accelerated sulfur-34 ions.[16]

Experiments have been performed in 2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus 280Ds, produced through the nuclear reaction:

232
90Th + 48
20Ca → 280
110Ds* → fission

The result revealed how compound nuclei such as this fission predominantly by expelling magic and doubly magic nuclei such as 132Sn (Z=50, N=82). No darmstadtium atoms were obtained.[17] A compound nucleus is a loose combination of nucleons that have not arranged themselves into nuclear shells yet. It has no internal structure and is held together only by the collision forces between the target and projectile nuclei. It is estimated that it requires around 10−14 s for the nucleons to arrange themselves into nuclear shells, at which point the compound nucleus becomes a nuclide, and this number is used by IUPAC as the minimum half-life a claimed isotope must have to potentially be recognised as being discovered.[18][19]

As decay product
List of darmstadtium isotopes observed by decay
Evaporation residueObserved darmstadtium isotope
277Cn273Ds[20]
285Fl, 281Cn277Ds[21]
291Lv, 287Fl, 283Cn279Ds[22]
288Mc, 284Nh, 280Rg; 292Lv, 288Fl, 284Cn280Ds ?
293Lv, 289Fl, 285Cn281Ds[23]

Darmstadtium has been observed as a decay product of copernicium. Copernicium currently has seven known isotopes, four of which have been shown to undergo alpha decays to become darmstadtium nuclei, with mass numbers between 273 and 281. Darmstadtium isotopes with mass numbers 277, 279 and 281 to date have only been produced by copernicium nuclei decay. Parent copernicium nuclei can be themselves decay products of flerovium or livermorium. Darmstadtium may also have been produced in the electron capture decay of roentgenium nuclei which are themselves daughters of nihonium, moscovium, or tennessine. To date, no other elements have been known to decay to darmstadtium.[19] For example, in 2004, the Dubna team (JINR) identified darmstadtium-281 as a product in the decay of livermorium via an alpha decay sequence:[23]

293
116Lv
 → 289
114Fl
 + 4
2He
289
114Fl
 → 285
112Cn
 + 4
2He
285
112Cn
 → 281
110Ds
 + 4
2He

Retracted isotopes
280Ds

The first synthesis of element 114 resulted in two atoms assigned to 288Fl, decaying to the 280Ds, which underwent spontaneous fission. The assignment was later changed to 289Fl and the darmstadtium isotope to 281Ds. Hence, 280Ds remained unknown until 2016, when it was populated by the hitherto unknown alpha decay of 284Cn (previously, that nucleus was only known to undergo spontaneous fission).

277Ds

In the claimed synthesis of 293Og in 1999, the isotope 277Ds was identified as decaying by 10.18 MeV alpha emission with a half-life of 3.0 ms. This claim was retracted in 2001. This isotope was finally created in 2010 and its decay data supported the fabrication of previous data.[24]

273mDs

In the synthesis of 277Cn in 1996 by GSI (see copernicium), one decay chain proceeded via 273Ds, which decayed by emission of a 9.73 MeV alpha particle with a lifetime of 170 ms. This would have been assigned to an isomeric level. This data could not be confirmed and thus this isotope is currently unknown or unconfirmed.

272Ds

In the first attempt to synthesize darmstadtium, a 10 ms SF activity was assigned to 272Ds in the reaction 232Th(44Ca,4n). Given current understanding regarding stability, this isotope has been retracted from the table of isotopes.

Nuclear isomerism
The current partial decay level scheme for 270Ds proposed following the work of Hofmann et al. in 2000 at GSI[13]
281Ds

The production of 281Ds by the decay of 289Fl or 293Lv has produced two very different decay modes. The most common and readily confirmed mode is spontaneous fission with a half-life of 11 s. A much rarer and as yet unconfirmed mode is alpha decay by emission of an alpha particle with energy 8.77 MeV with an observed half-life of around 3.7 min. This decay is associated with a unique decay pathway from the parent nuclides and must be assigned to an isomeric level. The half-life suggests that it must be assigned to an isomeric state but further research is required to confirm these reports.[23] It was suggested in 2016 that this unknown activity might be due to 282Mt, the great-granddaughter of 290Fl via electron capture and two consecutive alpha decays.[25]

271Ds

Decay data from the direct synthesis of 271Ds clearly indicates the presence of two nuclear isomers. The first emits alpha particles with energies 10.74 and 10.69 MeV and has a half-life of 1.63 ms. The other only emits alpha particles with an energy of 10.71 MeV and has a half-life of 69 ms. The first has been assigned to the ground state and the latter to an isomeric level. It has been suggested that the closeness of the alpha decay energies indicates that the isomeric level may decay primarily by delayed isomeric transition to the ground state, resulting in an identical measured alpha energy and a combined half-life for the two processes.[26]

270Ds

The direct production of 270Ds has clearly identified two nuclear isomers. The ground state decays by alpha emission into the ground state of 266Hs by emitting an alpha particle with energy 11.03 MeV and has a half-life of 0.10 ms. The metastable state decays by alpha emission, emitting alpha particles with energies of 12.15, 11.15, and 10.95 MeV, and has a half-life of 6 ms. When the metastable state emits an alpha particle of energy 12.15 MeV, it decays into the ground state of 266Hs, indicating that it has 1.12 MeV of excess energy.[13]

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing darmstadtium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

ProjectileTargetCN1n2n3n
62Ni208Pb270Ds3.5 pb
64Ni208Pb272Ds15 pb, 9.9 MeV

Fission of compound nuclei with Z=110

Experiments have been performed in 2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus 280Ds. The nuclear reaction used is 232Th+48Ca. The result revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as 132Sn (Z=50, N=82).[27]

Theoretical calculations

Decay characteristics

Theoretical calculation in a quantum tunneling model reproduces the experimental alpha decay half live data.[28][29] It also predicts that the isotope 294Ds would have alpha decay half-life of the order of 311 years.[30][31]

Evaporation residue cross sections

The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.

DNS = Di-nuclear system; σ = cross section

TargetProjectileCNChannel (product)σmaxModelRef
208Pb 64Ni272Ds1n (271Ds)10 pbDNS[32]
232Th 48Ca280Ds4n (276Ds)0.2 pbDNS[33]
230Th 48Ca278Ds4n (274Ds)1 pbDNS[33]
238U 40Ar278Ds4n (274Ds)2 pbDNS[33]
244Pu 36S280Ds4n (276Ds)0.61 pbDNS[34]
248Cm 30Si278Ds4n (274Ds)65.32 pbDNS[34]
250Cm 30Si280Ds4n (276Ds)3.54 pbDNS[34]

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