1984Mu17: ²⁰⁸Pb(⁵⁸Fe,n) E=5.02 MeV/α at GSI using the UNILAC heavy ion accelerator. In-flight separation of evaporation residues was done USING SHIP (1979Mu14); see 1984Mu07 for details of the experimental SET-up. The excitation energy of the compound system was 18 MeV 2. a total OF 1×10¹² particles/s were delivered over 240 hours. An approximate mass determination was done using tof information and implantation energy. α and SF events detected by an array of seven position sensitive SURFACE barrier detectors; calibration error of |+15 keV estimated for 8.5 MeV|<Eα|<10 MeV and |+25 keV for Eα>10 MeV.

1984Mu17 quoted an average Eα=10.36 MeV 3 corresponding to a half-life of 1.8 ms +22-7. The assignments were made placing reliance on the fact that the daughter α signals could be assigned to known transitions belonging to the expected daughter nuclei of ²⁶⁵Hs. The production cross-section was 19 pb +18-11 at the 18 MeV 2 excitation energy. 1987Mu15 computed an estimate of randomness for the above decay chains to be 2×10^-15, 2×10^-15 and 2×10^-14 respectively.

1984DeZO, 1984Og02, 1984Og03: ²⁰⁸Pb(⁵⁸Fe,n) E=5.5 MeV/α at Dubna using the U400 cyclotron with a beam intensity of ≈1×10¹³ particles per second. On-line detection of SF (solid-state track detectors) and off-line detection of α’s after radiochemical separation of long-lived daughters. Beam dose of 3×10¹⁸ particles with three α events corresponding to the decay of the daughter ²⁵³Es (production cross-section of 4 pb) reported. Seven spontaneous fission tracks were detected corresponding to α decay with T_1/2=8 ms +20-4. If these all correspond to the spontaneous fission of ²⁶⁵Hs, T_1/2(SF)>20 ms.

1992Ba77: the IUPAC/IUPAP TWG assessment was that the Darmstadt work presented was sufficiently convincing to be accepted as a discovery. Simultaneous and independent work in Darmstadt (1984Mu17) and Dubna (1984Og02) established the formation of element 108. The major credit was accorded to Darmstadt.

1995Ho03: ²⁰⁸Pb(⁵⁸Fe,n). 79 events from GSI/SHIP attributed to the decay ²⁶⁵Hs. 75 α decays of ²⁶⁵Hs were observed during excitation FUNCTION measurements using the reaction ²⁰⁸Pb(⁵⁸Fe,n). α total of 4.4×10¹⁸ projectiles over 4 weeks of irradiation yielded a width for the excitation function of 4.8 MeV 7 with a cross-section maximum of 63 pb 10. Assignments were made by the consistency of LOWER chain member properties with known values. Two α-energies could be ASSIGNED to ²⁶⁵Hs: Eα1=10.310 MeV 20 and Eα2=10.578 MeV 20. It was suggested that within the statistical uncertainties both transitions DECAYED with a half life of 1.55 ms 20. The measurements confirmed the three decay chains reported by 1984Mu17. 1995Ho03 also reported four α decay chains as daughter products of ²⁶⁹Ds. The reaction used was ²⁰⁸Pb(⁶²Ni,n) E=5 MeV/α with a cross-section of 3.5 pb +27-18 (4 EVENTS). Total of 2.2×10¹⁸ projectile particles on 99.0% enriched Pb TARGET. Eight targets were mounted on a wheel with a diameter of 310 mm ROTATING at 1125 rpm. EVR’s separated by velocity filter SHIP. FOUR position and time correlated chains of α particle EVENTS were observed. α energies and time intervals BETWEEN successive decays could be determined. The events were ASSIGNED to the decay of ²⁶⁹Ds by consistency of lower chain MEMBER energies and lifetimes with known Hs, Sg, Rf and No data. The MEASURED α energies (to within |+20 keV) and emission times for the nuclei in each α-decay sequence are tabulated.

1997Ho14: ²⁰⁸Pb(⁵⁸Fe,n) E=283.9 MeV. Continued excitation function measurements near the maximum measured for ²⁶⁵Hs by 1995Ho03. α total DOSE of 0.64×10¹⁸ ions over 2.5 days yielded 20 decay chains of ²⁶⁵Hs. THE resulting cross section was 60 pb 14 which fits well into the DISTRIBUTION data measured by 1995Ho03. α Gaussian fit to the data RESULTED in a height of 66 pb 8, FWHM=4.8 MeV 6, and an excitation energy of 13.9 MeV 3, in agreement with the previously measured values resulting from 75 decay chains. The data are not corrected for finite TARGET thickness.

1998Ho13: while providing an overview of earlier work 95 events from ²⁰⁸Pb(⁵⁸Fe,n), 1998Ho13 note that the two α decay energies Eα=10.310 MeV 20 and Eα=10.578 MeV 20 assigned to ²⁶⁵Hs correspond, respectively, to the two half-lives: T_1/2=1.7 ms 3 and T_1/2=0.8 ms 2. It is further suggested that while the experiments where ²⁶⁵Hs was DIRECTLY produced do not conclusively support an assignment to DIFFERENT levels, the fact that all the four decays from ²⁶⁹Ds REPORTED by 1995Ho03 attributed to ²⁶⁵Hs are related to the weaker 10.58 MeV transition rather than the stronger line observed by direct production, would indicate that two levels do exist. Although an ASSIGNMENT to ground and excited states was not possible, all measured decays from the parent ²⁶⁹Ds proceeded via this hitherto unidentified transition. The evaluator notes that one of the four ²⁶⁹Ds α chains reported by 1995Ho03 was retracted by 2002Ho11. The mean energy for the remaining three chains is 10.555 MeV 20 corresponding to a half-life of 0.70 ms +96-26 computed using the method of 1984Sc13.

1999He11: following a reanalysis of all GSI data (more than 100 events), two half-lives were reported suggesting that decays originate from two different levels. The longer half-life of 2.0 ms +3-2 was connected with decays with energy Eα=10301 keV 15 about 90% of the time and assigned to the ground state. Less intense transitions with the same half-life have energies of Eα=10426 keV 15, 10371 keV 15, and 10244 keV 15. The shorter half-life of 0.75 ms +17-12 was connected about 63% of the time with Eα=10572 keV 15 and assigned to an isomeric state. Less intense transitions with the same half-life have energies OF 10726 keV 15, 10517 keV 15, and 10336 keV 15. These transitions, however, require further experimental investigation and confirmation (2007HoZR). For the ²⁶¹Sg daughter, a careful analysis of those events FOLLOWING ²⁶⁵Hs or ^265mHs did not point to any significant DIFFERENCES in α-energies or half-lives.

2002Ho11: retraction of second event dated 11 November 1994 of ²⁶⁹Ds and daughters reported by 1995Ho03 following reanalysis of original data from which this sequence could not be reconstructed.

2007HoZR: after reviewing their data on ²⁶⁵Hs presented in 1998Ho13 and 1999He11, 2007HoZR conclude that the two main transitions given in 1998Ho13 and the interpretation given there is correct. The additional transitions mentioned in 1999He11 are based on single events or tails of the main lines and require confirmation and further experimental studies.

2009He20: direct synthesis in experiments performed at GSI with the reaction ²⁰⁸Pb(⁵⁸Fe,n) with the UNILAC. The maximum cross-section was 0.063 nb 10 (1995Ho03). EVRs were measured with SHIP in a 16 strip Si pips detector to measure time, position and kinetic energy of the residues and decays. The experimental set-up and other details are described in 2004He28 and 2006He27. The α spectra could be divided into 5 groups. The α energy groups with 10282, 10428 and 10312 agree within error bars and are attributed to the same nuclear level, ²⁶⁵Hs(1). The mean half-life is T_1/2=1.9 ms 2. The energy group at 10538 keV has a T_1/2= 0.3 ms +2-1 and describes a different level. The group with energy 10573 (T_1/2=1.1 ms) cannot be unambiguously assigned and is tentatively proposed to be a part of the first level ²⁶⁵Hs(1) WITH contributions from the second level ²⁶⁵Hs(2), T_1/2=0.3 ms. based on decay data, the authors find no reason to assume two levels in the daughter nucleus ²⁶¹Sg. They observe that an isomeric state in ²⁶⁵Hs is also supported by the findings of 1995Ho03.

2010Dw01: estimate mass excess of ²⁶⁵Hs from systematics. The revised value after implementing SHIPTRAP data into AME evaluations is 121065 89 over 121170 140 from 2003Au03.

2011Sa41: direct synthesis with GARIS at RIKEN using the reaction ²⁰⁸Pb(⁵⁸Fe,1n) at centre-of-target beam energies of 284.1 MeV (7 events), 285.5 MeV (3 events), 287.0 MeV (18 events), 290.0 MeV (1 event) and 294.1 MeV (2 events). Cross-sections at each energy were respectively 25 pb +13-9, 51 pb +46-29, 41 pb +12-10, 6.6 pb +152-55, 5.4 pb +74-36 and 2.8 pb +65-23 at (1σ c.i.). The purpose of the experiment was to improve the data for ²⁶⁴Hs. EVRs from GARIS were guided into a detector system at the focal plane. Transmission efficiency of EVRs was about 80%. EVRs were identified by genetic correlations α-α or α-SF. The low energy resolution of the detector prevented a clear separation of ²⁶⁵Hs(1)and ²⁶⁵Hs(2) on the basis of α-particle energies. 31 events attributed to ²⁶⁵Hs were measured using the ²⁰⁸Pb target and experimenters suggest that both states are observed. Two states with an average energy of 10.14 MeV 4 and a half life of 0.13 ms +22-8 are suggested either as due to partial energy deposition of a known state or a newly observed transition. Evaluator notes that the spread of lifetimes ranging from 21.5 ms to 0.154 ms over 30 measured decays is large. The combined half life for 29 observed events (excluding the 21.5 ms value) is 2.45 ms +56-38 (estimated by evaluator) in reasonable agreement with the ²⁶⁵Hs(1) state.

Theory: see Nuclear Science References

Other: 2005StZX, 2009Mo34. 1998Ho13 provide an overview of earlier work with ²⁰⁸Pb(⁵⁸Fe,n).

Assignment: ²⁰⁸Pb(⁵⁸Fe,n) (2009He20), ²⁰⁸Pb(⁵⁸Fe,n) E=5.02 MeV/α (1984Mu17), parent of ²⁶¹Sg and ²⁵⁷Rf and ²⁰⁸Pb(⁵⁸Fe,n) E=5.5 MeV/α (1984Og02).

Two levels corresponding to Eα=10.399 MeV 15 (average for 4 energies attributed to decay to same nuclear level) and Eα=10.538 MeV 15 are populated (2009He20) in good agreement with 1998Ho03.

The two levels are denoted ²⁶⁵Hs(1) (presumed g.s.) and ²⁶⁵Hs(2) respectively though there may be some mixing of levels (2009He20). Both levels are expected to feed the g.s. Of ²⁶¹Sg.

Line intensities could not be deduced due to energy summing with conversion electrons.

Levels: The evaluator does not believe there is enough evidence to support the 0.0⁺x level proposed by 1999Ar21.