1989Mu09: Direct synthesis at GSI using the reaction ²⁰⁹Bi(⁵⁴Cr,2n). The ⁵⁴Cr beam was provided by UNILAC at 4.87-5.07 MeV/u corresponding to excitation energies of the compound system from 15 MeV to 30 MeV. See ²⁶²Bh Adopted Levels for experimental details. 10 α-decay events were attributed to the decay of ²⁶¹Bh. Three decay energy groups were measured: 10.40 (4 events), 10.10 (4 events) and 10.03 MeV (2 events) with an uncertainty of ± 30 keV (1988MuZX). Mass assignments were based on correlations with the decay of ²⁵⁷Db and the discrimination between ²⁷¹Bh and ²⁶²Bh was based on the correlation to grand- daughters. α total half life of 11.8 ms +53-28 was reported for the three energy groups. The authors note that this value is not in agreement with 1976Og02 or 1988Fl02. No spontaneous fission events could be assigned to this nucleus. The highest production cross-section was 36 pb +22-14 at an excitation energy of 24 MeV 2. The fission branch is estimated to be less than about 10% corresponding to a lower limit SF half- life of 12 s. 1988MuZX estimate the upper limit for the fission cross- section for an isotope of element 107 at <10 pb.

2006Fo02: Direct synthesis in an experiment to measure the excitation function for ²⁶²Bh using the reaction ²⁰⁸Pb(⁵⁵Mn,n) at beam energies of 260, 264 and 268 MeV at centre of target. The experiments were carried out at LBNL using the 88-inch cyclotron and the BGS. See ²⁶²Bh Adopted Levels for experimental details. Two α-decay chains assigned to this nucleus (2n channel) were observed at an energy of 268.0 MeV at center of target. The α energies were 10.189 MeV and 10.346 MeV with lifetimes of 12.8 ms and 17.5 ms respectively. Of these, the first values could be assigned with greater confidence. Authors quote an estimated half-life of 10 ms +14-5 from both events.

2008Ne08: Direct synthesis at the 88-Inch cyclotron facility at LBNL using ²⁰⁹Bi(⁵⁴Cr,2n) at beam energies of 253.5, 257.1, 260.9, 264.7, 268.4 and 272.3 MeV and ²⁰⁸Pb(⁵⁵Mn,2n) at 273.0, 278.0, 283.0 MeV at centre of target. See ²⁶²Bh Adopted Levels for experimental details. 7 α-decay chains were assigned to this nucleus. 5 events were measured with the ⁵⁴Cr beam at 264.7 MeV (1 event, Eα=10.285 MeV), 268.4 MeV (1 event, Eα=0.602 MeV (esc)) and 272.3 MeV (3 events, Eα= 10.113, 10.165 and 9.989 MeV). The half-life corresponding to all 7 decays was 6.7 ms +38-18 shorter than those from 1989Mu09 and 2006Fo02. Experimenters conclude that better statistics would improve the value. No SF events or decays suggesting ε to ²⁶¹Sg were observed. Cross-sections were 67 pb +65-36 at 272.3 MeV; 28 pb +65-23 at 268.4 MeV and 8 pb +18-7 at 264.7 MeV with the ⁵⁴Cr beam, and 43 pb +57-28 at 273.0 MeV with the ⁵⁵Mn beam.

2010He11: Direct synthesis in experiments performed at GSI using the reaction ²⁰⁹Bi(⁵⁴Cr,2n) at a beam energy of 271 MeV corresponding to an excitation energy of 22 MeV, the predicted maximum of the 2n channel. The purpose of the experiment was to settle the question of whether there was an isomeric state in this nucleus. Targets were mounted on a rotating wheel and EVR’s leaving the target were implanted into a position sensitive 16 strip Si PIPS detector at the focal plane of SHIP. Assuming a 40% efficiency for SHIP, the total cross-section was 64 pb 15. γ-rays emitted in prompt or delayed coincidence with particles were measured using a Ge clover detector consisting of 4 crystals. Experimental setup was as in 2004He28 and 2006He27. α total projectile dose of 8x10¹⁷ ions was realized after irradiating for 50 hours. 18 α-decay chains were observed and the energies were divided into groups below and above 10.16 MeV. Three approximate α-energy groups are suggested with 10.030, 10.100 and 10.400 MeV with an average energy around 10.177 MeV. Experimenters suggest that levels below an energy of 10.16 MeV may represent favoured transitions, possibly the ground state. α ground state configuration of 5/2^-[512] is suggested with a HF of 4.6 for an unhindered transition and the experimenters attribute all observed α-decays to this transition. Since a more accurate determination of the energies to enable a decay scheme was not possible and observed decays are assigned to a single state around 10 MeV and the spread of energies was attributed to energy summing between α-particles and conversion electrons. α common half-life of 11.8 ms +39-24 for all events is derived since the life-times of the different groups did not suggest decays from different levels. The value is in agreement with 1989Mu09. No SF events within 200 ms of EVR implantation were observed and an upper limit of |< 5% is estimated.

Other: 1976Og01, 1976Og02 and 1988Fl02 reported SF half-lives of 2 ms (with a fission branch of 20%), 1 to 2 ms and 2.8 ms +21-11 respectively for ²⁶¹Bh which have not been confirmed. 1988MuZX show excitation functions for ²⁰⁹Bi+⁵⁴Cr at energies ranging from 4.98 to 5.05 MeV/u.

Theory: See Nuclear Science References.

Assignment: ²⁰⁹Bi(⁵⁴Cr,2n) at 4.87-5.07 MeV/u (1989Mu09) and ²⁰⁹Bi(⁵⁴Cr,2n) at a beam energy of 271 MeV (2010He11).

Levels: 2010He11 found no evidence for an isomer in ²⁶¹Bh.