1971Fl02: ²⁶¹Db produced by ²⁴³Am(²²Ne,4n) (97% ²⁴³Am and 3% ²⁴¹Am target) at Dubna. Recoil atoms were stopped on an endless Ni belt. 105 phosphate glass fission fragment detectors (95% efficiency) were placed along the belt.

Summary of measurements and conclusions:

1. In bombarding ²⁴³Am with ²²Ne, a spontaneously fissioning isotope with T_1/2=1.8 s 6 is produced.

2. From angular distributions of the recoil atoms, the isotope with T_1/2≈2 s has Z=105.

3. Excitation function behavior indicates that the SF emitter with T_1/2≈2 s is formed by a compound nucleus reaction with the evaporation of neutrons supporting the assignment of Z=105 and yielding a most probable mass of 261.

4. The yield of the spontaneously fissioning isotope of Z=105 corresponds to σ≈5×10^-24 cm² suggesting that the isotope decays primarily by α emission.

T_1/2(SF) is estimated to be 0.1 to 100 s. Experimenters state that no definite conclusions can be drawn from this work.

1971Gh01: ²⁶¹Db produced by ²⁵⁰Cf(¹⁵N,4n) E=83 MeV (6.1% ²⁴⁹Cf, 86.5% ²⁵⁰Cf, 6.8% ²⁵¹Cf, and 0.6% ²⁵²Cf target) and ²⁴⁹Bk(¹⁶O,4n) E=92 MeV (<10% ²⁴⁹Bk target) at the Lawrence Berkeley Laboratory Heavy-ion Linear Accelerator (HILAC). Recoil atoms were deposited by He jet onto the periphery of a vertically mounted wheel. The wheel rotated periodically to place collected recoil atoms next to a series of Au-Si surface-barrier detectors. Seven detector stations were placed at 45 degree intervals around the wheel. α complex α peak around 8.9 MeV in the (¹⁵N,4n) measurements was assigned to ²⁶¹Db and its daughter, 8.87-MeV 0.6-sec ²⁵⁷Lr (1971Es01). Excluding ²⁵⁷Lr produced directly, the whole complex decayed with T_1/2=1.8 s 6 (same T_1/2 as the 8.93-MeV group). Activities left in the detectors had 10 counts in the 8.75- to 9.0 MeV region for a 37-μAh experiment with a distribution of 5, 1, 1, and 3 counts in the first four stations. Within the 2-sec shuttle period, the quadrants had 4, 5, 0, and 1 counts, respectively. This is compatible with the alpha-recoil daughter being ²⁵⁷Lr. In the (¹⁶O,4n) measurement 25 counts in the 8.93-MeV peak and 7 alpha-recoil events in the 8.75- to 8.9-MeV range in the off-wheel position observed for a 127-μAh bombardment. Additional evidence for the isotopic assignment was provided by time-correlation measurements; T_1/2=2 s 1 for the 8.93-MeV mother group activity and 0.8 s +5-3 for the daughter activity which is consistent with ²⁵⁷Lr. 13 correlated pairs recorded in the ²⁵⁰Cf bombardment with an expected number of random correlations of about 0.5 in the 8.7 to 9.1 MeV energy interval. Properties attributed to ²⁶¹Db (²⁶¹Ha) are Eα=8.93 MeV for the energy group corresponding to a half-life of 2 s 1.

1998La30: ²⁶¹Db produced via ²⁴³Am(²²Ne,4n) E=116 MeV (72% ²⁴³Am, 28% ²⁴¹Am target; ²²Ne⁺⁶ beam) and ²⁵⁰Cf(¹⁵N,4n) E=84 MeV (79.5% ²⁵⁰Cf, 10.2% ²⁴⁹Cf, 10.2% ²⁵¹Cf target; ¹⁵N⁺⁴ beam) reactions at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. Transport time from target to collection foil was 1.0 s 3. Transport and deposition efficiency was about 86% 10 for (¹⁵N,4n) and about 74% 10 for (²²Ne,4n). Six pairs of passivated ion-implanted planar silicon detectors employed to measure the energies of α particles and SF fragments. Assuming %α=100, the production cross section is 0.51 nb 20 for ²⁵⁰Cf(¹⁵N,4n) E=84 MeV and 0.25 nb 11 for ²⁴³Am(²²Ne,4n) E=116 MeV. The assignment to ²⁶¹Db was based on consistency of α particle energies and life-time measurements with previous work.

The experimenters state that the lifetimes are consistent with a 1.8 s half-life (α decay) and estimate T_1/2(sf)>10 s. The upper limit of the sf branch is estimated to be 18%.

2004Ga29: daughter of ²⁶⁵Bh produced by the ²⁴³Am(²⁶Mg,4n) reaction at 168 MeV. The study was carried out at the sector focus cyclotron of the Heavy Ion Research Facility (HIRFL), Lanzhou, China by a Chinese collaboration. The reaction cross-section along with other key experimental quantities are not provided. See ²⁶⁵Bh for experimental details. Eight α decay sequences were attributed to parent ²⁶⁵Bh and ²⁶¹Db is the second event in each chain. The average decay properties, presumably for all eight events, provided by the experimenters for this nuclide are Eα=8.93 MeV 4 with a lifetime of 1.8 s (Fig 2) corresponding to a half-life of 1.7 s +79-49 using the MLDS code. The evaluators note that the half-life of 8 events attributed to this nuclide and listed in Table 1 is 1.72 s +94-45 using the methods of 1984Sc13.

2013AsZZ: α preliminary report of a chemistry experiment with the reaction ²⁴⁸Cm(¹⁹F,6n)²⁶¹Db, E(beam)=113 MeV, at the Tokai tandem accelerator complex, Japan. The experiment was set up to measure α-γ coincidences. 40 α-decay events were attributed to ²⁶¹Db with Eα=8930 keV and T_1/2<4 s. No further details are provided.

Theory: See Nuclear Science References.

Others: see 1968Fl09, 1970ZvZZ, 1970FlZZ, 1970FlZY, 1970FlZX, 1971FlZV, and 1971Dr01 for early work, 1992Ba77 and 2009Og07. 1977Be36 provides calculated excitation functions (page 188).

Assignment: produced by ²⁴³Am(²²Ne,4n) (1971Fl02). Angular distributions and excitation functions, ²⁵⁰Cf(¹⁵N,4n) E=83 MeV (6.1% ²⁴⁹Cf, 86.5% ²⁵⁰Cf, 6.8% ²⁵¹Cf, and 0.6% ²⁵²Cf target) and ²⁴⁹Bk(¹⁶O,4n) E=92 MeV (<10% ²⁴⁹Bk target) (1971Gh01), and ²⁴³Am(²²Ne,4n) E=116 MeV (72% ²⁴³Am, 28% ²⁴¹Am target) and ²⁵⁰Cf(¹⁵N,4n) E=84 MeV (79.5% ²⁵⁰Cf, 10.2% ²⁴⁹Cf, 10.2% ²⁵¹Cf target) (1998La30)