Comparison of complementary reactions for the production of ${}^{261,262}\mathrm{Bh}$

Two heavy-ion induced fusion reactions producing ${}^{261,262}\mathrm{Bh}$ were studied using the Berkeley Gas-filled Separator at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. An excitation function for the production of ${}^{262}\mathrm{Bh}$ via the reaction ${}^{209}\mathrm{Bi}({}^{54}\mathrm{Cr},n){}^{262}\mathrm{Bh}$ was measured with a maximum cross section from a fit to the data of 430 ± 110 pb observed at a compound nucleus excitation energy of 15.7 MeV. New data have been measured for the 1$n$ exit channel of the ${}^{208}\mathrm{Pb}({}^{55}\mathrm{Mn},\hspace{0.5em}n){}^{262}\mathrm{Bh}$ reaction. We present an updated excitation function with an observed maximum cross section of $530\pm 100$ pb at a compound nucleus excitation energy of 14.1 MeV. Events corresponding to the 2$n$ exit channel for the ${}^{209}\mathrm{Bi}({}^{54}\mathrm{Cr},2n){}^{261}\mathrm{Bh}$ and ${}^{208}\mathrm{Pb}({}^{55}\mathrm{Mn},2n){}^{261}\mathrm{Bh}$ reactions were also observed and are presented as partial excitation functions. The measured decay properties correspond well with existing experimental data. We compare these experimental results to cross section predictions from a model by Świa˛tecki et al. and discuss entrance channel effects on the magnitude of 1$n$ cross sections.

Figure 1

Decay properties of ${}^{262}{\mathrm{Bh}}^{g,m}$, ${}^{261}\mathrm{Bh}$ and their associated daughter products [6, 7, 23, 31, 32, 33, 34].

Figure 2

Measured excitation functions for the ${}^{208}\mathrm{Pb}({}^{55}\mathrm{Mn},\mathit{xn}){}^{263\text{−}x}\mathrm{Bh}$ [2(a)] and ${}^{209}\mathrm{Bi}({}^{54}\mathrm{Cr},\mathit{xn}){}^{263\text{−}x}\mathrm{Bh}$ [2(b)] reactions. Points from the 1$n$ and 2$n$ exit channels are indicated by filled black squares and filled red circles, respectively. Fits to the data as in [29] are indicated by black lines. The fit maxima are 530 ± 100 pb at an excitation energy of 14.1 ± 0.4 MeV, and 430 ± 110 pb at 15.7 ± 0.5 MeV for the ${}^{55}\mathrm{Mn}\hspace{0.5em}+\hspace{0.5em}{}^{208}\mathrm{Pb}$ and ${}^{54}\mathrm{Cr}\hspace{0.5em}+\hspace{0.5em}{}^{209}\mathrm{Bi}$ reactions, respectively. The three points lowest in energy in 2(a) are re-evaluated data from Folden et al. [12]. Arrows on abscissa indicate barrier location as discussed in the text.

Figure 3

Measured excitation functions for the ${}^{209}\mathrm{Bi}({}^{54}\mathrm{Cr},n){}^{262}\mathrm{Bh}$ reaction, studied at the LBNL and the GSI [6, 7]. Open squares represent data from GSI, filled squares from this work, a horizontal dash represents our upper limit, and the solid line is the fit from the maximum likelihood method.