Identification of the New Isotope ${}^{244}\mathrm{Md}$

In an experiment performed at Lawrence Berkeley National Laboratory’s 88-inch cyclotron, the isotope ${}^{244}\mathrm{Md}$ was produced in the ${}^{209}\mathrm{Bi}({}^{40}\mathrm{Ar},5n)$ reaction. Decay properties of ${}^{244}\mathrm{Md}$ were measured at the focal plane of the Berkeley Gas-filled Separator, and the mass number assignment of $A=244$ was confirmed with the apparatus for the identification of nuclide $A$. The isotope ${}^{244}\mathrm{Md}$ is reported to have one, possibly two, $\alpha$-decaying states with $\alpha$ energies of 8.66(2) and 8.31(2) MeV and half-lives of ${0.4}_{-0.1}^{+0.4}$ and $\sim 6\mathrm{s}$, respectively. Additionally, first evidence of the $\alpha$ decay of ${}^{236}\mathrm{Bk}$ was observed and is reported.

Figure 1

Schematic of the coupled BGS plus FIONA setup with the labels indicating the positions of (1) BGS, (2) BGS focal-plane detector, (3) gas catcher, (4) RFQ cooler, (5) RFQ trap, (6) acceleration region, (7) focusing element and horizontal and vertical steerers, (8) shielding wall, (9) focusing element and horizontal and vertical steerers, (10) diagnostic DSSD detector, (11) trochoid spectrometer, and (12) FIONA focal-plane detector. The purple shaded area and line represent the trajectory of the ions as they travel through the BGS and FIONA.

Figure 2

(Top) Experimental data from an example ${{}^{199-201}\mathrm{At}}^{1+}$ calibration run showing the $A/q$ separation. (Bottom) Location of the detection of ${\mathrm{Md}}^{2+}$ ions after FIONA was scaled from $(A/q{)}_{\mathrm{cal}}=200/1$ to $(A/q{)}_{\mathrm{new}}=247/2$. The dotted line highlights the correlation in the position that the ${}^{200}{\mathrm{At}}^{1+}$ and ${\mathrm{Md}}^{2+}$ ions were detected, which led to an $A=247$ identification for the delivered ${\mathrm{Md}}^{2+}$ ions.

Figure 3

(Top) Experimental data from an example ${{}^{198-199}\mathrm{At}}^{1+}$ calibration run showing the $A/q$ separation. (Bottom) Location of the detected ${\mathrm{Md}}^{2+}$ ions after FIONA was scaled from $(A/q{)}_{\mathrm{cal}}=198/1$ to $(A/q{)}_{\mathrm{new}}=244/2$. The dotted line highlights the correlation in the position that the ${}^{198}{\mathrm{At}}^{1+}$ and ${\mathrm{Md}}^{2+}$ ions were detected, which led to an $A=244$ identification for the delivered ${\mathrm{Md}}^{2+}$ ions.

Figure 4

Partial decay scheme for ${}^{244}\mathrm{Md}$, ${}^{240}\mathrm{Es}$, and ${}^{236}\mathrm{Bk}$ created on the basis of the observed events listed in Table 1. Tentative assignments are shown as dashed lines. When possible, the presented half-life of the isotope is an average from several observed events. Otherwise, it is shown just as an approximation from a single decay event. The proposed decay scheme is in agreement with what has been observed for ${}^{240}\mathrm{Es}$ [24]. Energy values are averages of those presented in Table 1 are given in keV.