Direct measurement of atomic number for superheavy nuclei search*

A direct measurement of the atomic number is demanded for the experiments of the superheavy nuclei synthesis such as 119th element search, since the conventional method of analyzing the alpha-decay chain have a limitation of identification for spontaneous-fission nuclei. We have developed a Bragg curve detector(BCD) employing a digital signal processing technique to improve the separation efficiency especially for low-energy superheavy ions. Although the height of Bragg peaks induced by heavy ions of less than 1.5 MeV/u are not proportional to the incident energy, the waveform analysis makes it possible to identify the nuclei having the different atomic number.

The performance test of the developed detector was performed at Kyushu University Center for Accelerator and Beam Applied Science. The heavy ion beams supplied from the Tandem accelerator were scattered and injected to the BCD. The measured waveforms of the BCD well matched to the simulation results using Garfield++ with a field map obtained from Gmsh and Elmer. A sufficiently high separation efficiency was achieved at the same energy particles with different atomic number.