Generation and Investigation of radium muonic atoms in thin solid hydrogen films

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In this research, we proposed to implant radium isotopes in solid hydrogen films to form muonic atoms with unstable nuclei, and conduct muonic X-ray spectroscopy to determine transfer rates, isotope shifts and nuclear charge radii. The originality of this method was based on the muon transfer reaction mechanism to higher Z nuclei in solid hydrogen to efficiently produce muonic atoms, since only a very small concentration of nuclei (ppm level) is required to perform muonic X-ray spectroscopy experiments. The goal of this project was to develop a new ion source that can produce long-lived radioactive radium isotope ions, in order to be implanted in solid hydrogen films and produce muonic atoms with radioactive nuclei. This new ion source needed to be designed so that it can be used with the existing experimental apparatus (μA^*) for muonic atom spectroscopy with implanted ions in solid hydrogen films installed at the RIKEN-RAL Muon Facility. The main achievement of this 3 years project w … More as the construction of a new surface ionization ion source with the aim of using in the future radioactive isotopes. A surface ionization type ion source was selected because it is capable of producing ions from alkali and alkaline-earth metals with high efficiency, which is ideal to produce radium isotope ions, but also to produce many other stable ion beams for optimization and tuning purposes. In the case of radium, since there are no stable isotopes, the element barium is selected because it is in the same group and has similar ionization energy. Therefore, by mixing stable barium isotope as a marker, it is possible to first adjust and optimize efficiently the experimental conditions using stable nucleus, and then switch easily to unstable nucleus to perform the experiment with radium ions. This new surface ionization ion source was tested last year at KURRI (Research Reactor Institute, Kyoto University). Barium ions were successfully ionized and barium beams of several μA were produced. The stability of the ion source was also examined, and no significant beam deterioration was observed after several hours of operation. In January 2006, it was shipped to the Rutherford Appleton Laboratory in the UK, and installed on the μA^* experimental apparatus at RIKEN-RAL port 4 area. The installation went smoothly, and is now almost completed. The first experiment using the new ion source is scheduled sometime this autumn. Barium beams will be produced and implanted in solid hydrogen films to conduct muonic X-ray spectroscopy experiments. The first experimental results will be reported in a later publication. However, before any radium radioactive isotopes can be used in this system, several modifications and improvements to the existing μA^* apparatus will be required to handle radioactive materials safely. In particular, the pumping system will need to be upgraded and an exhaust stack installed. Local radiation shielding will also be needed around the ion source. Less