Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - FNPMLS (Fundamental nuclear properties measured with laser spectroscopy)

Teaser

The prime research theme of this project is the study of short-lived exotic nuclei with laser spectroscopy. Over the next 5 years my team will study the role of three-nucleon forces and their associated influence on nuclear structure and the limits of nuclear existence. This...

Summary

The prime research theme of this project is the study of short-lived exotic nuclei with laser spectroscopy. Over the next 5 years my team will study the role of three-nucleon forces and their associated influence on nuclear structure and the limits of nuclear existence. This work will investigate the interplay between tensor and central forces and the associated effect on quantum shells in exotic nuclear systems.The FNPMLS project will study how the shape of the nucleus is modified at the limits of nuclear existence. We will use innovative laser spectroscopy methods to achieve these goals. The project will be carried out at the ISOLDE facility, CERN, which is the premier radioactive beam facility at the precision frontier. The proposed research activity closely matches the NuPECC (Nuclear Physics European Collaboration Committee) 2010 Long Range Plan. The wider scientific impact of this research will influence modelling explosive stellar processes and nuclear synthesis, understanding the structure of astrophysical compact-objects such as neutron stars and predicting regions of enhanced stability in the super heavy elements. The FNPMLS project will develop ultra-sensitive methodologies that set a new paradigm in laser spectroscopy. It builds on the cutting edge technology of collinear resonance ionization spectroscopy (CRIS) that I have developed during my STFC Advanced Fellowship. The CRIS technique combines the high resolution nature of collinear laser spectroscopy with the high sensitivity of resonance ionization spectroscopy. The research programme and investment outlined in this proposal will place my team in a unique and world leading position. This work will happen in advance of the next generation of radioactive beam facility such as SPIRAL2, FAIR and FRIB and will provide the essential ingredients for future fundamental questions.

The techniques developed within this project will have impact beyond the field of nuclear physics. The ability to sort and select individual atoms of a specific isotope from a haystack of more than 1000 billion interfering atoms passing through the system every second has applications in mass spectrometry. The developments in the FNPMLS project have already demonstrated methods that can be used to enhance the suppression of interference species in ICP-MS and IRMS by several orders of magnitude. This will have impact in a variety of industries and areas such as food safety, forensics as well as archaeology and environmental sciences.

Work performed

Since the beginning of this project to the end of the reporting period the following key results have been achieved:
A significant upgrade and consolidation of the experiment has taken place to improve the vacuum within the laser-atom interaction region allowing it to operate at below 10-10 mbar. This has required a new unit for neutralizing the ion beam. The neutralization unit or charge exchange cell can be operated at a temperature of 460C and does not require additional liquid cooling circuits. Reducing the pressure in the interaction region will significantly reduce the detected background during experiments. The equipment is now ready for the 2017 measurements.

We have developed a method of using CW lasers for resonance ionization which has been used to measure the hyperfine structure of 219Fr with a linewidth of 20 MHz but with the same sensitivity as the lower resolution methods previously employed. This represents a factor of 70 increase in resolution.This work has already been published in Physical Review Letters.

A first experiment has been conducted on the exotic copper isotopes and has successfully measured the isotopes 76-78Cu with yields down to less than 30 atoms per second with a background rate of one count in 400 seconds. This has demonstrated the ability to measure 79-81Cu and an experiment is planned for 2017.

Final results

A critically important step beyond state of the art has been the ability to measure exotic isotopes with such high resolution (and therefore high sensitivity). We have developed a method for significantly reducing the effects of power broadening and AC Stark line distortions, which typically reduce the spectral resolution by broadening the line width. This has been achieved by using CW lasers that have been modulated and then the light separated in time from the ionization (or probe) laser. This will significantly improve the selectivity of resonance ionization spectroscopy while not introducing any compromise on the the sensitivity.