TRIGA-TRAP Project

Introduction

TRIGA-Trap [1] is a double-Penning trap mass spectrometer at the research reactor TRIGA Mainz.

Fig. 1: Top view on the TRIGA-Trap setup. The fission products produced by the TRIGA reactor (upper left corner) are ionized in the surface ion source located in the high-voltage cage below the platform (upper right corner). The experiments are performed in the Penning-trap mass spectrometer TRIGA-Trap (lower right corner).

Concerning detection techniques, the setup features the commonly applied time-of-flight and phase-imaging ion cyclotron resonance methods as well as the narrow-band FT-ICR technique as described here. Within the TRIGA-Trap project we installed for the very first time a Penning trap at a nuclear research reactor in order to have access to neutron-rich fission products. Moreover, samples of stable nuclides as well as of heavy elements above uranium are available for off-line measurements. Masses of these nuclides are of high importance among others for reliable nucleosynthesis calculations in nuclear astrophysics and for investigations of nuclear structure.

Currently a high temperature surface ion source is installed which in connection with a gas-jet transport system enables access to certain fission products [2]. For this purpose a 30 kV high voltage platform has been installed. The mass separation after the ion source is carried out by a 90° dipole magnet with a resolution of about 300. The cooler and buncher COLETTE [3], which has been transferred from CERN to TRIGA-Trap, is installed in order to prepare cooled ion bunches for the connected experiments [4].

TRIGA-Trap is one of the development platforms for the future MATS  experiment within NUSTAR  at FAIR. We develop and test devices and experimental procedures for MATS.

The research within the framework of the TRIGA-TRAP project has close affiliations with the goals of the Extreme Matter Institute (EMMI)  at GSI/Darmstadt . The institute was created by the Helmholtz Alliance "Extremes of Density and Temperature: Cosmic Matter in the Laboratory". This Alliance connects GSI with 7 national partners (among them the Max Planck Institute for Nuclear Physics at Heidelberg) as well as 4 international partners. With EMMI Europe will get a unique infrastructure for interdisciplinary investigations of matter under extreme conditions.

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Applications for mass measurements with TRIGA-TRAP

The chemical composition of our universe has many surprising features: Why is iron so much more abundant than heavier elements such as gold? Why are there heavy elements at all and how did they come into existence? The properties of atomic nuclei, especially their masses, play a crucial role in these fundamental questions at the interface of nuclear and astrophysics. TRIGA-TRAP aims for mass measurements on neutron rich nuclei located in the least explored region of the chart of nuclides (see Figure below) that are important for the rapid neutron capture process. In addition, heavy nuclides above uranium can be studied off-line. The high- precision mass value yields the total nuclear binding energy of the nuclei relevant for nuclear structure studies since the binding energy is the result of the forces present in a nucleus.

Fig. 2: Fission production rates with a 300μg Cf-249 target and a neutron flux of 1.8 x 10¹¹ n/(cm² s) as obtained at TRIGA in the steady state operation mode [1]. The blue line marks the border of experimental mass uncertainties (delta m) of larger than 10keV. The red line shows the expected path of the r-process [5].

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References

[1]	J. Ketelaer et al., Nucl. Instrum. Meth. A 594, 162-177 (2008)
[2]	J. Grund et al., Nucl. Instrum. Meth. A 972, 164013 (2020)
[3]	D. Lunney et al., Nucl. Instrum. Meth. A 598, 379-387 (2009)
[4]	T. Beyer et al., Appl. Phys. B 114, 129-136 (2014)
[5]	J. J. Cowan et al., Phys. Today 57, 47 (2004)