202 FRIB Graduate Brochure

Andreas Stolz
Professor, Operations Department Head
Keywords: Rare Isotope Production with Fragment Separators, Structure of
Nuclei at the Limits of Existence, Particle Detector Development
s
Experimental Nuclear Physics
About
• MS, Physics, Technological University of Munich 1995
• PhD, Physics, Technological University of Munich,
2001
• Joined the laboratory in June 2001
• stolz@frib.msu.edu
Research
My primary research interest is centered on the production
of rare isotope beams with fragment separators and the
study of the structure of nuclei at the limits of existence.
At FRIB, rare-isotope beams are produced by projectile
fragmentation. The coupled cyclotrons accelerate stable
ions to a velocity up to half the speed of light. The fast ions
then impinge on a production target where they break up
into fragments of different mass and charges. Most of the
fragments are unstable, and many of them have an unusual
ratio of protons and neutrons. To study their properties,
the fragments of interest need to be separated from all
other produced particles. The A1900 fragment separator
at FRIB filters rare isotopes by their magnetic properties
and their energy loss in thin metal foils. Detector systems
installed in the path of the beam allow the unambiguous
identification of every single isotope transmitted through
the device. The large acceptance of the separator
together with intense primary beams from the cyclotrons
allow access to the most exotic nuclei that exist, some
of which were observed for the first time at FRIB. The
investigation of the limits of nuclear stability provides a
key benchmark for nuclear models and is fundamental to
the understanding of the nuclear forces and structure.
Another research area is the development of particle
detectors made from diamond produced by chemical
vapor. Radioactive beam facilities of the newest generation
can produce rare isotope beams with very high intensities.
The special properties of diamond allow the development
of radiation-hard timing and tracking detectors that can
be used at incident particle rates up to 108 particles per
second. Detectors based on poly-crystalline diamond were
built and tested at FRIB and excellent timing properties
were achieved. Those detectors have been successfully
used as timing detectors in several FRIB experiments.
First, detectors based on single-crystal diamond showed
superior efficiency and energy resolution. Further
development will continue with the investigation of
properties of single-crystal diamond detectors and the
production of position-sensitive detectors with larger
active areas.
Selected Publications
Degradation of single crystal diamond detectors in swift
heavy ion beams, A. Bhattacharya et al., Diamond and
Related Materials 70, 124 (2016)
Evidence for a Change in the Nuclear Mass Surface with
the Discovery of the Most Neutron-Rich Nuclei with 17 ≤ Z
≤ 25, O.B. Tarasov et al., Phys. Rev. Lett. 102, 142501 (2009)
First observation of two-proton radioactivity in 48 Ni, M.
Pomorski et al., Phys. Rev. C 83, 061303 (2011).
Particle identification plot showing the energy loss in a
silicon detector as a function of time-of-flight through
the A1900 fragment separator. The separator tune was
optimized for 60 Ge, a rare isotope observed for the first
time at FRIB.
77
2022_FRIB_Graduate_Brochurev4.indd 77
10/29/2021 3:33:57 PM