Beta-decay experiments

The rapid neutron capture process (r-process) takes place in an environment with a very high neutron density, like the outflow of material ejected by the merger of two neutron stars, and produces the heaviest chemical elements found in nature. Most of the unstable isotopes formed during the r-process are expected to decay by delayed-neutron emission: a radioactive decay mode where one or more neutrons are emitted immediately following the beta-decay (from neutron unbound states in the daughter nuclei). Nuclear data on this kind of decay is essential to construct reliable models of the r-process. Our current focus for decay experiments is with the Beta-delayed neutrons at RIKEN (BRIKEN) collaboration. BRIKEN is a setup that combines the intense beams of neutron-rich isotopes from the Radioactive Isotope Beam Factory (RIBF) in RIKEN, Japan, with the large neutron detection efficiency of 3He proportional counters, making many r-process isotopes within reach of experiments for the first time.
BRIKEN collaboration

Members of the BRIKEN collaboration after completing a successfull run of beta-delayed neutron measurements at the Radioactive Isotope Beam Factory (RIBF) laboratory in Japan.

BRIKEN setup

BRIKEN setup at the F11 experimental area of RIBF; a detailed description can be found in NIMA 925, 133.

Time-of-Flight Mass Measurements

Mass is a fundamental property of an atomic nucleus. As elegantly summarized in a famous physics equation, E=mc2, the nuclear mass (m) is directly related to the nuclear energy (E) that tightly binds protons and neutrons in a nucleus. Most methods to measure nuclear masses rely on the motion of a nucleus as it interacts with external electromagnetic fields. In the case of the time-of-flight technique, we use a spectrometer beamline (e.g. the S800 at the NSCL) and a precise measurement of the time-of-flight and magnetic rigidity of the beam ions as our measurement tools. The technique can be applied to very unstable isotopes with low beam rates, and address questions about neutron stars (PRL 107, 172503) and nucleosynthesis of heavy elements during the r-process.
TOF experiment setup

Experimental setup for TOF experiments at the National Superconducting Cyclotron Laboratory (NSCL) (NIMA 696, 171).

Collaborators during experiment e12022

Discussing the preparations for NSCL experiment e12022 (August 2018), a collaboration that was lead by Prof. Mike Famiano of Western Michigan University.

Development of Radiation Detectors

In the CMU detector development lab we work in high-resolution timing detectors. Radiation detectors that can measure precisely the time of interaction with the particles in an ion beam are an essential component of many experimental setups. We are currently working with detectors for time-of-flight (TOF) mass measurement experiments and for particle identification of isotopes in fast ion beams (NIM A 974, 164199). The detector lab includes a test stand with a pico-second laser source and high-resolution timing electronic modules.
Test of new TOF detector

At CMU we have developed a new timing detector for TOF mass measurement experiments, with an intrinsic resolution bellow 10 picoseconds. The photo shows CMU and WMU students preparing to test the detector with a proton beam at the WMU tandem accelerator.

Analyzing Results.

The Large Area Timing Scintillator detector (LAST) is a prototype for a time-of-flight detector under development for the focal plane of the S800 spectrometer of the National Superconducting Cyclotron Laboratory. We use a picosecond pulsed laser source at CMU to characterize the detector and optimize its design.

Computational Nuclear Astrophysics

The r-process process is responsible for the production of roughly half of the elements heavier than iron. R-process models are very sensitive to the nuclear physics data required to calculate the nuclear reactions that drive the synthesis of these elements. We use nuclear reaction network codes to simulate the r-process and evaluate how our nuclear physics experiments can help to understand unsolved mysteries of the r-process; for example its site or sites, or its contribution through the history of chemical enrichment of our galaxy. This work is done in close collaboration with astrophycicists within the Joint Institute for Nuclear Astrophysics (JINA).
r-process abundances

Elemental abundances for an r-process during a neutron-star black-hole merger calculated with the SkyNet code, using two different theoretical models for beta-decay rates. The simulations were done by Tom Chapman as part of his senior capstone project.