Zach Kohley



Coincident Fission Fragment Detector (CFFD):

The production of superheavy nuclei has been accomplished almost completely through the use of the heavy-ion fusion mechanism.   In order to understand the dynamics of heavy-ion fusion reactions we want to measure the binary decay products from the quasifission reactions (hinderance of fusion) and fusion-fission reactions (compound nucleus was formed). These measurements are accomplished with the CFFD.

The primary detectors for the CFFD (Coincidence Fission Fragment Detector) are four large area (30 cm x 40 cm) position sensitive parallel plate avalanche counters (PPACs).  Each PPAC consists of two 0.6um foils with 1 mm spaced gold strips evaporated (40 in the X-direction and 30 in the Y-direction) and a center foil.  When a fission-like fragment passes into a PPAC an electron avalanche will be produced.  The PPAC allows for the the position of each fragment and the time when it arrived at the detector to be measured.  Inside the CFFD vacuum chamber there is also a microchannel plate (MCP) detector that provides a measure of the beam profile and a "time zero" signal. Two silicon monitoring detectors are also used to measure Rutherford scattering for calibration purposes. 

Using the position and timing information of the PPACs, we can use the kinematics of a reaction to reconstruct the mass ratio and angular distribution of the two fission-like fragments.  This information allows us to study and understand the dynamics of heavy-ion fusion reactions.


MoNA-LISA and Sweeper Magnet

The isotopes we study can be so short-lived that we never get a chance to examine them directly.  Extremely neutron-rich isotopes that exist beyond the dripline (termed unbound) will “decay” by emitting neutron(s) almost immeditaely after begin formed (10e-21 sec).   Thankfully, we can study the decay of these extremely exotic isotopes using the MoNA LISA-Sweeper experimental set-up. This allows for the neutron(s) and chaged particle remaining from the decay to be measured.

MoNA LISA (short for the Modular Neutron Array and the Large multi-Institutional Scintillator Array) gives us the ability to detect neutrons using its 288 plastic scintillator bars.  When a neutron hits a bar, light is emitted.  The light travels to both ends of the bar, and the timing of this light is used to determine the flight path and time of flight of the neutrons.

Meanwhile, the Sweeper magnet uses the positive charge on the remaining particle to “sweep” or divert the remaining charged particle into a detector box.  A series of detectors allows us to identify the particle and its energy.

By combining the information we gain from MoNA LISA and the Sweeper, we can reconstruct a picture of our desired isotope in order to study it. Additionally, our group has expanded the applications of the MoNA-LISA-Sweeper setup to be used for studying the nuclear Equation fo State.