1m. A(Z,N) -> A(Z+2 , N-2) + 2e + 2 ν e. COBRA Double Beta Decay Experiment D.Y. Stewart , Dr. Y.A. Ramachers, Prof. P.F.Harrison Experimental Particle Physics Group University of Warwick. Comparison of Shielding Designs:
A(Z,N) -> A(Z+2 , N-2) + 2e + 2νe
COBRA Double Beta Decay Experiment
D.Y. Stewart, Dr. Y.A. Ramachers, Prof. P.F.Harrison
Experimental Particle Physics Group
University of Warwick
Comparison of Shielding Designs:
A number of configurations of materials eg. type of material, ordering of materials and thickness’, for shields were simulated using MCNPX based on previous simulations. These designs were then compared to existing shielding designs in use by other experiments. Std’s are existing designs, Prim’s are Warwick’s designs. Prim1|3 is “the best”allowing the fewest neutrons to pass through, showing our layer design is worthwhile.
107 neutrons fired into a block of material
Liquid Scintillator Testing:
A(Z,N) -> A(Z+2 , N-2) + 2e
Warwick’s Involvement: Development of an optimal shielding design
ββ decays of interest typically have energy release of > 2MeV but there are many forms of radiation which have similar signatures. The result is background interference.
Experimental challenge = background control
64-Crystal Array Set-up
A number of designs and combinations of materials were tested using the simulation packages MCNP and GEANT4. The overall shielding design is to be optimised for shielding against neutrons. A variety of neutron absorbers were tested using MCNP so a comparison between them could be made, the results are shown below.
The above picture shows a side profile view of the layers of shielding in the design. This design was simulated using GEANT4 with 200 neutrons yr-1m-2,the high energy neutron flux at Gran Sasso. 50,000 high energy neutron events were simulated (equivalent to 52.27 years of running) and only 3x108 counts/year/KgKeV were detected by the crystals. This corresponds to less than 1 neutron per year!
3-Dimensional view of COBRA – simulated using GEANT4, crystals at the centre surrounded by shielding layers.