Research: NUCIFER
Original motivation
The large amounts of electron antineutrinos produced in nuclear reactors provide information
related to the isotopic composition of the reactor core and its thermal power. There is an interest
in using antineutrino detectors as a potential safeguard tool. Therefore the studies within
the NUCIFER project [1] are dedicated to a large extent to safeguard and non-proliferation applications.
For example, the detection of a change in the antineutrino spectrum consistent with the removal of
a large quantity of 239Pu from the reactor would raise suspicions. The NUCIFER experiment was proposed
to IAEA (International Atomic Energy Agency) in October 2008 [2]. To allow that the antineutrino detector
can be placed very near to the reactor core (ca. 10 m) the detector should be compact, remote
controlled, safe and moveable. The detector is currently operated at the OSIRIS research reactor
at CEA-Saclay, France.
Do sterile neutrinos exist?
Recently a possible new application for this experiment of major scientific impact appeared. The
NUCIFER experiment could investigate an anomaly observed in the data of several reactor neutrino
experiments around the world. Measured values of the electron antineutrino flux appear to be only
94% of the value expected from theory [3]. So far, it is unknown whether this is due to unknown physics
that might involve weak mixing with a sterile neutrino or due to an overseen issue either related to
the experimental measurements or the theoretical flux calculations.
Detector design
The detector target is a 850 liter Gadolinium doped liquid scintillator filled into a cylindrical
stainless steel vessel. As in other reactor neutrino experiments as Double Chooz the antineutrinos
are detected via the inverse beta decay on Hydrogen nuclei of the target scintillator resulting in a
coincidence signal (separated by several microseconds) of a prompt (positron energy) and delayed
(neutron capture on Gadolinium isotopes) event. The scintillation light produced in the prompt and
delayed signal is detected by 16 photomultiplier tubes (PMTs) on top of the detector. Between the PMTs
and the target liquid there is a 25 cm thick acrylic buffer disk. Layers of polyethylene (15 cm) and
lead (10 cm) protect the target liquid against external radioactivity mainly originating from the
nearby research reactor. There is also an active veto made of 5 cm thick plastic scintillator panels.
The data acquisition system (DAQ) is build with commercial VME and NIM modules and it is operated with
a software interface written in LabView. Regular calibrations allow to monitor detector performance and
stability.
NUCIFER at the MPIK
MPIK provides the Gadolinium loaded organic target scintillator for the NUCIFER experiment. The main
challenge in developing metal loaded scintillator is to ensure long term stability of the optical
parameters as light yield and transparency. Similar methods as for the production of the Double Chooz
target scintillator [4] are applied and identical components are used. The concentrations of the individual
components were tuned to optimize background reduction in NUCIFER. In particular the target liquid was
tuned to allow for a pulse shape discrimination of fast neutron events, a main background source in the
experiment, and the coincidence time window is shortened due to an increased Gd-concentration.
Our group will also contribute to the analysis of the experiment, especially to learn more about the
reactor neutrino anomaly described above.
Future goals
In the future the NUCIFER detector might be used at a commercial reactor in France as well. Concerning
the search for sterile neutrinos new detectors are planned optimized for the needs of such an experiment.
The design and results of the NUCIFER experiment provide important input information for such
expermiments trying to solve the reactor neutrino anomaly.
References
[1] A. Porta for the NUCIFER collaboration, "Reactor Neutrino Detection for Non Proliferation with the
NUCIFER Experiment", IEEE proceedings, 10.1109/ANIMMA.2009.5503653 (2009).
[2] Focused Workshop on Antineutrino Detection for safeguard Applications, Final Report of IAEA Workshop,
IAEA Headquarters, Vienna (2008).
[3] G. Mention et al., Phys. Rev. D83, 073006 (2011).
[4] C. Aberle et al., JINST, 7, P06008 (2012).
Contact:
-
Dr. Christian Buck
Tel: 06221 516829
E-Mail: Christian.Buck@mpi-hd.mpg.de
- Prof. Dr. Manfred Lindner
Tel:06221 516800
E-Mail: manfred.lindner@mpi-hd.mpg.de