To achieve the Earth antineutrino tomography requires a number of crucial steps, each followed by a go/no-go decision. This has the advantages that the programme has well defined stages, each stage being precisely defined by the end of its predecessor. It starts out relatively small with an appropriate budget and will grow in time both in size and in budget.
Stage 1 (completed)
The first stage of the detector development mainly took place in South Africa and involved the mimicking of the antineutrino capture reaction by the scattering of neutrons from protons in a boron-loaded scintillation liquid. This experimental investigation was combined with Monte Carlo simulations to investigate the effect of boron loading on the direction sensitivity. The results have been published in two publications:
R.J. de Meijer, F.D. Smit, F.D. Brooks, R.W. Fearick, H.J. Wörtche and F. Mantovani, Towards Earth AntineutRino TomograpHy (EARTH), Earth, Moon and Planets, 99, (2006), 193-206.
F.D. Smit, R.J. de Meijer, F.D. Brooks, R.W. Fearick, H.J. Wörtche, Neutron detection, the key to direction sensitive geoneutrino detectors, Proceedings of Science, FNDA (2006) 96.
Based on these experiences, a next generation detector has been designed and a number of potential scintillator materials have been selected for optimizing the detector performance.
Parallel to this detector development, a literature investigation was made on the feasibility and implications of nuclear georeactors in the Earth’s core-mantle boundary. The results have been discussed in Nature News and were published in the South African Journal of Science:
- P. Ball, Are there nuclear reactors at Earth's core? Nature News, , (2008) doi:10.1038/news.2008.822.
- R.J. de Meijer, and W. van Westrenen, The feasibility and implications of nuclear georeactors in Earth’s core-mantle boundary region, South African Journal of Science, 104, (2008), 111-118.
Using fast digital ADCs and developing a special algorithm, the Signal and More group at the KVI, University Groningen, the Netherlands were able to show that the arrival time difference between two pulse-generator pulses, one direct and the other delayed by 10 ns, could be measured with a precision of 10 ps.
Stage 2 (~three years)
After stage 1 it has become clear that the programme is technically feasible by testing prototype detectors at a set-up near a nuclear power plant. Here the programme is likely to produce a first spin-off: a prototype detector for monitoring and safeguarding nuclear power plants. Initially we will mainly focus on characterisation of the antineutrino signal, but a detector system, Geoneutrinos in ZA (GiZA) has been designed in which the positions of both the positron and neutron will be determined from the arrival time differences of the light signals at the various detectors. The algorithm mentioned in stage 1 will be used to investigate the possibilities for real signals.
One of the tasks for this stage is to examine and optimize the background reduction due to cosmic rays and environmental gamma-radiation. In collaboration with the University of Jyväskylä, Finland, we are discussing applying their new design of scintillator detectors and testing them together with GiZA in the underground laboratory at Pyhäsalmi, Finland. Part of this task will be to test the detectors in an underground mine under more realistic conditions as well as to install and test the data transfer and storage.
Stage 3 (~three years)
Stage 3 involves the construction of the proto-type detector for reactor monitoring. We expect that after optimizing GiZA, a multi-detector system will be designed and built to be installed near a nuclear power plant. Initially the summed volume of these detectors is expected to be 500-1000 litres. At this stage it is too early to speculate on the precise configuration. With the modular set-up of our detectors we expect to have more flexibility in placing the detectors around the reactor core. At the end of this stage the feasibility of a 3D-tomography image of the reactor core should be tested.
If finances allow, we will construct a second system for underground measurements. The count rates of signal and background will guide us in the further optimisation of the antenna concept.
During this stage we expect that techniques will be developed for improving the detector system, data acquisition and data handling. If proven to be reliable, these techniques will be incorporated in our detector systems and their data handling and storage.
For this stage the experience with the proto-type monitoring and safeguarding detector will influence our underground detector and visa versa. The first antenna will be further extended until a first impression on the radiogenic heat sources is obtained and it becomes more evident where and how other antennas are to be built: the globalisation of the project takes place.