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Johannes Gutenberg-University, Institute for Nuclear Chemistry

Ultra-cold neutrons (UCN) offer unique opportunities for studying the properties of the free neutron with exceptionally high precision. Properties as its lifetime can be measured with unprecedented accuracy.

UCN sources are under construction at different research centres worldwide in order to tackle the existing count-rate limitations in these kinds of experiments. Low-power reactors, such as TRIGA Mainz with its inherent safety, are strongly competitive due to the possibility to pulse the reactor every five minutes (peak power 250 MW) and produce a high density of UCN that ideally meet the requirements of storage experiments, where the trap must be filled with a similar frequency. With a recently installed super-thermal UCN source at TRIGA a density of 10 UCN/cm3 in a 10 litre storage volume has been achieved. Background interference during data taking is essentially zero since the reactor is off during the measurements. Low magnetic noise is another quality feature of this reactor.

Within PRISMA the TRIGA reactor is transformed into a world-leading user facility, which will be open to researchers from all over the world who want to perform new high-precision experiments with UCN. Our goal is to reach a UCN density of ~100/cm3. PRISMA provides the infrastructure to sustain long-term experiments at a facility well suited for UCN-storage experiments. The conversion to a full user facility is ongoing: A He-liquefier with a capacity of 14 l/h has been commissioned in autumn 2014. New staff for user operation has been hired. In parallel the upgrade of the UCN-source from its present 10 UCN/cm3 is ongoing. A UCN density of ~50/cm3 in the near future is expected.

An important step is also the transfer of the UCN from the source to the experiment. For high transmission efficiency a sputter facility is in operation at the Institute of Physics. Here neutron guide tubes of high quality (low losses and high reflective Fermi potential) are produced for the experiments at TRIGA as well as for experiments at other UCN facilities. The highlight here is the production of neutron guides internally coated with 58Ni, the material which is best suited for neutron guidance (highest Fermi Potential). The coating of the extraction volume of the UCN source with 58Ni is also a crucial part for its upgrade.

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