The NPP instruments

The Nuclear and Particle Physics Group operates 4 scheduled instruments: Two instruments (PN1 - fission spectrometer "LOHENGRIN" and PN3 - high resolution gamma-ray spectrometers "GAMS") deal mainly with nuclear physics and applied nuclear physics aspects. Two other ones (PF1 - intense cold neutron beam facility and PF2 - ultracold neutron facility) are covering mainly neutron particle physics aspects. Additionally to the scheduled instruments there exists a thermal neutron interferometer (S18) which is operated as a CRG C instrument.


The recoil mass separator for unslowed fission products LOHENGRIN uses fission products originating from a source of fissile isotopes placed in a beam tube (H9) near the core of the reactor. Specific fission products are selected by a combination of a magnetic and an electric sector field whose deflections are perpendicular to each other. The freely recoiling fission products are analyzed according to their energy over ionic charge (E/q) and mass over ionic charge (A/q) ratios. The main directions of research on PN1 were in the past centered around studies of the fission process but are now more and more concentrated on spectroscopy of very neutron rich nuclei. To this purpose two Germanium Clover detectors and ancillary detectors were purchased in the M0 phase of the Millenium project. 


The high resolution gamma ray facility GAMS makes use of the fact that at the ILL reactor one can obtain extremely high specific activities when exploiting thermal neutron capture at an in-pile target facility. This allows to aim for the application of gamma spectroscopy with the highest possible energy resolution. Gamma rays emerging from the in-pile targets are successively diffracted by two crystals (either flat or bent). The diffraction angles are controlled by high resolution interferometers. The technique allows to obtain a resolution of ΔE/E which approaches the 1 ppm level. Many studies on this facility have contributed to our understanding of the structure of nuclei. Others are devoted to the determination of standards and fundamental constants. The measurement of Doppler profiles induced by the recoil which nuclei experience when they emit gamma rays allows to deduce information about short lifetimes of excited nuclear states and gives insight into the low-energy slowing down process of atoms in matter. 


The intense cold polarized / unpolarized neutron beam facility PF1B is installed at the end position of the cold ballistic supermirror guide H113. This guide offers a neutron flux density of 1.8x1010 neutrons cm-2s-1. The guide cross section is 6x20 cm2. Neutron particle and nuclear physics experiments which have recently been carried out comprise measurements of neutron decay asymmetry coefficients and of properties of the neutron, studies of asymmetries in neutron capture reactions and neutron induced fission, nuclear spectroscopy of fission products, and measurements of fission cross-sections and yields of ternary particles in fission.


The ultracold neutron facility PF2 was built by TU Munich in collaboration with ILL. At the experimental positions it provides a density of 50 cm-3 of ultracold neutrons (UCN) with speeds less than 6 m/s. UCN are produced at the top end of a vertical guide where neutrons with speeds of 50 m/s are converted by the so-called Steyerl turbine into UCN with about 5 m/s. The UCN are then led by horizontal guides to several experiments in parallel. There is also an output for very cold neutrons (VCN) with a wavelength of 100Å. As the neutron is electrically neutral this offers specific experimental advantages such as (for UCN) the option for storage in traps. Consequently the majority of measurements carried out at PF2 use this feature. Experiments carried out recently on this facility concerned - amongst others - the measurement of the neutron lifetime, the measurement of the neutron electric dipole moment and the study of "anomalous losses" of stored neutrons. 


The CRG C instrument S18 is a perfect crystal neutron interferometer which can also be configured as a high resolution Bonse Hart camera. This instrument can be used for precise measurement of neutron scattering lengths and for basic neutron quantum optics studies and related phenomena.