Instrument Description

Reactor hall level C, cold guide H172
13.6 m downstream the vertical liquid-deuterium neutron cold source
graphite crystals intercalated with potassium
8.9 A monochromatic neutrons reflected towards guide H172A
Ultra Cold Neutron (UCN) source
Small size  4 He source 5 liters
Environment setup
Anti-vibration and levelling systems  
Clean-room class 1
at position of the GRANIT optical elements
transport mirror

25 x 30 cm 2

(gravitational quantum states in flow-through mode)

specular trap

30 x 30 cm 2  with vertical walls of ~ 500 µm

(gravitational quantum states in storage mode)

nuclear-track position-sensitive UCN detectors spatial resolution ~1 µm
low-background  3 He UCN counters background ~10 -4  s -1
one- and two-dimensional UCN detectors

spatial resolution of ~100 µm

(to be developed)

The GRANIT project consists of designing and building a second-generation gravitational neutron spectrometer with ultra-high resolution. Its key property is the storage of UCN in a selected gravitationally bound state for extended period of time using a closed specula trap. The high quality of mirrors needed for the trap is at the edge of modern technology.

According to the uncertainty principle, longer observation time corresponds to better defined energy of a state. Resonant transitions between the states allow us to measure energy precisely. Such precision measurements constrain acceptable external perturbations, such as vibrations or magnetic fields.
As the fraction of gravitationally bound neutrons is extremely small, we develop neutron detectors with extremely low backgrounds, UCN sources with maximum neutron density, and neutron transport systems with minimal losses. Nearly every component of the GRANIT spectrometer is constructed for the first time and has no analogs.

The GRANIT spectrometer will be a unique tool for carrying out a wide range of investigations in particle fundamental physics (neutron electric charge, spin-dependent or spin-independent short-range forces), foundations of quantum mechanics, in surface physics, as well as for development of experimental techniques and their applications.
The GRANIT project is being constructed in the framework of ANR (Agence Nationale de la Recherche, France) grant of 600 K€ received in 2005 by a joint collaboration ILL-LPSC-LMA. The physical program to be carried out using the GRANIT spectrometer involves a number of scientific institutions from France, USA, Germany, and Russia.