n_TOF

n_TOF
Landua, Fabienne · CC BY 4.0 · source
Name	n_TOF
Type	Research facility
Location	CERN, Meyrin
Established	2001
Operator	CERN
Primary beam	Proton beam from the Proton Synchrotron
Mission	Neutron time-of-flight measurements for nuclear physics, astrophysics, and applications

n_TOF is a neutron time-of-flight research facility at CERN designed for high-resolution measurements of neutron-induced reaction cross sections. It serves experiments in nuclear physics, nuclear astrophysics, radiation protection, and nuclear engineering, providing a pulsed neutron source driven by the Proton Synchrotron (PS). The facility supports collaborations involving institutions such as INFN, CEA, IPN Orsay, ITER Organization, and national laboratories across Europe and beyond.

Overview

n_TOF was commissioned to exploit the long flight path and high instantaneous neutron flux produced when protons from the Proton Synchrotron (PS) strike a heavy metal spallation target. The facility produces a broad neutron energy spectrum used to measure capture, fission, and scattering cross sections relevant to the s-process (nucleosynthesis), r-process (nucleosynthesis), reactor design studies at Generation IV research initiatives, and transmutation research tied to programs at ITER Organization and national waste-management agencies. The user base includes collaborations with European Organization for Nuclear Research partners, universities such as University of Milan, Uppsala University, and laboratories like Los Alamos National Laboratory and Oak Ridge National Laboratory.

Facility and Beamline Description

The source is a spallation target irradiated by short pulses from the Proton Synchrotron (PS), producing neutrons captured into a flight path evacuated or filled with controlled gas. The primary beamline geometry includes a long flight path of about 185 metres to the experimental area, optimizing energy resolution via time-of-flight techniques and reducing background from prompt gamma-flash and scattered neutrons. The facility layout connects to experimental halls and detector stations that host arrays such as C6D6 detectors, 4π calorimeters, and fission-fragment detectors. Support infrastructure integrates cryogenic systems shared with cryostats used in low-temperature measurements and electronics racks synchronized to timing signals from the PS RF system.

Experimental Techniques and Instrumentation

Experiments use time-of-flight measurement, capture gamma-ray spectroscopy, and fission fragment detection to obtain reaction cross sections. Instruments include liquid scintillators, low-efficiency gamma detectors like C6D6 for capture yield, total absorption calorimeters for resonance studies, microsecond timing chains synchronized to the Proton Synchrotron (PS), and parallel plate avalanche counters for charged-particle identification. Sample handling and activation analysis require gloveboxes and hot cells similar to systems found at Institute Laue–Langevin and other major neutron facilities. Data acquisition systems implement digitizers and time-to-digital converters analogous to those used in experiments at GSI Helmholtz Centre for Heavy Ion Research and STFC Rutherford Appleton Laboratory.

Scientific Programs and Key Results

Research at the facility has produced high-precision cross sections for isotopes crucial to stellar nucleosynthesis such as measurements impacting models of the s-process (nucleosynthesis) in asymptotic giant branch stars and branching points involving isotopes studied at institutions like Max Planck Institute for Astrophysics. Results have refined neutron capture rates for actinides relevant to reactors and waste transmutation programs linked to Generation IV concepts and accelerator-driven systems endorsed by European Commission projects. The program has yielded resonance parameters for isotopes of uranium, thorium, and plutonium that inform evaluations in nuclear data libraries maintained by organizations such as the NEA Data Bank and International Atomic Energy Agency. Collaborative campaigns have addressed dosimetry standards referenced by ICRU and IAEA guidelines.

Data Analysis and Simulation Methods

Analysis workflows combine time-of-flight spectra unfolding, resonance shape analysis, and Monte Carlo simulation of neutron transport. Codes and tools employed include deterministic and stochastic transport packages similar to GEANT4, resonance analysis using R-matrix implementations comparable to those in SAMMY, and activation calculation frameworks akin to FISPACT for inventory and decay heat studies. Uncertainty quantification and covariance evaluations align with methodologies advocated by the Nuclear Energy Agency and national metrology institutes such as PTB and NPL to produce evaluated data compatible with libraries like ENDF/B, JEFF, and JENDL.

Safety and Radiation Protection

Radiation protection at the facility follows CERN radiation safety protocols and international best practices from ICRP and IAEA. Shielding design around the spallation target, beamline collimators, and experimental halls uses multilayered materials and access controls comparable to those implemented at other high-intensity neutron sources such as ISIS Neutron and Muon Source and Spallation Neutron Source. Active monitoring employs area dosimeters, personal dosimetry managed by occupational health services similar to those at CERN, and interlocked control systems coordinated with the Proton Synchrotron (PS) operations group to ensure safe beam delivery and sample handling under radiological constraints.

Future Developments and Upgrades

Planned upgrades focus on increased beam intensity, improved detector arrays, and enhanced data acquisition throughput to meet demands of programs connected to nuclear astrophysics campaigns and reactor-related measurements driven by collaborations with European Commission initiatives. Prospective enhancements include new calorimeter concepts, advanced digital electronics inspired by developments at GSI Helmholtz Centre for Heavy Ion Research and Brookhaven National Laboratory, and integration with multi-institution consortia involving INFN, CEA, and national metrology institutes to extend measurement capabilities for isotopes prioritized by international committees such as the NEA and IAEA.

Category:Neutron facilities