Measurement of the n_TOF beam profile with a micromegas detector

A Micromegas detector was used in the neutron Time-Of-Flight (n_TOF) facility at CERN to evaluate the spatial distribution of the neutron beam as a function of its kinetic energy. This was achieved over a large range of neutron energies by using two complementary processes: at low energy by capture of a neutron via the 6Li(n,[alpha])t reaction, and at high energy by elastic scattering of neutrons on gas nuclei (argon+isobutane or helium+isobutane). Data are compared to Monte Carlo simulations and an analytic function fitting the beam profile has been calculated with a sufficient precision to use in neutron capture experiments at the n_TOF facility.http://www.sciencedirect.com/science/article/B6TJM-4BRSWVV-3/1/01dd54d28c7a57560574f1adfbd8a2f

A low-mass neutron flux monitor for the n_TOF facility at CERN

A small-mass system has been developed for monitoring the flux of neutrons with energy up to 1 MeV at the new time-of-flight facility at CERN, n_TOF. The monitor is based on a thin Mylar foil with a Li-6 deposit, placed in the neutron beam, ; an array of Silicon detectors, placed outside the beam, for detecting the products of the Li-6(n, alpha)H-3 reaction. The small amount of material on the beam ensures a minimal perturbation of the flux and minimizes the background related to scattered neutrons. Moreover, a further reduction of the gamma-ray background has been obtained by constructing the scattering chamber hosting the device in carbon fibre. A detailed description of the flux monitor is here presented, together with the characteristics of the device, in terms of efficiency, resolution and induced background. The use of the monitor in the measurement of neutron capture cross-sections at n_TOF is discussed

Neutron capture cross section measurement of ¹⁵¹Sm at the CERN neutron time of flight facility (n_TOF)

The Sm-151(n,gamma)Sm-152 cross section has been measured at the spallation neutron facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. The new facility combines excellent resolution in neutron time-of-flight, low repetition rates, and an unsurpassed instantaneous luminosity, resulting in rather favorable signal/background ratios. The Sm-151 cross section is of importance for characterizing neutron capture nucleosynthesis in asymptotic giant branch stars. At a thermal energy of kT=30 keV the Maxwellian averaged cross section of this unstable isotope (t(1/2)=93 yr) was determined to be 3100+/-160 mb, significantly larger than theoretical predictions

New experimental validation of the pulse height weighting technique for capture cross-section measurements

The accuracy of the pulse height weighting technique for the determination of neutron capture cross-sections is investigated. The technique is applied to measurements performed with C6D6 liquid scintillation detectors of two different types using capture samples of various dimensions. The data for well-known (n, gamma) resonances are analyzed using weighting functions obtained from Monte Carlo simulations of the experimental set-up. Several causes of systematic deviation are identified and their effect is quantified. In all the cases measured the reaction yield agrees with the standard value within 2%