J.M. O'Donnell

Background identification and suppression for the measurement of (n,γ) reactions with the DANCE array at LANSCE

Abstract In the commissioning phase of the DANCE project (Detector for Advanced Neutron Capture Experiments) measurements have been performed with special emphasis on the identification and suppression of possible backgrounds for the planned (n,γ) experiments. This report describes several background sources, observed in the experiment or anticipated from simulations, which will need to be suppressed in this and in similar detectors that are planned at other facilities. First successes are documented in the suppression of background from scattered neutrons captured in the detector as well as from the internal radiation. Experimental results and simulations using the GEANT code are compared.

Acquisition-analysis system for the DANCE (detector for advanced neutron capture experiments) BaF/sub 2/ gamma-ray calorimeter

The DANCE detector is a segmented 4/spl pi/ gamma-ray calorimeter for measuring (n, /spl gamma/) and (n,fission) cross-sections of stable and long-lived radioactive isotopes. DANCE uses waveform digitization to acquire the basic gamma-ray data, which maximizes the information available for event reconstruction, but has necessitated the development of several techniques for handling the resulting high data rates. This paper describes the basic experimental requirements for acquisition and analysis and how we have satisfied these requirements primarily by extending existing acquisition and analysis frameworks.

Time-of-flight measurement of fast neutrons with Timepix detectors

Timepix pixel detectors have been used to study the response of silicon hybrid pixel detectors to fast neutrons from a pulsed neutron beam at WNR FP30R, a 14 m long flight path, in the Los Alamos Neutron Science Center. Neutrons with kinetic energies up to 600 MeV were available. In order to enhance the conversion of neutrons to energetic charged particles, several converter foils and filters were attached to the 300 μm thick silicon sensor, i.e. polyethylene, polyethylene with aluminum, 6LiF, 6LiF with aluminum, aluminum. The Time-of-Arrival mode of the Timepix detectors has permitted the application of the Time-of-Flight (TOF) technique for the assignment of the detected interactions in the form of clusters (groups of adjacent pixels) in the pixel matrix, to the kinetic energies of the incident neutrons. It was found that, for lower neutron energies ( ~ MeV range) the cluster rates below the polyethylene and the polyethylene and aluminum region, produced by recoil protons, are a good measure for the mean kinetic energies of neutrons. For energies above 50 MeV nuclear reactions in the silicon dominate the detector response. In this energy range the shape of the clusters indicates the neutron kinetic energy.

Spin measurements for

We have determined the spins

^{147}

J

Sm

of resonances in the

+n

^{147}\mathrm{Sm}

resonances: Further evidence for non-statistical effects

(

{pi}{sup +}+d{r_arrow}p+p reaction between 18 and 44 MeV

n,\ensuremath{\gamma}

Measurement of the {sup 157}Gd(n,{gamma}) reaction with the DANCE {gamma} calorimeter array

) reaction by measuring multiplicities of