David M. Gilliam

Improved determination of the neutron lifetime.

The most precise determination of the neutron lifetime using the beam method was completed in 2005 and reported a result of τ(n)=(886.3±1.2[stat]±3.2[syst]) s. The dominant uncertainties were attributed to the absolute determination of the fluence of the neutron beam (2.7 s). The fluence was measured with a neutron monitor that counted the neutron-induced charged particles from absorption in a thin, well-characterized 6Li deposit. The detection efficiency of the monitor was calculated from the areal density of the deposit, the detector solid angle, and the evaluated nuclear data file, ENDF/B-VI 6Li(n,t)4He thermal neutron cross section. In the current work, we measure the detection efficiency of the same monitor used in the neutron lifetime measurement with a second, totally absorbing neutron detector. This direct approach does not rely on the 6Li(n,t)4He cross section or any other nuclear data. The detection efficiency is consistent with the value used in 2005 but is measured with a precision of 0.057%, which represents a fivefold improvement in the uncertainty. We verify the temporal stability of the neutron monitor through ancillary measurements, allowing us to apply the measured neutron monitor efficiency to the lifetime result from the 2005 experiment. The updated lifetime is τ(n)=(887.7±1.2[stat]±1.9[syst]) s.

Fast neutron detection with 6Li-loaded liquid scintillator

We report on the development of a fast neutron detector using a liquid scintillator doped with enriched 6 Li. The lithium was introduced in the form of an aqueous LiCl micro-emulsion with a di-isopropylnaphthalene-based liquid scintillator. A 6 Li concentration of 0.15 % by weight was obtained. A 125 mL glass cell was lled with the scintillator and irradiated with ssion-source neutrons. Fast neutrons may produce recoil protons in the scintillator, and those neutrons that thermalize within the detector volume can be captured on the 6 Li. The energy of the neutron may be determined by the light output from recoiling protons, and the capture of the delayed thermal neutron reduces background events. In this paper, we discuss the development of this 6 Li-loaded liquid scintillator, demonstrate the operation of it in a detector, and compare its eciency and capture lifetime with Monte Carlo simulations. Data from a boron-loaded plastic scintillator were acquired for comparison. We also present a pulse-shape discrimination method for dierentiating between electronic and nuclear recoil events based on the Matusita distance between a normalized observed waveform and nuclear and electronic recoil template waveforms. The details of the measurements are discussed along with specics of the data analysis and its comparison with the Monte Carlo simulation.

Measurement of the Neutron Lifetime by Counting Trapped Protons in a Cold Neutron Beam

A measurement of the neutron lifetime

Measurement of the Neutron Lifetime Using a Proton Trap

{\ensuremath{\tau}}_{n}

Mass assay and uniformity tests of boron targets by neutron beam methods

performed by the absolute counting of in-beam neutrons and their decay protons has been completed. Protons confined in a quasi-Penning trap were accelerated onto a silicon detector held at a high potential and counted with nearly unit efficiency. The neutrons were counted by a device with an efficiency inversely proportional to neutron velocity, which cancels the dwell time of the neutron beam in the trap. The result is

Absolute neutron counting based on B-10 alpha-gamma coincidence methods

{\ensuremath{\tau}}_{n}=(886.3\ifmmode\pm\else\textpm\fi{}1.2[\mathrm{stat}]\ifmmode\pm\else\textpm\fi{}3.2[\mathrm{sys}])\phantom{\rule{0.3em}{0ex}}s

Determination of the neutron lifetime by counting trapped protons

, which is the most precise measurement of the lifetime using an in-beam method. The systematic uncertainty is dominated by neutron counting, in particular, the mass of the deposit and the

Pass-Fail Testing: Statistical Requirements and Interpretations.

^{6}\mathrm{Li}

The characterisation of 10B and 6LiF reference deposits by the measurement of neutron induced charged particle reactions

(n,t)