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.

A measurement of the neutron lifetime τ n 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 τ n = (886.6 ± 1.2[stat] ± 3.2[sys]) s, 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 6 Li(n,t) cross section. The measurement technique and apparatus, data analysis, and investigation of systematic uncertainties are discussed in detail.

One of the most striking predictions of Einstein's special theory of relativity is also perhaps the best known formula in all of science: E=mc(2). If this equation were found to be even slightly incorrect, the impact would be enormous--given the degree to which special relativity is woven into the theoretical fabric of modern physics and into everyday applications such as global positioning systems. Here we test this mass-energy relationship directly by combining very accurate measurements of atomic-mass difference, Delta(m), and of gamma-ray wavelengths to determine E, the nuclear binding energy, for isotopes of silicon and sulphur. Einstein's relationship is separately confirmed in two tests, which yield a combined result of 1-Delta(mc2)/E=(-1.4+/-4.4)x10(-7), indicating that it holds to a level of at least 0.00004%. To our knowledge, this is the most precise direct test of the famous equation yet described.

Accurate measurement of the lifetime of the neutron (which is unstable to beta decay) is important for understanding the weak nuclear force 1 and the creation of matter during the Big Bang 2 . Previous measurements of the neutron lifetime have mainly been limited by certain systematic errors; however, these could in principle be avoided by performing measurements on neutrons stored in a magnetic trap 3 .Neutral and charged particle traps are widely used tool for studying both composite and elementary particles, because they allow long interaction times and isolation from perturbing environments 4 . Here we report the magnetic trapping of neutrons.The trapping region is filled with superfluid 4 He, which is used to load neutrons into the trap and as a scintillator to detect their decay. Static magnetic traps are formed by creating a magnetic field minimum in free space.The confining potential depth (D) of such a trap is determined by the magnetic moment of the trapped species (µ) and the difference (∆B) between the magnitude of the field at the edge of the trap and at the minimum, D = µ∆B. A particle in a low-field-seeking state (one with its magnetic moment anti-parallel with the local magnetic field vector) is pushed towards the trap minimum. Low-field-seeking particles with total energy less than D are energetically forbidden from leaving the trapping region. For atoms and molecules with a magnetic moment of one Bohr magneton it is possible to produce trap depths of ∼ 1 K. The trap depth for a neutron in the same trap would be only ∼ 1 mK, because of its much smaller magnetic moment. Despite this difficulty, magnetic trapping of the neutron was proposed as early as 1961 by Vladimirskiȋ 11 .His proposed technique was later used to confine neutrons using a combination of gravity and magnets 12 . A separate effort to trap neutrons using a similar loading method to our work (but different detection scheme) was unsuccessful because of the high temperature of the helium 2 during the loading phase 13 .Crucial to the utility of traps are the techniques used to load them. In order to catch a particle in a static conservative trap, its energy must be lowered while it is in the potential well. Atoms and molecules have been cooled and loaded into magnetic traps by scattering with either cryogenic surfaces 14, 15 , cold gases 16 or photons from a laser beam (laser cooling) 17 .Neutrons, however, cannot be loaded by such methods because they cannot be excited optically and interact too weakly with atoms to be effectively cooled by a gas. Direct thermalization with a cold solid or liquid is generally precluded by the high probability for neutron absorption in the vast majority of materials.Our trapping of neutrons relies on a loading technique that employs the "superthermal process" 18 . A neutron with kinetic energy near 11 K (where the free neutron and superfluid helium dispersion curves cross) that passes through the helium-filled trapping region can lose nearly all of its energy through the creation of a single phonon. N...

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