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C. M. O'Shaughnessy,
R. Golub,
K. W. Schelhammer,
C. M. Swank,
P. -N. Seo,
P. R. Huffman, S. N. Dzhosyuk,
C. E. H. Mattoni,
L Yang,
J. M. Doyle,
K. J. Coakley,
A. K. Thompson,
H. P. Mumm,
S. K. Lamoreaux,
G Yang
[show abstract]
[hide abstract]
ABSTRACT: The neutron beta-decay lifetime plays an important role both in understanding weak interactions within the framework of the Standard Model and in theoretical predictions of the primordial abundance of 4He in Big Bang Nucleosynthesis. In previous work, we successfully demonstrated the trapping of ultracold neutrons (UCN) in a conservative potential magnetic trap. A major upgrade of the apparatus is nearing completion at the National Institute of Standards and Technology Center for Neutron Research (NCNR). In our approach, a beam of 0.89 nm neutrons is incident on a superfluid 4He target within the minimum field region of an Ioffe-type magnetic trap. A fraction of the neutrons is downscattered in the helium to energies <200 neV, and those in the appropriate spin state become trapped. The inverse process is suppressed by the low phonon density of helium at temperatures less than 200 mK, allowing the neutron to travel undisturbed. When the neutron decays the energetic electron ionizes the helium, producing scintillation light that is detected using photomultiplier tubes. Statistical limitations of the previous apparatus will be alleviated by significant increases in field strength and trap volume resulting in twenty times more trapped neutrons.
05/2009;
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L Yang,
C R Brome,
J S Butterworth, S N Dzhosyuk,
C E H Mattoni,
D N McKinsey,
R A Michniak,
J M Doyle,
R Golub,
E Korobkina,
C M O'Shaughnessy,
G R Palmquist,
P-N Seo,
P R Huffman,
K J Coakley,
H P Mumm,
A K Thompson,
G L Yang,
S K Lamoreaux
[show abstract]
[hide abstract]
ABSTRACT: We describe the design, construction, and performance of three generations of superconducting Ioffe magnetic traps. The first two are low current traps, built from four racetrack shaped quadrupole coils and two solenoid assemblies. Coils are wet wound with multifilament NbTi superconducting wires embedded in epoxy matrices. The magnet bore diameters are 51 and 105 mm with identical trap depths of 1.0 T at their operating currents and at 4.2 K. A third trap uses a high current accelerator-type quadrupole magnet and two low current solenoids. This trap has a bore diameter of 140 mm and tested trap depth of 2.8 T. Both low current traps show signs of excessive training. The high current hybrid trap, on the other hand, exhibits good training behavior and is amenable to quench protection.
Review of Scientific Instruments 04/2008; 79(3):031301. · 1.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Magnetically stabilized luminescence is observed in hexagonal boron nitride. The luminescence is induced by absorption of cold neutrons and is in the visible region. In the absence of a magnetic field, the photon emission level is observed to decay over several hundred seconds. A fraction of this luminescence can be suppressed if the temperature is T <~ 0.6 K and the magnetic field is B >~ 1.0 T. Subsequent to irradiation and suppression, luminescence can be induced by an increase in T or lowering of B. Possible explanations include stabilization of triplet states or the localization and stabilization of excitons. Comment: 11 pages, 7 figures, to appear in the Journal of Luminescence
03/2001;
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C. R. Brome,
J. S. Butterworth, S. N. Dzhosyuk,
C. E. H. Mattoni,
D. N. McKinsey,
J. M. Doyle,
P. R. Huffman,
M. S. Dewey,
F. E. Wietfeldt,
R. Golub,
K. Habicht,
G. L. Greene,
S. K. Lamoreaux,
K. J. Coakley
[show abstract]
[hide abstract]
ABSTRACT: Three-dimensional magnetic confinement of neutrons is reported. Neutrons are loaded into an Ioffe-type superconducting magnetic trap through inelastic scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low energy and in the appropriate spin state are confined by the magnetic field until they decay. The electron resulting from neutron decay produces scintillations in the liquid helium bath that results in a pulse of extreme ultraviolet light. This light is frequency downconverted to the visible and detected. Results are presented in which 500 +/- 155 neutrons are magnetically trapped in each loading cycle, consistent with theoretical predictions. The lifetime of the observed signal, 660 s +290/-170 s, is consistent with the neutron beta-decay lifetime. Comment: 17 pages, 18 figures, accepted for publication in Physical Review C
03/2001;
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[show abstract]
[hide abstract]
ABSTRACT: Recent success in magnetic confinement of ultracold neutrons (UCN) in a
Ioffe-type superconducting magnetic trap should lead to an improved
measurement of the neutron lifetime τ_n. The trap is loaded through
inelastic scattering of 0.89 nm neutrons with phonons in superfluid
^4He. Trapped neutrons are detected when they beta decay; energetic
decay electrons ionize helium atoms in the superfluid resulting in
efficient conversion of electron kinetic energy into light
(scintillation). The advantages of this technique over previous
experiments are continuous detection of scintillations from decay
electrons and the elimination of wall losses and betatron oscillations.
Analysis indicates that systematic errors due to neutron losses should
be controllable to 10-5τ_n. We are presently upgrading
our apparatus in preparation for a lifetime measurement by constructing
a larger, deeper magnetic trap and implementing techniques to
substantially reduce backgrounds. These improvements, should increase
the number of detected trapped neutrons by two orders of magnitude. With
these improvements a measurement of τn at the
5×10-4 level of accuracy should be possible within the
next year, given the flux available from the NG-6 beam line at NIST,
Gaithersburg.
09/2000; -1.
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P. R. Huffman,
C. R. Brome,
J. S. Butterworth,
K. J. Coakley,
M. S. Dewey, S. N. Dzhosyuk,
R. Golub,
G. L. Greene,
K. Habicht,
S. K. Lamoreaux,
C. E. H. Mattoni,
D. N. McKinsey,
F. E. Wietfeldt,
J. M. Doyle
[show abstract]
[hide abstract]
ABSTRACT: Accurate measurement of the lifetime of the neutron (which is unstable to beta decay) is important for understanding the weak nuclear force and the creation of matter during the Big Bang. 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. 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. 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. Neutrons have a lifetime in the trap of 750 +330/-200 seconds, mainly limited by their beta decay rather than trap losses. Our experiment verifies theoretical predictions regarding the loading process and magnetic trapping of neutrons. Further refinement of this method should lead to improved precision in the neutron lifetime measurement.
01/2000;
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[show abstract]
[hide abstract]
ABSTRACT: The neutron-induced low temperature (below 5 K) luminescence of neutron shielding and scintillation detection materials is studied. Strong luminescence is observed for the neutron absorbing materials boron nitride (BN) and lithium fluoride (LiF). A measurable, but substantially smaller luminescence is observed from boron oxide (B2O3). An upper bound of 10−3 was determined for the fraction of the luminescence due to time-correlated multiphoton events in the BN. Other materials tested – boron carbide (B4C), polymethyl methacrylate (PMMA or acrylic), expanded polytetrafluoroethylene (PTFE) with an evaporated coating of the downconverting fluor tetraphenyl butadiene (TPB) and a boron/lithium loaded glass – displayed no detectable luminescence. The boron/lithium loaded glass was determined to activate, by the secondary reaction 16O(T,n)18F, with the triton produced in the neutron capture reaction 6Li(n,T)4He.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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C.M. O’Shaughnessy,
R. Golub,
K.W. Schelhammer,
C.M. Swank,
P.-N. Seo,
P.R. Huffman, S.N. Dzhosyuk,
C.E.H. Mattoni,
L. Yang,
J.M. Doyle,
K.J. Coakley,
A.K. Thompson,
H.P. Mumm,
S.K. Lamoreaux,
D.N. McKinsey,
G. Yang
[show abstract]
[hide abstract]
ABSTRACT: The neutron beta-decay lifetime plays an important role both in understanding weak interactions within the framework of the Standard Model and in theoretical predictions of the primordial abundance of 4He in Big Bang Nucleosynthesis. In previous work, we successfully demonstrated the trapping of ultracold neutrons in a conservative potential magnetic trap. A major upgrade of the apparatus is nearing completion at the National Institute of Standards and Technology Center for Neutron Research (NCNR). In our approach, a beam of 0.89 nm neutrons is incident on a superfluid 4He target within the minimum field region of an Ioffe-type magnetic trap. A fraction of the neutrons is downscattered in the helium to energies , and those in the appropriate spin state become trapped. The inverse process is suppressed by the low phonon density of helium at temperatures less than 200 mK, allowing the neutron to travel undisturbed. When the neutron decays the energetic electron ionizes the helium, producing scintillation light that is detected using photomultiplier tubes. Statistical limitations of the previous apparatus will be alleviated by significant increases in field strength and trap volume resulting in twenty times more trapped neutrons.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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[show abstract]
[hide abstract]
ABSTRACT: The 10 B(a; n) 13 N reaction is studied as an activation process in a variety of solid boron-containing neutron shielding materials. The source of a-particles is the neutron capture reaction 10 B(n; a) 7 Li. Samples of boron carbide, boron oxide, and boron nitride are irradiated with thermal neutrons and the rate of 13 N production is determined. 13 N promptly decays, emitting a positron. This positron efficiently annihilates with electrons in the material and the resultant 511 keV gamma ray is detected. For each of the above-mentioned materials, the rate of 13 N production is (1–2) · 10 À10 per captured neutron.
40.Mc. 2940(29).
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D N Mckinsey,
C R Brome, S N Dzhosyuk,
R Golub,
K Habicht,
P R Huffman,
E Korobkina,
S K Lamoreaux,
C E H Mattoni,
A K Thompson,
L Yang,
J M Doyle
[show abstract]
[hide abstract]
ABSTRACT: The time dependence of extreme ultraviolet EUV fluorescence following an ionizing radiation event in liquid helium is observed and studied in the temperature range from 250 mK to 1.8 K. The fluorescence exhibits significant structure including a short (10 ns) strong initial pulse followed by single photons whose emission rate decays exponentially with a 1.6-s time constant. At an even longer time scale, the emission rate varies as ''1/time'' inversely proportional to the time after the initial pulse. The intensity of the ''1/time'' component from particles is significantly weaker than those from particles or neutron capture on 3 He. It is also found that for particles, the intensity of this component depends on the temperature of the superfluid helium. Proposed models describing the observed fluorescence are discussed.
20.
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[show abstract]
[hide abstract]
ABSTRACT: Long-lived phosphorescence has been observed emanating from superfluid helium following excitation by ionizing radiation. This extreme ultraviolet light is predominantly from the radiative decay of metastable He2(a3Σu+) molecules and is detected through frequency down-conversion and photon counting techniques. This allows measurement of the phosphorescence lifetime in a low-molecular-density regime that is not dominated by two-body reactions. A phosphorescence lifetime of 13±2 s is observed.
Phys. Rev. A. 59(1).
