@article{hayen_choi_combs_taylor_baeßler_birge_broussard_crawford_fomin_gericke_et al._2023, title={Precision pulse shape simulation for proton detection at the Nab experiment}, volume={107}, ISSN={["2469-9993"]}, url={https://link.aps.org/doi/10.1103/PhysRevC.107.065503}, DOI={10.1103/PhysRevC.107.065503}, abstractNote={The Nab experiment at Oak Ridge National Laboratory, USA, aims to measure the beta-antineutrino angular correlation following neutron $\beta$ decay to an anticipated precision of approximately 0.1\%. The proton momentum is reconstructed through proton time-of-flight measurements, and potential systematic biases in the timing reconstruction due to detector effects must be controlled at the nanosecond level. We present a thorough and detailed semiconductor and quasiparticle transport simulation effort to provide precise pulse shapes, and report on relevant systematic effects and potential measurement schemes.}, number={6}, journal={PHYSICAL REVIEW C}, publisher={American Physical Society}, author={Hayen, Leendert and Choi, Jin Ha and Combs, Dustin and Taylor, R. J. and Baeßler, Stefan and Birge, Noah and Broussard, Leah J. and Crawford, Christopher B. and Fomin, Nadia and Gericke, Michael and et al.}, year={2023}, month={Jun} }
 @article{tang_watkins_clayton_currie_fellers_hassan_hooks_ito_lawrence_macdonald_et al._2021, title={Ultracold neutron properties of the Eljen-299-02D deuterated scintillator}, volume={92}, ISSN={["1089-7623"]}, DOI={10.1063/5.0030972}, abstractNote={In this paper, we report studies of the Fermi potential and loss per bounce of ultracold neutrons (UCNs) on a deuterated scintillator (Eljen-299-02D). These UCN properties of the scintillator enable its use in a wide variety of applications in fundamental neutron research.}, number={2}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Tang, Z. and Watkins, E. B. and Clayton, S. M. and Currie, S. A. and Fellers, D. E. and Hassan, Md T. and Hooks, D. E. and Ito, T. M. and Lawrence, S. K. and MacDonald, S. W. T. and et al.}, year={2021}, month={Feb} }
 @article{sun_adamek_allgeier_bagdasarova_berguno_blatnik_bowles_broussard_brown_carr_et al._2020, title={Improved limits on Fierz interference using asymmetry measurements from the Ultracold Neutron Asymmetry (UCNA) experiment}, volume={101}, ISSN={2469-9985 2469-9993}, url={http://dx.doi.org/10.1103/PhysRevC.101.035503}, DOI={10.1103/PhysRevC.101.035503}, abstractNote={The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the β-decay asymmetry parameter, A₀, for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their β-decay electrons are detected with ≈4π acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to b_n, the Fierz interference term in the neutron β-decay rate. In this work, we determine b_n from the energy dependence of A₀ using the data taken during the UCNA 2011-2013 run. In addition, we present the same type of analysis using the earlier 2010 A dataset. Motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new b_n measurement using the weighted average of our asymmetry dataset fits, to obtain b_n = 0.066±0.041_(stat)±0.024_(syst) which corresponds to a limit of −0.012 < b_n < 0.144 at the 90% confidence level.}, number={3}, journal={Physical Review C}, publisher={American Physical Society (APS)}, author={Sun, X. and Adamek, E. and Allgeier, B. and Bagdasarova, Y. and Berguno, D. B. and Blatnik, M. and Bowles, T. J. and Broussard, L. J. and Brown, M. A.-P. and Carr, R. and et al.}, year={2020}, month={Mar} }
 @article{pattie_callahan_cude-woods_adamek_broussard_clayton_currie_dees_ding_engel_et al._2018, title={Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection}, volume={360}, ISSN={1095-9203}, url={https://doi.org/10.1126/science.aan8895}, DOI={10.1126/science.aan8895}, abstractNote={How long does a neutron live?
          
            Unlike the proton, whose lifetime is longer than the age of the universe, a free neutron decays with a lifetime of about 15 minutes. Measuring the exact lifetime of neutrons is surprisingly tricky; putting them in a container and monitoring their decay can lead to errors because some neutrons will be lost owing to interactions with the container walls. To overcome this problem, Pattie
            et al.
            measured the lifetime in a trap where ultracold polarized neutrons were levitated by magnetic fields, precluding interactions with the trap walls (see the Perspective by Mumm). This more precise determination of the neutron lifetime will aid our understanding of how the first nuclei formed after the Big Bang.
          
          
            Science
            , this issue p.
            627
            ; see also p.
            605
          }, number={6389}, journal={SCIENCE}, publisher={American Association for the Advancement of Science (AAAS)}, author={Pattie, R. W., Jr. and Callahan, N. B. and Cude-Woods, C. and Adamek, E. R. and Broussard, L. J. and Clayton, S. M. and Currie, S. A. and Dees, E. B. and Ding, X. and Engel, E. M. and et al.}, year={2018}, month={May}, pages={627–631} }
 @article{brown_dees_adamek_allgeier_blatnik_bowles_broussard_carr_clayton_cude-woods_et al._2018, title={New result for the neutron <mml:mi>β-asymmetry parameter A<mml:msub>0</mml:msub></mml:mi> from UCNA}, volume={97}, ISSN={2469-9985 2469-9993}, url={http://dx.doi.org/10.1103/physrevc.97.035505}, DOI={10.1103/physrevc.97.035505}, abstractNote={Background: The neutron β-decay asymmetry parameter A_0 defines the angular correlation between the spin of the neutron and the momentum of the emitted electron. Values for A_0 permit an extraction of the ratio of the weak axial-vector to vector coupling constants, λ≡gA/gV, which under assumption of the conserved vector current hypothesis (gV=1) determines gA. Precise values for gA are important as a benchmark for lattice QCD calculations and as a test of the standard model. 
Purpose: The UCNA experiment, carried out at the Ultracold Neutron (UCN) source at the Los Alamos Neutron Science Center, was the first measurement of any neutron β-decay angular correlation performed with UCN. This article reports the most precise result for A_0 obtained to date from the UCNA experiment, as a result of higher statistics and reduced key systematic uncertainties, including from the neutron polarization and the characterization of the electron detector response. 
Methods: UCN produced via the downscattering of moderated spallation neutrons in a solid deuterium crystal were polarized via transport through a 7 T polarizing magnet and a spin flipper, which permitted selection of either spin state. The UCN were then contained within a 3-m long cylindrical decay volume, situated along the central axis of a superconducting 1 T solenoidal spectrometer. With the neutron spins then oriented parallel or anti-parallel to the solenoidal field, an asymmetry in the numbers of emitted decay electrons detected in two electron detector packages located on both ends of the spectrometer permitted an extraction of A_0. 
Results: The UCNA experiment reports a new 0.67% precision result for A_0 of A_0=−0.12054(44)_(stat)(68)_(syst), which yields λ=gA/gV=−1.2783(22). Combination with the previous UCNA result and accounting for correlated systematic uncertainties produces A0=−0.12015(34)stat(63)syst and λ=gA/gV=−1.2772(20). 
Conclusions: This new result for A0 and gA/gV from the UCNA experiment has provided confirmation of the shift in values for gA/gV that has emerged in the published results from more recent experiments, which are in striking disagreement with the results from older experiments. Individual systematic corrections to the asymmetries in older experiments (published prior to 2002) were >10%, whereas those in the more recent ones (published after 2002) have been of the scale of <2%. The impact of these older results on the global average will be minimized should future measurements of A0 reach the 0.1% level of precision with central values near the most recent results.}, number={3}, journal={Physical Review C}, publisher={American Physical Society (APS)}, author={Brown, M. A.-P. and Dees, E. B. and Adamek, E. and Allgeier, B. and Blatnik, M. and Bowles, T. J. and Broussard, L. J. and Carr, R. and Clayton, S. and Cude-Woods, C. and et al.}, year={2018}, month={Mar}, pages={035505} }
 @article{sun_adamek_allgeier_blatnik_bowles_broussard_brown_carr_clayton_cude-woods_et al._2018, title={Search for dark matter decay of the free neutron from the UCNA experiment: n -> X plus e(+)e(-)}, volume={97}, ISSN={["2469-9993"]}, DOI={10.1103/physrevc.97.052501}, abstractNote={It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of the possible final states discussed includes a single χ along with an e^+e^− pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ∼4π acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). The summed kinetic energy (E_(e^+e^−)) from such events is used to set limits, as a function of the χ mass, on the branching fraction for this decay channel. For χ masses consistent with resolving the neutron lifetime discrepancy, we exclude this as the dominant dark matter decay channel at ≫ 5σlevel for 100 keV 90% confidence level.}, number={5}, journal={PHYSICAL REVIEW C}, author={Sun, X. and Adamek, E. and Allgeier, B. and Blatnik, M. and Bowles, T. J. and Broussard, L. J. and Brown, M. A-P and Carr, R. and Clayton, S. and Cude-Woods, C. and et al.}, year={2018}, month={May} }
 @article{morris_adamek_broussard_callahan_clayton_cude-woods_currie_ding_fox_hickerson_et al._2017, title={A new method for measuring the neutron lifetime using an in situ neutron detector}, volume={88}, ISSN={1089-7623}, url={http://dx.doi.org/10.1063/1.4983578}, DOI={10.1063/1.4983578}, abstractNote={In this paper, we describe a new method for measuring surviving neutrons in neutron lifetime measurements using bottled ultracold neutrons (UCN), which provides better characterization of systematic uncertainties and enables higher precision than previous measurement techniques. An active detector that can be lowered into the trap has been used to measure the neutron distribution as a function of height and measure the influence of marginally trapped UCN on the neutron lifetime measurement. In addition, measurements have demonstrated phase-space evolution and its effect on the lifetime measurement.}, number={5}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, publisher={AIP Publishing}, author={Morris, C. L. and Adamek, E. R. and Broussard, L. J. and Callahan, N. B. and Clayton, S. M. and Cude-Woods, C. and Currie, S. A. and Ding, X. and Fox, W. and Hickerson, K. P. and et al.}, year={2017}, month={May}, pages={053508} }
 @article{pattie_adamek_brenner_brandt_broussard_callahan_clayton_cude-woods_currie_geltenbort_et al._2017, title={Evaluation of commercial nickel-phosphorus coating for ultracold neutron guides using a pinhole bottling method}, volume={872}, ISSN={1872-9576}, DOI={10.1016/j.nima.2017.07.051}, abstractNote={We report on the evaluation of commercial electroless nickel phosphorus (NiP) coatings for ultracold neutron (UCN) transport and storage. The material potential of 50~$\mu$m thick NiP coatings on stainless steel and aluminum substrates was measured to be $V_F = 213(5.2)$~neV using the time-of-flight spectrometer ASTERIX at the Lujan Center. The loss per bounce probability was measured in pinhole bottling experiments carried out at ultracold neutron sources at Los Alamos Neutron Science Center and the Institut Laue-Langevin. For these tests a new guide coupling design was used to minimize gaps between the guide sections. The observed UCN loss in the bottle was interpreted in terms of an energy independent effective loss per bounce, which is the appropriate model when gaps in the system and upscattering are the dominate loss mechanisms, yielding a loss per bounce of $1.3(1) \times 10^{-4}$. We also present a detailed discussion of the pinhole bottling methodology and an energy dependent analysis of the experimental results.}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Pattie, R. W., Jr. and Adamek, E. R. and Brenner, T. and Brandt, A. and Broussard, L. J. and Callahan, N. B. and Clayton, S. M. and Cude-Woods, C. and Currie, S. A. and Geltenbort, P. and et al.}, year={2017}, month={Nov}, pages={64–73} }
 @article{hickerson_sun_bagdasarova_bravo-berguno_broussard_brown_carr_currie_ding_filippone_et al._2017, title={First direct constraints on Fierz interference in free-neutron beta decay}, volume={96}, number={4}, journal={Physical Review C}, author={Hickerson, K. P. and Sun, X. and Bagdasarova, Y. and Bravo-Berguno, D. and Broussard, L. J. and Brown, M. A. P. and Carr, R. and Currie, S. and Ding, X. and Filippone, B. W. and et al.}, year={2017} }
 @article{hickerson_sun_bagdasarova_bravo-berguno_broussard_brown_carr_currie_ding_filippone_et al._2017, title={First direct constraints on Fierz interference in free-neutron beta decay (vol 96, 042501, 2017)}, volume={96}, ISSN={["2469-9993"]}, DOI={10.1103/physrevc.96.059901}, abstractNote={Received 3 November 2017DOI:https://doi.org/10.1103/PhysRevC.96.059901©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayElectroweak interactionElectroweak interactions in nuclear physicsExtensions of fermion sectorNeutron physicsParticle decaysParticle interactionsPhysical SystemsNeutronsParticles & FieldsNuclear PhysicsAccelerators & Beams}, number={5}, journal={PHYSICAL REVIEW C}, author={Hickerson, K. P. and Sun, X. and Bagdasarova, Y. and Bravo-Berguno, D. and Broussard, L. J. and Brown, M. A. -P. and Carr, R. and Currie, S. and Ding, X. and Filippone, B. W. and et al.}, year={2017}, month={Nov} }
 @article{broussard_alarcon_baessler_barron palos_birge_bode_bowman_brunst_calarco_caylor_et al._2017, title={Neutron decay correlations in the Nab experiment}, volume={876}, ISSN={1742-6596}, DOI={10.1088/1742-6596/876/1/012005}, abstractNote={The Nab experiment will measure the correlation a between the momenta of the beta particle and antineutrino in neutron decay as well as the Fierz term b which distorts the beta spectrum.}, journal={XL SYMPOSIUM ON NUCLEAR PHYSICS 2017 (COCOYOC2017)}, author={Broussard, L. J. and Alarcon, R. and Baessler, S. and Barron Palos, L. and Birge, N. and Bode, T. and Bowman, J. D. and Brunst, T. and Calarco, J. R. and Caylor, J. and et al.}, year={2017} }
 @article{seestrom_adamek_barlow_blatnik_broussard_callahan_clayton_cude-woods_currie_dees_et al._2017, title={Total cross sections for ultracold neutrons scattered from gases}, volume={95}, ISSN={2469-9993}, DOI={10.1103/physrevc.95.015501}, abstractNote={We have followed up on our previous measurements of upscattering of ultracold neutrons (UCNs) from a series of gases by making measurements of total cross sections on the following gases hydrogen, ethane, methane, isobutene, n-butane, ethylene, water vapor, propane, neopentane, isopropyl alcohol, and ^3He. The values of these cross sections are important for estimating the loss rate of trapped neutrons due to residual gas and are relevant to neutron lifetime measurements using UCNs. The effects of the UCN velocity and path-length distributions were accounted for in the analysis using a Monte Carlo transport code. Results are compared to our previous measurements and with the known absorption cross section for ^3He scaled to our UCN energy. We find that the total cross sections for the hydrocarbon gases are reasonably described by a function linear in the number of hydrogen atoms in the molecule.}, number={1}, journal={PHYSICAL REVIEW C}, author={Seestrom, S. J. and Adamek, E. R. and Barlow, D. and Blatnik, M. and Broussard, L. J. and Callahan, N. B. and Clayton, S. M. and Cude-Woods, C. and Currie, S. and Dees, E. B. and et al.}, year={2017}, month={Jan} }
 @article{wei_broussard_hoffbauer_makela_morris_tang_adamek_callahan_clayton_cude-woods_et al._2016, title={Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy}, volume={830}, ISSN={0168-9002}, url={http://dx.doi.org/10.1016/j.nima.2016.05.058}, DOI={10.1016/j.nima.2016.05.058}, abstractNote={Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15 $\mu$m has been achieved, which is equivalent to an UCN energy resolution below 2 pico-electron-volts through the relation $\delta E = m_0g \delta x$. Here, the symbols $\delta E$, $\delta x$, $m_0$ and $g$ are the energy resolution, the spatial resolution, the neutron rest mass and the gravitational acceleration, respectively. A multilayer surface convertor described previously is used to capture UCNs and then emits visible light for CCD imaging. Particle identification and noise rejection are discussed through the use of light intensity profile analysis. This method allows different types of UCN spectroscopy and other applications.}, journal={Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, publisher={Elsevier BV}, author={Wei, Wanchun and Broussard, L.J. and Hoffbauer, M.A. and Makela, M. and Morris, C.L. and Tang, Z. and Adamek, E.R. and Callahan, N.B. and Clayton, S.M. and Cude-Woods, C. and et al.}, year={2016}, month={Sep}, pages={36–43} }
 @article{wang_hoffbauer_morris_callahan_adamek_bacon_blatnik_brandt_broussard_clayton_et al._2015, title={A multilayer surface detector for ultracold neutrons}, volume={798}, DOI={10.1016/j.nima.2015.07.010}, abstractNote={A multilayer surface detector for ultracold neutrons (UCNs) is described. The top $^{10}$B layer is exposed to the vacuum chamber and directly captures UCNs. The ZnS:Ag layer beneath the $^{10}$B layer is a few microns thick, which is sufficient to detect the charged particles from the $^{10}$B(n,$\alpha$)$^7$Li neutron-capture reaction, while thin enough so that ample light due to $\alpha$ and $^7$Li escapes for detection by photomultiplier tubes. One-hundred-nm thick $^{10}$B layer gives high UCN detection efficiency, as determined by the mean UCN kinetic energy, detector materials and others. Low background, including negligible sensitivity to ambient neutrons, has also been verified through pulse-shape analysis and comparisons with other existing $^3$He and $^{10}$B detectors. This type of detector has been configured in different ways for UCN flux monitoring, development of UCN guides and neutron lifetime research.}, journal={Nuclear Instruments & Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors, and Associated Equipment}, author={Wang, Z. H. and Hoffbauer, M. A. and Morris, C. L. and Callahan, N. B. and Adamek, E. R. and Bacon, J. D. and Blatnik, M. and Brandt, A. E. and Broussard, L. J. and Clayton, S. M. and et al.}, year={2015}, pages={30–35} }
 @article{sjue_broussard_makela_mcgaughey_young_zeck_2015, title={Radial distribution of charged particles in a magnetic field}, volume={86}, ISSN={1089-7623}, url={http://dx.doi.org/10.1063/1.4906547}, DOI={10.1063/1.4906547}, abstractNote={The radial spread of charged particles emitted from a point source in a magnetic field is a potential source of systematic error for any experiment where magnetic fields guide charged particles to detectors with finite size. Assuming uniform probability as a function of the phase along the particle’s helical trajectory, an analytic solution for the radial probability distribution function follows which applies to experiments in which particles are generated throughout a volume that spans a sufficient length along the axis of a homogeneous magnetic field. This approach leads to the same result as a different derivation given by Dubbers et al., Nucl. Instrum. Methods Phys. Res., Sect. A 763, 112–119 (2014). But the constant phase approximation does not strictly apply to finite source volumes or fixed positions, which lead to local maxima in the radial distribution of emitted particles at the plane of the detector. A simple method is given to calculate such distributions, then the effect is demonstrated with data from a 207Bi electron-conversion source in the superconducting solenoid magnet spectrometer of the Ultracold Neutron facility at the Los Alamos Neutron Science Center. Implications for neutron beta decay spectroscopy are discussed.}, number={2}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, publisher={AIP Publishing}, author={Sjue, S. K. L. and Broussard, L. J. and Makela, M. and McGaughey, P. L. and Young, A. R. and Zeck, B. A.}, year={2015}, month={Feb}, pages={023102} }
 @article{seestrom_adamek_barlow_broussard_callahan_clayton_cude-woods_currie_dees_fox_et al._2015, title={Upscattering of ultracold neutrons from gases}, volume={92}, ISSN={1089-490X}, DOI={10.1103/physrevc.92.065501}, abstractNote={We present measurements of the upscattering cross sections of ultracold neutrons (UCNs) from room-temperature hydrogen, deuterium, neon, argon, xenon, ${\mathrm{C}}_{4}{\mathrm{H}}_{10}, \mathrm{C}{\mathrm{F}}_{4}$, and air. The values of these cross sections are important for estimating the loss rate of trapped neutrons due to residual gas and are therefore of importance for neutron lifetime measurements using UCNs. Cross sections were obtained from a combined analysis of the UCN attenuation in a gas cell and direct measurement of the neutrons upscattered in the cell. The effects of the UCN velocity and path-length distributions were accounted for using a Monte Carlo transport code. Results are compared with measurements at higher neutron energy as well as with calculations.}, number={6}, journal={PHYSICAL REVIEW C}, author={Seestrom, S. J. and Adamek, E. R. and Barlow, D. and Broussard, L. J. and Callahan, N. B. and Clayton, S. M. and Cude-Woods, C. and Currie, S. and Dees, E. B. and Fox, W. and et al.}, year={2015}, month={Dec} }
 @article{salas-bacci_mcgaughey_baessler_broussard_makela_mirabal_pattie_pocanic_sjue_penttila_et al._2014, title={Characterization of large area, thick, and segmented silicon detectors for neutron beta-decay experiments}, volume={735}, journal={Nuclear Instruments & Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors, and Associated Equipment}, author={Salas-Bacci, A. and McGaughey, P. L. and Baessler, S. and Broussard, L. and Makela, M. F. and Mirabal, J. and Pattie, R. W. and Pocanic, D. and Sjue, S. K. L. and Penttila, S. I. and et al.}, year={2014}, pages={408–415} }
 @article{sharapov_morris_makela_saunders_adamek_bagdasarova_broussard_cude-woods_fellers_geltenbort_et al._2013, title={Measurements of ultracold neutron upscattering and absorption in polyethylene and vanadium}, volume={88}, ISSN={1089-490X}, DOI={10.1103/physrevc.88.037601}, abstractNote={The study of neutron cross sections for elements used as efficient “absorbers” of ultracold neutrons (UCN) is crucial for many precision experiments in nuclear and particle physics, cosmology and gravity. In this context, “absorption” includes both the capture and upscattering of neutrons to the energies above the UCN energy region. The available data, especially for hydrogen, do not agree between themselves or with the theory. In this report we describe measurements performed at the Los Alamos National Laboratory UCN facility of the UCN upscattering cross sections for vanadium and for hydrogen in CH_2 using simultaneous measurements of the radiative capture cross sections for these elements. We measured σ_(up)=1972±130 b for hydrogen in CH_2, which is below theoretical expectations, and σ_(up)=25±9 b for vanadium, in agreement with the expectation for the neutron heating by thermal excitations in solids.}, number={3}, journal={PHYSICAL REVIEW C}, author={Sharapov, E. I. and Morris, C. L. and Makela, M. and Saunders, A. and Adamek, Evan R. and Bagdasarova, Y. and Broussard, L. J. and Cude-Woods, C. B. and Fellers, Deion E. and Geltenbort, Peter and et al.}, year={2013}, month={Sep} }
 @article{sharapov_morris_makela_saunders_adamek_broussard_cude-woods_fellers_geltenbort_hartl_et al._2013, title={Upscattering of ultracold neutrons from the polymer [C6H12](n)}, volume={88}, ISSN={1089-490X}, DOI={10.1103/physrevc.88.064605}, abstractNote={It is generally accepted that the main cause of ultracold neutron (UCN) losses in storage traps is upscattering to the thermal energy range by hydrogen adsorbed on the surface of the trap walls. However, the data on which this conclusion is based are poor and contradictory. Here we report a measurement, performed at the Los Alamos National Laboratory UCN source, of the average energy of the flux of upscattered neutrons after the interaction of UCN with hydrogen bound in the semicrystalline polymer PMP (trade name TPX), [C_6H_(12)]_n. Our analysis, performed with the mcnp code which applies the neutron-scattering law to UCN upscattered by bound hydrogen in semicrystalline polyethylene, [C_2H_4]_n, leads us to a flux average energy value of 26±3 meV, in contradiction to previously reported experimental values of 10 to 13 meV and in agreement with the theoretical models of neutron heating implemented in MCNP.}, number={6}, journal={PHYSICAL REVIEW C}, author={Sharapov, E. I. and Morris, C. L. and Makela, M. and Saunders, A. and Adamek, Evan R. and Broussard, L. J. and Cude-Woods, C. B. and Fellers, Deion E. and Geltenbort, Peter and Hartl, M. and et al.}, year={2013}, month={Dec} }