اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدImproved determination of thermal cross section of 14N(n,p)14C for the neutron lifetime measurement
100
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
In a neutron lifetime measurement at the Japan Proton Accelerator Complex, the neutron lifetime is calculated by the neutron decay rate and the incident neutron flux. The flux is obtained due to counting the protons emitted from the neutron absorption reaction of ${}^{3}{rm He}$ gas, which is diluted in a mixture of working gas in a detector. Hence, it is crucial to determine the amount of ${}^{3}{rm He}$ in the mixture. In order to improve the accuracy of the number density of the ${}^{3}{rm He}$ nuclei, we suggested to use the ${}^{14}{rm N}({rm n},{rm p}){}^{14}{rm C}$ reaction as a reference because this reaction involves similar kinetic energy as the ${}^{3}{rm He}({rm n},{rm p}){}^{3}{rm H}$ reaction and a smaller reaction cross section to introduce reasonable large partial pressure. The uncertainty of the recommended value of the cross section, however, is not satisfied with our requirement. In this paper, we report the most accurate experimental value of the cross section of the ${}^{14}{rm N}({rm n},{rm p}){}^{14}{rm C}$ reaction at a neutron velocity of 2200 m/s, measured relative to the ${}^{3}{rm He}({rm n},{rm p}){}^{3}{rm H}$ reaction. The result was 1.868 $pm$ 0.003 (stat.) $pm$ 0.006 (sys.) b. Additionally, the cross section of the ${}^{17}{rm O}({rm n},{rm alpha}){}^{14}{rm C}$ reaction at the neutron velocity is also redetermined as 249 $pm$ 6 mb.
قيم البحث
اقرأ أيضاً
The use of argon as a detection and shielding medium for neutrino and dark matter experiments has made the precise knowledge of the cross section for neutron capture on argon an important design and operational parameter. Since previous measurements
were averaged over thermal spectra and have significant disagreements, a differential measurement has been performed using a Time-Of-Flight neutron beam and a $sim$4$pi$ gamma spectrometer. A fit to the differential cross section from $0.015-0.15$,eV, assuming a $1/v$ energy dependence, yields $sigma^{2200} = 673 pm 26 text{ (stat.)} pm 59 text{ (sys.)}$,mb.
The part-per-million measurement of the positive muon lifetime and determination of the Fermi constant by the MuLan experiment at the Paul Scherrer Institute is reviewed. The experiment used an innovative, time-structured, surface muon beam and a nea
r-4pi, finely-segmented, plastic scintillator positron detector. Two in-vacuum muon stopping targets were used: a ferromagnetic foil with a large internal magnetic field, and a quartz crystal in a moderate external magnetic field. The experiment obtained a muon lifetime 2 196 980.3(2.2) ps (1.0 ppm) and a Fermi constant 1.166 378 7(6) 10^-5 GeV^-2 (0.5 ppm). The thirty-fold improvement in the muon lifetime has proven valuable for precision measurements in nuclear muon capture and the commensurate improvement in the Fermi constant has proven valuable for precision tests of the standard model.
In stars with temperatures above 20*10^6 K, hydrogen burning is dominated by the CNO cycle. Its rate is determined by the slowest process, the 14N(p,gamma)15O reaction. Deep underground in Italys Gran Sasso laboratory, at the LUNA 400 kV accelerator,
the cross section of this reaction has been measured at energies much lower than ever achieved before. Using a windowless gas target and a 4pi BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn. The Gamow peak has been covered by experimental data for several scenarios of stable and explosive hydrogen burning. In addition, the strength of the 259 keV resonance has been remeasured. The thermonuclear reaction rate has been calculated for temperatures 90 - 300 *10^6 K, for the first time with negligible impact from extrapolations.
We report an improved measurement of the free neutron lifetime $tau_{n}$ using the UCN$tau$ apparatus at the Los Alamos Neutron Science Center. We counted a total of approximately $38times10^{6}$ surviving ultracold neutrons (UCN) after storing in UC
N$tau$s magneto-gravitational trap over two data acquisition campaigns in 2017 and 2018. We extract $tau_{n}$ from three blinded, independent analyses by both pairing long and short storage-time runs to find a set of replicate $tau_{n}$ measurements and by performing a global likelihood fit to all data while self-consistently incorporating the $beta$-decay lifetime. Both techniques achieve consistent results and find a value $tau_{n}=877.75pm0.28_{text{ stat}}+0.22/-0.16_{text{ syst}}$~s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.
The 235U(n,f) cross section was measured in a wide energy range at n_TOF relative to 6Li(n,t) and 10B(n,alpha), with high resolution and in a wide energy range, with a setup based on a stack of six samples and six silicon detectors placed in the neut
ron beam. This allowed us to make a direct comparison of the reaction yields under the same experimental conditions, and taking into account the forward/backward emission asymmetry. A hint of an anomaly in the 10{div}30 keV neutron energy range had been previously observed in other experiments, indicating a cross section systematically lower by several percent relative to major evaluations. The present results indicate that the evaluated cross section in the 9{div}18 keV neutron energy range is indeed overestimated, both in the recent updates of ENDF/B-VIII.0 and of the IAEA reference data. Furthermore, these new high-resolution data confirm the existence of resonance-like structures in the keV neutron energy region. The new, high accuracy results here reported may lead to a reduction of the uncertainty in the 1{div}100 keV neutron energy region. Finally, the present data provide additional confidence on the recently re-evaluated cross section integral between 7.8 and 11 eV.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
