scholarly journals Neutron lifetime measurement with pulsed cold neutrons

2020 ◽  
Author(s):  
K Hirota ◽  
G Ichikawa ◽  
S Ieki ◽  
T Ino ◽  
Y Iwashita ◽  
...  
Keyword(s):  
Decay Rate ◽  
Reaction Rate ◽  
Proton Accelerator ◽  
Neutron Decay ◽  
Spallation Neutron Source ◽  
Neutron Lifetime ◽  
Cold Neutrons ◽  
Research Complex ◽  
Gas Chamber ◽  
Pulsed Neutron

Abstract The neutron lifetime has been measured by comparing the decay rate with the reaction rate of 3He nuclei of a pulsed neutron beam from the spallation neutron source at the Japan Proton Accelerator Research Complex (J-PARC). The decay rate and the reaction rate were determined by simultaneously detecting electrons from the neutron decay and protons from the 3He(n, p) 3H reaction using a gas chamber of which working gas contains diluted 3He. The measured neutron lifetime was 898 ± 10stat+15−18sys s.

scholarly journals New project for precise neutron lifetime measurement at J-PARC

2019 ◽  
Vol 219 ◽  
pp. 03003 ◽  
Author(s):  
Naoki Nagakura ◽  
Katsuya Hirota ◽  
Sei Ieki ◽  
Takashi Ino ◽  
Yoshihisa Iwashita ◽  
...  
Keyword(s):  
Big Bang ◽  
Proton Accelerator ◽  
Neutron Lifetime ◽  
Big Bang Nucleosynthesis ◽  
Cold Neutrons ◽  
Beam Experiment ◽  
Research Complex ◽  
Time Projection ◽  
Beta Decays

The decay lifetime of free neutrons (∼880 s) is an important parameter of the weak interaction and for Big Bang Nucleosynthesis. However, results of measurements currently show discrepancies depending on the method used. As most experiments nowadays employ ultra cold neutrons, we have developed a new cold-beam experiment which we perform at the Japan Proton Accelerator Research Complex. As a special feature, a polarized neutron beam is bunched by a spin flip chopper. A time projection chamber operated with He and CO2 gas, including a well-controlled amount of 3He, is used for detection of the beta-decays and simultaneous determination of the beam intensity. Using the data between 2014 and 2016, we evaluated our first, preliminary result of the neutron lifetime as 896 ± 10(stat.) −10+14(sys.) s. We plan several upgrades to achieve our precision goal of 1 s.

Using Pulsed Cold Neutrons to Measure Neutron Lifetime

2021 ◽  
Vol 1 ◽  
Keyword(s):  
Neutron Lifetime ◽  
Cold Neutrons ◽  
Neutron Beams ◽  
Pulsed Neutron

Scientists measure the lifetime of a neutron with pulsed neutron beams to explore the cause of a puzzling discrepancy in their previously measured lifetime.

scholarly journals Measurements of the Neutron Lifetime

Atoms ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 70 ◽  
Author(s):  
F. Wietfeldt
Keyword(s):  
Nuclear Physics ◽  
Neutron Decay ◽  
Neutron Lifetime ◽  
The Past ◽  
Free Neutron ◽  
Mean Lifetime ◽  
Fundamental Process ◽  
Beam Method ◽  
The Subject ◽  
Particle Decays

Free neutron decay is a fundamental process in particle and nuclear physics. It is the prototype for nuclear beta decay and other semileptonic weak particle decays. Neutron decay played a key role in the formation of light elements in the early universe. The precise value of the neutron mean lifetime, about 15 min, has been the subject of many experiments over the past 70 years. The two main experimental methods, the beam method and the ultracold neutron storage method, give average values of the neutron lifetime that currently differ by 8.7 s (4 standard deviations), a serious discrepancy. The physics of neutron decay, implications of the neutron lifetime, previous and recent experimental measurements, and prospects for the future are reviewed.

scholarly journals Improved accuracy in the determination of the thermal cross section of ${}^{14}{\rm N}({\rm n},{\rm p}){}^{14}{\rm C}$ for neutron lifetime measurement

2019 ◽  
Vol 2019 (9) ◽  
Author(s):  
R Kitahara ◽  
K Hirota ◽  
S Ieki ◽  
T Ino ◽  
Y Iwashita ◽  
...  
Keyword(s):  
Cross Section ◽  
Lifetime Measurement ◽  
Reaction Cross ◽  
Proton Accelerator ◽  
Incident Neutron ◽  
Neutron Lifetime ◽  
The Cross ◽  
Thermal Cross Section ◽  
Improved Accuracy

Abstract In a neutron lifetime measurement at the Japan Proton Accelerator Complex, the neutron lifetime is calculated from the neutron decay rate and the incident neutron flux. The flux is obtained by 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 have suggested using the ${}^{14}{\rm N}({\rm n},{\rm p}){}^{14}{\rm C}$ reaction as a reference because this reaction involves similar kinetic energy to the $^3$He(n,p)$^3$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 $^{14}$N(n,p)$^{14}$C reaction at a neutron velocity of 2200 m s$^{-1}$, measured relative to the $^3$He(n,p)$^3$H reaction. The result was 1.868 $\pm$ 0.003 (stat.) $\pm$ 0.006 (sys.) b. Additionally, the cross section of the $^{17}$O(n,$\alpha$)$^{14}$C reaction at the neutron velocity is also redetermined as 249 $\pm$ 6 mb.

Measurement of Prompt Neutron Decay Constant of CFBR-II at Near Delayed Criticality Using Randomly Pulsed Neutron Method

2013 ◽  
Author(s):  
Lingli Song ◽  
Jiansheng Li ◽  
Haojun Zhou ◽  
Yu Jin
Keyword(s):  
Liquid Scintillation ◽  
Decay Constant ◽  
Detection System ◽  
Prompt Neutron ◽  
Neutron Decay ◽  
Timing Uncertainty ◽  
Neutron Method ◽  
Pulsed Neutron ◽  
Liquid Scintillation Detector ◽  
Good Agreement

Prompt neutron decay constant of CFBR-II (China’s Fast Burst Reactor) was measured by the randomly pulsed neutron method when the reactor was at the reactivity of −0.1$. A liquid scintillation detector was used to detect the leakage neutrons and the timing uncertainty of the detection system was less than 3ns. The detector and the Cf-252 fast ionization chamber were placed at several positions. Totally 5 prompt neutron timing distribution curves were obtained and the prompt neutron decay constant was 0.610us−1 in average with the uncertainty of 0.030us−1, which was in good agreement with the M.C. calculation.

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