Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMeasurement of the Free Neutron Lifetime using the Neutron Spectrometer on NASAs Lunar Prospector Mission
266
0
0.0
(
0
)
Authors
Jack T. Wilson
Ask ChatGPT about the research
No Arabic abstract
We use data from the Lunar Prospector Neutron Spectrometer to make the second space-based measurement of the free neutron lifetime finding $tau_n=887 pm 14_text{stat}{:^{+7}_{-3:text{syst}}}$ s, which is within 1$sigma$ of the accepted value. This measurement expands the range of planetary bodies where the neutron lifetime has been quantified from space, and by extending the modeling to account for non-uniform elemental composition, we mitigated a significant source of systematic uncertainty on the previous space-based lifetime measurement. This modeling moves space-based neutron lifetime measurement towards the ultimate goal of reducing the magnitude of the systematics on a future space-measurement to the level of those seen in laboratory-based experiments.
rate research
Read More
We establish the feasibility of measuring the neutron lifetime via an alternative, space-based class of methods, which use neutrons generated by galactic cosmic ray spallation of planets surfaces and atmospheres. Free neutrons decay via the weak interaction with a mean lifetime of around 880 s. This lifetime constrains the unitarity of the CKM matrix and is a key parameter for studies of Big-Bang nucleosynthesis. However, current laboratory measurements, using two independent approaches, differ by over 4$sigma$. Using data acquired in 2007 and 2008 during flybys of Venus and Mercury by NASAs MESSENGER spacecraft, which was not designed to make this measurement, we estimate the neutron lifetime to be $780pm60_textrm{stat}pm70_textrm{syst}$ s, thereby demonstrating the viability of this new approach.
We present the status of current US experimental efforts to measure the lifetime of the free neutron by the beam and bottle methods. BBN nucleosynthesis models require accurate measurements with 1 second uncertainties, which are currently feasible. For tests of physics beyond the standard model, future efforts will need to achieve uncertainties well below 1 second. We outline paths achieve both.
We assess local-time variations of epithermal-neutron count rates measured by the Lunar Prospector Neutron Spectrometer. We investigate the nature of these variations and find no evidence to support the idea that such variations are caused by diurnal variations of hydrogen concentration across the lunar surface. Rather we find an anticorrelation between instrumental temperature and epithermal-neutron count rate. We have also found that the measured counts are dependent on the temperatures of the top decimeters of the lunar subsurface as constrained by the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment temperature measurements. Finally, we have made the first measurement of the effective leakage depth for epithermal-neutrons of ~20 cm.
A measurement of the neutron lifetime $tau_{n}$ 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 $tau_{n} = (886.6pm1.2{rm [stat]}pm3.2{rm [sys]})$ 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({it{n,t}}) cross section. The measurement technique and apparatus, data analysis, and investigation of systematic uncertainties are discussed in detail.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
