Related Experiment Video
Updated: Aug 11, 2026
10:42
Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh
Published on: May 3, 2019
Measurement of the neutron lifetime using a proton trap
M S Dewey1, D M Gilliam, J S Nico
1National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Physical Review Letters
|November 13, 2003
Summary
This study precisely measured the neutron lifetime using in-beam neutron and proton counting. The new neutron lifetime value is 886.8 seconds, offering improved accuracy for fundamental physics research.
Area of Science:
- Nuclear Physics
- Particle Physics
- Metrology
Background:
- The neutron lifetime is a fundamental constant in particle physics.
- Previous measurements have shown significant discrepancies, necessitating precise new determinations.
Purpose of the Study:
- To report a new, highly precise measurement of the neutron decay lifetime.
- To utilize an in-beam method for absolute counting of neutrons and decay protons.
Main Methods:
- Absolute counting of in-beam neutrons and their decay protons.
- Proton confinement in a quasi-Penning trap and detection with a silicon detector.
- Measurement of neutron beam fluence via capture in a 6LiF foil detector with known efficiency.
Main Results:
- The measured neutron lifetime is tau(n) = (886.8 ± 1.2 [stat] ± 3.2 [syst]) s.
- This result represents the most precise neutron lifetime measurement to date using an in-beam technique.
Conclusions:
- The new measurement provides a more accurate value for the neutron lifetime.
- Dominant systematic uncertainties arise from the 6LiF deposit mass and the 6Li(n,t) cross section.
Related Concept Videos
02:48Radioactive Decay and Radiometric Dating
Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. The number of disintegrations per unit time is called the activity (A), which is directly proportional to the number of nuclei in the sample. The decay constant (λ) is an average probability of decay per nucleus in unit time.
03:20Nuclear Transmutation
Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with another particle. The first manmade nucleus was produced in Ernest Rutherford’s laboratory in 1919 by a transmutation reaction, the bombardment of one type of nuclei with other nuclei or with neutrons. Rutherford bombarded nitrogen-14 atoms with high-speed α particles from a natural radioactive isotope of radium and observed protons being...
01:10¹H NMR of Labile Protons: Temporal Resolution
Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
01:14Atomic Nuclei: Nuclear Spin State Population Distribution
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
01:19Mass Analyzers: Common Types
The quadrupole mass analyzer consists of four cylindrical metal rods arranged in a diamond carrying a DC voltage and a radio-frequency AC voltage. The motion of ions through the quadrupole depends on the field strength, causing only ions of a certain m/z to resonate successfully and strike the detector at a given field strength. Though the transmission rate for these analyzers is high, the exact elemental composition of the sample is not determined because of low resolution; however, they are...
01:28Atomic Nuclei: Types of Nuclear Relaxation
Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...