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Content archived on 2022-12-23

Experimental discovery and spectrum measurement of radiative neutron decay

Objective

The aim of this proposal is to discover the process of radiative neutron beta-decay and to measure for the first time the gamma-quanta spectrum for this process, in the region from about 50keV up to the endpoint (at about 800keV). The relevance of this experiment is determined by the fact that the radiative decay branch is experimentally well investigated for all elementary particle decays with charged particles in the final states, except for the neutron. It is important to note in this respect that the observation of the radiative decay of the neutron allows detecting gamma-quanta with extremely low energy, compared to the radiative decay of other particles where it is impossible to detect gamma-quanta with energy less than several MeV. The accuracy this proposal is aiming at for the branching ratio measurement is about 10%.

At present the accuracy of life-time and correlation coefficient measurements in the decay of the free neutron is sufficiently high so that the radiative corrections can be extracted by combining the results of these measurements. However, the experimental investigation of the radiative decay of the neutron that is proposed here has a fundamental character because it will allow to determine the value of the most important part of these radiative corrections for the first time in a direct way, independent of possible systematic errors in the life-time and correlation coefficient experiments.

It is proposed to use for this experiment mainly experimental equipment that is already existing and that was constructed for correlation measurements in ordinary neutron beta-decay. This set-up consists of a vacuum chamber with proton and electron detectors inside. The layout of this chamber allows for the replacement of the old electron detector and installation of a new-sectioned electron-gamma detector, which will register coincidences of electrons and gamma-quanta in separate sections. Important tasks in relation to the development of new experimental equipment for this project are the calculation, assembling and testing of this electron-gamma detector, which will be optimised to detect gamma-quanta in the energy domain from less than 50 to about 800keV. It was suggested to conduct this experiment on the cold neutron beam at ILL in Grenoble, where now already several teams that are involved in the project presented here are carrying out correlation measurements in neutron beta-decay with the experimental equipment mentioned above. It is planned to record gamma-electron coincidences, gamma-proton coincidences, as well as triple coincidences of all three particles. This will allow to identify the radiative decay events with almost 100% probability.

A proposal was submitted to the ILL program advisory committee and subsequently approved.

It is important to note that the proposed experiment will be the first experimental investigation to put into evidence and measure the energy spectrum of radiative neutron beta-decay and that the results of the measurements to be carried out will be the basis for future experimental investigations of this rare neutron decay mode. Indeed, these measurements will most probably only be the first of a series since it is expected that they will open the possibility to carry out correlation experiments between the radiative gamma-quanta and the protons and electrons in radiative neutron decay.

Call for proposal

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Funding Scheme

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Coordinator

Katholieke Universiteit Leuven
EU contribution
No data
Address
200 D Celstijnenlaan
3001 Leuven
Belgium

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Total cost
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Participants (3)