The course of an experiment

The physicist's objective

A physicist's work at GANIL involves the study of a nucleus which he thinks may have particular properties. He may try to reveal a given property by implementing nuclear reactions, which are designed to occur during the experiment.

For example, the team of physicists tries to demonstrate the existence of a tetraneutron, a highly exotic type of nucleus, formed by 4 neutrons bound together for a very short period of time.

Proposal for an experiment

The physicist determines the conditions of his experiment, during which it is planned to bombard a target with an ion beam.

First, he selects a stable element, which will constitute the primary beam, how much energy is required, as well as the number of particles per second in the beam. He also determines which target will enable the production of the stable or radioactive nuclei to be investigated. He then calculates all of the nuclear reactions that will take place.

After having chosen the particles to be detected and identified, and the most appropriate detectors for his objective to be reached, he presents the concept of the experiment to a panel of experts, which meets twice a year. This panel analyzes the proposal and grants a certain beam time allocation, which varies from a few days to about 2 weeks.

Preparing the experiment

The physicist will then have a few months to prepare his experiment, adjust his detection device, and produce his target. He may use already existing elements.
To prove the presence of the tetraneutron, the experimenters chose a beam of Oxygen-18, a stable isotope which is the most neutron rich form of oxygen. The target is made of beryllium, which is a light and low-density material. The neutrons are to be detected by the DEMON detection system.

Preparing the experimental room

During the week before the experiment, physicists and technicians install the various systems in the experimental room, test and calibrate the detection instruments.

Data acquisition

The physicist develops the electronics which will be used to acquire the data.
Each equipment rack has its own function: for instance, to convert analog outputs (current, voltage) from the detectors into digital signals recorded on the computer. It may also amplify and shape the signals.

The experiment


The experimental logbook is at the heart of the experiment. All operating parameters of each of the experiment's components are recorded hour after hour. The physicist returns to his lab, with his experimental logbook, and with his data stored on a hard drive. Using processing and simulation software which he develops himself, he analyzes all of the data, from which he derives the scientific outcome.

Course of the experiment

The physicist monitors the course of the experiment and identifies the particles on monitors, which display the operating status of the detectors, in order to:

• Identify the particles produced during the experiment by means of the energy they release in a solid detector (left screen).
• Discriminate between neutrons and gamma rays penetrating the neutron detector (right screen).

Publication of results


The physicist then returns to his laboratory and analyzes, together with other colleagues, students and post-docs, the data collected during his experiment.
He then publishes the results in English, in an appropriate specialized scientific journal: Nuclear physics A, Physical Review Letters, … and also presents them to the nuclear physics community, at specialized conferences.