LPHE - TP4 - Accelerateur Van De Graaf
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TP4: Fusion reaction with a Van De Graaf accelerator

The aim of this experiment is to provide evidence that a fusion reaction between tritium and accelerated deuterium ions is happening. Deuterium ions are accelerated using a \vdg accelerator up to 300keV, and collide into a tritium fixed target. The two particles can undergo a nuclear fusion reaction producing a helium nucleus and a neutron. Detecting those particles, and making sure their characteristics correspond to the ones predicted proves that this reaction is indeed taking place. In this specific case, the alpha particle and the neutron have to be detected in coincidence, and the speed of the neutrons is measured and compared to the theoretical calculation.

Although consisting of a fusion reaction, the study does not focus on producing energy, since the deuterium needs to be accelerated for the reaction to happen admittedly far below critical regime. The present experiment is at a more fundamental level, like the ones carried out at CERN. Although much smaller in size and targeting at the scale of nuclei, the fundamental principles and techniques remain the same: colliding particles, detecting the products of the reaction and see whether it is consistent with theory.

And most important of all you will a trigger circuit, an essential component of every modern particle physics experiment. Nowadays accelerator can produce billions of collisions per second and the limit of modern analyses is the ability of store and analyse all those events. A trigger identifies so called "interesting events" and records them on the computer only if they have interesting characteristics. This makes a first selection and prevents from recording huge amounts of useless data.

This laboratory work will allow you to perform a "pocket LHC experiment" and to become familiar with particle physics experiments. The trigger circuit, based on coincidence, will be built, calibrated and timed properly. Then, several well chosen measurements within the available time can be taken to study the response of the detector. Finally the obtained data will be analysed using ROOT, the data analysis framework most used in particle physics.

Plan de travail

You will work on this experiment 1 day per week for 12-13 weeks
  • Days 1: Introduction. Explanation of the experiment and the setup. Explanation of the components that you will use. Get a Cobalt source and have a look at some signals. Calculate the theoretical value for the neutron speed and start buiding the circuit.
  • Day 2-4: Build the circuit. Try to understand step by step the response of the detector. Take some data and start having a look. Install ROOT and learn how to fo fits with RooFit. Calibrate the time measurement.
  • Day 5-6: Switch on the accelerator, move from the calibration detector for photons to the alpha detector. Optimise the setup. Take data and have a look at the energy spectra.
  • Day 7-8: Accelerator on. Take measurements at different positions to measure neutron speed. Analyse data. Take background runs. Eventually try to do some small simulation.
  • Day 9-13: Analyse data, take extra data runs if needed. Write the report.