The SEN group, through the measurement of certain properties of beta decay and in particular those of fission products, has built up a coherent research activity enabling it to build bridges between several disciplines of fundamental and applied physics. The process of beta decay is involved in a wide range of fields including physics, nuclear data, chemistry and medicine. b) Why is the study of beta decay interesting? The half life ( t 1/2 ) of a nucleus being related to lambda by the equation t 1/2 =ln2/λ, on can then calculate its half life. Integrating N(p) over the whole possible momenta taken by the emitted electrons gives access to the transition rate, λ, the radioactive decay constant representing the probability of decay, per unit of time, of a radioactive nucleus. It belongs to the physics topics studied by the SEN group (see e-shape, summation, structure). C is an additional corrective term which has been refined many times since the original Fermi theory. The product of a phase space term (involving the momentum p and the kinetic energy T e of the electron and the Q β of the decay), with the Fermi function, F, taking into account the effect of the coulomb field of the daughter nucleus (atomic number Z') on the particles produced, and with an interaction term between the initial and final states, involving the nuclear matrix elements M fi. With a few approximations, this could be written as follows: Fermi could now build his theory and calculate the shape of the energy spectrum of the electrons (or antineutrinos produced). In the case of beta minus decay, for example, a neutron in a mother nucleus could change into a proton in the daughter nucleus produced and this was accompanied by the emission of two particles: the beta particle (the electron) and an antineutrino. This issue had been solved at the beginning of the thirties with the discovery of the neutron and of the neutrino. Unlike the radioactivities α and γ, the beta particles produced were not monoenergetic but were distributed along an energy spectrum that challenged the law of energy conservation among others. For nearly 30 years, it was an enigma for the theories of the time, which regularly came up against new experimental observations that failed to describe it. The first type of radioactivity to have been observed as early as 1900, beta radioactivity was the most difficult to explain amoung the three alpha, beta and gamma radioactivities. Risk prevention and infrastructure managementġ - Beta decay in a few words a) Discovery and the Fermi theory. Presentations at conferences, seminars and posters.Laboratoire de physique subatomique et des technologies associées
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