Nuclear physicists at the Technical University of Munich are also planning high-precision measurements. The researchers want to determine whether neutrons react to electric fields. If neutrons have an electric dipole moment, this might help explain what happened after the Big Bang, within the first seconds of the universe. "In our universe, there is matter, but nearly no antimatter. Both matter and antimatter were probably created in equal parts with the Big Bang and then immediately annihilated again to energy. Apparently, during this process some matter was left - the stuff of which we and the universe around us consists. "We want to appraoch the answer to the question of why there’s an asymmetry between matter and antimatter with the high-precision study of the properties of neutrons", summarizes Tobias Lins, member of the research group at the TU Munich.
By measuring the electric dipole moment of a neutron, theories can be tested that try to extend the Standard Model. According to the Standard Model, the electric dipole moment of a neutron is far too small to be measured by means of today's technologies. Pursuant to theories that extend the Standard Model, there must be a much larger electric dipole moment, which is in a range that should be able to be demonstrated experimentally.
Once more, the magnetic field of the Earth and those of transformers, motors, electric appliances or even metal doors cause problems. The suitable magnetic shield was developed at the Technical University of Munich by the research group led by Prof. Peter Fierlinger. At the setup, inter alia, PTB, IMEDCO (shield) and Rohrer (amplifier) are involved.
The result is a unique magnetically shielded laboratory with a damping factor of more than one million against external interference in the micro-Tesla range at frequencies in the millihertz area - a world record. "This is a great achievement, because attenuation in the low frequency region is especially difficult", says Tobias Lins. The magnetic field inside the chamber is only a few 100 pT and is smaller than the average magnetic field between the stars of the universe.
The new, almost magnetic free space allows to improve the accuracy of recent measurements of the electric dipole moment of the neutron by a factor of 100 and thus to advance into the dimension of the theoretically predicted size of the phenomenon.
The outer part of the Munich laboratory consists of a magnetically shielded room (MSR) of two shells Magnifer, a highly magnetizable alloy. Each of these shells consists of 2 x 1 mm thick heat-treated Magnifier-sheets. An 8 mm thick aluminum shell in between is supposed to shield the higher frequencies. The shield absorbs the field lines of external magnetic fields and thus prevents their penetration in the interior of the experiment.
Whether for the direct measurement of brain waves or for the determination of the neutron-torque - in order to achieve these low magnetic field strengths a reliable degaussing of the magnetic shields is required. A basis for this is a current-regulated amplifier, tailored for the specific application.
High attenuation factors can only be created by large amounts of magnetizable alloys, however, to achieve the smallest possible residual field is a challenge. This requires a carefully designed shielding and an efficient degaussing. The term 'degaussing' is misleading in this context, since the shielding does not demagnetize, but perfectly adapts the magnetic field to the environment, called equilibration. For this purpose, the shielding material is alternately magnetized in opposite directions, with the strength of the magnetization decreasing continuously until the desired state of equilibrium is reached. To achieve this balance a sophisticated configuration of coils, transformers, amplifiers, digital and analogue technology is needed. Critical is the amplifier, the noise of which must be small and the zero line extremely stable and accurately adjusted.