Ppt – statické momenty jader – metody jejich měření powerpoint presentation – id 4385593 76 gas station hours

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• In conventional NMR a relatively small nuclear polarization is generated by applying a large magnetic field after which it is tilted with a small RF magnetic field. An inductive pickup coil is used to detect the resulting precession of the nuclear magnetization. Typically one needs about 1018 nuclear spins electricity voltage in canada to generate a good NMR signal with stable nuclei. Consequently conventional NMR is mostly a bulk probe of matter. On the other hand, in related nuclear methods such as muon spin rotation (μSR) or β-detected NMR (β-NMR) a beam of highly polarized radioactive nuclei (or muons) is generated and then implanted into the material. The polarization tends to be much higher – between 10% and 100%. Most importantly, the time evolution of the spin polarization is monitored through the anisotropic decay properties of the nucleus or muon which requires about 10 orders of magnitude fewer spins. For this reason nuclear methods are well suited to studies of dilute impurities, small structures or interfaces where there are few nuclear spins.

• The target is located at the entrance of the FRagment Separator (FRS), a magnetic high resolution spectrometer. Depending gas out on the operation mode, the FRS can provide cocktail beams (a mixture of nuclei, which are characterized by similar mass-to-charge ratio) or monoisotopic beams. At relativistic velocities the reaction products leave the production target as highly-charged ions and mainly bare ions occur. The ions are injected as a bunch of about 400 ns pulse length into the ESR. After injection, the ESR is used as high-resolution mass analyzer, and the masses are determined from the precise measurement of their revolution frequencies.

• For an unambiguous relation between frequency and mass, the second (velocity dependent) term on the rhs of the equation on next slide must be canceled and two methods apply. For SMS, the ESR is operated with gt = 2.4, electron cooling is applied so that Dv/v → 0; and the revolution frequency is determined eon gas card top up from a Schottky-noise analysis. For IMS, the ESR is operated in the isochronous mode at gt = 1.4: Ions are injected with a suitable velocity so that their Lorentz factor g = gt; and their revolution frequency is determined from their time-of-flight (TOF) for each turn.

• ISOLTRAP is a triple trap mass spectrometer connected to the on-line mass separator ISOLDE. There, the radionuclides are produced by bombarding a thick target with 1.4 GeV proton. The produced nuclides diffuse out of the target and are ionized either by surface, plasma or resonant laser ionization. The 60 keV ion beam is mass separated in a magnetic spectrometer with gas exchange in the lungs a resolving power (m/Dm) of up to 8000 and delivered to different experiments.

• ISOLTRAP measures the mass m via the determination of the cyclotron frequency nc = (1/2p)(q/m)B of ions with charge q stored in a homogeneous and stable magnetic field B. The main components of the ISOLTRAP setup are shown in the Fig. on next page. It consists of three traps that perform specific tasks: (i) the radiofrequency quadrupole (RFQ) used as a beam conditioning trap in which the 60-keV ISOLDE beam is decelerated, cooled, and bunched to adapt the beam to the requirements of ISOLTRAP with respect to its time structure and emittance gas and supply shreveport; (ii) the preparation Penning trap, in which contaminant ions are removed by a mass-selective buffer gas cooling technique; and (iii) the precision Penning trap for the actual mass measurement.

• In the time-of-flight ion–cyclotron resonance (TOF-ICR) detection technique the ions are first prepared at a well-defined radius of the magnetron motion. Here, the orbital frequency and, therefore, the orbital magnetic moment m as well as the associated energy E = m.B, are small. By application of a resonant quadrupolar excitation, with an appropriate choice of amplitude and excitation time, the magnetron motion is completely converted into the (modified) cyclotron motion while the radial radius remains constant.

• When the ions are ejected from the trap after one full conversion (by lowering the trapping potential of the downstream end electrode) at initially low axial velocity they drift along the axis out of the magnetic field. In passing through the magnetic field gradient the ions get accelerated due to the gradient force and thus the axial grade 9 electricity unit test answers velocity of the ions increases.

• In each of several experimental cycles, different excitation frequencies are applied. Since the magnetic moment and the radial energy of the ions are larger in resonance due to the higher frequency of the cyclotron motion as compared to the magnetron frequency, the resonantly excited ions arrive earlier at the detector than those ions that have been excited non-resonantly.

• A variation of the quadrupole frequency rf results in a characteristic time-of-flight cyclotron resonance curve. The theoretically expected line shape for such a resonance is mainly determined by the Fourier transformation of the rectangular time excitation profile and is similar to the absolute value of the so called sinc(x)-function f(x)=sin(ax)/(ax).

• The target is located at the entrance of the FRagment Separator (FRS), a magnetic high resolution gaslighting spectrometer. Depending on the operation mode, the FRS can provide cocktail beams (a mixture of nuclei, which are characterized by similar mass-to-charge ratio) or monoisotopic beams. At relativistic velocities the reaction products leave the production target as highly-charged ions and mainly bare ions occur. The ions are injected as a bunch of about 400 ns pulse length into the ESR. After injection, the ESR is used as high-resolution mass analyzer, and the masses are determined from the precise measurement of their revolution frequencies.

• For an unambiguous relation between frequency and mass, the second (velocity dependent) term on the rhs of the equation on next slide must be canceled and two methods apply. For SMS, the ESR is operated with gt = 2.4, electron cooling is applied so that Dv/v → 0; and the revolution frequency is determined from a Schottky-noise analysis. For IMS, the ESR power quiz questions is operated in the isochronous mode at gt = 1.4: Ions are injected with a suitable velocity so that their Lorentz factor g = gt; and their revolution frequency is determined from their time-of-flight (TOF) for each turn.