café com física - ciclo de palestras
palestras de 2015
palestras informais abertas a todos (sala conf. 14:00h ::0.0)
Randolf Pohl (MPQ, Minique),
Nuclear structure from laser spectroscopy of muonic atoms
We have recently established laser spectroscopy of muonic atoms as a tool to
measure properties of the lightest nuclei from the proton to helium-4. In
muonic atoms, the heavy muon orbits a bare nucleus with a 200 times smaller
Bohr radius, compared to its electronic counterpart. This results in a
tremendously increased sensitivity (200^3) of the muonic atom's S-states to
the finite charge and magnetic radius of the nucleus.
Our proton charge radius Rp=0.84087(39) fm is ten times more accurate, but 7
sigma discrepant from the world average, which is based on elastic
electron-proton scattering and precision spectroscopy of regular (electronic)
hydrogen. Possile explanations of this ``proton radius puzzle'' include
unexpected behaviour of the proton and to physics beyond the Standard Model.
Our new data on muonic deuterium and helium may help to understand this puzzle,
and will ultimately determine the radii of the lightest nuclei with 10 times
João Carvalho (CFC)
A three-dimensional computational model of tumor growth and angiogenesis
A three-dimensional model of tumor evolution, with a reduced number of parameters, was designed and tested. It considers the existence of cancer stem cells at the origin of tumor cell clusters, and the effect of tumor cells migration. The simulation model also includes the creation of new capillaries. The results show that, even with such a simple model, some of the processes and the values of the parameters are fundamental to initiate an invasive tumor. Hints of therapy strategies were obtained from the progression of the tumor growth.
Kiwamu Saito (LIP)
Scintillation mechanism in helium mixed with xenon
When scintillation in rare gases is used in radiation detectors, it is expected that the detectors show better time resolution in comparison with radiation detectors measuring charge signals caused by ionization particles. Although 3He, one of isotopes of helium, is widely used as medium to detect neutrons, it is difficult to apply to a scintillation detector as a gas scintillator because of a long decay time (about 10 ms) and luminescence wavelengths lying in vacuum ultraviolet (60-100 nm). In order to solve these problems, we have been studied a possibility to exchange a luminescence origin from helium to xenon by adding a small amount of xenon to helium. The reasons we selected xenon are that a decay time of an excited xenon dimer is fastest (about 99 ns) among rare gases and its peak wavelength in luminescence spectra of that is about 173 nm. In this talk, I would like to talk about the scintillation properties and mechanism in helium mixed with xenon.