ExperimentsInModernPhysics

• Not very well writen, but a lot of useful infomation. Only read what I needed for MPL first pass. Will come back for more!
• A defining charactersitic of present-day physics is that many of the quantities used to describe physical phenomena are quantized.
• kT = 40 eV at 300 K
• Energy levels in atoms become energy bands in solids.
• Nearly every measurement made in a physics laboratory comes down to determining a voltage, so it is important to have a basic understanding of electronic circuits.
• The impedance: Z(w) for capacitors is 1/(iwC) w->0: like a broken circuit w->inf: like a short circuit
• A capacitor stores energy in an electric field, an inductor stores energy in a magnetic field.
• An inductor is to a large extent, the opposite of a capacitor. Z(w) = iwL. w->0 behaves lika short circuit w->inf: like a open circuit
• Usually wires are coated with an isulator so that it will not short to its surroundings. If a wire is supposed to carry some small signal, then it will need to be "sheilded", that is covered with another conductor (outside the insulator) so that the external environment does not add noise. Coaxial cable is a popular sheilded wire.
• There will be reflections in the transmission if the impedence of the capble is not matched to the load.
• The gain of an amplifier with negative feedback depends on the ratio of the pair of resistor values and not the gain of the amplifier. Its hard to get resistor values to change, so the amplifier circuit is very stable.

[skip to ch 8]

• An approximate universal figure for the energy loss of a relativistic single charged particle in any matterial is 2 MeV /(g/cm2)
• The advantage of proportial counters likes in the detection of very low-energy X-rays or gamma rays, which can hardly penetrate a scintillation crystal, and when in addition good energy resolution is required. eg: in Mossbauer where it is necessary to identify a 14.4 keV gamma ray in a strong background of 5 and 123 keV photons.
• The efficiency of Geiger counters is 90% or higher for charged particles, but for photons its much lower, on the order of 1-2%.
• The appropriate detector for measurements of the energy of gamma rays is an inorganic crystal.
• Solid state detectors: ~solid-state ionization chambers have two basic advantages over a gas-filled chamber a) Lower energy required for the creation of an electron-ion pair (3 eV vs 30 eV in a gas) => stronger signal and better statistics. b) The stopping power is 10³ that of a gas-filled device.
• Earths atmosphere is 10 X₀ -> all strongly interacting particles are absorbed before sea level.
• CR flux ~300/m² s