i felt in love with nuclear physics !
let me show you some of my result with my wilson cloud chamber experiment, sorry for OFF topic :beer: :
The diffusion cloud chamber is a device which can reveal the path of ionized, subatomic particle, travelling at relativistic speed.
The diffusion cloud chamber can only detect charged particles : muon, electron, positon, proton, kaon...or indirect one created by neutral particle :gamma, neutron, K0... . It was invented (the expansion one) bye Charles Wilson in 1911. The diffusion cloud chamber allow to see continuous interactions of particle when the bottom is cooled at low temperature (this one is about -37°C with some peltiers). When we put some alcohol in the top of the chamber (Isopropyl alcoohol ), the vapors falls to the bottom and cools down : but not all the vapor condense, there is some which stay in vapor state, making a metastable layer of supersaturated alcoohol above the surface. Once a charged particle pass through this layer, it ionize some of the molecules of air or alcoohol : the ions created act as condensation nucleus and the alcoohol suddenly condense on this newly created ions, making a track of droplet following the path of the particle. The bigger is the track, the more ionizing is the particle (for example with the alphas).
Some interactions of my setup :
Alpha particle close up. An ionized cloud of alcoohol atom is surrounding the path of the particle. Alpha particles : are He2+ nucleus, 7350 times more heavier than electron so are not easily deflected by electromagnetic interaction. Due to their mass, their speed is lower and because of the high charge, alpha particle lose rapidly their energies with ionization, thus are easily absorbed by materials. Kinetic energy range from 3 to 7 MeV. For an alpha particle of 5 MeV (from Am241) :
15.000km.s-1, 5000 ionization per μm in water, maximum range of 50μm in water or 4 cm in air.
241Am decay (above, there is a source of Am in the chamber) : Americium 241 is a by product of the fission of 235U and decay into 237Np with the emission of 5.5 Mev alpha particles, 60 keV gamma rays and few keV conversion or Auger electrons . It has a half life of 432.2 years. The amount of 241Am in the picture is about 1μCi. The end of alpha track is often dense due to the “Bragg” peak.
Bêta particles : are electron or positon which have the same mass but opposite charge. Their speed is close to the speed of light (1 Mev~0.941c). Due to their little mass, they are easily deflected by electromagnetic interaction. Because they can easily accelerate when they come close to an atom, they lose most of their energies with Bremsstrahlung. They produce less ionization than alpha particle due to their monocharge, thus have a higher range. Positron when thermalized, annihilate with an electron to form gamma rays. For a bêta particle about 2 MeV :
Range : 6 meters in air, 1 cm in water, 3 mm in aluminium, 10 ionizations per μm in water.
Above picture is a "Delta ray " : An energetic beta particle (often electron) is knocking orbiting electron out of one atom. We can see the original electron deflected with an ejected electron at a few keV of energy.
Gamma rays : They are not detected in a cloud chamber because these “particles” which are also electromagnetic radiation, are neutral. They can interact in matter with photoelectric, compton, or pair creation effect and produce charged particle which are detectable. Photoelectric effect is the transfert of all the gamma’s energy to an electron which is ejected from an atom. Compton effect is the inelastic scattering of a gamma with an electron who are ejected. When gamma energy is above 2x0.511 keV, the gamma can disappear and form a pair of bêta particles. For a gamma of 1 MeV, it need 900 meters of air to absorb 50% of the gamma, 5.1 cm of concrete, or 0.85 cm of lead.
The picture above show some Photoelectric or Compton effect : In air, gamma do mostly photoelectric interaction under 30 keV, compton above 30 keV and pair creations above 10 Mev. Above, an electron is ejected by a gamma ray.
Gamma Annihilation (pair creation) : A magnetic field about 0.5T (direction of B into the paper) deflect the electron toward right and the positon to left when a gamma annihilate. The radius of curvature is given by the Lorentz’s Force by R=mv(Bq)-1.
Thoron decay : Some 232Th nucleus (T1/2=14.1x109 years) decay successively to 220Rn in the mineral. Thoron is a gas with a half life of 55s. It decay through alpha emission to 216Po which have an half life of 0.14s. Thus, 216Po decay immediately into 212Pb with an alpha disintegration. We can see some V or L shape : it is the simultaneous disintegration of 220Rn and 216Po.
A big one here with explanation :
About 10,000 muons reach every square meter of the earth's surface a minute. Traveling at relativistic speeds, muons can penetrate tens of meters into rocks and other matter before attenuating as a result of absorption or deflection by other atoms. Paralell track of muons come from the same cosmic ray shower .
Muon decay (above) : A track enter in left in the cloud chamber and is not really deflected by the magnetic field, due to a high mass. Then it "kinks" and is deflected to left by the magnetic field : it’s now a lighter particle, a positon which in fact come from a μ+ decay. The two neutrino are not detected.
Momentum transfert : The annihilation of a gamma produce a pair of bêta particles. The magnetic field, which go into the paper, deflect the positron towards left. But something happen, mid flight : Strangely, the positron start curving in the opposite direction as if it had suddenly become negatively charged. What has happened is that the positon has run head-on into an electron, transferring all its momentum to that electron. This can only happen if the mass of the positon is equal to that of the electron. The positon that stops would eventually have annihilated.
Elastic proton scattering : a very rare event which come from hours of movie. A cosmical proton interact with the glass wall of the chamber, ejecting another proton. The two protons are visible and entering in the bottom of the picture. One of the protons then collides with another proton which either comes from a water molecule (one of its two hydrogens atoms), or one of the hydrogen atoms in the alcohol molecule. This collision kicks the proton out of the water molecule and we now see both the scattered original proton and the new proton kicked out of the water molecule.
The most striking signature is that the angle between the 2 emerging protons is 90 degrees (it appears a little bigger than 90° because the tracks are pointing away from the camera).
Elastic scattering of two equal mass particles, where one is initially stationary, always gives an angle of 90 degrees between the two final particles.
