Open days at Rudjer Boskovic Institute 2005:Einstein and Particles

As part of the Open Days at IRB, celebrating the year of physics, memmbers of DEP together with students from the Physics Department of the University of Zagreb constructed two types of cosmic ray detectors, and demonstrated them to the public. The text (in Croatian) introducing the basic physics can be found here .

Detecting cosmic rays using scintillators

Two scintillators were connected to photomultiplers and these hooked to a NIM pulse shaper, discriminator and coincidence unit. The output of each signal is passed on to a digital oscilloscope, triggered by the coincidence signal. Also, the coincidence signal was hooked to a speaker, giving a beep after a particle passed through both units.

The full setup	The two photomultiplier tubes/scintilators on top of each other	NIM logic setup	Two signals in coincidence shown on the oscillator. On top is the machine which goes PING

Detecting cosmic rays using a cloud chamber

A cloud chamber was also built to detect cosmic rays. A rectangular plexiglas box (25cm 15cm 15cm) with no top (actually a fish tank bought at a pet shop) had a sponge glued to the bottom, and the insides covered in black. Ethanol (95%) was placed freely on the sponge, and the box turned upside down on an aluminum plate covered in black velvet. Below the aluminum dry ice was placed to cool the bottom of the box. The steep temperature gradient for the evaporating alcohol creates a supersaturated state near the bottom. A passing charged particle ionizes the air and causes the alcohol around the path to condense, creating a visible trail. Light was shined from an opening in the back, and after about 5-10 minutes tracks could be seen from an opening in the front. In practice it was difficult to achieve the right conditions (temperature gradient, correct concentration of alcohol, correct ligthning, correct viewing angles...), but when all was right the tracks were clearly visible. If you want to do a cloud chamber yourself, some useful inks are : here, and here, and here, and here.

The cloud chamber is on the left	A mpg of some truly impresive cosmic tracks	Less impresive, but visible	Less impresive, but visible

Some more videos taken of cosmics, where the tracks can not be seen, or are only barely visible are at here and here and here and here and here and here and here and here .

Organizers and other pictures

Vuko scaring the audience with the question "can you feel the muons" as they place their hands between the scintillators	Goran next to the cloud chamber. The TRUE secret to seeing muons is 95% pure and hidden in his right hand...	Proud Andrej in front of the finally working scintillator setup	Tome demonstrating how big the magnets at CERN are
Soja (Neven) explaining the Big Bang meaning of it all	Lovro happy the cloud chamber works	Vedran trying to impress the girls	Dario wondering where have all the muons gone
Sasa going from quarks to time dilation	Tome, Vuko, Soja, Tanja, Vedran, and Neva:Soja's budding scientist	The poster	The NIM logic unit setup in all its gory detail

Organizers: Tome Anticic, Vuko Brigljevic, Sasa Ceci, Andrej Ficnar, Dario Hrupec, Vedran Nikolic, Goran Niksic, Lovro Prepolec, Natko Skukan, Neven Soic, Tatjana Susa, Branimir Zauner