1. SURVEY AND STUDY OF COSMIC RAYS STUDENTS: Campogiani Giovanna Claps Martina Corridori Giuliano Flamini Chiara Lupidi Sara Mesghali Fabio Silvestri Alessandra TUTORS: Benussi Luigi Passamonti Luciano Pierluigi Daniele Summer Stage 2006

2. What are cosmic rays? Cosmic rays are the only direct sample of matter that comes from the Deep Space. The study of this kind of events helps us understanding the history and the physical elements of our galaxy. Cosmic rays coming from space hit the elementary particles of our atmosphere and, by interacting with them they produce other elementary particles such as electrons, muons, and a small part of antimatter.

3. The existence of cosmic rays was discovered by the scientist Victor Hesse through an experiment that had worth him the Nobel in 1936. In 1912, Hesse loaded on an aerostatic balloon a device to measure the charged particles and undertaken a journey than showed like the quantity of particles (and therefore of radiation) increased with the altitude, that meant the radiations measured did not come directly from the land, but from the space, hence the name of Cosmic Rays. Afterward the scientistic community started to study cosmic rays with grewing interest and in 1937 the physic Anderson discovered the existence of muons and antimatter. We know that cosmic rays are ancient and that they come from the universe thanks to the discovery of a cosmic ray with an energy of 10 20 eV, that is supposed to come from the Big Bang. To study cosmic rays in Italy, in 1982, was built the underground the Gran Sasso laboratory. Being under kilometres of stone, the laboratory is very importante to avoid an interference with other smaller particles of entity, screened from the mountain.

4. How to point out the cosmic rays? The study of cosmic rays is carried out with different kind of detectors; in our case we used plastic scintillators. They consist of various parts: Scintillator. Leader of light. Photomultiplier (fotocatode, dinodes, anode). Partitor (resistance, capacitor). The elettronic components used in our experience are: Discriminator. Coincidence. TDC (time to digital converter).

5. The scintillator is composed from doped pexiglass with naftalene (9%). Naftalene is used because it increases the capacity of producing light when hit by a charged particle. The scintillator is covered with a layer of aluminium and a black tape, in order to avoid to capture also the photons from ambient light. When a Cosmic ray passes through the scintillator the Naftalene electrons are excited to higher energy atomic level and they emit light when they go back to their “natural” state Connected to the scintillator using a special neck, there is the light-guide (also in plexiglass but not doped). It conveys the photons produced in the scintillator directing them towards the photocatod of the photomultiplier. Also the light-guide is darkened with the black tape.

6. The photomulplier It is a device used to amplify the numebr of electrons by means of the photoelectric effect. It is made of a series of electrodes (dinodes) to which is applied an electric field to accelerate and to guide electrons long the photomultiplier In order to distribute the electric field to all the dinodes is used a voltage-divider (made of capaciters and resistors)

7. Discriminator It’s an electronic device that receives analogical signals from the photomultiplier and then changes them in digital signals; moreover it eliminates the “noise”. In our experiments we have used a discriminator with double threshold, one for every scintillator. Coincidence The signals of the two scintillators, once discriminated, arrive both to the coincidence unit. The coincidence is used in order to select the events corresponding to a single cosmic ray passing both scintillators.

8. TDC (Time To Digital Converter) A START signal (given from the coincidence,) enters the TDC and gives the start to a “clock” that counts times until the STOP of the second signal (coming form one scintillator, opportunely delayed). The out of the TDC is an entire number corresponding to the number of unit of time (in nanoseconds) elapsed between start and stop. The TDC and the Status A, lodge din the crate CAMAC, dialogue with the PC through the SCSI interface.

9. Electonics Diagramm 80859095100105 0 100 200 300 400 500 Count TDC channels

10. The curve of Gauss represents a distribution that indicates the fluctuation of the measurements; it’s a bell shape curve that depends on the arithmetic mean (m) and the standard deviation (σ). The value of σ is proportional to the probability to find errors. where: M = arithmetic mean  = standard deviation (   = variance) The distribution of Gauss    xconexf x 2 2 2 )M( 2 1 )(  

11. COSMIC RAYS SPEED MEASURE To calculate cosmic rays speed we used the formula  mS001,0133,0 0   t S v      mS001,0157,4 1   mSSS002,0024,4001,0133,0001,0157,4 01 

12. TIME 0 TIME 1 707172737475767778798081828384858687888990 0 100 200 300 400 500 Chi^2= 509.69757 R^2= 0.9866 y0-6.59591±9.1352 xc80.47651±0.07904 w5.24328±0.20933 A3228.42791±152.53542 Count TDC Channels Count Gaussian 80859095100105 0 100 200 300 400 500 Chi^2= 726.94418 R^2= 0.97153 y016.57666±8.50305 xc94.01036±0.10689 w4.8697±0.25557 A2551.74476±146.73139 Count TDC channels Count Gaussian

13.   st st 9 1 9 0 10*11,001,94 10*08,048,80        ssttt 99 01 10*19,053,1310*08,048,8011,001,94      s m s m t S v 9 9 10*002,0297,0 10*08,053,13 002,0024,4          s m v 6 10*9,141,297  CONCLUSION: The values we found out in our statistic show that cosmic rays travel at a speed near the one of light, as we expected to be.