SURVEY AND STUDY OF COSMIC RAYS

1
SURVEY AND STUDY OF COSMIC RAYS
Summer Stage 2006

• STUDENTS
• Campogiani Giovanna
• Claps Martina
• Corridori Giuliano
• Flamini Chiara
• Lupidi Sara
• Mesghali Fabio
• Silvestri Alessandra

TUTORS Benussi Luigi Passamonti
Luciano Pierluigi Daniele
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 1020eV, 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
Coincidence
Its 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.
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
500
400


300
Count
200
100
0
80
85
90
95
100
105
TDC channels
10
The distribution of Gauss

• The curve of Gauss represents a distribution that
  indicates the fluctuation of the measurements
  its a bell shape curve that depends on the
  arithmetic mean (m) and the standard deviation
  (s). The value of s is proportional to the
  probability to find errors.
• where
• M arithmetic mean
• s standard deviation
• (s2 variance)

2
-
x
)
M
(
1
-

lt
lt

-

2
s
x
con
e
x
f
)
(
2
p
s
2

11
COSMIC RAYS SPEED MEASURE
To calculate cosmic rays speed we used the formula
12
TIME 0
TIME 1
Count
Count
Gaussian
Gaussian
500
500
400
400
300
300
Count
Count
200
200
100
100
0
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
0
80
85
90
95
100
105
TDC Channels
TDC channels
Chi2
726.94418
Chi2
509.69757

R2
0.9866
R2
0.97153

y0
-6.59591

9.1352
y0
16.57666

8.50305

xc
80.47651

0.07904
xc
94.01036

0.10689
w
5.24328

0.20933
A
3228.42791

152.53542
w
4.8697

0.25557
A
2551.74476

146.73139
13
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.