Transcript COSMIC RAYS

COSMIC RAYS
An Overview
Cosmic rays-a long story
• C.T.R Wilson discovered in 1900 the
continuous atmospheric ionization. It was
believed to be due to the natural radiation
of the Earth. In other words, from the
ground up.
• Wilson noticed the reappearance of drops
of condensation in expanded dust free gas,
the first cloud chamber.
Condensation tracks on ions
• Wilson suspected the
tracks might be
condensation on
nuclei - ions that were
the cause of the
“residue” conductivity
of the atmosphere.
The Wilson Cloud Chamber
Where did the ions come from?
• At the beginning of the 20th century
scientists were puzzled by the fact that
more radiation existed in the environment
than could be explained by natural
background radiation
• The debate was solved on a balloon flight
in 1912 from the University of Vienna.
Victor Hess
• In 1912 a Victor Hess, a German scientist,
took a radiation counter (a simple gold leaf
electroscope) on a balloon flight.
• He rose to 17, 500 feet (without oxygen)
and measured the amount of radiation
increase as the balloon climbed.
Victor Hess and the Balloon
• Victor discovered that
up to about 700 m the
ionization rate
decreased but then
increased with
altitude showing an
outer space origin for
ionization.
Not from the Sun
• During subsequent flights Hess determined
that the ionizing radiation was not of solar
origin since it was similar for day and
night.
• It was initially believed that the radiation
consisted of gamma rays only.
• But there was still a dispute as to whether
the radiation was coming from above or
from below.
Birth Cries of the Atoms
• In 1925 Robert
Millikan of Caltech
introduced the term
“cosmic rays” after
concluding that the
particles came from
above not below a
cloud chamber.
• He used elaborate
electroscopes.
Cosmic Ray Electroscope
• Electroscope of cosmic
ray apparatus used by
Millikan. Millikan and a
fellow scientist,
Compton, were locked in
a debate about the nature
of cosmic rays. Compton
won, arguing that they
were charge particles.
Millikan believed they
were uncharged.
The nature of the rays:
Muons and Protons
• Seth Nedermeyer and Carl Anderson discover
muons in cosmic rays.
• T.H. Johnson discovered that the ionization rate
increased from east to west viewing angle
indicating they were positively charged particles
(protons). The increase occurs because the rays
are deflected by the earths magnetic field, which
changes in its strength with latitude.
Charged Particles!
• In 1929 a Russian scientists, D. Skobelzyn,
discovered ghostly tracks made by cosmic
rays in a cloud chamber.
• Also in 1929 Bothe and Kolhorster verified
that the cloud chamber tracks were curved.
Thus the cosmic radiation was charged
particles.
The Caltech Cloud Chamber
• Milliken became President of Caltech and
was instrumental in the building of a high
magnetic field cloud chamber.
• Carl Anderson and Milliken made
numerous photographs of both positive and
negative particles tracks.
• The conclusion was that the positive
particles must be protons.
Occhialini and Blackett
• Giuseppe Occhialini and Patrick Blackett
devised a method of making cosmic rays
take their own photographs.
• They observed in 1932 the formation of
multiple particles, pair production.
• Occasionally they observed the production
of particle showers using lead and copper
plated places in the cloud chamber.
Extensive air showers
• Pierre Auger noticed that
two detectors located
several meters apart
detected particles at the
same time. He
discovered EAS, showers
of secondary nuclei
produced by the
interaction of the primary
particle with air
molecules. (1938)
EAS
• It is the secondary
particles resulting
from the
interaction of the
the primary particle
that are detected by
the detectors used
in our detectors
and others arrays.
An Extensive Air Shower
• Cosmic rays enter the
earth’s upper
atmosphere and
interact with nuclei.
• Secondary particles
result that also
interact.
• The shower grows
with time.
• Certain particles
never reach the
surface.
• Some particles, such
as muons, do reach
the surface and can be
detected.
• It is these that we
wish to detect.
Other tools: The emulsion plate
• The study of cosmic rays was greatly
enhanced by the use of photographic
emulsion plates. The plates were taken to
numerous places, including the Pyrenees
and left for extended periods of time.
• The results were images of complete pion
decays including the discovery of the so
called “strange particles”.
The Spark Chamber
• In the 1960’s spark
chambers were
common. When a
charged particle
ionizes gas between
the plates, sparks fly
along the track,
marking the track of
the particle.
Early Discoveries from CR
• The mass of the proton was determined to a 15%
error (Anderson, Chadwick)
• The discovery of the antiparticle of the electron,
the positron (Klemperer).
• The discovery of the mesotron, with mass
between the electron and the proton
• The first evidence of meson decay (Williams and
Roberts)
• The measurement of the decay (Rossi)
• The discovery of He nuclei and heavier elements
in CR (Frier)
Present Cosmic Ray Studies
• Cosmic Ray studies continue in spite of the
development of high energy particle
accelerators.
• The energy of the highest energy cosmic
rays still cannot be duplicated in
accelerators.
• The field is still very active as indicated by
the presentation of over 300 papers at the
most recent international conference on
cosmic rays.
What are cosmic rays?
• Primaries are particles
with energies from 109
eV to 1021 eV.
• An eV is a unit of energy.
A 40 W reading light uses
about 1034 eV of energy
in one hour.
(from James Pinfoli,
[email protected])
Cosmic rays within the
range of 1012 eV to 1015
eV have been determined
to be:
50% protons
25% alpha particles
13% C, N, and O nuclei
<1% electrons
<0.1% gammas
The Energy Spectrum
• Existing models for
the production of
cosmic rays only
work to 1015 eV.
• CR in excess of 1019
eV are believed to
come from sources
relatively close to our
Galaxy, but the
sources are unknown.
– The highest
energies!
(from,www.phys.
washington.edu)
The Oh My God Particle
• In 1991 at the Fly’s Eye
CR observatory in Utah a
primary particle of 3 x
1020 eV was recorded.
This is the equivalent of
51 joules
• At present particle
accelerators can reach
energies of 1012 eV.
• The Fly Eye
•
(from www.physics.adelaide.edu)
The AGASMA EVENT
In Japan, in 1993, the worlds largest array
recorded a large air shower believed to be
the result of a primary particle measured at
1021 eV. These particles have energies six
times higher than present theories allow.
The mystery is, of course, what is the source
of the high energy particles including these
ultrahigh energy particles.
Where do they come from?
• Low energy rays (less than 10 GeV) come
from the sun.
• Supernovae may be the source of particles
up to 1015 eV.
• The sources for ultrahigh cosmic rays are
probably, active galactic nuclei and gamma
ray bursts.
(www.phys.washington.edu)
Supernovas
• Nuclei receive energy
from the shock wave of
the supernova explosion.
• The energy spectrum
indicates that most of the
supernova particles have
less than 1015 eV
•
(image
from:www.drjoshuadavidstone.com/
astro/supernova.jpg
The ultra high particles?
• Without going into great detail the problem with
the source of the UHECR is that to achieve the
high energies they must originate in a very large
extragalactic field or from a process that doesn’t
require such distance.
• Suggestions abound but there is not a agreement
as to the origin. Maybe there isn’t a single
source.
• One suggestions is that UHECRE’s originate
from the decay of more primary particles
resulting from the big bang.
A Summary
• Lower energy, < 1016
eV:
– Direct observation
possible, 85% are
protons.
– Most likely source are
supernova shock wave
acceleration.
– These are particles
below the knee in the
energy spectrum.
• Ultra High energy, >
1016 eV.
– Only indirect EAR
shower information is
available.
– Source of the particles
with > 1016 eV is
unknown.
High School Based Detectors
Numerous detector arrays using high schools
as sites for individual detectors have been
built or are in the process of development.
The projects range from arrays using
hundreds of detectors covering thousands
of km2 to small arrays involving only a few
detectors in an area only a few hundred
meters square.
CHICOS (California high school cosmic ray
observatory)
• Operated by Caltech,
CHICOS is an active
research array with a goal
to study CR is the range
of 1018 to 1021 eV using
refurbished detectors
from a neutrino
experiment and 1 m2
scintillators
• Currently 51 sites are
setup and working.
• Image from
www.chicos.caltech.edu
ALTA (University of Alberta Large Time
Coincidence Array)
• The stated purpose of the
ALTA project is to search
for time correlations
between EAS’s.
• At present 16 high
schools are involved.
• The project is part of the
Canadian learning
standards with students
receiving credit.
•
(image from www.physics.ubs.ca)
ALTA MAP
ALTA DETECTOR MAP
Hinton
Size of planned
Auger detector
Fort McMurray
EDMONTON
CROP (Cosmic Ray Observatory Project,
University of Nebraska)
• A project to study EAS
from particles > 1018 eV.
• Thirty operating schools
covering 75000 sq miles
is the goal of the project.
• Detectors are 1 m2
scintillators donated by
the Chicago Air Shower
Array.
• Image from Marion High
School.
Http://marian.creighton.
edu
SALTA (Snowmass Area Largescale Time-coincidence Array)
• A project to set up
detectors in Colorado.
• Linking high schools via
Internet connecting to
form a large array.
• A modern hot-air balloon
flight in 2001 reenacted
Hess’s 1912 flight.
Image from:
http://faculty.washington.
edu/~wilkes
WALTA (Washington Large Area Time Array)
• A project of the
University of
Washington.
• As of late 2002
eighteen high schools
around Seattle are
participating. See
image. (from
www.phys.washington.edu )
The Pitt/UMSL Projects
A project of the
University of Pitt and
University of Mo at
St. Louis.
The project involves
high school teachers
building and using
scintillator type
detectors aimed at
muon detection.
Tentative Plans: 3-week quarknet workshop.
Summer, 2004 Julia Thompson
Prof. of Physics, Univ. of Pittsburgh
Adjunct Prof. of physics and/or in participating in a proposed
project to put cosmic ray detectors in high schools, eventually
perhaps linking them into a shared network. Teachers can register
for 1-3 credit hours from UMSL for the workshop, and will receive a
personal stipend of $300./week, Physics, Univ. of Missouri at St.
Louis
A 3-week summer workshop for physics teachers is expected at the
University of Missouri at St. Louis (UMSL) in summer, 2004.
through the quarknet program
The workshop would be open to area high school physics teachers
interested in expanding their knowledge of current modern and a
$250. instructional materials stipend.