the cosmic ray observatory project high energy physics group the university of nebraska-lincoln...

The Cosmic Ray Observatory Project High Energy Physics Group The University of Nebraska-Lincoln

Ionization Detectors

Henri Becquerel (1852-1908) received the 1903 Nobel Prize in Physics for the discovery of natural radioactivity.

Wrapped photographic plateshowed clear silhouettes, whendeveloped, of the uranium saltsamples stored atop it.

1896 While studying photographic images of various fluorescent and phosphorescent materials, Becquerel finds potassium-uranyl sulfate spontaneously emits radiation capable of penetrating

•thick opaque black paper•aluminum plates•copper plates

Exhibited by all known compounds of uranium (phosphorescent or not) & metallic uranium itself.



1930s plates coated with thick photographic emulsions (gelatins carrying silver bromide crystals) carried up mountains or in balloons clearly trace cosmic ray tracks through their depth when developed

•light produces spots of submicroscopic silver grains•a fast charged particle can leave a trail of Ag grains

•1/1000 mm (1/25000 in) diameter grains

•small singly charged particles - thin discontinuous wiggles•only single grains thick

•heavy, multiply-charged particles - thick, straight tracks

November 1935 Eastman Kodak plates carried aboard Explorer II’s record altitude (72,395 ft) manned

flight into the stratosphere

1937 Marietta Blau and HertaWambacher report “stars” of tracksresulting from cosmic ray collisionswith nuclei within the emulsion



1937 Marietta Blau andHerta Wambacher

report “stars” of tracks resulting from cosmic

ray collisions with nuclei within the emulsion



1894 After weeks in the Ben Nevis Observatory, British Isles, Charles T. R. Wilson begins study of cloud formation

•a test chamber forces trapped moist air to expand•supersaturated with water vapor•condenses into a fine mist upon the dust particles in the air

•each cycle carried dust that settled to the bottom•purer air required larger, more sudden expansion

•observed small wispy trails of droplets forming without dust to condense on!



1937-1939

Cloud chamber photographs by George Rochester and J.G. Wilson of Manchester University showed the large number of particles contained within cosmic ray showers.



1952 Donald A. Glaser invents the bubble chamber

•boiling begins at nucleation centers (impurities) in a liquid•along ion trails left by the passage of charged particles

•in a superheated liquid tiny bubbles form for about 10 msec before being obscured by a rapid, agitated “rolling” boil

•hydrogen, deuterium, propane(C3H6) or Freon(CF3Br) is stored as a liquid at its boiling point by external pressure (5-20 atm)•super-heated by sudden expansion created by piston or diaphragm•bright flash illumination and stereo cameras record 3D images through the depth of the chamber (~6m resolution possible)

•a strong (2-3.5 tesla) magnetic field can identify the sign of a particle’s charge and its momentum (by the radius of its path)

1960 Glaser awarded the Nobel Prize for Physics



Spark Chambers

• High Voltage across two metal plates, separated by a small (~cm) gap can break down.

d

+++

+++

+

+

+

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-



• If an ionizing particle passes through the gap producing ion pairs, spark discharges will follow it’s track.

• In the absence of HV across the gap, the ion pairs usually recombine after a few msec, but this means you can apply the HV after the ion pairs have formed, and still produce sparks revealing any charged particle’s path!

• Spark chambers (& the cameras that record what they display) can be triggered by external electronics that “recognize” the event topology of interest.



HV pulse

Logic Unit

A

B

C

Incoming particle

Outgoing particles



1968-70 Georges Charpak develops the multiwire proportional chamber

1992 Charpak receives the Nobel Prize in Physics for his invention



20 m dia 2 mm spacing

argon-isobutane

spatial resolutions < 1mm possible



The Detector

in various stages of assembly

the cosmic ray observatory project high energy physics group the university of nebraska-lincoln...

Documents