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

Wrapped photographic plate showed clear silhouettes, when developed, of the uranium salt samples 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.

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

Ionization Detectors 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 Herta Wambacher

report “stars” of tracks resulting from cosmic ray collisions with nuclei within the emulsion

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

Ionization Detectors

1937

Marietta Blau

and

Herta Wambacher

report “stars” of tracks resulting from cosmic ray collisions with nuclei within the emulsion

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

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

Ionization Detectors

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.

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

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

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

Ionization Detectors 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(C 3 H 6 ) as a liquid

at its boiling point

or Freon(CF by external pressure 3 Br) is stored (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 ( ~6 m m 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

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

Ionization Detectors

Spark Chambers

+ + + + + + + + +

d

•

High Voltage

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

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

Ionization Detectors

• 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

external electronics by that “recognize” the event topology of interest.

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

Ionization Detectors B

Incoming particle

A C

HV pulse Logic Unit

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

Outgoing particles

Ionization Detectors 1968-70 Georges Charpak

develops the

multiwire proportional chamber

1992 Charpak

receives the

Nobel Prize

in Physics for his invention

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

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

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

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

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

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

Ionization Detectors 20

m

m dia argon-isobutane 2 mm spacing

spatial resolutions < 1mm possible

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

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

Ionization Detectors The Detector in various stages of assembly The Cosmic Ray Observatory Project High Energy Physics Group The University of Nebraska-Lincoln

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

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

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