Marc Vincent L. Olap BS Chemistry 321

8/14/2019 Marc Vincent L. Olap BS Chemistry 321

1/24

Marc Vincent L. Olap

BS Chemistry 321

DETECTORS


2/24

A device used to detect, track, and/or identifyhigh-energy particles, such as those producedby nuclear decay, cosmic radiation, orreactions in a particle accelerator

Modern detectors are also used as calorimetersto measure the energy of the detectedradiation.

They may also be used to measure otherattributes such as momentum, spin, charge

etc. of the particles.

What are Detectors?


3/24

Medical diagnostic

Radioactive dating measurement

Measuring radiation background

Measuring the mass, energy, and momentum

of particles created in high energy nuclearreaction

Uses of Detectors


4/24

Detectors designed for modern acceleratorsare huge, both in size and in cost.

The term counter is often used instead ofdetector, when the detector counts theparticles but does not resolve its energy orionization.

Particle detectors usually can also trackionizing radiation (high energy photons oreven visible light).

Description


5/24

Before the time of the big particleaccelerators, physicists had used:

Bubble chamber

Wilson cloud chamber (diffusion chamber)

Photographic plates

HISTORY


6/24

Bubble Chamber a ve sse l fille d w ith a

su p e rh e a te d tra n sp a re n t(liq u id m o st o fte n liq u id)h y d ro g e n u se d to d e te cte le ctrica lly ch a rg e d

p a rticle s m o vin g th ro u g h it

It w as in ve n te d in 1 9 5 2 b y

. ,D o n a ld A G la ser fo r w h ichh e w a s a w a rd e d th e 1 9 6 0

N o b e lPrize in P h ysics
http://en.wikipedia.org/wiki/File:Bubble-chamber.svg


7/24

Normally made by filling a large cylinder with aliquid heated to just below its boiling point.

As particles enter the chamber, a pistonsuddenly decreases its pressure, and theliquid enters into a superheated, metastablephase.

Charged particles create an ionisation track,around which the liquid vaporises, formingmicroscopic bubbles.

Function and Use


8/24

Bubble density around a track is proportional to

a particle's energy loss.Bubbles grow in size as the chamber expands,

until they are large enough to be seen or

photographed.

Several cameras are mounted around it,allowing a three-dimensional image of an

event to be captured. Bubble chambers withresolutions down to a few m have beenoperated.


9/24


10/24

v The first tracks. -observed in John Wood's 1 5

(~ . )inch 3 8 cm liquid,hydrogen bubble chamber in

.1954


11/24


12/24

It contains gas that has been supercooled tojust below its usual condensation point.

An energetic particle passing through ionizesthe gas along the particles path.

The ions serve as center for condensation ofthe supercooled gas.

The track of particle can be seen with thenaked eye and can be photograph.

A magnetic field can be applied to determined

the charges of particles, as well as theirmomentum and energy.


13/24

v C lo u d ch a m b e r w ith visib le tra cks fro m( , : - ; ,io n izin g ra d ia tio n sh o rt th ick p a rticle s lo n g: - )th in p a rticle s


14/24

Preceded photographic film as a means of

photography.

A light-sensitive emulsion of silver salts wasapplied to a glass plate.

This form of photographic material largelyfaded from the consumer market in the earlyyears of the 20th century, as moreconvenient and less fragile films were

introduced.

Photographic Plates


15/24

However, photographic plates were in wide useby the professional astronomical communityas late as the 1990s. Such plates respond to~2% of light received.

Glass plates were far superior to film forresearch-quality imaging because they wereextremely stable and less likely to bend ordistort, especially in large-format frames forwide-field imaging.


16/24

,A G FA p h o to g ra fic p la te s1 8 8 0

N eg a tive p la te


17/24

Many of the detectors invented and used so far

are ionization detectors (of which gaseousionization detectors and semiconductor

detectors are most typical) and scintillationdetectors

Others are completely different principles have

also been applied, like erenkov light andtransition radiation.

Examples and types


18/24

Gaseous ionization detectors

Ionization chamber

- the simplest of all gas-filled radiationdetectors, and is used for the detection ormeasurement of ionizing radiation

Ion chamber, showing drift of ions. Incident radiation is the dotted line.

Commonly used detectors forParticle and Nuclear Physics


19/24

Proportional counter

- a measurement device to count particles

of ionizing radiation and measure theirenergy--

Geiger-Mller tube

- is the sensing element of a Geiger

counter instrument that can detect a singleparticle of ionizing radiation, and typicallyproduce an audible click for each


20/24


21/24

Solid-state detectors

Cherenkov detector

- a particle detector using the mass-dependent threshold energy of Cherenkovradiation. This allows a discrimination between

a lighter particle (which does radiate) and aheavier particle (which does not radiate)

Scintillation counter

- sensor, called a scintillator, consists of atransparent crystal, usually phosphor,plastic (usually containing anthracene), ororganic liquid (see liquid scintillation

counting) that fluoresces when struck byionizing radiation


22/24

Semiconductor detector

- a device that uses a semiconductor(usually silicon or germanium) to detecttraversing charged particles or the absorptionof photons

Transition radiation detector

- a particle detector using the -dependentthreshold of transition radiation in a stratified

material. It contains many layers of materialswith different indices of refraction


23/24

Calorimeters

- an experimental apparatus that measures

the energy of particles. Most particles enterthe calorimeter and initiate a particleshower and the particles' energy isdeposited in the calorimeter, collected, andmeasured


24/24

The EnD!!!

Marc Vincent L. Olap BS Chemistry 321

Documents

Transcript of Marc Vincent L. Olap BS Chemistry 321