Radiation Detectors

Front 1

Ionization is the process of removing one or more electrons from a neutral atom
Loss of negative charge leaving atom positively charged

Back 1

Electron-Ion Pair

Front 2

The number of ion pairs produced per centimeter of travel through matter

Specific Ionization = # Ion Pairs Produced /
Path Length

Back 2

Specific Ionization

Front 3

The _____ ray is a photon of electromagnetic radiation with a very short wavelength and high energy

Back 3

gamma

Front 4

It is emitted from an unstable atomic nucleus and has high penetrating power

Back 4

gamma ray

Front 5

The _____ particle is a helium nucleus produced from the radioactive decay of heavy metals and some nuclear reactions

Back 5

Alpha

Front 6

_____ often occurs among nuclei that have a favorable neutron/proton ratio, but contain too many nucleons for stability.

Back 6

Alpha Decay

Front 7

The _____ has a single negative or positive electrical charge and a very small mass

Back 7

beta

Front 8

The specific ionization of a _____ particle is low due to its small mass, small charge, and relatively high speed of travel.

Back 8

beta

Front 9

The _____ factor designates the increase in ion pairs when the initial ion pairs create additional ion pairs.
The relationship between the applied voltage and pulse height in a detector is very complex.

Back 9

gas amplification

Front 10

This multiplication of electrons is termed ______

Back 10

gas amplification.

Front 11

_____ of ions at electrode prevents additional electrons from reaching electrode

Back 11

Positive sheath

Front 12

More sensitive than proportional counters
Used mostly for portable hand held meters
Operates in the GM region of gas amplification
Large pulses
Large gas amplification effect
pulse height independent of type of radiation, so discrimination is not possible

Back 12

Geiger-Muller Detector

Front 13

Three classes of Phosphors

Back 13

Inorganic crystals
Organic crystals
Plastic phosphors

Front 14

Radiation excites electron in crystal
Photoelectric effect
Electron lowers in energy state and produces light pulses

Back 14

Scintillation Crystal (phosphor)

Front 15

Can determine energy and count rate of gamma rays
Detector is normally scintillation type
Multi-channel Pulse Height Analyzer
Separates pulses based on pulse height
Pulse height proportional to energy of incident radiation

Back 15

Gamma Spectroscopy

Front 16

In Gamma Spectroscopy the Detector is normally ________

Back 16

scintillation type

Front 17

Separates pulses based on pulse height
Pulse height proportional to energy of incident radiation

Back 17

Multi-channel Pulse Height Analyzer

Front 18

Used for monitoring reactor core
No voltage applied – “self powered”
Central wire absorbs neutron and emits a beta
β decay time dependent on type of central wire
Becomes more positive and causes current to flow
Very simple – little instrumentation; lasts longer than boron detectors

Back 18

Self Powered Neutron Detectors

Front 19

Neutron induced fission to detect neutrons
Similar to ion chamber
Coating material is highly enriched U235
Fission particle enters chamber
Fragment has high energy – more ionizations
Much higher pulse than a gamma produces
Can be used as pulse and current detectors
Wide range; used in source and intermediate range

Back 19

Wide Range Fission Chamber

Front 20

Material placed in core and exposed
Size of wire / foil known
Once activated removed from core and counted

Back 20

Foil and Flux Wire

Front 21

Turns dark when exposed
Darker = more exposure
Exposure to neutrons causes individual proton recoil tracks
Can be counted for exposure

Back 21

Photographic Film

Front 22

Ratio of electrical output signal of the detector to electrical noise generated in cable run or in the instrument

Back 22

S-N Ratio

Front 23

Sense pulse height and electrically discriminates, has high and low value set

Back 23

Discriminator

Front 24

Defined as a mechanism in which data is represented by continuously variable physical properties
Used in contrast to digital to refer to the circuits in which the magnitude of the signal carries the information

Back 24

Analog

Front 25

The exponent that indicates the power to which a number is raised to produce a given number

Back 25

Logarithm

Front 26

The amount of time it takes for power to change by a factor of e (2.718)

Back 26

Period

Front 27

rate of change information
How fast power is changing by x10

Back 27

Decades Per Minute (DPM)

Front 28

Measurement of quantity that can be represented on a scale

Back 28

Scalar

Front 29

LIST the type of detector used in each of the following nuclear instruments:

Source Range
Intermediate Range
Power Range

Back 29

Source Range
Proportional or Ion chamber
We use ion chamber

Intermediate Range
Compensated Ion Chamber

Power Range
Uncompensated Ion Chamber

Front 30

State the reason gamma compensation is NOT required in the power range

Back 30

Neutron – Gamma ratio very high

Front 31

Amps signal to useful level

Back 31

Linear Amplifier

Front 32

Reactor Protection Interface Purpose?

Back 32

Scrams and Rodblocks

Front 33

Converts detector output signal to a signal proportional to the log of the detector current

Back 33

Log Amplifier

Front 34

Provides an output proportional to the rate of change of power

Back 34

Differentiator

Front 35

Control rod blocks
Reactor scrams

Back 35

Reactor Protection Interface

Front 36

Pulse height only several millivolts
Raises pulse height to several volts

Back 36

Linear Amplifier

Front 37

Passes only pulses of desired magnitude
Excludes noise and gamma pulses

Back 37

Discriminator

Front 38

Pulses integrated to give logarithm of count rate

Back 38

Pulse Intergrator

Front 39

Gamma Spectroscopy:

Can determine energy and count rate of gamma rays
Detector is normally _____
Multi-channel Pulse Height Analyzer
Separates pulses based on pulse height
Pulse height proportional to energy of incident radiation

Back 39

scintillation type

Front 40

Separates pulses based on pulse height
Pulse height proportional to energy of incident radiation

Back 40

Multi-channel Pulse Height Analyzer

Front 41

Vacuum tube with photocathode
Amplifies light input

Back 41

Photomultiplier Tube Operation

Front 42

Solid state detector
______ crystal (phosphor)
Radiation excites electron in crystal
Photoelectric effect
Electron lowers in energy state and produces light pulses

Back 42

Scintillation Counter

Front 43

Operates in the GM region of gas amplification
Large pulses
Large gas amplification effect
pulse height independent of type of radiation, so discrimination is not possible
Positive Ion Sheath forms
Positive sheath of ions at electrode prevents additional electrons from reaching electrode
More sensitive than proportional counters
Used mostly for portable hand held meters

Back 43

Geiger-Muller Detector

Front 44

Microscope with a graduated scale in eyepiece used to observe movement of quartz fiber.
Portable, dependable, simple, accurate, and sensitivity

Back 44

Electroscope Ion ChamberSelf Reading Pocket Dosimeter

Front 45

_______ consist of two separate chambers
one coated with boron, and one not.
Coated chamber is sensitive to both gamma rays and neutrons
Uncoated chamber is sensitive only to gamma rays
Subtraction of these currents is done electrically
net output of both detectors is read on a single ammeter.

Back 45

Compensated ion chambers

Front 46

The plates in an ______ are normally enclosed in metal
Gamma rays penetrate
Betas / alphas stopped by metal wall
For alpha and beta detection a thin wall or "window."
Window of almost any thickness however will prevent alpha particle from entering

Back 46

ionization chamber

Front 47

molecules have a weaker affinity for electrons than chamber gas; ionized atoms of chamber gas readily take electrons from ____ molecules
Ionized molecules of____ reach chamber wall instead of chamber gas

Back 47

quench gas