radiation dosimeters

RADIATION DOSIMETERS

INTRODUCTIONGeneral requirements for dosimetersDosimeter is a device that measures

directly or indirectlybull Exposurebull Kermabull Absorbed dosebull Equivalent dosebull Or other related quantitiesThe dosimeter along with its reader is

referred to as adosimetry system

INTRODUCTIONA useful dosimeter exhibits the following

propertiesbull High accuracy and precisionbull Linearity of signal with dose over a wide

rangebull Small dose and dose rate dependencebull Flat Energy responsebull Small directional dependencebull High spatial resolutionbull Large dynamic range

PROPERTIES OF DOSIMETERS Accuracy specifies the proximity of the

mean value of a measurement to the true value

Precision specifies the degree of reproducibility of a measurement

NoteHigh precisionis equivalent to small standard deviation

PROPERTIES OF DOSIMETERS

Examples for use of precision and accuracy

High precision High precision Low precision Low precision and and and and High accuracy Low accuracy High accuracy Low accuracy

PROPERTIES OF DOSIMETERSNote The accuracy and precision

associated with a measurement is often expressed in terms of its uncertainty

PROPERTIES OF DOSIMETERSNew Concept by the International

Organization for Standardization (ISO) Guide to the expression of uncertainty in measurementldquo

This new guide serves as a clear procedure for characterizing the quality of a measurement

It is easily understood and generally accepted

It defines uncertainty as a quantifiable attribute

PROPERTIES OF DOSIMETERS Standard uncertainty is the uncertainty of a

result expressed as standard deviation Type A standard uncertainty is evaluated by

statistical analysis of a series of observations

Type B standard uncertainty is evaluated by means other than statistical analysis This classification is for convenience of discussion only

It is not meant to indicate that there is a difference in the nature of

the uncertainty such as random or systematic

PROPERTIES OF DOSIMETERS Combined uncertainties The determination of the final result is normally

based on several componentsLinearity The dosimeter reading should be linearly

proportional to the dosimetric quantity Beyond a certain range usually a non-

linearity sets in This effect depends on the type of dosimeter


Two possible cases

Case Abull linearitybull supralinearitybull saturation

Case Bbull linearitybull saturation

PROPERTIES OF DOSIMETERSDose rate dependence MD may be called the response of a dosimeter

system When an integrated response is measured the

dosimetric quantity should be independent of the dose rate dDdt of the quantity

Other formulationThe response MD should be constant for different

dose rates (dDdt)1 and (dDdt) 2 M = 1048577 (M D)(dD dt)dt M = (M D)1048577 (dD dt)dt

PROPERTIES OF DOSIMETERS Energy The response of a dosimetric

system isgenerally a function of the radiation energy The term radiation quality is often used to

express a specific distribution of the energy of radiation

Therefore a dependence on energy can also be called a dependence on radiation quality

Since calibration is done at a specified beam quality a reading should generally be corrected if the users beam quality is not identical to the calibration beam quality

PERSONAL DOSIMETERSA small radiation monitoring device worn by

persons entering environments that may contain radiation

Desirable characteristics Should be lightweight durable and reliableShould be inexpensive

WHO SHOULD WEAR A PERSONAL DOSIMETER Healthcare or laboratory workers in non-

emergency environments that may contain radiation Examples radiology nuclear medicine and

radiation oncology department staff Workers in emergency environments that

may contain radiation Examples first responders and first receivers

Workers in industrial environments where radiation is used Examples nuclear power plant workers or

employees at radiation sterilizing facilities

WHERE ARE PERSONAL DOSIMETERS USUALLY WORN Flat badges are usually worn on the torso at

the collar or chest level but can be worn on the belt or forearm

Ring shaped badges can be worn on the finger when dose to the finger may exceed dose to the badge worn elsewhere on the body

First responders and first receivers Wear water-resistant personal dosimeters on the

outer layer of personal protective equipment (PPE)

Should be able to easily see and hear a dosimeter alarm while wearing PPE

May wear a personal dosimeter underneath waterproof outerwear

TYPES OF PERSONNEL DOSIMETERS

Film badgePocket ionization chambersThermo luminescent dosimeters (TLD)Optically stimulated luminescence (OSL)Solid State

FILM BADGE Most widely used and most economical Consists of three parts

Plastic film holder Metal filters Film packet

Can read x gamma and beta radiation Accurate from 10mrem - 500rem Developed and read by densitometer A certain density value equals a certain level of

radiation Read with a control badge Results generally sent as a printout

ADVANTAGES AND DISADVANTAGES OF THE FILM BADGE Lightweight durable

portable Cost efficient Permanent legal record Can differentiate between

scatter and primary beam Can discriminate between

x gamma and beta radiation

Can indicate direction from where radiation came from

Control badge can indicate if exposed in transit

Only records exposure where itrsquos worn

Not effective if not worn Can be affected by heat

and humidity Sensitivity is decreased

above and below 50 keV

Exposure cannot be determined on day of exposure

Accuracy limited to + or - 20

POCKET DOSIMETER The most sensitive personnel dosimeter Two types

Self-readingNon self-reading

Can only be read once Detects gamma or x-radiation

ADVANTAGES AND DISADVANTAGES OF THE POCKET DOSIMETER

Small compact easy to use

Reasonably accurate and sensitive

Provides immediate reading

Expensive Readings can be

lost Must be read

each day No permanent

record Susceptible to

false readout if dropped or jarred

THERMO LUMINESCENT DOSIMETERS(TLD) Looks like a film badge Contains a lithium fluoride crystal Responds to radiation similarly to

skin Measured by a TLD analyzer Crystal will luminescence if exposed

to radiation then heated More accurate than a film badge

ADVANTAGES AND DISADVANTAGES OF THE THERMOLUMINESCENT DOSIMETER

Crystals contained in TLD interact with ionizing radiation as tissue does

Determines dose more accurately

The initial cost is greater than that of a film badge

Can only be read once

Records exposure only where worn

OPTICALLY STIMULATED LUMINESCENCE (OSL)bull ldquoCapturesrdquo information in an Aluminum

Oxide matrixbull Releases information by laser stimulationbull Can be reread after processingbull Durablebull Landauer Only

SOLID STATE

Provides instantaneous information regarding dose accumulation

Simple to use Not a ldquolegalrdquo record Dose range device dependent

HOW TO WEAR THE RADIATION DOSIMETER

THANKS

Radiation Dosimeters

INTRODUCTION

INTRODUCTION (2)


PROPERTIES OF DOSIMETERS (2)








Personal Dosimeters

Who should wear a personal dosimeter

Where are personal dosimeters usually worn

Types of personnel dosimeters

Film Badge

Advantages And Disadvantages Of The Film Badge

Pocket Dosimeter

Advantages And Disadvantages Of The Pocket Dosimeter

Thermo luminescent Dosimeters(TLD)

Advantages And Disadvantages Of The Thermoluminescent Dosimeter

Optically stimulated luminescence (OSL)

Solid State

How to wear the Radiation Dosimeter

Thanks

INTRODUCTIONGeneral requirements for dosimetersDosimeter is a device that measures

directly or indirectlybull Exposurebull Kermabull Absorbed dosebull Equivalent dosebull Or other related quantitiesThe dosimeter along with its reader is

referred to as adosimetry system





























Two possible cases























































lost Must be read















SOLID STATE




THANKS


INTRODUCTION

INTRODUCTION (2)










Personal Dosimeters




Film Badge


Pocket Dosimeter





Solid State


Thanks





























Two possible cases























































lost Must be read















SOLID STATE




THANKS


INTRODUCTION

INTRODUCTION (2)










Personal Dosimeters




Film Badge


Pocket Dosimeter





Solid State


Thanks





















































lost Must be read















SOLID STATE




THANKS


INTRODUCTION

INTRODUCTION (2)










Personal Dosimeters




Film Badge


Pocket Dosimeter





Solid State


Thanks












SOLID STATE




THANKS


INTRODUCTION

INTRODUCTION (2)










Personal Dosimeters




Film Badge


Pocket Dosimeter





Solid State


Thanks


THANKS


INTRODUCTION

INTRODUCTION (2)










Personal Dosimeters




Film Badge


Pocket Dosimeter





Solid State


Thanks

radiation dosimeters

Health & Medicine

radiation energy

energy of radiation

radiation examples

dose equivalent dose

term radiation quality

certain level of radiation

beta radiation accurate

dosimeter system