1. INSTRUMENTATIONS AND METHODS IN RADIOLOGICAL MEASURING AND MONITORING

2. Contents Introduction Monitoring Instrument Personnel Monitoring
Area Monitoring
Record Keeping
Summary

3. Introduction
Radiation is a hazard that cannot be sensed directly by any of the five senses.
Working with radiation sources must be carried out with due consideration given on proper selection and use of measuring instruments and an effective monitoring programme.

4. Introduction
Radiological monitoring is required to be established as prescribed in the Basic Safety Standards with the following objectives:
To assess the radiation exposure situation in compliance with regulatory requirements.
To verify the effectiveness of radiation protective measures provided at work places.
To identify occurrence of any abnormal radiation exposure situation in work places.
To keep a constant surveillance over the working environment and to detect the quantity and extent of contamination.

5. Introduction
The programme covers both radiation and contamination and may consists of the following components:
Personnel monitoring
Work place monitoring
Environmental monitoring

6. Introduction
Personnel monitoring and work places (environmental) monitoring are carried out:
To control occupational exposure of working personnel.
Work place (environmental) monitoring is more toward controlling public exposure.

7. Monitoring Instrument
The basic interaction of radiation with matter is the excitation or ionization of an atom or a molecule.
All detectors of ionizing radiation make use of ionization and excitation process.

8. Monitoring Instrument
There are direct or indirect measurements of ionization.
Selection of a specific measuring device depends on several factors including:
Relative intensity of the radiation.
Required measurement accuracy.

9. Monitoring Instrument
Measurement
X-ray beam exposure
Environment exposure
Personnel exposure
Radioactivity
Device
Ionization chambers
Survey meters
Film badges
Thermoluminescene
Dosimeters
Scintillation detectors
Activity calibrators

10. Monitoring Instrument
Types of Radiation Detector
Classified according to the medium of
interactions of the radiation:
Gas-filled Detector
Liquid Detector
Solid State Detector

11. Monitoring Instrument
1. Gas-filled Detectors
Used for charged particles producing ionization in gas filled chamber.
Most common detectors are:
Ionization Chambers
Proportional Counters
Geiger-Muller Counters

12. Monitoring Instrument
1. Gas-filled Detectors
Main differences among the three types of gas-filled detectors lie in:
Gas used.
Pressure at which the gas is maintained within the chamber.
Voltage level that is maintained between the central electrode and walls of the chamber.

13. Monitoring Instrument
The different region of operation of gas filled detector for two different energies

14. Monitoring Instrument
2. Scintillation Counter
Scintillation can be produced using solid medium and this is the underlying mechanism for the sodium iodide thallium-activated detector, NaI(Tl).
Measures the light released by a crystal after an interaction with radiation.
Consists of:
Single crystal [NaI(Tl), anthracene]
Photomultiplier tubes [PMT’s]

15. Monitoring Instrument
Photon crystal light PMT
electrical pulse
When excited by an X-ray or gamma ray photon, the crystal produces a burst of light.
PMT detects that light and generates a corresponding electrical signal.

16. Monitoring Instrument
Photomultiplier tube
Vacuum tube light
pulse of charge
PMT is a vacuum tube, when exposed to a very faint flash of light, will generates a pulse of charge.

17. Monitoring Instrument
Photocathode
Converts light to electron
light photon photocathode
photoelectron photoelectric interaction
When light photon of sufficient energy strikes the photocathode, it ejects a photoelectron due to the photoelectric effect.
Photocathode material is usually a mixture of alkali metals, which make the PMT sensitive to photons throughout the visible region of the electromagnetic spectrum.

18. Monitoring Instrument
Crystals and PMT’s

19. Monitoring Instrument
Dynode

20. Monitoring Instrument
Dynodes multiply the electrons.
Every photoelectron is accelerated to the first dynode - ejects several secondary electrons.
Secondary electron heads for the second dynode, where the process repeats itself.
Amplification depends on the number of dynodes and the accelerating voltage.
Amplified electrical signal is collected at an anode at ground potential, which can be measured.

21. Monitoring Instrument
3. Solid State Detector
Maximize ionizing radiation capture.
Use of devices employing semiconductors.
Electron-hole pairs created along the path taken by the charged particle (primary radiation or secondary particle) through the detector.
Motion in an applied electric field generates the basic electrical signal from the detector.

22. Monitoring Instrument
Schematic of Semiconductor Detector

23. Monitoring Instrument
Silicon Detector
Lithium-Drifted Silicon Detector
Germanium Detector

24. Monitoring Instrument
Silicon (Si) Detector
Atomic number 14.
Extremely low noise, which results from the use of high- resistivity Si substrates.
A low-leakage-current fabrication process.
Germanium (Ge) Detector
Excellent energy resolution, potentially high spatial resolution, large active volumes leading to high detector efficiencies, simplified fabrication, and enabling unique detector geometries and detection schemes.

25. Monitoring Instrument
Advantages:
Long life expectancy.
Improved reliability- the readings more stable than other detector.
Improved maintainability -semiconductor detectors operate at a fixed.
Low voltage, the need for work in adjusting the detectors is greatly reduced.
Miniaturization - semiconductor detectors are small - makes it possible to reduce the size of the detector equipment, thereby both saving space and reducing.
Compact design.

26. Monitoring Instrument
Disadvantages:
Lower sensitivity.
Poor energy resolution, scatter rejection.
Poor spectral performance.
Voltage supplied must large enough.
Too high energy photon.

27. Monitoring Instrument
1. Ionization Chamber
Best used as photon measuring instruments but can be modified to monitor for alpha, beta, and even neutron radiation.
Less sensitivity compared to G-M counter but can be used in high counting rate situations.
Have good energy dependence characteristics.
Examples are Condensed r-Meter, fluoroscopic survey meter and “Cutie Pie”.

28. Monitoring Instrument
Ionization Chamber

29. Monitoring Instrument
Ionization Chamber

30. Monitoring Instrument
Ionization Chamber

31. Monitoring Instrument
Ionization Chamber

32. Monitoring Instrument
Ionization Chamber

33. Monitoring Instrument
2. Proportional Counters
A type of gas-filled detector
Proportional tubes are almost always operated in pulse mode.
Rely on the phenomenon of gas multiplication to amplify the charge represented by the original ion pairs created within the gas.
One important application is the detection and spectroscopy of low energy X-radiation.
Widely applied in the detection of neutrons.

34. Monitoring Instrument
Proportional Counter

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3. Geiger-Muller (GM) Counter
Useful for monitoring low-level beta and gamma radiation.
High sensitivity.
Meters of choice for monitoring contamination and searching of lost radiation sources.
Relatively long dead time and makes them unsuitable for accurate counting at high counting rates.

36. Monitoring Instrument
Geiger-Muller Tube

37. Personnel Monitoring
BSS require personnel monitoring to be carried out individually on personnel who work in controlled areas and selectively in supervised areas.
Occupational exposure received by working personnel can be delivered by:
Sources outside the body, in the form of external radiation.
Radioactive materials deposited in the body as a result of intake of radioactive contaminants while working with the materials.

38. Personnel Monitoring
BSS require the radiation dose from external radiation and internal contamination to be added up to represent an individual dose in a year.
Special devices worn by personnel or used to measure the radiation dose received while working with radiation sources or working in classified areas.

39. Personnel Monitoring
Personnel Monitoring Instrument for External Radiation
Called dosimeter.
Used to measure radiation from sources outside the body.
Required on personnel who work with all types of radiation sources except alpha, low energy beta and low energy gamma emitters.
Instrument used should be suitable to the type of radiation involved and the range of the radiation exposure level expected.

40. Personnel Monitoring
Most commonly used dosimeters are film badges, Thermoluminescent Dosimeters (TLDs) badges and pen dosimeters.
Device must be worn at the place that can represent whole body exposure.
Additional dosimeter should be worn on parts of the body which is expected to receive higher radiation exposure than whole body dosimeter, e.g. TLD ring.

41. Personnel Monitoring
Film Badges

42. Personnel Monitoring Film
Photographic emulsions mounted in plastic then wrapped in thin, light tight paper, sandwich fashion and placed in plastic holder called cassette.
Contains cutaway portions to allow the entrance of beta particles.
Contain various filters- usually copper, cadmium, aluminum and lead to help distinguish photons of different energies.
Able to be clipped on workers’ clothing allowing the measure of total, or whole body, exposure and also the ability to distinguish the types, energy and direction of radiation.

43. Personnel Monitoring
Film and TLD

44. Personnel Monitoring TLDs
Thermoluminescene is a process in which materials emit light when they are heated.
Certain thermoluminescence materials can be used as dosimeters because the amount of light emitted is proportional to the amount of radiation absorbed by the material before.

45. Personnel Monitoring
Substances that possess the property of thermoluminescence are nonmetallic crystalline solids.
Electrons in a crystal exist in distinct energy levels, called bands.
When electrons in a crystal absorb energy, they move to higher energy band.

46. Personnel Monitoring
These excited electrons get trapped in a higher energy state until the crystal is heated to a specific temperature.
At that temperature, the electrons return to their normal or ground state, radiating their extra energy in the form of visible light photons.
The amount of light obtained is proportional to the energy absorbed by the crystal.

47. Personnel Monitoring Two materials used in TLD are:
lithium fluoride
calcium fluoride
These materials consist of small crystal that can be used in a powdered form or molded into various shapes.

48. Personnel Monitoring Two step procedure in TLD First step Second step
Expose the TLD material to the radiation.
Second step
Place the irradiated TLD material in a special reader unit.
Unit heats the TLD material and measures the amount of light emitted during the heating process.
Heating frees the trapped electrons and allows them to drop to their normal low energy positions.
Energy difference between the two electron locations is given off in the form of light.

49. Personnel Monitoring
Light is measured by a photomultiplier tube in the TLD reader which is “light tight”.
Signal from the photomultiplier tube is amplified and displayed on a digital meter usually in units of electric charge, microcoulomb (mC), nanocoulomb (nC) or directly as mSv, cGy, gray etc.

50. Personnel Monitoring Advantages of TLD over films: Can be reused.
Can be made tissue-equivalent.
Not as sensitive to moderate heat as is film.
More responsive to a wide photon energy range.
More sensitive to radiation.
Disadvantages over film:
Expensive.
Non-permanent record.

51. Personnel Monitoring
TLD

52. Personnel Monitoring
TLD
Extremity
Whole body

53. Personnel Monitoring Direct Reading Dosimeter
Simple ion-chamber personnel monitor shaped like a pen.
Two kinds of ion-chamber monitors:
Self-reading pocket monitor: direct reading.
Condenser-type pocket chamber: requires a separate device for both charging and obtaining results.

54. Personnel Monitoring Ionization Chamber
Instrument for detecting ionizing radiation by measuring the amount of charge liberated by the interaction of the radiation with suitable gases.
Designed for measurement in low energy x-ray and electron beam.
Chambers consist of a volume of air located between two electrodes, mounted on insulating material.
Battery or any other power supply maintains an electric field between the positive anode and negative cathode.
Electrodes collect the ions formed within the air volume.

55. Personnel Monitoring
Radiation penetrates the gas in chamber, entering through a thin gas-tight window.
Liberates electrons from the gas atoms, creating positive charged ions.
Electric field present in the gas sweeps these electrons
and ions out of gas.
Electrons moving to the anode and positive ions migrating more slowly because of their mass, towards cathode.

56. Personnel Monitoring Monitoring for internal contamination inhalation;
Required to be carried out on personnel who work with open or unsealed radioactive sources or in places where contamination is confirmed to be present.
Radioactive materials can enter the body through:
inhalation;
Ingestion; or
the skin.

57. Personnel Monitoring Monitoring for internal contamination
Special instrumentation is used to assess the intake and retention of radioactive materials in the body.
There are two common methods used to determine the internal contamination namely:
bioassay; and
whole body counting

58. Personnel Monitoring Bioassay
Indirect method used to assess intake of radioactive materials into body.
Common method used to assess intake of alpha, beta and low energy gamma emitters, e.g. radium-226, strontium-90, phosphorus-32, tritium and iodine-125.
Examples of bioassay material, urine, faeces and sweat.

59. Personnel Monitoring
Once concentration and type of radionuclides in certain organ is determined, it is then converted into radiation dose using a mathematical model of human beings and the input data of standard human biological parameters.
The measured concentration of radionuclides can also be traced back to the actual amount at the time of intake using the standard excretion rate of human beings and this estimated amount of intake can then be compared with the allowable Annual Limit of Intake (ALI) stipulated in the Basic Safety Standard.

60. Personnel Monitoring
Monitoring of thyroid

61. Personnel Monitoring Whole body counting
Direct method of measuring intake of radioactive materials into the body.
Using a specially designed spectrum analyzer and counter system.
System is made sensitive enough to detect and measure weak
Transmitted gamma radiation emitted by radionuclides deposited in a particular organ in body.
Two types of whole body counting system commonly used for the purpose of internal dose assessment:
chair type
shielded room type

62. Personnel Monitoring Chair Type
Shape of a chair with three detectors positioned in the directions that allow for optimum measurement of radionuclides deposited in three critical organs, namely lung, stomach and thyroid.
To minimize interference from the background radiation, the system is normally provided with adequate thickness of shielding material on both the detectors and the subject to be measured.

63. Personnel Monitoring Shielded Room Type
Low background counting room where the room is all around shielded from the background radiation.
Ordinary gamma spectrometry system equipped with gamma analysis software.
Measured concentration of radionuclides, traced back to the actual amount at the time of intake and compared with ALI.
Calibration of the system is done using standard radiation sources on human phantom.

64. Personnel Monitoring
Whole Body Monitoring

65. Personnel Monitoring
All survey monitors are calibrated by the manufacturer at the time of production.
Changes in the characteristics of the individual components of the instrument may cause a change in instrument response. It is compulsory that survey meters be calibrated periodically as stipulated by the appropriate authority.

66. Personnel Monitoring Personnel Contamination
Personnel contaminated externally is monitored using a portable radiation monitor or a fixed monitor called hand and foot monitor.
All personnel working in radioactive work places must check for contamination on their body and ensure that they are clean before leaving the areas.

67. Area Monitoring
Work places where radiation sources are installed or used are required to be monitored regularly.
Important to establish classification of the work place or to verify the validity of classification of the work area.
Covers both radiation and contamination, and the latter usually includes surface and airborne contaminations.

68. Area Monitoring
Work Place Monitoring Instrumentation for External Radiation
Measurements can be made in situ using either portable measuring instruments (survey meters) or stationary monitors.
Latter types of instrumentation are usually equipped with alarm system that can be triggered off if the radiation level exceeds its preset limit.
Measurements for work place monitoring can also be made using personnel dosimeters over a certain period of time e.g. one month.

69. Area Monitoring
Types of Radiation Monitoring Instrumentation for External Radiation and Their Operational Principles
The instrumentation used is usually portable

70. Area Monitoring Instrumentation Operating Procedures
It is very important to know correct operation of the instruments and proper techniques used in carrying out the monitoring.
The followings are standard operating procedures in using portable survey meters:
Check calibration validity period of the instruments.
Switch the power of the instrument ON and wait for stability.

71. Area Monitoring
Check the battery of the instrument and it should be more than 50 % of the battery scale.
Check response of the instrument against a check source and the reading should be as expected.
Switch the instrument’s scale to the maximum range.
Switch on audible signal.

72. Area Monitoring
Bring the instrument to the work place for measurement and switch to lower scale if there is no response.
The probe protective cover should be removed when measuring beta radiation.
Measurements should be made with the detector’s position similar to its position when calibrated.
Switch the instrument OFF once the measurement is completed.

73. Area Monitoring Steps in area monitoring:
 Establish layout plan by referring to the plot plan of the area to be monitored.
Area monitoring for external radiation can be done actively or passively.
Active monitoring:
Use mobile / portable radiation detector e.g. survey meter.
Passive monitoring:
Use a fixed radiation detector e.g. TLD.

74. Area Monitoring Contamination
Contamination monitoring is very important to be carried out in places where radioactive contamination is likely to occur.
It consists of monitoring for personnel contamination, surface contamination in work places, airborne contamination in work places and environmental contamination.

75. Area Monitoring Types of Monitoring Instrumentation Used
The detector used depends on type of radiation involved in the contamination.
Alpha contamination, the detector used is usually of scintillation type (ZnS), proportional counter and solid-state detector.
Beta-gamma contamination, the most commonly used detector is G-M detector and scintillation detector.
The G-M detector has an advantage in term of more sensitive compare to other detectors but it looses out in term of response time.

76. Area Monitoring
There are basically two types of area monitoring and measurement methods used in radioactive contamination.
These methods depends on whether they are for:
surface; or
environmental contamination.

77. Area Monitoring Surface contamination monitoring:
Carried out either directly using a monitoring instrumentation; or
Indirectly based on the smear sample collected from the contaminated surfaces subsequently measured using a monitoring instrumentation.

78. Area Monitoring
A direct method is measurements made in-situ using a portable contamination monitor:
Carried out by moving slowly the portable contamination monitor over the suspected area of contamination.
Probe should also be brought to as close as possible but without touching the surface being monitored.
Instrumentation should be properly calibrated to reflect the actual level of contamination from its direct readings.

79. Area Monitoring Indirect method of monitoring:
Has an advantage over the direct method in case of high background radiation at the monitoring site but it suffers from lower collection efficiency of the contaminants.
Collection efficiency of the contaminant on the smear sample depends on several factors:
physical condition of surface;
smear material used;
application of chemical; and
pressure applied when taking sample.
Smear sample is subsequently counted for its contamination level using a suitable counter.

80. Area Monitoring Environmental contamination:
Any release of radioactive materials into the environment will be monitored to ensure that the amount released is within the authorized limit.
Monitoring is carried out by direct and indirect method.
Environmental contamination may be measured in biotic and abiotic systems.

81. Area Monitoring Methods and Monitoring of Airborne Contamination
 Airborne contamination monitors may be divided into:
for radioactive particles in air;
for radioiodine in air; and
for radioactive gases in air.

82. Area Monitoring Airborne contamination:
Monitored indirectly using air sampler together with filter system.
Collect the contaminants.
Counting instrumentation for radionuclide identification.
Determination of its concentration.

83. Area Monitoring Data Interpretation
Exposure and contamination data obtained are analysed and interpreted with reference to authorized and acceptable standards.
For individual monitoring, the limits most commonly used in the control of external radiation are Equivalent Dose and Effective Dose.
Derived Dose Limits (e.g. ALI and DAC) are used in estimating risk from intake or radioactive materials.
For area monitoring, radiological risk are usually calculated and reported in terms of the activity concentrations of radionuclides, and external radiation.

84. Area Monitoring Characteristics in the selection of survey meters:
Characteristics of survey meters:
Radiological characteristics
measuring quantity for external radiation;
repeatability or reproducibility;
exactness and scale linearity;
measurement range;
effect of dose rate on instrument readings;
instrument response time;
energy-response dependence;
isotropy and geotropism; and
effect of mixed radiation fields.

85. Area Monitoring Characteristics related to the condition of use:
Small, lightweight, easily carried and of convenient design for making the necessary measurement;
Have a long battery life and use normal battery that is low cost and lightweight;
Have a smooth surface and a finish that does not contaminate readily and can be easily decontaminated; and
Rugged, resistance to temperature, pressure, humidity, dust, wind, light immersion, electric and magnetic fields, rough treatment, acid fumes, salt spray etc.

86. Area Monitoring Selection of survey meter will involve:
Instrument for measuring sealed gamma ray and X-ray sources; and
Instrument for measuring unsealed sources.

87. Area Monitoring Calibration of survey meters is to:
Ensure that the instrument is working properly and functions reliably in the dose range specified and within the whole energy range employed;
Estimate errors in the instrument reading or if possible, to improve overall accuracy of the measurement;
Establish a national network of traceability in radiation measurements;
Comply with legal requirements as gazetted in the Atomic Energy Licensing Act, 1984 and its subsidiary legislations.

88. Record Keeping The registrant or licensee should maintain:
Exposure records
Medical records for each worker
Results from workplace monitoring
Records on public protection

89. Record Keeping Other records to be maintained:
The authorization or registration documents.
Training provided (initial and refresher):
Name of trainers
Name of trainees
Date and length of the training
List of the topics addressed
Copy of the certificates of training

90. Record Keeping Other records to be maintained: Personnel exposure
Radiation surveys or wipe tests
Instrument calibration
Waste disposal
Radiation incidents
Audits and reviews

91. Record Keeping
The records kept with respect to all radiation activities represent the main proof that an authorized user has of his compliance with the radiation protection regulations.
These are important for legal purposes as well as for effective administration of the radiation-protection program.

92. Summary

93. Thank You for your attention