This presentation includes introduction to radiation, the basic knowledge of various radiations units, types of detectors which are being used to measure that radiation units and this presentation includes personal monitoring devices likes film badge dosimeter, thermoluminescent dosimeter (TLD), Optically stimulated luminescent dosimeter (OSL) and pocket dosimeters. in these slides very simple english language is used and the arrangement of the topics in the presentation is well managed . these presentation is usually for the radiographers and a radiotechnologist for which the basic knowledge of radiation units and it's measurements is crucial.

1. RADIATIONS UNITS AND IT’S MEASUREMENT
PRESENTED BY:- SAGAR
CHAULAGAIN
BSC.MIT 1ST YEAR
MAHARAJGUNJ MEDICAL CAMPUS
(IOM)
ROLL NO.:- 157
1

2. Contents:-
Introduction
to radiation
Various
Radiations
units
Radiation
detection and
measurement
Gas filled detectors
Scintillation detectors
Semiconductor detectors
Dosimeter
and its types
Film badge dosimeter
Thermo-luminescent dosimeter
Optically stimulated luminescence dosimeter
Pocket dosimeter
Direct ion storage dosimeter
2

3.  Emission or transmission of energy in the form of waves and
particle through space or a material medium
 High energy radiation cause ionization so called ionizing
radiation for example :- X-rays , Gamma rays .
 Low energy radiation do not able to ionize the atom so called
non –ionizing radiation for example :- UV ray, IR ray
Introduction To Radiation:- 3

4. Radiation units
 Units of radioactivity
 Units of exposure
 Units of radiation absorption
 Unit of equivalent and effective dose
4

5.  The SI units of activity of a radioactive source is measured in
becquerels (Bq).
 1 Becquerel =1 disintegration per second
 It’s common unit is MBq = 10^6 Bq
 Traditionally the amount of radioactivity is determined by
estimating the no. of Curies (Ci).
 1 curie = 3.7x10^10 disintegrations per sec.
Radiation units for activity
5

6. Radiation units for exposure
 Exposure is the measure of the ionization produced in air by X-
rays or gamma rays.
 Air kerma /Gya is the unit of radiation exposure or intensity.
 Air kerma is the kinetic energy transferred from photons to
electrons during ionization and excitation
 Air kerma is applicable to indirectly ionizing radiations such as
photons and neutrons.
6

7.  Commonly expressed in roentgen (R).
R = 2.580 × 10–4 C/kg.
 Radiation monitors are usually calibrated in roentgens
 The output of x-ray imaging systems is usually specified in
milliroentgens (mR).
Radiation units for exposure 7

8. Radiation units for absorption
 Absorbed dose is the amount of radiation energy absorbed per unit
mass of the medium at a point of interest.
 It’s SI units is J/kg or Gyt.
 The gray (Gy) is the unit of radiation absorbed dose.
 Biologic effects usually are related to the radiation absorbed dose.
 the absorbed dose depends on the type of tissue being irradiated.
8

9.  Unlike Kerma, absorbed dose is defined for all types of ionizing
radiation (i.e., directly and indirectly ionizing)
 The older unit of absorbed dose is the RAD.
 One rad is equal to 0.01 J/kg . Thus, there are 100 rads in a gray, and
1 rad =10 mGy.
 If the energy imparted to charged particles is deposited locally and
the bremsstrahlung produced by the energetic electrons is negligible,
the absorbed dose will be equal to the kerma.
Radiation units for absorption 9

10. Imparted energy
 The total amount of energy deposited in matter, called the
imparted energy (E).
 It is the product of the dose and the mass over which the
energy is imparted.
 The unit of imparted energy is the joule.
10

11. Unit of Equivalent dose
 Not all types of ionizing radiation cause the same biological
damage per unit absorbed dose.
 The product of the absorbed dose (D) and the radiation
weighing factor is the equivalent dose (H).
H = DWr
 The SI unit for equivalent dose is joule per kilogram with the
special name of the sievert (Sv), where 1 Sv =1 J /kg.
11

12. 12

13. Dose equivalent
 The quantity equivalent dose (H) was replaced by a similar
quantity, called the dose equivalent.
 the dose equivalent, which is the product of the absorbed
dose and the quality factor (Q)
H =DQ
 It’s SI unit is sievert (Sv).
13

14.  The traditional unit for both the dose equivalent and the
equivalent dose is the rem.
 A sievert is equal to 100 rem, and 1 rem is equal to 10 mSv.
 Occupational radiation monitoring devices are analyzed in
terms of sievert
 Doses of radiation received by workers are recorded in rem.
14

15. Unit of Effective dose
 Biological tissues vary in sensitivity to the effects of ionizing
radiation.
 Tissue weighting factors (wT) were also established by the ICRP for
the various sensitivity of tissue to radiation.
 The sum of the products of the equivalent dose to each organ or
tissue irradiated (HT) and the corresponding weighting factor (wT)
for that organ or tissue is called the effective dose (E)
15

16.  Effective dose =∑ D x Wr x Wt
 The effective dose is expressed in the same units as the
equivalent dose (sievert or rem).
 For the whole body the ICRP recommends the use of effective
dose for defining safety standards. Eg:- Annual dose limits.
Unit of Effective dose 16

17. Collective dose
 Relates to expose groups or population.
 It is defined as the product of the average mean dose to a
population and number of person exposed.
 SI unit for collective dose is man-sievert.
17

18. 18

19. Special Quantities of Radiologic Science & Their
Associated Special Units
Quantity SI Unit Customary Unit
Radioactivity Baquerel (Bq) Curie (Ci)
Exposure Air kerma (Gya) Roentgen (R)
Absorbed dose Grey (Gyt) rad
Equivalent dose Sievert (Sv) rem
Effective dose Sievert (Sv) rem
19

20. 20

21. Radiation detection and measurement
 The detection and measurement of ionizing radiation are the
basis for the majority of diagnostic imaging.
 It can be done by using various types of detectors.
 Detectors are classified on the basis of;-
1. By their detection method
2. By the type of information produced
21

22. 22
Detector
Detection
method
Gas filled
detector
Ionization
chamber
Proportional
Counters
Geiger-
Mueller
Counters
Scintillation
Detectors
Semiconducto
r detector
Type of
information
produced
Spectroscopy Dosimeter

23. Gas filled detectors
 It consists of a volume of gas between two electrodes, with an
electric potential difference applied between the electrodes.
 Ionizing radiation forms ion pairs in the gas.
 In most detectors, the cathode is the wall of the container that
holds the gas and the anode is a wire inside the container.
23

24.  When a small voltage is applied, some of the cations are
attracted to the cathode and some of the electrons or anions
are attracted to the anode before they can recombine.
 The electric current is generated which can be measured with
a sensitive ammeter or other electrical circuitry.
24

25. 25

26. 26
Fig:-Gas-filled detector

27. Ionization chamber
 Measures exposure rates which is used for area surveys and an
accurate integrating exposure instruments .
 This device measures X-ray , gamma ray and also record beta radiation
.
 Used to monitor diagnostic X-ray installations, measures fluoroscopic
scatter radiation exposure rates ,exposure rates of therapeutic dose
and cumulative exposure received outside protective barriers.
27

28. Proportional Counters
 Amount of charge collected from each interaction is proportional to the
amount of energy deposited in the gas of the counter by the interaction.
 Serves no useful purpose in diagnostic imaging because it has low
efficiencies for detecting x-rays and gamma rays.
 It is generally used in a laboratory setting to detect and differentiate
alpha and beta radiations.
 More sensitive than ionization chamber .
28

29. Geiger-Mueller Counters
 Serves as primary radiation survey instrument.
 GM survey meters are very inefficient detectors of x-rays and
gamma rays, which tend to pass through the gas without
interaction.
 the GM counter cannot truly measure exposure rates, and so its
reading must be considered only an approximation.
 It contains audible sound system that alerts the operator to
presence of ionizing radiations.
29

30.  are particularly applicable for leak testing and detection of
radioactive contamination.
 Not suitable for use in pulsed radiation fields .
 It suffer from very long dead times , ranging from tens to
hundred of milliseconds.
 May become paralysed in very high radiation field and yield a
zero reading.
30

31. Scintillation Detectors
 It emits visible light or ultraviolet radiation after the
interaction of ionizing radiation with the material.
 are the oldest type of radiation detectors.
 these are used in conventional film-screen radiography, many
direct digital radiographic image receptors, fluoroscopy,
scintillation cameras, CT scanners, and positron emission
tomography (PET) scanners.
31

32.  most scintillation detectors incorporate a means of signal
amplification.
 In conventional film-screen radiography, photographic film is
used to amplify and record the signal. In other applications,
electronic devices such as photomultiplier tubes (PMTs),
photodiodes, or image-intensifier tubes convert the light into
electrical signals
32

33.  It belongs to solid state detectors.
 Certain organic and inorganic crystals contains activator
atoms emits scintillations upon absorption of radiations and
are referred as phosphors.
 High atomic number phosphors are mostly used for the
measurement of X-ray , gamma rays while plastic scintillation
are mostly used with beta particles.
33

34. Semi-conductor detectors
 Semiconductors are materials whose electrical conductivities are less
than those of metals but more than those of insulators.
 Silicon and germanium are common semiconductor materials.
 Semiconductor detectors are semiconductor diodes designed for the
detection of ionizing radiation
 Amount of charge generated by an interaction is proportional to the
energy deposited in the detector by the interaction; therefore,
semiconductor detectors are spectrometers.
34

35.  The energy resolution of germanium semiconductor detectors is
greatly superior to that of NaI scintillation detectors.
 Liquid nitrogen–cooled germanium detectors are widely used for the
identification of individual gamma ray–emitting radionuclides in
mixed radionuclide.
 Semiconductor detectors are seldom used for medical imaging
devices because of high expense, because of low quantum detection
efficiencies in comparison to scintillators such as NaI.
35

36. Radiation monitoring
 Individual is monitored for both safety and regulatory purpose.
 Occupational Radiation Monitoring is required if there is any
likelihood that an individual will receive more than 1/10 of the
recommended dose.
 In radiologic technology, 95% of the occupational exposure
comes from fluoroscopy and mobile radiography.
36

37. Radiation monitoring device
 There are four main types of individual radiation recording
devices called personnel dosimeters used in diagnostic
radiology and nuclear medicine:
1) Film badges
2) TLDs
3) OSL dosimeters
4) Pocket dosimeter
37

38. Film badges
 consists of a small sealed packet of radiation sensitive film, placed
inside a light tight special plastic holder with windows &
appropriate filters.
 Radiation striking the emulsion causes a darkening of the
developed film.
 The amount of darkening increases with the absorbed dose to the
film emulsion and is measured with a densitometer.
38

39. Film badges
 The film emulsion contains grains of AgBr, resulting in a higher
effective atomic number than tissue; therefore, the dose to the film
is not equal to the dose to tissue.
 Most film badges can record doses from about 100 μSv to 15 Sv
for photons and from 500 μSv to 10 Sv for beta radiation.
 The film in the badge is usually replaced monthly and sent to the
commercial supplier for processing.
39

40. 40

41. Advantage of film badges
 Film badges are small, lightweight, inexpensive, and easy to
use and are portable .
 Can differentiate between scatter and primary beam and
differentiate between X-ray , gamma ray and beta radiation.
 Permanent legal record .
41

42. Disadvantage of film badges
 Exposure to excessive moisture or temperature can damage
the film emulsion, making dose estimates difficult or
impossible.
 Only records exposure where it is worn.
 Sensitivity is decreased above and below 50 KeV
 Not immediate reading.
42

43.  are excellent personnel and environmental dosimeters.
 Very suitable for clinical dosimeter
 It is based on principle of thermoluminescence.
 This badge uses special chemical compounds that retain
energy from radiation exposure and emit light when heated
by means of thermal stimulation.
Thermo-Luminescent Dosimeter 43

44. Thermo-Luminescent Dosimeter
 contain storage phosphors in which electrons raised to excited states
by ionizing radiation, become trapped in excited states.
 When these trapped electrons are released, either by heating or by
exposure to light, they fall to lower energy states with the emission of
light.
 The amount of light emitted can be measured and indicates the
radiation dose received by the phosphor material.
44

45. Thermo-Luminescent Dosimeter
 The most commonly used TLD material for personnel dosimetry is
lithium fluoride (LiF).
 LiF TLDs have a wide dose response range of 100 μSv to 10 Sv and
are reusable.
 their effective atomic number is close to that of the tissue;
therefore, the dose to the LiF chip is close to the tissue dose.
 TLDs do not provide a permanent record, because heating the chip
to read the exposure removes the deposited energy.
45

46. 46

47. Thermo-Luminescent Dosimeter
 TLDs are routinely used in nuclear medicine
as extremity dosimeters.
 Ring badges TLDs is used to measure
extremity dose and consists of a single LiF
crystal inside a plastic holder.
 Ring badges should be worn on the
dominant hand
47

48. Fig:- principle of TLDs and OSL dosimeter
48

49. 49

50. Practical consideration
 TLD must be calibrated before it can be used.
 Since the response of the TLD material is affected by their previous
radiation history and thermal history, the material must be annealed to
remove residual effect.
 TLD should be worn at chest region.
 TLD is changed in every 3 months.
 The TLD badge should be stored away from light, radiation and dust
when it is not in use.
50

51. Advantages of TLDs
 can be used over a long time interval .
 their effective atomic number is close to that of the tissue.
 Not sensitive to heat or humidity and chemically inert.
 More sensitive and accurate.
51

52. Disadvantages of TLDs
 more expensive than film badges.
 TLDs do not provide a permanent record.
 Don’t give immediate dose readings.
 Need to be read every 3 months.
52

53. Optically stimulated luminescent
dosimeter
 Becomes commercially available as an alternative to TLDs.
 The principle of OSL is similar to that of TLDs, except that the
release of trapped electrons and light emission are stimulated
by laser light instead of by heat.
 Crystalline aluminum oxide activated with carbon (Al2O3:C) is
commonly used.
53

54. Optically stimulated luminescent
dosimeter
 these OSL dosimeters have a broad dose response range, and
are capable of detecting doses as low as 10 μSv.
 the Al2O3 has a higher effective atomic number than soft
tissue.
 OSL dosimeter has filters over the sheet of OSL material that
are used to estimate dose to soft tissue, as in film badges.
54

55. Optically stimulated luminescent
dosimeter
 TLDs or OSL dosimeters are the dosimeters of choice when
longer dose assessment intervals (e.g., quarterly) are required.
 OSL is more sensitive than TLDs.
55

56. 56

57. Advantages of OSL dosimeter
 They can be reread several times .
 An image of the filter pattern can be produced to differentiate
between static (i.e., instantaneous) and dynamic (i.e., normal)
exposure.
57

58. Disadvantages of OSL dosimeter
 More expensive than TLDs.
 Do not gives immediate readings.
 No permanent record.
58

59. Pocket dosimeter
 Also named as direct-reading dosimeters, self reading pocket
dosimeter and pocket electroscope.
 Named as they are commonly carried in the pocket.
 It works by measuring the decrease in electrostatic charge on
a metal conductor in an ionization chamber, due to ionization
of the air in the chamber by radiation electrode.
59

60. Pocket dosimeter
 The major disadvantage to film, thermoluminescent, and OSL
dosimeters is that the accumulated dose is not immediately
displayed.
 Pocket dosimeters measure radiation exposure and can be
read immediately.
 The analog version of the pocket dosimeter is the pocket ion
chamber.
60

61. Pocket dosimeter
 Pocket ion chambers can typically detect photons of energies
greater than 20 keV.
 Pocket ion chambers are available in a variety of ranges; the
most commonly used models measure exposures from 0 to
200 mR or 0 to 5 R.
 Digital pocket dosimeters can be used in place of pocket ion
chambers.
61

62. Pocket dosimeter
 Digital pocket dosimeters use solid-state electronics and
either Geiger-Mueller (GM) tubes or radiation-sensitive
semiconductor diodes to measure and display radiation dose
in a range from approximately 10 μSv to 100 mSv.
 Pocket dosimeters can be utilized when high doses are
expected, such as during cardiac catheterization or
manipulation of large quantities of radioactivity.
62

63. fig:- analog and digital pocket dosimeters
63

64. Advantages of pocket dosimeter
 These devices are small (the size of a pen) and easy to use.
 Gives immediate reading.
 Reusable.
64

65. Disadvantages of pocket dosimeter
 they may produce erroneous readings if bumped or dropped.
 although reusable, do not provide a permanent record of
exposure.
 low accuracy.
65

66. Direct Ion Storage Dosimeters
 are a relatively new technology in which a nonvolatile analog
memory cell, surrounded by a gas-filled ion chamber, is used
to record radiation exposure.
 The dose recorded by the dosimeter can be read at any time
by connecting it to the USB port of any computer with
Internet access.
66

67. 67

68. Advantages of Direct Ion Storage
Dosimeters
 It has broad dose and photon energy response range.
 unlimited real-time dose readings by the user without the
need for a special reader.
 online management of dosimeter assignment and dosimetry
reports.
 elimination of the periodic distribution and collection of
dosimeters
 No delay and cost associated with returning the dosimeters
for processing by the dosimetry vendor.
68

69. Disadvantages of direct ion storage
dosimeters
 Include initial cost of the dosimeters.
 More costly replacement of lost dosimeters.
 The need for users to upload dosimetry information
periodically.
 The current version of this dosimeter cannot be used to
measure exposure to beta radiation.
69

70. 70

71. Problems with dosimeters
 Dosimeters being left in radiation fields when not worn.
 contamination of a dosimeter itself with radioactive material.
 lost and damaged dosimeters.
 people not wearing dosimeters when working with radiation
sources.
71

72. Summary
 Various units of radiation are :-
 Exposure = Roentgen / Air kerma
 Absorbed dose =Rad / gray
 Effective dose = Rem /Sv
 Radiation monitoring devices do not provide protection from the
radiation, it just measures the radiation absorbed by an individual.
 There are mainly 4 types of Personal monitoring devices or dosimeter ;-
film badges, TLDs, OSL dosimeter & pocket dosimeter.
72

73. reference
 Radiologic science for technologist by SC Bushong 11th
edition.
 The Essential Physics of Medical Imaging by Bushberg
 Christensen's Physics of Diagnostic Radiology 4th edition.
 Various online source
73

74. Thank
you
74