The document discusses various quantities used to measure radiation exposure and dose. It defines key terms like exposure, absorbed dose, equivalent dose, and effective dose. Exposure is a measure of radiation concentration at a point, while absorbed dose expresses the energy absorbed in a specific tissue. Equivalent dose accounts for radiation type by applying weighting factors, and effective dose considers dose to different organs via tissue weighting factors. Operational quantities like ambient dose equivalent are used for practical radiation monitoring since equivalent dose is not directly measurable. Different types of radiation detectors are also overviewed, including gas-filled detectors, scintillators, and semiconductors.

1. INTERACTION OF RADIATION WITH
MATTER
Several terms are used to define the quantity or amount
of radiation energy (or dose) transferred to and
absorbed by different media, such as air or biological
material.

2. Radiation Quantities
There are many different physical quantities that can
be used to express the amount of radiation
delivered to a human body. Generally, there are
both advantages and applications as well as
disadvantages and limitations for each of the
quantities.
Two types of radiation quantities:
I) those that express the concentration of radiation
at some point, or to a specific tissue or organ,
II) those that express the total radiation delivered
to a body.
Exposure
Absorbed Dose

3. Exposure
Exposure is a radiation quantity that expresses the
concentration of radiation delivered to a specific
point, such as the surface of the human body.
Knowing the exposure tells us nothing about the total
radiation imparted to a body.
The conventional unit is the Roentgen (R)
and
the SI unit is the Coulomb/kg of air (C/kg of air).
(1 R = 2.58 x 10-4 C/kg)
or 1 C/kg of air = 3876 R

4. Exposure rate
Exposure rate refers to the amount of gamma or X
radiation, in R, transferred to air per unit time (e.g.,
R/hr or R/yr).
Commonly used sub-units of the roentgen are the
milliroentgen (mR) and the microroentgen (µR) for
exposure, with corresponding subunits of mR/hr or
µR/hr for exposure rates.
The unit roentgen may be used to measure gamma or
X radiation only.

5. • Radiation exposure to humans can be broadly
classified as:
• Internal exposure
• External exposure
• We will discuss monitoring of external
exposures.

6. The aim of external exposure monitoring is measurement of:
• Radiation levels in and around work areas
(equipment: area monitor).
• Levels around radiation therapy equipment or source
containers
(equipment: area monitor).
• Equivalent doses received by individuals working with
radiation
(equipment: personal monitor).

7. Results of external exposure monitoring is used:
• To assess workplace conditions and individual exposures;
• To ensure acceptably safe and satisfactory radiological
conditions in the workplace;
• To keep records of monitoring over a long period of time,
for the purposes of regulation or as good practice.

8. Radiation monitoring instruments are
classified as:
Area survey meters Personal dosimeters
(or area monitors) (or individual dosimeters)
Radiation monitoring instruments must be calibrated in terms of
appropriate quantities for radiation protection.

9. Dosimetric quantities for radiation
protection
• Recommendations regarding dosimetric
quantities and units in radiation protection
dosimetry are set forth by the International
Commission on Radiation Units and
Measurements (ICRU).
• The recommendations on the practical
application of these quantities in radiation
protection are established by the International
Commission on Radiological Protection (ICRP).

10. Absorbed dose (D)
• The absorbed dose (D) is the radiation
quantity used to express the concentration of
radiation energy actually absorbed in a
specific tissue.
• The SI unit of absorbed dose is the joule per
kilogram, also assigned the special name the
gray (1 Gy = 1 joule/kg). The conventional
unit of absorbed dose is the rad
(1 rad = 100 ergs per gram = 0.01 Gy).

11. Absorbed Dose
Absorbed dose in tissue cannot be measured directly
by any practical methods. Dose measuring devices,
dosimeters, can be placed on the surface, but it is
generally not reasonable to insert them into most
internal tissues or organs. The absorbed dose in most
body tissues is usually determined by indirect means.
A common method is to first determine the entrance
surface exposure, or air kerma, over the tissue or organ
of interest and then use published dose factors to
calculate the dose in a specific tissue location.

12. Air kerma
• Air kerma is used to express the radiation concentration delivered
to a point, such as the entrance surface of a patient's body.
• The quantity, kerma, originated from the acronym, KERMA, for
Kinetic Energy Released per unit MAss (of air). It is a measure of
the amount of radiation energy actually deposited in or absorbed
in a unit mass of air.
• Air kerma is just the Absorbed Dose in air.
• It is expressed in the units of joule per kilogram, J/kg. This is also
the unit gray, Gy, used for absorbed dose.

13. Absorbed Dose
•Another indirect method used to determine dose is to actually
measure the dose in a "phantom".
•A phantom is a block of some material (usually plastic or
water) that has the same radiation absorption properties as
tissue.
•The phantom should be approximately the same size and
shape as the body section in which the dose is to be
determined.
•A dosimeter is inserted into the phantom and it is then
exposed to radiation using known exposure factors.
•These measured dose values in the phantom can them be
used to estimate patient dose values by applying appropriate
factors to account for different exposure conditions.

14. Equivalent dose H
The definition for equivalent dose H deals
with two steps:
• Assessment of the organ dose DT
• Introduction of radiation-weighting factors
to account for the biological effectiveness
of the given radiation in inducing
deleterious health effects.

15. Definition of organ dose DT (step 1)
• The organ dose DT is defined as the mean
absorbed dose ("physical" dose) in a specified
tissue or organ T of the human body given by
where
• mT is the mass of the organ or tissue under consideration.
• ЄT is the total energy imparted by radiation to that tissue or
organ.
Equivalent dose H

16. • Introduction of radiation-weighting factors (step 2)
• The organ dose DT multiplied by a radiation-weighting factor wR to
account for the biological effectiveness of the given radiation in
inducing deleterious health effects
HT = DT,R.WR
where DT,R is the absorbed dose delivered by radiation type R
averaged over a tissue or organ T.
The resulting quantity is called the equivalent dose HT.
The SI unit of equivalent dose is J/kg or sievert (Sv).
Equivalent dose H

17.  Radiation-weighting factors wR:
for x rays, γ rays and electrons: wR= 1
for protons: wR = 5
for α particles: wR = 20
for neutrons, wR depends on energy wR = from 5 to 20
Equivalent dose H

18. Dosimetric quantities for radiation
protection
• The equivalent dose H is not directly
measurable.
• There are no laboratory standards to obtain
traceable calibration for the radiation monitors
using this quantity.
Operational quantities have been
introduced that can be used for
practical measurements and serve
as a substitute for the quantity
equivalent dose H.

19. Appropriate quantities for radiation monitoring
• Operational quantities are based on the equivalent
dose at a point in the human body (or in a phantom).
• They relate to the type and energy of the radiation
existing at that point.
• They can, therefore, be calculated on the basis of the
fluence (number of particles that enter a sphere of unit
cross-sectional area) at that point.

20. Appropriate quantities for area monitoring
• It is desirable to assess the quantity of equivalent dose in a
phantom approximating the human body.
• The phantom selected for this purpose is the so-called
ICRU sphere.
• The ICRU sphere, 30 cm in diameter, is a tissue equivalent
sphere.
• Composition:
– Oxygen 76.2%
– Carbon 11.1%
– Hydrogen 10.1%
– Nitrogen 2.6%

21. Appropriate quantities for area monitoring
• For area monitoring, two operational quantities have been
introduced, based on the ICRU sphere.
• These two quantities additionally refer to:
• Weakly penetrating radiation
or
• Strongly penetrating radiation
• In practice, the term ‘weakly penetrating’ radiation usually
applies to:
• Photons below 15 keV
and
• Beta rays

22. Appropriate quantities for area monitoring
• The two operational quantities used for area
monitoring are:
– Ambient dose equivalent H*(d)
– Directional dose equivalent H'(d)
• where d refers to a certain depth in the ICRU sphere.

23. Ambient dose equivalent
• The ambient dose
equivalent H*(d) is the
dose equivalent that would
be produced by the
corresponding aligned and
expanded field in the ICRU
sphere at a depth d on the
radius opposing the
direction of the aligned
field.
The SI unit of ambient dose equivalent is the Sievert (Sv). The conventional
unit is rem.
1 Sievert = 100 rem

24. Ambient dose equivalent
Relevant depths in the ICRU sphere for strongly and weakly
penetrating radiation
– The relevant depth in the ICRU sphere for strongly penetrating
radiation is d = 10 mm.
– The relevant depths in the ICRU sphere for weakly penetrating
radiation are:
• d = 0.07 mm used for skin
• d = 3.0 mm used for eye lens

25. Ambient dose equivalent
The ambient
dose equivalent
for strongly
penetrating
radiation
H*(10 mm)

26. Directional dose equivalent
• The directional dose equivalent H'(d,Ω) is the dose
equivalent that would be produced by the
corresponding expanded field in the ICRU sphere at
a depth d on a radius in a specified direction Ω (omega).
• The SI unit of directional dose
equivalent is the sievert (Sv).

27. Directional dose equivalent
The directional
dose equivalent
for weakly
penetrating
radiation
H'(0.07mm,Ω)

28. Operational Quantity for Individual Monitoring
• The operational quantity for individual monitoring is the
personal dose equivalent Hp(d).
• The personal dose equivalent is the equivalent dose in
soft tissue below a specified point on the body at an
appropriate depth d.
• The relevant depth for strongly penetrating radiation is
d = 10 mm.
• The relevant depth for weakly penetrating radiation is:
• d = 3.0 mm used for eye lens
• d = 0.07 mm used for skin

29. Summary of operational quantities

30. Summary of operational quantities

31. Effective Dose
• Effective dose is a very useful radiation quantity for expressing relative risk
to humans, both patients and other personnel.
• It takes into account the specific organs and areas of the body that are
exposed. The point is that all parts of the body and organs are not equally
sensitive to the possible adverse effects of radiation, such as cancer
induction and mutations.
• For the purpose of determining effective dose, the different areas and
organs have been assigned tissue weighting factor (wT) values. For a
specific organ or body area the effective dose is:
Effective Dose (Gy) = Absorbed Dose (Gy) x wT
• If more than one area has been exposed, then the total body effective dose
is just the sum of the effective doses for each exposed area.

32. Tissue Weighting Factor (WT)
Tissue Weighting Factor
Gonads 0.25
Breast 0.15
Red Bone Marrow 0.12
Lung 0.12
Thyroid 0.03
Bone Surface 0.03
Remainder 0.3
Total Body 1.0

33. • There have been many different systems of units developed to express
the values of the various physical quantities.
• In more recent times the metric system has gradually replaced some of
the other more traditional or classic systems.
• This is also true for the units used for many of radiation quantities.
Radiation Units

34. Radiation Detection and
Measurement
We need to understand the basic theory and
operation of various radiation detectors

35. AREA SURVEY METERS
Radiation instruments used as survey
monitors can be divided into two groups of
detectors:
Gas filled detectors: Solid state detectors:
1. Ionization chambers 1. Scintillator
2. Proportional counters 2. Semiconductor detectors.
3. Geiger-Mueller (GM) counters

36. 36
Radiation Detection and
Measurement
Fundamentals
 Radiation detectors:
 collect the charge produced by
ionizing radiation
 have a specific collection volume
 respond based on the relative
number of particles collected

37. 37
Direct & Indirect Ionization
 Direct ionization
 Radiation entity itself produces ions
 Alpha particles
 Beta particles
 Indirect ionization
 Radiation entity interacts with detector
wall to produce high energy electron
 X-rays
 Gamma rays

38. 38
Gas-filled Detectors

39. 39
Gas-Filled Detector
Components
 High-voltage source
 Counting chamber
 Counting gas (“fill gas”)
 Two, coaxial electrodes well insulated
from each other
 Electron-pairs
 produced by radiation in fill gas
 move under influence of electric field
 produce measurable current on
electrodes, or
 transformed into output pulse

40. 40
Gas-filled Detectors - general
example
wall
fill gas
R
Output
Pulse
A
or
Anode (+)
Cathode (-)
_ +
C
HV

41. 41
Direct Ionization Process
wall
Incident
charged
particle
e -
e -
e -
e -
e -
e -
e -
e -
Particle has sufficient energy to
penetrate the entrance window
and interact with the gas.
“Entrance Window”

42. 42
Indirect Ionization Process
wall
Incident photon Photon interacts with the inner
detector wall, releasing energetic
electrons that ionize the gas.

43. 43
Competing Processes -
recombination
R
Output
e -
e -
+
+

44. 44
Scintillation Detectors

45. 45
“Scintillator”
 Typically, a crystal that produces a flash
of light when radiation interacts
 Light flash may be in the visible range
 An activator is added to provide “sites”
for scintillation
 Various physical & chemical scintillators
 Solids, liquids, gases
 Inorganics, organics

46. 46
Detecting the
“Flash of Light”
 Quantification of output requires light
detection and then signal amplification
 Accomplished with a photomultiplier tube
 Photocathode
 Series of dynodes
 Anode
 The scintillating crystal and PMT are
placed together as one unit and optically
coupled

47. 47
Incident
Photon
Scintillation
Event
Reflective coating
Scintillation crystal
Photocathode
Electrons
Dynodes
Aluminum housing
Cutaway diagram of
scintillator and PMT
Photoelectron

48. 48
Major components of Photo multiplier tube
n Photocathode
u Converts photon to electron
n Dynodes
u electrodes which eject multiple electrons after
being struck by an initiating electron
u Multiple dynodes can result in a signal gain of 6 or
7 orders of magnitude
n Anode
u accumulates all electrons produced from final
dynode
n Resistor
u collected electrons (charge) pass through resistor
to generate voltage pulse

49. 49
Semiconductors

50. 50
Semiconductors - Detection
Mechanism
Si
Si
Si
Si
Si
Si
Schematic view of Silicon lattice
(dots represent electrons in the covalent bond)
Pure Si is a poor electrical conductor

51. 51
Mechanism
Conduction Band
Valence Band
Energy
1.08 eV Forbidden Gap
Pure Si is a poor electrical conductor (nearly
all electrons are in the valence band).
Representation of energy levels of crystalline Si.

52. 52
Donor Impurities
Si
Si
Si
Si
Si
P
Silicon lattice, “doped” with a donor impurity
(note the extra electron)
Pure semiconductors that have been altered by the presence of dopants are
known as extrinsic semiconductors

53. 53
n-type Silicon
Conduction Band
Valence Band
Energy
0.05 eV
Donor level
Schematic diagram of energy levels in n-type silicon
Silicon with a donor impurity is said to be
of an n-type because of additional
negative charge carriers (electrons)

54. 54
Acceptor
Impurities
Si
Si
Si
Si
Si
B
Silicon lattice, doped with an acceptor impurity
(note the missing electron, and the missing bond)

55. 55
p-type Silicon
Conduction Band
Valence Band
Energy
0.08 eV
Acceptor level
Schematic diagram of energy levels in p-type Silicon
Silicon with an acceptor impurity is said
to be of a p-type because of additional
positive charge carriers (holes)
The conduction band is the range of electron energies, sufficient to free an electron from binding with its
individual atom and allow it to move freely within the atomic lattice of the material.

56. 56
Semiconductors
n Radiation is detected by measuring
the physical movement of electrons
(or holes) through the silicon
n These electrons (or holes) are made
mobile by interactions from ionizing
radiation
n Both n-type and p-type structures
are needed to make a radiation
detector

57. 57
p-n Junctions
n-type
silicon
p-type
silicon
o
o
o
o
o
o
o
o
o o
“Depletion Region”
n-type
silicon
p-type
silicon
o
o
o
o
o
o
oo
o
o
o
o
“Measurement” is made of
current across the junction.

58. 58
p-n Junctions
n-type
silicon
p-type
silicon
o
o
o
o
o
o
oo
o
o
o
o
n-type
silicon
p-type
silicon
o
o
o
o
o
o
o
o
o
o
+ _
“Reverse Bias”
Noisy; poor
performance
“Non-biased”

59. Operating Principles of
Semiconductor detectors
 Si semiconductor is a layer of p-type Si
in contact with n-type Si.
 What happens when this junction is
created?
 Electrons from n-type migrate across
junction to fill holes in p-type
 Creates an area around the p-n junction
with no excess of holes or electrons
 Called a “depletion region”
 Apply (+) voltage to n-type and (-) to p-
type:
 Depletion region made thicker
 Called a “reverse bias”

60. 60
Neutron Detectors
n Neutrons, being uncharged, can’t
be detected directly
n A nuclear reaction must take place
n Radiation instrumentation detects
the products of the nuclear
reaction, and not the neutron itself
n For example, in a gas-filled
detector …..

61. 61
Neutron Detectors
n BF3 used as fill-gas; the neutron
interacts with boron and creates alpha
particle; alpha particle ionizes the
gas; the neutron is “detected”
n Can also detect fission fragments
B + n a + Li
10 1 4 7
5 0 2 3

62. 62
Summary
 The basic way in which a radiation detector operates
is radiation detectors:
 collect the charge produced by ionizing radiation
 have a specific collection volume
 respond based on the relative number of particles
collected
n A general description of these detector types and
mechanism describing their operation is
 Gas-filled
 Scintillation
 Semiconductors
 Neutron

63. 63

64. n The conduction band is the range of electron
energies, higher than that of the valence band,
sufficient to free an electron from binding with its
individual atom and allow it to move freely within
the atomic lattice of the material. Electrons within
the conduction band are mobile charge carriers
in solids, responsible for conduction of electric
currents in metals and other good electrical
conductors.
n The valence band is the highest range of
electron energies in which electrons are normally
present at absolute zero temperature.
64

65. n Solid state detectors are those using advanced materials such as
semiconductors. These detectors are generally used in the same
manner as scintillator-based detectors. Advanced materials such
as silicon or germanium or the recently popular cadmium zinc
telluride (CdZnTe) offer better energy resolution, less noise, and
better spatial resolution than the standard scintillators. This will
allow scientists to more carefully measure gamma-ray line
emission. Some materials, such as germanium, require more care
than scintillators, such as cooling them to low operating
temperatures. They also tend to be more expensive.
65