ASTM E1894-18

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1894 − 13a E1894 − 18
Standard Guide for
Selecting Dosimetry Systems for Application in Pulsed
X-Ray Sources
This standard is issued under the fixed designation E1894; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide provides assistance in selecting and using dosimetry systems in flash X-ray experiments. Both dose and dose-rate
techniques are described.
1.2 Operating characteristics of flash X-ray sources are given, with emphasis on the spectrum of the photon output.
1.3 Assistance is provided to relate the measured dose to the response of a device under test (DUT). The device is assumed to
be a semiconductor electronic part or system.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E170 Terminology Relating to Radiation Measurements and Dosimetry
E666 Practice for Calculating Absorbed Dose From Gamma or X Radiation
E668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Determining Absorbed Dose in
Radiation-Hardness Testing of Electronic Devices
E1249 Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon Electronic Devices Using Co-60
Sources
2.2 ISO/ASTM Standards:
ISO/ASTM 51261 Practice for Calibration of Routine Dosimetry Systems for Radiation Processing
ISO/ASTM 51275 Practice for Use of a Radiochromic Film Dosimetry System
ISO/ASTM 51310 Practice for Use of a Radiochromic Optical Waveguide Dosimetry System
2.3 International Commission on Radiation Units (ICRU) and Measurements Reports:
ICRU Report 14 Radiation Dosimetry: X rays and Gamma Rays with Maximum Photon Energies Between 0.6 and 50 MeV
ICRU Report 17 Radiation Dosimetry: X rays Generated at Potentials of 5 to 150 kV
ICRU Report 34 The Dosimetry of Pulsed Radiation
ICRU Report 51 Quantities and Units in Radiation Protection Dosimetry
ICRU Report 60 Fundamental Quantities and Units for Ionizing Radiation
ICRU Report 76 Measurement Quality Assurance for Ionizing Radiation Dosimetry
ICRU Report 77 Elastic Scattering of Electrons and Positrons
ICRU Report 80 Dosimetry Systems for Use in Radiation Processing
ICRU Report 85a Fundamental Quantities and Units for Ionizing Radiation
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applications and is the direct responsibility of Subcommittee E10.07 on
Radiation Dosimetry for Radiation Effects on Materials and Devices.
Current edition approved Aug. 1, 2013Dec. 1, 2018. Published September 2013December 2018. Originally approved in 1997. Last previous edition approved in 2013 as
E1894 – 13.E1894 – 13a. DOI: 10.1520/E1894-13A.10.1520/E1894-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
For referenced ISO/ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from the International Commission on Radiation Units and Measurements, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1894 − 18
3. Terminology
3.1 absorbed dose—quotient of dε¯/dm, where dε¯ is the mean energy imparted by ionizing radiation to matter of mass dm:
dε¯
D 5 (1)
dm
See ICRU Report 85a. The special name for the unit for absorbed dose is the gray (Gy).
1 Gy 5 1J/kg (2)
Formerly, the special unit for absorbed dose was the rad, where 1 rad = 100 erg/g.
1 rad 5 0.01 Gy (3)
Since the absorbed dose due to a given radiation field is material dependent, it is important to include the material composition
for which the dose is being reported, e.g., 15.3 Gy(LiF).
3.1 absorbed dose enhancement—increase (or decrease) in the absorbed dose (as compared to the equilibrium absorbed dose)
at a point in a material of interest. This can be expected to occur near an interface with a material of higher or lower atomic number.
3.2 converter—a target for electron beams, generally of a high atomic number material, in which bremsstrahlung X-rays are
produced by radiative energy losses of the incident electrons.
3.4 dosimeter—a device that, when irradiated, exhibits a quantifiable change in some property of the device which can be related
to absorbed dose in a given material using appropriate analytical instrumentation and techniques.
3.3 dosimetry system—a system used for determining absorbed dose, consisting of dosimeters, measurement instruments, and
their associated reference standards, and procedures for the system’s use.
3.4 DUT—device under test. This is the electronic component or system tested to determine its performance during or after
irradiation.
3.5 endpoint energy—endpoint energy refers to the peak energy of the electron beam, usually in MeV, generated in a flash X-ray
source and is numerically equal to the maximum voltage in MV. The word endpoint refers to the highest photon energy of the
bremsstrahlung spectra, and this endpoint is equal to the maximum or peak in the electron energy. For example, if the most
energetic electron that strikes the converter is 10 MeV, this electron produces a range of bremsstrahlung photon energies but the
maximum energy of any photon is equal to 10 MeV, the endpoint energy. Most photons have energies one-tenth to one-third of
the maximum electron energy for typical flash X-ray sources in the 10 MV to 1 MV endpoint voltage region, respectively.
3.6 endpoint voltage—Endpoint voltage refers to the peak voltage across a bremsstrahlung diode in a flash X-ray source. For
example, a 10-MV flash X-ray source is designed to reach a peak voltage of 10-MV across the anode-cathode gap which generates
the electron beam for striking a converter to produce bremsstrahlung.
3.7 equilibrium absorbed dose—absorbed dose at some incremental volume within the material in which the condition of
electron equilibrium (the energies, number, and direction of charged particles induced by the radiation are constant throughout the
volume) exists. For lower energies where bremsstrahlung production is negligible the equilibrium absorbed dose is equal to the
kerma.
NOTE 1—For practical purposes, assuming the spatial gradient in the X-ray field is small over the range of the maximum energy secondary electrons
generated by the incident photons, the equilibrium absorbed dose is the absorbed dose value that exists in a material at a distance from any interface with
another material greater than this range.
4. Significance and Use
4.1 Flash X-ray facilities provide intense bremsstrahlung radiation environments, usually in a single sub-microsecond pulse,
which often fluctuates in amplitude, shape, and spectrum from shot to shot. Therefore, appropriate dosimetry must be fielded on
every exposure to characterize the environment, see ICRU Report 34. These intense bremsstrahlung sources have a variety of
applications which include the following:
4.1.1 Generation of X-ray and gamma-ray environments similar to that from a nuclear weapon burst.
4.1.1 Studies of the effects of X-rays and gamma rays on materials.
4.1.2 Studies of the effects of radiation on electronic devices such as transistors, diodes, and capacitors.
4.1.4 Vulnerability and survivability testing of military systems and components.
4.1.3 Computer code validation studies.
4.2 This guide is written to assist the experimenter in selecting the needed dosimetry systems (not all radiation parameters must
be measured in a given experiment) for use at pulsed X-ray facilities. This guide also provides a brief summary of the information
on how to use each of the dosimetry systems. Other guides (see Section 2) provide more detailed information on selected dosimetry
systems in radiation environments and should be consulted after an initial decision is made on the appropriate dosimetry system
to use. There are many key parameters which describe a flash X-ray source, such as dose, dose rate, spectrum, pulse width, etc.,
E1894 − 18
such that typically no single dosimetry system can measure all the parameters simultaneously. However, it is frequently the case
that not all key parameters must be measured in a given experiment.
5. General Characteristics of Flash X-ray Sources
5.1 Flash X-ray Facility Considerations—Flash X-ray sources operate like a dental X-ray source but at much higher voltages
and intensities and usually in a single, very short burst, see ICRU Report 17. A high voltage is developed across an anode-cathode
gap (the diode) and field emission creates a pulsed electron beam traveling from the cathode to the anode. A high atomic–number
element such as tantalum is placed on the anode to maximize the production of bremsstrahlung created when the electrons strike
the anode. Graphite or aluminum is usually placed downstream of the converter to stop the electron beam completely but let the
X-radiation pass through. Finally, a debris shield made of Kevlar or low-density polyethylene is sometimes necessary to stop
exploding converter material from leaving the source. All of these components taken together form what is commonly called a
bremsstrahlung diode.
5.2 Relationship Between Flash X-ray Diode Voltage and X-ray Energy of Bremsstrahlung—Flash X-ray sources produce
bremsstrahlung by generating an intense electron beam which then strikes a high atomic number (Z) converter such as tantalum.
The electron-solid interactions produce “braking” radiation or, in German, bremsstrahlung. Fig. 1 shows the typical range of
photon energies produced by three different sources. If the average radiation produced is in the 20–100 keV region, the source is
said to be a medium–hard X-ray simulator. If the average photon energy is in the 100–300–keV 100 – 300 keV region, the term
used is “hard X-ray simulator.” At the high end of the flash X-ray range are sources which produce an average photon energy of
around 2 MeV. Because this photon energy is in the typical gamma-ray spectral range, the source is called a gamma-ray simulator.
5.2.1 The average energy of the bremsstrahlung spectrum, E¯ , through an optimized converter can be estimated using the
photon
following relationship (1) in the medium-hard X-ray region (50 keV < : E¯ > 500 keV) is given empirically by,
photon
¯ 1/2
E '5 ε (1)
photon
¯
E 5 k·=ε where 5.1,k,18.9 (1)
photon
where E¯ is the average energy of the bremsstrahlung photons in keV and ε is the average energy of the electrons in the
photon
electron beam incident on the converter in keV. The value of k depends on the converter thickness: thin targets will have val-
ues at the lower end of the range while thick targets optimized for higher incident energies will have values at the upper end.
When an optimized bremsstrahlung converter is used, a rule-of-thumb may be used that the average photon energy is about ⁄5
or ⁄6 of the electron endpoint energy (1). For a fixed converter design, the photon energy away from the optimization point is
roughly proportional to the square root of the electron endpoint energy with the proportionality factor varying between about 5
and 19 depending upon the design point (1). This equation and Fig. 1 indicate that most of the photons have energies much
less than the endpoint electron energy, or in voltage units, the flash X-ray voltage. Additionally, the bremsstrahlung spectrum
is very non-Gaussian so caution must be exercised in using the average energy of the distribution for dosimetry planning.
FIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray Sources
The boldface numbers in parentheses refer to the list of references at the end of this standard.
E1894 − 18
6. Measurement Principles
6.1 Typically in flash X-ray irradiations, one is interested in some physical change in a critical region of a device under test
(DUT). The dosimetry associated with the study of such a physical change may be broken into three parts:
6.1.1 Determine the absorbed dose in a dosimeter.
6.1.2 Using the dosimeter measurement, estimate the absorbed dose in the region and material of interest in the DUT.
6.1.3 If required, relate the estimated absorbed dose in the DUT to the physical change of interest (holes trapped, interface states
generated, photocurrent produced, etc.)
6.2 This section will be concerned with the first two of the above listed parts of dosimetry: (1) what is necessary to determine
a meaningful absorbed dose for the dosimeter and (2) what is necessary to extrapolate this measured dose to the estimated dose
in the region of interest. The final step in dosimetry, associating the absorbed dose with a physical change of interest, is outside
the scope of this guide.
6.3 Energy Deposition:
6.3.1 Secondary Electrons—Both in the case of absorbed dose in the DUT and absorbed dose in the dosimeter, the energy is
deposited largely by secondary electrons. That is, the incident photons interact with the material of, or surrounding, the DUT or
the dosimeter and lose energy to Compton electrons, photoelectrons, and Auger electrons. The energy which is finally deposited
in the material is deposited by these secondary particles.
6.3.2 Transport of Photons—In some cases, it is necessary to consider the transport and loss of photons as they move to the
region whose absorbed dose is being determined. A correction for the attenuation of an incident photon beam is an example of such
a consideration.
6.3.3 Transport of Electrons—Electron transport may cause energy originally imparted to electrons in one region to be carried
to a second region depending on the range of the electrons. As a resu
...

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Contact ASTM International (www.astm.org) for the latest information
Designation: E1894 − 18
Standard Guide for
Selecting Dosimetry Systems for Application in Pulsed
X-Ray Sources
This standard is issued under the fixed designation E1894; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ISO/ASTM Standards:
ISO/ASTM 51261 Practice for Calibration of Routine Do-
1.1 This guide provides assistance in selecting and using
simetry Systems for Radiation Processing
dosimetry systems in flash X-ray experiments. Both dose and
ISO/ASTM 51275 Practice for Use of a Radiochromic Film
dose-rate techniques are described.
Dosimetry System
1.2 Operating characteristics of flash X-ray sources are
ISO/ASTM 51310 Practice for Use of a Radiochromic
given, with emphasis on the spectrum of the photon output.
Optical Waveguide Dosimetry System
1.3 Assistance is provided to relate the measured dose to the
2.3 International Commission on Radiation Units (ICRU)
response of a device under test (DUT). The device is assumed
and Measurements Reports:
to be a semiconductor electronic part or system.
ICRU Report 14 Radiation Dosimetry: X rays and Gamma
Rays with Maximum Photon Energies Between 0.6 and 50
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard- MeV
ICRU Report 17 Radiation Dosimetry: X rays Generated at
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- Potentials of 5 to 150 kV
ICRU Report 34 The Dosimetry of Pulsed Radiation
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. ICRU Report 51 Quantities and Units in Radiation Protec-
tion Dosimetry
2. Referenced Documents
ICRU Report 60 Fundamental Quantities and Units for
Ionizing Radiation
2.1 ASTM Standards:
E170 Terminology Relating to Radiation Measurements and ICRU Report 76 Measurement Quality Assurance for Ioniz-
ing Radiation Dosimetry
Dosimetry
E666 Practice for Calculating Absorbed Dose From Gamma ICRU Report 77 Elastic Scattering of Electrons and Posi-
trons
or X Radiation
E668 Practice for Application of Thermoluminescence- ICRU Report 80 Dosimetry Systems for Use in Radiation
Processing
Dosimetry (TLD) Systems for Determining Absorbed
ICRU Report 85a Fundamental Quantities and Units for
Dose in Radiation-Hardness Testing of Electronic Devices
Ionizing Radiation
E1249 Practice for Minimizing Dosimetry Errors in Radia-
tion Hardness Testing of Silicon Electronic Devices Using
3. Terminology
Co-60 Sources
3.1 absorbed dose enhancement—increase (or decrease) in
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear the absorbed dose (as compared to the equilibrium absorbed
Technology and Applications and is the direct responsibility of Subcommittee
E10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.
Current edition approved Dec. 1, 2018. Published December 2018. Originally
approved in 1997. Last previous edition approved in 2013 as E1894 – 13a. DOI: For referenced ISO/ASTM standards, visit the ASTM website, www.astm.org,
10.1520/E1894-18. or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Standards volume information, refer to the standard’s Document Summary page on
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM the ASTM website.
Standards volume information, refer to the standard’s Document Summary page on Available from the International Commission on Radiation Units and
the ASTM website. Measurements, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1894 − 18
dose) at a point in a material of interest. This can be expected 4.1.2 Studies of the effects of radiation on electronic devices
to occur near an interface with a material of higher or lower such as transistors, diodes, and capacitors.
atomic number. 4.1.3 Computer code validation studies.
4.2 This guide is written to assist the experimenter in
3.2 converter—a target for electron beams, generally of a
selecting the needed dosimetry systems for use at pulsed X-ray
high atomic number material, in which bremsstrahlung X-rays
facilities. This guide also provides a brief summary of the
are produced by radiative energy losses of the incident elec-
information on how to use each of the dosimetry systems.
trons.
Other guides (see Section 2) provide more detailed information
3.3 dosimetry system—a system used for determining ab-
on selected dosimetry systems in radiation environments and
sorbed dose, consisting of dosimeters, measurement
should be consulted after an initial decision is made on the
instruments, and their associated reference standards, and
appropriate dosimetry system to use. There are many key
procedures for the system’s use.
parameters which describe a flash X-ray source, such as dose,
3.4 DUT—device under test. This is the electronic compo-
dose rate, spectrum, pulse width, etc., such that typically no
nent or system tested to determine its performance during or
single dosimetry system can measure all the parameters simul-
after irradiation. taneously. However, it is frequently the case that not all key
parameters must be measured in a given experiment.
3.5 endpoint energy—endpoint energy refers to the peak
energy of the electron beam, usually in MeV, generated in a
5. General Characteristics of Flash X-ray Sources
flash X-ray source and is numerically equal to the maximum
5.1 Flash X-ray Facility Considerations—Flash X-ray
voltage in MV. The word endpoint refers to the highest photon
sources operate like a dental X-ray source but at much higher
energy of the bremsstrahlung spectra, and this endpoint is
voltages and intensities and usually in a single, very short
equal to the maximum or peak in the electron energy. For
burst, see ICRU Report 17. A high voltage is developed across
example, if the most energetic electron that strikes the con-
an anode-cathode gap (the diode) and field emission creates a
verter is 10 MeV, this electron produces a range of bremsstrahl-
pulsed electron beam traveling from the cathode to the anode.
ung photon energies but the maximum energy of any photon is
A high atomic–number element such as tantalum is placed on
equal to 10 MeV, the endpoint energy. Most photons have
the anode to maximize the production of bremsstrahlung
energies one-tenth to one-third of the maximum electron
created when the electrons strike the anode. Graphite or
energy for typical flash X-ray sources in the 10 MV to 1 MV
aluminum is usually placed downstream of the converter to
endpoint voltage region, respectively.
stop the electron beam completely but let the X-radiation pass
3.6 endpoint voltage—Endpoint voltage refers to the peak
through. Finally, a debris shield made of Kevlar or low-density
voltage across a bremsstrahlung diode in a flash X-ray source.
polyethylene is sometimes necessary to stop exploding con-
For example, a 10-MV flash X-ray source is designed to reach
verter material from leaving the source. All of these compo-
a peak voltage of 10-MV across the anode-cathode gap which
nents taken together form what is commonly called a
generates the electron beam for striking a converter to produce
bremsstrahlung diode.
bremsstrahlung.
5.2 Relationship Between Flash X-ray Diode Voltage and
3.7 equilibrium absorbed dose—absorbed dose at some
X-ray Energy of Bremsstrahlung—Flash X-ray sources produce
incremental volume within the material in which the condition
bremsstrahlung by generating an intense electron beam which
of electron equilibrium (the energies, number, and direction of
then strikes a high atomic number (Z) converter such as
charged particles induced by the radiation are constant
tantalum. The electron-solid interactions produce “braking”
throughout the volume) exists. For lower energies where
radiation or, in German, bremsstrahlung. Fig. 1 shows the
bremsstrahlung production is negligible the equilibrium ab-
typical range of photon energies produced by three different
sorbed dose is equal to the kerma.
sources. If the average radiation produced is in the 20–100 keV
region, the source is said to be a medium–hard X-ray simulator.
NOTE 1—For practical purposes, assuming the spatial gradient in the
X-ray field is small over the range of the maximum energy secondary If the average photon energy is in the 100 – 300 keV region, the
electrons generated by the incident photons, the equilibrium absorbed
term used is “hard X-ray simulator.” At the high end of the
dose is the absorbed dose value that exists in a material at a distance from
flash X-ray range are sources which produce an average photon
any interface with another material greater than this range.
energy of around 2 MeV. Because this photon energy is in the
typical gamma-ray spectral range, the source is called a
4. Significance and Use
gamma-ray simulator.
4.1 Flash X-ray facilities provide intense bremsstrahlung
5.2.1 The average energy of the bremsstrahlung spectrum,
¯
radiation environments, usually in a single sub-microsecond
E , through an optimized converter can be estimated using
photon
pulse, which often fluctuates in amplitude, shape, and spectrum
the following relationship (1) :
from shot to shot. Therefore, appropriate dosimetry must be
¯
E 5 k·=ε where 5.1,k,18.9 (1)
photon
fielded on every exposure to characterize the environment, see
¯
where E is the average energy of the bremsstrahlung
photon
ICRU Report 34. These intense bremsstrahlung sources have a
variety of applications which include the following:
4.1.1 Studies of the effects of X-rays and gamma rays on 5
The boldface numbers in parentheses refer to the list of references at the end of
materials. this standard.
E1894 − 18
FIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray Sources
photons in keV and ε is the average energy of the electrons
dosimetry, associating the absorbed dose with a physical
in the electron beam incident on the converter in keV. The
change of interest, is outside the scope of this guide.
value of k depends on the converter thickness: thin targets
6.3 Energy Deposition:
will have values at the lower end of the range while thick
targets optimized for higher incident energies will have val-
6.3.1 Secondary Electrons—Both in the case of absorbed
ues at the upper end. When an optimized bremsstrahlung
dose in the DUT and absorbed dose in the dosimeter, the
converter is used, a rule-of-thumb may be used that the aver-
energy is deposited largely by secondary electrons. That is, the
1 1
age photon energy is about ⁄5 or ⁄6 of the electron endpoint
incident photons interact with the material of, or surrounding,
energy (1). For a fixed converter design, the photon energy
the DUT or the dosimeter and lose energy to Compton
away from the optimization point is roughly proportional to
electrons, photoelectrons, and Auger electrons. The energy
the square root of the electron endpoint energy with the pro-
which is finally deposited in the material is deposited by these
portionality factor varying between about 5 and 19 depend-
secondary particles.
ing upon the design point (1). This equation and Fig. 1 indi-
6.3.2 Transport of Photons—In some cases, it is necessary
cate that most of the photons have energies much less than
to consider the transport and loss of photons as they move to
the endpoint electron energy, or in voltage units, the flash
the region whose absorbed dose is being determined. A
X-ray voltage. Additionally, the bremsstrahlung spectrum is
correction for the attenuation of an incident photon beam is an
very non-Gaussian so caution must be exercised in using the
example of such a consideration.
average energy of the distribution for dosimetry planning.
6.3.3 Transport of Electrons—Electron transport may cause
energy originally imparted to electrons in one region to be
6. Measurement Principles
carried to a second region depending on the range of the
6.1 Typically in flash X-ray irradiations, one is interested in
electrons. As a result, it is necessary to consider the transport
some physical change in a critical region of a device under test
and loss of electrons as they move into and out of the regions
(DUT). The dosimetry associated with the study of such a
whose absorbed dose is being determined. In particular, it is
physical change may be broken into three parts:
necessary to distinguish between equilibrium and non-
6.1.1 Determine the absorbed dose in a dosimeter.
equilibrium conditions for electron transport.
6.1.2 Using the dosimeter measurement, estimate the ab-
6.3.3.1 Charged Particle Equilibrium—In some cases, the
sorbed dose in the region and material of interest in the DUT.
numbers, energies, and angles of particles transported into a
6.1.3 If required, relate the estimated absorbed dose in the
region of interest are approximately balanced by those trans-
DUT to the physical change of interest (holes trapped, interface
ported out of that region. Such cases form an important class of
states generated, photocurrent produced, etc.)
limiting cases which are particularly easy to interpret. (See
“Equilibrium Absorbed Dose” in 3.7.)
6.2 This section will be concerned with the first two of the
above listed parts of dosimetry: (1) what is necessary to 6.3.3.2 Dose Enhancement—Because photoelectron pro-
determine a meaningful absorbed dose for the dosimeter and duction per atom is roughly proportional to the atomic number
(2) what is necessary to extrapolate this measured dose to the raised to the fourth power for energies less than 100 keV (2),
estimated dose in the region of interest. The final step in one expects more photoelectrons to be produced in high atomic
E1894 − 18
number layers than in low atomic number layers for the same ate equilibrating layer. In this case, the range of the secondary
photon fluence and spectrum. Thus, there may be a net flow of electrons will be large in comparison to the size of the TLD.
energetic electrons from the high atomic number layers into the Thus the dose measured will be the equilibrium dose in the
low atomic number layers. This non–equilibrium flow of TLD (with a small correction for the differences in the stopping
electrons may result in an enhancement of the dose in the
...