ASTM E1894-24

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.
Designation: E1894 − 24
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-
MeV
dance with internationally recognized principles on standard-
ICRU Report 17 Radiation Dosimetry: X rays Generated at
ization established in the Decision on Principles for the
Potentials of 5 to 150 kV
Development of International Standards, Guides and Recom-
ICRU Report 34 The Dosimetry of Pulsed Radiation
mendations issued by the World Trade Organization Technical
ICRU Report 51 Quantities and Units in Radiation Protec-
Barriers to Trade (TBT) Committee.
tion Dosimetry
2. Referenced Documents
ICRU Report 60 Fundamental Quantities and Units for
Ionizing Radiation
2.1 ASTM Standards:
ICRU Report 76 Measurement Quality Assurance for Ioniz-
E170 Terminology Relating to Radiation Measurements and
ing Radiation Dosimetry
Dosimetry
ICRU Report 77 Elastic Scattering of Electrons and Posi-
E666 Practice for Calculating Absorbed Dose From Gamma
trons
or X Radiation
ICRU Report 80 Dosimetry Systems for Use in Radiation
E668 Practice for Application of Thermoluminescence-
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
the absorbed dose (as compared to the equilibrium absorbed
This guide is under the jurisdiction of ASTM Committee E10 on Nuclear
dose) at a location in a material of interest. This can be
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 May 1, 2024. Published May 2024. Originally
approved in 1997. Last previous edition approved in 2018 as E1894 – 18. DOI: For referenced ISO/ASTM standards, visit the ASTM website, www.astm.org,
10.1520/E1894-24. 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 − 24
expected to occur near an interface with a material of higher or 4.2 This guide is written to assist the experimenter in
lower atomic number. selecting the needed dosimetry systems for use at pulsed X-ray
facilities. This guide also provides a brief summary on how to
3.2 converter—a target for electron beams, generally a high
use each of the dosimetry systems. Other guides (see Section 2)
atomic number material, in which bremsstrahlung X-rays are
provide more detailed information on selected dosimetry
produced by radiative energy loss of the incident electrons.
systems in radiation environments and should be consulted
3.3 dosimetry system—a system used for determining ab-
after an initial decision is made on the appropriate dosimetry
sorbed dose which consists of dosimeters, measurement instru-
system to use. There are many key parameters which describe
ments with their associated reference standards, and proce-
a flash X-ray source, such as dose, dose rate, spectrum, pulse
dures for the system’s use.
width, etc., such that typically no single dosimetry system can
measure all the parameters simultaneously. However, it is
3.4 DUT—device under test. This is the electronic compo-
nent or system being tested to determine its performance frequently the case that not all key parameters must be
measured in a given experiment.
during and/or after irradiation.
3.5 endpoint energy—endpoint energy refers to the peak
5. General Characteristics of Flash X-ray Sources
energy of the electron beam, usually in MeV, generated in a
5.1 Flash X-ray Overview—Flash X-ray sources operate
flash X-ray source and is equal to the terminal voltage of the
like a dental X-ray source but at much higher voltages and
accelerator in megavolts (MV). The word “endpoint” refers to
intensities and usually in a single, very short burst, see ICRU
the highest photon energy of the bremsstrahlung spectra, and
Report 17. A high voltage is developed across an anode-
this endpoint is equal to the maximum or peak in the electron
cathode gap (the diode) and field emission creates a pulsed
energy. For example, if the most energetic electron that strikes
electron beam traveling from the cathode to the anode. A
the converter is 10 MeV, this electron produces a range of
high-atomic-number element such as tantalum is placed on the
bremsstrahlung photon energies but the maximum energy of
anode to maximize the production of bremsstrahlung created
any photon is equal to 10 MeV, the endpoint energy. Most
when the electrons strike the anode. Graphite or aluminum is
photons have energies one tenth to one third of the maximum
usually placed downstream of the converter to stop the electron
electron energy for typical flash X-ray sources in the 1 MV to
beam completely but let the X-radiation pass through. Finally,
10 MV endpoint voltage region, respectively.
a debris shield made of Kevlar or low-density polyethylene is
3.6 endpoint voltage—Endpoint voltage refers to the peak
sometimes necessary to stop exploding converter material from
voltage across a bremsstrahlung diode in a flash X-ray source.
leaving the source. All of these components taken together
For example, a 10-MV flash X-ray source is designed to reach
form what is commonly called a bremsstrahlung diode.
a peak voltage of 10 MV across the anode-cathode gap which
5.2 Relationship Between Flash X-ray Diode Voltage and
generates the electron beam for striking a converter to produce
X-ray Energy of Bremsstrahlung—Flash X-ray sources produce
bremsstrahlung.
bremsstrahlung by generating an intense electron beam which
3.7 equilibrium absorbed dose—absorbed dose within some
then strikes a high atomic number (Z) converter such as
incremental volume in the target material in which the condi-
tantalum. The electron-solid interactions produce “braking”
tion of electron equilibrium (the energies, number, and direc-
radiation or, in German, bremsstrahlung. Fig. 1 shows the
tion of charged particles induced by the radiation are constant
typical range of photon energies produced by flash X-ray
throughout the volume) exists. For lower electron energies,
sources with different electron endpoint energies. The data in
where bremsstrahlung production is negligible, the equilibrium
Fig. 1 is generated by tallying the photon spectrum using ITS
absorbed dose is equal to the kerma. 5
with optimized tantalum/carbon bremsstralung converters (1).
If the average radiation produced is in the 20 to 100 keV
NOTE 1—For practical purposes, assuming the spatial gradient in the
X-ray field is small over the range of the maximum energy secondary
region, the source is said to be a “medium X-ray simulator.” If
electrons generated by the incident photons, the equilibrium absorbed
the average photon energy is in the 100 to 300 keV region, the
dose is the absorbed dose value that exists in a material at a distance from
term used is “hard X-ray simulator.” At the high end of the
any interface with another material greater than this range.
flash X-ray range are sources which produce an average photon
4. Significance and Use energy of around 2 MeV. Because this photon energy is in the
typical gamma-ray spectral range, the source is called a
4.1 Flash X-ray facilities provide intense bremsstrahlung
“gamma-ray simulator.”
radiation environments, usually in a single sub-microsecond
5.2.1 The average energy of the bremsstrahlung spectrum,
pulse, which often fluctuates in amplitude, shape, and spectrum
¯
E , through an optimized converter can be estimated using
photon
from shot to shot. Therefore, appropriate dosimetry must be
the following relationship (1):
fielded on every exposure to characterize the environment, see
ICRU Report 34. These intense bremsstrahlung sources have a ¯
=
E 5 k· ε where 5.1,k,18.9 (1)
photon
variety of applications which include the following:
¯
where E is the average energy of the bremsstrahlung
photon
(1) Studies of the effects of X-rays and gamma rays on
photons in keV and ε is the average energy of the electrons in
materials.
(2) Studies of the effects of radiation on electronic devices
such as transistors, diodes, and capacitors.
The boldface numbers in parentheses refer to the list of references at the end of
(3) Computer code validation studies. this standard.
E1894 − 24
FIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray Sources with Optimized Bremsstrahlung Converters
the electron beam incident on the converter in keV. The value 6.3.1 Secondary Electrons—Both in the case of absorbed
of k depends on the converter thickness; thin targets will have dose in the DUT and absorbed dose in the dosimeter, the
values at the lower end of the range, while thick targets energy is deposited largely by secondary electrons. That is, the
optimized for higher incident energies will have values at the
incident photons interact with the material of, or surrounding,
upper end. When an optimized bremsstrahlung converter is
the DUT or the dosimeter and lose energy to Compton
used, a rule-of-thumb may be used that the average photon
electrons, photoelectrons, and Auger electrons. The energy
1 1
energy is about ⁄5 or ⁄6 of the electron endpoint energy (1). For
which is finally deposited in the material is deposited by these
a fixed converter design, the photon energy away from the
secondary particles.
optimization point is roughly proportional to the square root of
6.3.2 Transport of Photons—In some cases, it is necessary
the electron endpoint energy with the proportionality factor
to consider the transport and loss of photons as they move to
varying between about 5 and 19 depending upon the design
the region whose absorbed dose is being determined. A
point (1). This equation and Fig. 1 indicate that most of the
correction for the attenuation of an incident photon beam is an
photons have energies much less than the endpoint electron
example of such a consideration.
energy, or in voltage units, the flash X-ray voltage.
6.3.3 Transport of Electrons—Electron transport may cause
Additionally, the bremsstrahlung spectrum is very non-
energy originally imparted to electrons in one region to be
Gaussian so caution must be exercised in using the average
carried to a second region depending on the range of the
energy of the distribution for dosimetry planning.
electrons. As a result, it is necessary to consider the transport
6. Measurement Principles
and loss of electrons as they move into and out of the regions
whose absorbed dose is being determined. In particular, it is
6.1 Typically in flash X-ray irradiations, one is interested in
necessary to distinguish between equilibrium and non-
some physical change in a critical region of a device under test
equilibrium conditions for electron transport.
(DUT). The dosimetry associated with the study of such a
physical change may be broken into three parts:
6.3.3.1 Charged Particle Equilibrium—Occurs when the
(1) Determine the absorbed dose in a dosimeter.
numbers, energies, and angles of particles transported into a
(2) Using the dosimeter measurement, estimate the ab-
region of interest are approximately balanced by those trans-
sorbed dose in the region and material of interest in the DUT.
ported out of that region. (See “Equilibrium Absorbed Dose” in
(3) If required, relate the estimated absorbed dose in the
3.7.)
DUT to the physical change of interest (holes trapped, interface
6.3.3.2 Dose Enhancement—Because photoelectron produc-
states generated, photocurrent produced, etc.).
tion per atom is roughly proportional to the atomic number
6.2 This section will be concerned with the first two of the
raised to the fourth power for energies less than 100 keV (2),
above listed parts of dosimetry: (1) what is necessary to
one expects more photoelectrons to be produced in high atomic
determine a meaningful absorbed dose for the dosimeter, and
number layers than in low atomic number layers for the same
(2) what is necessary to extrapolate this measured dose to the
photon fluence and spectrum. Thus, there may be a net flow of
estimated dose in the region of interest. The final step in
energetic electrons from the high atomic number layers into the
dosimetry, associating the absorbed dose with a physical
low atomic number layers. This non-equilibrium flow of
change of interest, is outside the scope of this guide.
electrons may result in an enhancement of the dose in the low
6.3 Energy Deposition: atomic number layer. Dose enhancement problems are often
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