ASTM E1894-97(2002)
(Guide)Standard Guide for Selecting Dosimetry Systems for Application in Pulsed X-Ray Sources
Standard Guide for Selecting Dosimetry Systems for Application in Pulsed X-Ray Sources
SIGNIFICANCE AND USE
Flash x-ray facilities provide intense bremsstrahlung radiation environments, usually in a single sub-microsecond pulse, which unfortunately, often fluctuates in amplitude, shape, and spectrum from shot to shot. Therefore, appropriate dosimetry must be fielded on every exposure to characterize the environment. These intense bremsstrahlung sources have a variety of applications which include the following:
5.1.1 Generation of x–ray and gamma–ray environments similar to that from a nuclear weapon burst.
5.1.2 Studies of the effects of x–rays and gamma rays on materials.
5.1.3 Studies of the effects of radiation on electronic devices such as transistors, diodes, and capacitors.
5.1.4 Vulnerability and survivability testing of military systems and components.
5.1.5 Computer code validation studies.
This guide is written to assist the experimenter in selecting the needed dosimetry systems (often in an experiment not all radiation parameters must be measured) 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 3) 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., such that typically no single dosimetry system can measure all the parameters simultaneously.
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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E 1894 – 97 (Reapproved 2002)
Standard Guide for
Selecting Dosimetry Systems for Application in Pulsed
X-Ray Sources
This standard is issued under the fixed designation E 1894; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope E 170 Terminology Relating to Radiation Measurements
and Dosimetry
1.1 This guide provides assistance in selecting and using
E 665 Practice for Determining Absorbed Dose Versus
dosimetry systems in flash x-ray experiments. Both dose and
Depth in Materials Exposed to the X–ray Output of Flash
dose–rate techniques are described.
X–ray Machines
1.2 Operating characteristics of flash x–ray sources are
E 666 PracticeforCalculatingAbsorbedDosefromGamma
given, with emphasis on the spectrum of the photon output.
or X Radiation
1.3 Assistanceisprovidedtorelatethemeasureddosetothe
E 668 Practice for theApplication of Thermoluminescence-
response of a device under test (DUT). The device is assumed
–Dosimetry (TLD) Systems for Determining Absorbed
to be a semiconductor electronic part or system.
Dose in Radiation–Hardness Testing of Electronic De-
2. Contents
vices
E 1249 Practice for Minimizing Dosimetry Errors in Radia-
2.1 Section 1: Scope of guide.
tion Hardness Testing of Silicon Electronic Devices Using
2.2 Section 2: Outline.
Co–60 Sources
2.3 Section 3: Related ASTM and ICRU documents.
E 1261 Guide for Selection and Calibration of Dosimetry
2.4 Section 4: Definition of terms.
Systems for Radiation Processing
2.5 Section 5: Significance and use of this document for the
E 1275 Practice for Use of a Radiochromic Film Dosimetry
selection of dosimetry systems for use in pulsed x–ray sources.
System
2.6 Section 6: Description of large flash x–ray sources and
E 1310 Practice for Use of a Radiochromic Optical
their characteristics.
Waveguide Dosimetry System
2.7 Section 7: Measurement principles with an emphasis on
3.2 International Commission on Radiation Units (ICRU)
obtaining absorbed dose measurements for different spectral
and Measurements Reports:
conditions in the dosimeter, the DUT, and the relationship
ICRU Report 14–Radiation Dosimetry: X rays and Gamma
between them.
RayswithMaximumPhotonEnergiesBetween0.6and50
2.8 Section 8: The primary information in this guide. The
MeV
experimenterwillfinddetailsoneachdosimetrysystem.Listed
ICRU Report 17–Radiation Dosimetry: X rays Generated at
are details such as: 1) how the dosimeters works, i.e., physical
Potentials of 5 to 150 kV
principles, 2) typical applications or instrumentation configu-
ICRU Report 33–Radiation Quantities and Units
rations, 3) advantages, 4) limitations, 5) sensitivity 6) proce-
ICRU Report 34–The Dosimetry of Pulsed Radiation
dures for calibration and proper use and finally reproducibility
and accuracy.
4. Terminology
2.9 Section 9: Suggested documentation requirements.
4.1 Absorbed Dose—quotient of de¯/dm, where de¯ is the
2.10 Section 10: Description of how the experimenter de-
mean energy imparted by ionizing radiation to matter of mass
termines uncertainty in the dosimetry measurements.
dm:
2.11 Section 11: References.
d
D 5 e¯ . (1)
3. Referenced Documents
dm
3.1 ASTM Standards:
The special name for the unit for absorbed dose is the gray
(Gy).
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
Technology and Applications and is the direct responsibility of Subcommittee Annual Book of ASTM Standards, Vol 12.02.
94E 10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices. Available from the International Commission on Radiation Units and Measure-
Current edition approved June 10, 1997. Published July 1998. ments, 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.
E 1894
1Gy 5 1J/kg. (2)
5. Significance and Use
Formerly, the special unit for absorbed dose was the rad,
5.1 Flash x-ray facilities provide intense bremsstrahlung
where 1 rad = 100 erg/g.
radiation environments, usually in a single sub-microsecond
pulse, which unfortunately, often fluctuates in amplitude,
1 rad 5 0.01 Gy. (3)
shape, and spectrum from shot to shot. Therefore, appropriate
Because the magnitude of the absorbed dose is material
dosimetry must be fielded on every exposure to characterize
dependent, it is important to include the material composition
the environment. These intense bremsstrahlung sources have a
for which the dose is being reported, e.g., 15.3 Gy(LiF).
variety of applications which include the following:
4.2 AbsorbedDoseEnhancement—increase(ordecrease)in
5.1.1 Generation of x–ray and gamma–ray environments
the absorbed dose (as compared to the equilibrium absorbed
similar to that from a nuclear weapon burst.
dose) at a point in a material of interest. This can be expected
5.1.2 Studies of the effects of x–rays and gamma rays on
to occur near an interface with a material of higher or lower
materials.
atomic number.
5.1.3 Studiesoftheeffectsofradiationonelectronicdevices
4.3 Converter—a target for electron beams, generally of a
such as transistors, diodes, and capacitors.
high atomic number material, in which bremsstrahlung x rays
5.1.4 Vulnerability and survivability testing of military
are produced by radiative energy losses of the incident elec-
systems and components.
trons.
5.1.5 Computer code validation studies.
4.4 Dosimeter—A device that, when irradiated, exhibits a
5.2 This guide is written to assist the experimenter in
quantifiable change in some property of the device which can
selectingtheneededdosimetrysystems(ofteninanexperiment
be related to absorbed dose in a given material using appro-
not all radiation parameters must be measured) for use at
priate analytical instrumentation and techniques.
pulsed x–ray facilities. This guide also provides a brief
4.5 Dosimetry System—A system used for determining
summary of the information on how to use each of the
absorbed dose, consisting of dosimeters, measurement instru-
dosimetry systems. Other guides (see Section 3) provide more
ments,andtheirassociatedreferencestandards,andprocedures
detailedinformationonselecteddosimetrysystemsinradiation
for the system’s use.
environments and should be consulted after an initial decision
4.6 DUT—Device under test. This is the electronic compo-
is made on the appropriate dosimetry system to use. There are
nent or system tested to determine its performance during or
many key parameters which describe a flash x-ray source, such
after irradiation.
as dose, dose rate, spectrum, pulse width, etc., such that
4.7 Endpoint Energy—Endpoint energy refers to the peak
typically no single dosimetry system can measure all the
energy of the electron beam, usually in MeV, generated in a
parameters simultaneously.
flash x–ray source and is numerically equal to the endpoint
voltage in MV. The word endpoint refers to the highest photon
6. General Characteristics of Flash X-ray Sources
energy of the bremsstrahlung spectra, and this endpoint is
6.1 Flash X-ray Facility Considerations
equal to the maximum or peak in the electron energy. For
Flash x–ray sources operate like a dental x–ray source but at
example, if the most energetic electron that strikes the con-
much higher voltages and intensities and usually in a single,
verteris10MeV,thiselectronproducesarangeofbremsstrahl-
very short burst. A high voltage is developed across an
ung photon energies but the maximum energy of any photon is
equal to 10 MeV, the endpoint energy. Most photons have anode-cathode gap (the diode) and field emission creates a
pulsed electron beam traveling from the cathode to the anode.
energies one-tenth to one-third of the maximum electron
energy for typical flash x-ray sources in the 10 MV to 1 MV A high atomic–number element such as tantalum is placed on
the anode to maximize the production of bremsstrahlung
endpoint voltage region, respectively.
created when the electrons strike the anode. Graphite is usually
4.8 Endpoint Voltage—Endpoint voltage refers to the peak
placed downstream of the converter to stop the electron beam
voltage across a bremsstrahlung diode in a flash x-ray source.
completelybutletthexradiationpassthrough.Finally,adebris
For example, a 10-MV flash x-ray source is designed to reach
shield is sometimes necessary to stop exploding converter
a peak voltage of 10-MV across the anode-cathode gap which
material from leaving the source. All of these components
generates the electron beam for striking a converter to produce
taken together form what is commonly called a bremsstrahlung
bremsstrahlung.
diode.
4.9 Equilibrium Absorbed Dose—absorbed dose at some
6.2 Relationship Between Flash X-ray Diode Voltage and
incremental volume within the material in which the condition
X-ray Energy of Bremsstrahlung
of electron equilibrium (the energies, number, and direction of
Flash x-ray sources produce bremsstrahlung by generating an
charged particles induced by the radiation are constant
intense electron beam which then strikes a high atomic number
throughout the volume) exists. For lower energies where
(Z) converter such as tantalum. The electron-solid interactions
bremsstrahlung production is negligible the equilibrium ab-
sorbed dose is equal to the kerma. produce “braking” radiation or, in German, bremsstrahlung.
Fig. 1 shows the typical range of photon energies produced by
NOTE 1—For practical purposes, assuming the spatial gradient in the
three different sources. If the average radiation produced is in
x-ray field is small over the range of the maximum energy secondary
the 20–100 keVregion, the source is said to be a medium–hard
electrons generated by the incident photons, the equilibrium absorbed
x–ray simulator. If the average photon energy is in the
dose is the absorbed dose value that exists in a material at a distance from
any interface with another material greater than this range. 100–300–keV region, the term used is “hard x–ray simulator.”
E 1894
FIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray Sources
At the high end of the flash x–ray range are sources which 7.3.1 Secondary Electrons—Both in the case of absorbed
produce an average photon energy of around 2 MeV. Because dose in the DUT and absorbed dose in the dosimeter, the
this photon energy is in the typical gamma-ray spectral range, energy is deposited largely by secondary electrons. That is, the
the source is called a gamma–ray simulator. incident photons interact with the material of, or surrounding,
¯
the DUT or the dosimeter and lose energy to Compton
The average energy of the bremsstrahlung spectrum, E ,
photon
electrons, photoelectrons, and Auger electrons. The energy
through an optimized converter (1) in the medium–hard x–ray
¯
which is finally deposited in the material is deposited by these
region (50 keV < E > 500 keV) is given empirically by,
photon
secondary particles.
1/2
¯
E ' 5 e (4)
photon
7.3.2 Transport of Photons—In some cases, it is necessary
¯
where E is the average energy of the bremsstrahlung
to consider the transport and loss of photons as they move to
photon
photons in keV and e is the average energy of the electrons in the region whose absorbed dose is being determined. A
the electron beam incident on the converter in keV. This
correction for the attenuation of an incident photon beam is an
equation and Fig. 1 indicate that most of the photons have example of such a consideration.
energies much less than the endpoint electron energy, or in
7.3.3 Transport of Electrons—Electron transport may cause
voltage units, the flash x–ray voltage.
energy originally imparted to electrons in one region to be
carried to a second region depending on the range of the
7. Measurement Principles
electrons. As a result, it is necessary to consider the transport
and loss of electrons as they move into and out of the regions
7.1 Typically in flash x–ray irradiations, one is interested in
whose absorbed dose is being determined. In particular, it is
some physical change in a critical region of a device under test
necessary to distinguish between equilibrium and non-
(DUT). The dosimetry associated with the study of such a
equilibrium conditions for electron transport.
physical change may be broken into three parts:
7.3.3.1 Charged Particle Equilibrium—In some cases, the
7.1.1 Determine the absorbed dose in a dosimeter.
7.1.2 Using the dosimeter measurement, estimate the ab- numbers, energies, and angles of particles transported into a
region of interest are approximately balanced by those trans-
sorbed dose in the region and material of interest in the DUT.
7.1.3 If required, relate the estimated absorbed dose in the portedoutofthatregion.Suchcasesformanimportantclassof
limiting cases which are particularly easy to interpret. (See
DUTtothephysicalchangeofinterest(holestrapped,interface
“Equilibrium Absorbed Dose” in Section 4.6.)
states generated, photocurrent produced, etc.)
7.2 This section will be concerned with the first two of the 7.3.3.2 Dose Enhancement—Because photoelectron pro-
above listed parts of dosimetry: (1) what is necessary to duction per atom is roughly proportional to the atomic number
determine a meaningful absorbed dose for the dosimeter and raised to the fourth power for energies less than 100 keV (2),
(2) what is necessary to extrapolate this measured dose to the oneexpectsmorephotoelectronstobeproducedinhighatomic
estimated dose in the region of interest. The final step in number layers than in low atomic number layers for the same
dosimetry, associating the absorbed dose with a physical photon fluence and spectrum. Thus, there may be a net flow of
change of interest, is outside the scope of this guide. energeticelectronsfromthehighatomicnumberlayersintothe
7.3 Energy Deposition low atomic number layers. This non–equilibrium flow of
E 1894
electrons may result in an enhancement of the dose in the low stopping power for the electrons in the TLD material and the
atomic number layer. Dose enhancement problems are often material of the equilibrating layer.)
caused by high atomic number bonding layers (e.g., gold), and
7.4.2.4 Intermediate Cases
metallization layers (e.g., W–Si or Ta–Si).
7.4.2.4.1 The intermediate cases, where secondary electron
7.4 Absorbed Dose in Dosimeter ranges are neither small nor large in comparison to the
7.4.1 Equilibrium Absorbed Dose in Dosimeter dosimeter size, are cases where non
...
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