ASTM E1250-88(2005)

Standard Test Method for Application of Ionization Chambers to Assess the Low Energy Gamma Component of Cobalt-60 Irradiators Used in Radiation-Hardness Testing of Silicon Electronic Devices

SIGNIFICANCE AND USE
Although Co-60 nuclei only emit monoenergetic gamma rays at 1.17 and 1.33 MeV, the finite thickness of sources, and encapsulation materials and other surrounding structures that are inevitably present in irradiators can contribute a substantial amount of low-energy gamma radiation, principally by Compton scattering (1, 2).3 In radiation-hardness testing of electronic devices this low-energy photon component of the gamma spectrum can introduce significant dosimetry errors for a device under test since the equilibrium absorbed dose as measured by a dosimeter can be quite different from the absorbed dose deposited in the device under test because of absorbed dose enhancement effects (3, 4). Absorbed dose enhancement effects refer to the deviations from equilibrium absorbed dose caused by non-equilibrium electron transport near boundaries between dissimilar materials.
The ionization chamber technique described in this method provides an easy means for estimating the importance of the low-energy photon component of any given irradiator type and configuration.
When there is an appreciable low-energy spectral component present in a particular irradiator configuration, special experimental techniques should be used to ensure that dosimetry measurements adequately represent the absorbed dose in the device under test. (See Practice E 1249.)
SCOPE
1.1 Low energy components in the photon energy spectrum of Co-60 irradiators lead to absorbed dose enhancement effects in the radiation-hardness testing of silicon electronic devices. These low energy components may lead to errors in determining the absorbed dose in a specific device under test. This method covers procedures for the use of a specialized ionization chamber to determine a figure of merit for the relative importance of such effects. It also gives the design and instructions for assembling this chamber.
1.2 This method is applicable to measurements in Co-60 radiation fields where the range of exposure rates is 7 10 6 to 3 102 C kg 1 s1 (approximately 100 R/h to 100 R/s). For guidance in applying this method to radiation fields where the exposure rate is >100 R/s, see . Note 1See Terminology E 170 for definition of exposure and its units.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Dec-2004
• ICS: 31.020 - Electronic components in general
• Technical Committee: E10 - Nuclear Technology and Applications
• Drafting Committee: E10.07 - Radiation Dosimetry for Radiation Effects on Materials and Devices

Relations

• Replaces: ASTM E1250-88(2000) - Standard Test Method for Application of Ionization Chambers to Assess the Low Energy Gamma Component of Cobalt-60 Irradiators Used in Radiation-Hardness Testing of Silicon Electronic Devices
• Effective Date: 01-Jan-2005
• Replaced By: ASTM E1250-10 - Standard Test Method for Application of Ionization Chambers to Assess the Low Energy Gamma Component of Cobalt-60 Irradiators Used in Radiation-Hardness Testing of Silicon Electronic Devices
• Effective Date: 01-Dec-2010
• Referred By: ASTM F1892-12(2018) - Standard Guide for Ionizing Radiation (Total Dose) Effects Testing of Semiconductor Devices
• Effective Date: 01-Jan-2005
• Referred By: ASTM F1190-18 - Standard Guide for Neutron Irradiation of Unbiased Electronic Components
• Effective Date: 01-Jan-2005
• Referred By: ASTM E1854-19 - Standard Practice for Ensuring Test Consistency in Neutron-Induced Displacement Damage of Electronic Parts
• Effective Date: 01-Jan-2005
• Referred By: ASTM E1249-15(2021) - Standard Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon Electronic Devices Using Co-60 Sources
• Effective Date: 01-Jan-2005

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: E1250 – 88 (Reapproved 2005)
Standard Test Method for
Application of Ionization Chambers to Assess the Low
Energy Gamma Component of Cobalt-60 Irradiators Used in
Radiation-Hardness Testing of Silicon Electronic Devices
This standard is issued under the fixed designation E1250; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E170 TerminologyRelatingtoRadiationMeasurementsand
Dosimetry
1.1 Low energy components in the photon energy spectrum
E668 Practice for Application of Thermoluminescence-
ofCo-60irradiatorsleadtoabsorbeddoseenhancementeffects
Dosimetry(TLD)SystemsforDeterminingAbsorbedDose
in the radiation-hardness testing of silicon electronic devices.
in Radiation-Hardness Testing of Electronic Devices
These low energy components may lead to errors in determin-
E1249 Practice for Minimizing Dosimetry Errors in Radia-
ing the absorbed dose in a specific device under test. This
tion Hardness Testing of Silicon Electronic Devices Using
method covers procedures for the use of a specialized ioniza-
Co-60 Sources
tion chamber to determine a figure of merit for the relative
importance of such effects. It also gives the design and
3. Terminology
instructions for assembling this chamber.
3.1 absorbed dose, D—quotient of d ´¯by dm, where d ´¯is
1.2 This method is applicable to measurements in Co-60
−6
themeanenergyimpartedbyionizingradiationtothematterin
radiation fields where the range of exposure rates is 7 310
−2 −1 −1
a volume element and dm is the mass of matter in that volume
to3 310 Ckg s (approximately100R/hto100R/s).For
element.
guidance in applying this method to radiation fields where the
D 5 d´¯/dm (1)
exposure rate is >100 R/s, see Appendix X1.
3.2 absorbed dose enhancement factor— ratio of the ab-
NOTE 1—See Terminology E170 for definition of exposure and its
units. sorbed dose at a point in a material of interest to the
equilibrium absorbed dose in that same material.
1.3 The values stated in SI units are to be regarded as the
3.3 average absorbed dose—mass-weighted mean of the
standard. The values given in parentheses are for information
absorbed dose over a region of interest.
only.
3.4 average absorbed dose enhancement factor—ratio of
1.4 This standard does not purport to address all of the
the average absorbed dose in a region of interest to the
safety concerns, if any, associated with its use. It is the
equilibrium absorbed dose.
responsibility of the user of this standard to establish appro-
3.5 dosimeter—any device used to determine the equilib-
priate safety and health practices and determine the applica-
rium absorbed dose in the material and at the irradiation
bility of regulatory limitations prior to use.
position of interest. Examples of such devices include ther-
moluminescence dosimeters (TLDs), liquid chemical dosim-
2. Referenced Documents
2 eters, and radiochromic dye films. (See Practice E668, for a
2.1 ASTM Standards:
discussion of TLDs.)
3.6 equilibrium absorbed dose—absorbed dose at some
This method is under the jurisdiction of ASTM Committee E10 on Nuclear
incremental volume within the material in which the condition
Technology and Applications and is the direct responsibility of Subcommittee
of electron equilibrium (the energies, number, and direction of
E10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.
charged particles induced by the radiation are constant
Current edition approved Jan. 1, 2005. Published January 2005. Originally
approved in 1988. Last previous approved in 2000 as E1250-88(2000). DOI:
throughout the volume) exists. (See Terminology E170.)
10.1520/E1250-88R05.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1250 – 88 (2005)
4. Significance and Use
4.1 AlthoughCo-60nucleionlyemitmonoenergeticgamma
rays at 1.17 and 1.33 MeV, the finite thickness of sources, and
encapsulation materials and other surrounding structures that
areinevitablypresentinirradiatorscancontributeasubstantial
amount of low-energy gamma radiation, principally by Comp-
tonscattering(1,2). Inradiation-hardnesstestingofelectronic
devices this low-energy photon component of the gamma
spectrum can introduce significant dosimetry errors for a
device under test since the equilibrium absorbed dose as
measured by a dosimeter can be quite different from the
absorbed dose deposited in the device under test because of
absorbed dose enhancement effects (3, 4). Absorbed dose
enhancement effects refer to the deviations from equilibrium
FIG. 1 Schematic Diagram of Experimental Setup
absorbed dose caused by non-equilibrium electron transport
near boundaries between dissimilar materials.
6. Procedure
4.2 The ionization chamber technique described in this
6.1 Assemble the ionization chamber, bias supply, and
method provides an easy means for estimating the importance
electrometer as shown in Fig. 1.
of the low-energy photon component of any given irradiator
6.2 Turn on the bias supply, set the voltage to at least 60 V,
type and configuration.
and ensure that there is no appreciable leakage current (I -
4.3 When there is an appreciable low-energy spectral com-
leak
age< 0.1 pA). Turn the bias supply off.
ponent present in a particular irradiator configuration, special
6.3 Assemble the ionization chamber with the gold/
experimental techniques should be used to ensure that dosim-
aluminum electrodes (the gold sides facing the inside of the
etry measurements adequately represent the absorbed dose in
chamber). Place the ionization chamber in the irradiation
the device under test. (See Practice E1249.)
position of interest. For directional sources, position the
ionization chamber so that the direction of the main beam is
5. Apparatus
perpendicular to the electrode plates.
5.1 Ionization Chamber,aspeciallyfabricatedparallel-plate
6.4 Turn on the bias supply and measure the ionization
ionization chamber with interchangeable gold and aluminum
current, I , with the gold/aluminum electrodes in place, gold
Au
electrodes. A specific design is described in Appendix X2.
side facing inward.
5.2 Bias Supply, a battery or power supply capable of
6.5 Repeat steps 6.3 and 6.4 with aluminum electrodes and
delivering 60 to 100 V dc at a current up to 1 mA.
measure the ionization current I . The ionization chamber
Al
5.3 Electrometer, an electrometer or picoammeter capable
location and orientation shall be the same for both measure-
of measuring currents as low as 30 pA with a resolution of at
ments.
least 0.1 pA.
6.6 Calculate the ionization current ratio a as follows:
5.4 Twinaxial Cable, the twinaxial cable that connects the
a5 I / I (2)
Au Al
ionization chamber to the bias supply and electrometer is an
This ratio provides a figure of merit for the particular Co-60
integral part of the ionization chamber (see Fig. 1).
irradiator configuration under investigation.
NOTE 2—TheionizationchamberdimensionsgiveninAppendixX2are
appropriate to TWC 78-2 twinaxial cable. This cable has the following NOTE 3—Since the relationship between ionization chamber current
physical dimensions (all dimensions given in inches): and exposure rate depends on such environmental factors as temperature,
atmospheric pressure, and relative humidity, it is important to make the
Nominal outer diameter 0.242
Conductor spacing (center to center) 0.076 twomeasurementsofI andI asnearlyatthesametimeaspossibleto
Au Al
Conductor dielectric outer diameter 0.076
minimize the influence of environmental factors on the ratio I /I .
Au Al
Conductor diameter 0.037
7. Interpretation of Measurement Results
Other equivalent twinaxial cable types can be used, but the applicable
7.1 Low values of the figure of merit, a ('2 to 2.5) are
dimensionsoftheionizationchamberbody,clamp,stem,andcableclamp
nut in Appendix X2 must then be adjusted.
indicative of a relatively small low-energy photon component,
and high values of a (>5) indicate a very large low-energy
5.5 Triaxial Cable, the triaxial cable that connects the
photon component. Appendix X3 gives a table of measured
ionization chamber and the bias supply to the electrometer is
values of a for a variety of typical Co-60 irradiator facilities
usually supplied with the electrometer, and must be of a type
and experimental arrangements.
that is compatible with the electrometer type used (see Fig. 1).
NOTE 4—Monoenergetic 1.25 MeV photon radiation would theoreti-
callyproduceavalueof a=1.6.Althoughthisvalueisnotattainablewith
any realistic Co-60 irradiator configuration, it is a theoretical lower limit
The boldface numbers in parentheses refer to the list of references appended to
on a.
this test method.
7.2 If the measured value of a is >2.5, steps 6.1-6.5 should
Available from Trompeter Electronics, 31186 La Baya Dr., Westlake Village,
CA91362-4047. be repeated with the ionization chamber surrounded by a filter
E1250 – 88 (2005)
can or box of 1.5 to 2.0 mm (approximately 0.063 in.) of lead
on the outside and 0.7 to 1.0 mm (approximately 0.030 in.) of
aluminumontheinside.Useofsuchafilterwillnormallygive
a significant reduction in the low-energy component of the
spectrum (see Practice E1249).
7.3 By repeating the procedure for a number of source
configurations and filter options, the experimental conditions
can be determined that minimize the low-energy photon
component of the source spectrum and thus minimize the
dosimetry errors for the device under test.
8. Application to Hardness Testing
8.1 Estimating the Absorbed Dose Enhancement Factor:
8.1.1 Although it is not possible to determine the absorbed
dose enhancement factor for a particular geometry of a device
undertestusingthismethod,thefigureofmerit, a,canbeused
toestimateanupperboundfortheabsorbeddoseenhancement
factor near an interface between any two materials (5).
8.1.2 Aspecificexampleofrelatingthefigureofmerit, a,to
theabsorbeddoseenhancementisgivenin8.1.4forthecaseof
asilicon-goldinterface.Thisexampleisofparticularinterestin
radiation-hardnesstestingofsiliconelectronicdevicesbecause
it does exist for many devices, and is a worst-case configura-
tion.
NOTE 5—Silicon-gold interfaces in electronic devices typically consist
of relatively thin layers; however, the case considered here is an interface
between two layers each having a thickness capable of producing
absorbed dose equilibrium. This case has been used because it represents
aconfigurationthatisrelativelyeasytocalculate.Further,itgivesaworst
FIG. 2 Relationship for Estimating Absorbed Dose Enhancement
case estimate of the absorbed dose enhancement factor for a silicon-gold
Factor in Silicon at a Silicon-Gold Interface From the Ionization
interface.
Current Ratio
8.1.3 Theabsorbeddoseenhancementfactorattheinterface
is defined by the following:
case, the corresponding estimated absorbed dose enhancement
factorwouldbeabout3.0;therefore,neglectingthelowenergy
F ~Si:Au!5 D ~IF!/D ~eq! (3)
DE Si Si
spectral component would lead to a dosimetry error for a
where:
device under test of as much as a factor of 1.8. For such a
D (IF) = absorbed dose in silicon immediately adjacent
Si
configuration, the use of a lead-aluminum filter box would
to the silicon-gold interface, and
minimize the dosimetry error, and, therefore should be consid-
D (eq) = equilibrium absorbed dose in silicon.
Si
ered (see Practice E1249).
8.1.4 The relationship between the ionization current ratio,
8.2 Selecting a Lead-Aluminum Filter for Spectrum Hard-
a, and an estimate of F (Si:Au) is shown in Fig. 2.The basis
DE
ening:
for this relationship is discussed briefly in Appendix X4.
8.2.1 Except for very soft spectra, the use of a filter box of
1.5to2.0mm('0.063in.)ofleadonthesourceside,followed
NOTE 6—Based on the assumptions inherent in Fig. 2 and Appendix
X4, monoenergetic 1.25 MeV photon radiation will produce a value of by 0.7 to 1.0 mm ('0.030 in.) of aluminum on the test object
F (Si:Au)=1.64. Such a low value is not attainable in any practical
DE side, (see Practice E1249), will harden the spectrum suffi-
Co-60 irradiator configuration.
ciently to reduce a to#2.5 (see Table X3.1). This value of a
8.1.5 An estimated absorbed dose enhancement factor at a corresponds to a dosimetry error of less than 10%.
gold-silicon interface irradiated by a practical Co-60 source 8.2.2 Agreater wall thickness of lead for the filter box than
may be obtained by using Fig. 2. For example, a measured specified in 8.2.1 should be considered for a source configu-
ionization current ratio of 2.5 would be considered a good ration having a large fraction of low-energy photon compo-
figureofmeritforagivenirradiatorconfiguration.Inthiscase, nents; that is, for a > 6. For example, a wall thickness of 3.2
Fig. 2 gives an estimate of the absorbed dose enhancement mm('0.125in.)ofleadmaybeusefulforthecasesofthelast
factor of about 1.8 as compared to an estimated absorbed dose three entries in Table X3.1.
enhancement factor of 1.64 for monoenergetic 1.25 MeV
9. Precision and Bias
gamma radiation; therefore, the dosimetry error for a device
under test incurred by neglecting the low energy photon 9.1 The lowest ionization chamber current to which this
−6
component would be about 10%. On the other hand, a method is applicable is 30 pA (corresponding to 7 310 C
−1 −1
measured ionization current ratio of 7.5 would be considered a kg s [approximately100R/h]),whichcanbemeasuredwith
poorfigureofmeritforanotherirradiatorconfiguration.Inthis aprecisionof0.5pAor 61.7%,asspecifiedbytheinstrument
E1250 – 88 (2005)
manufacturer. The ratio I /I can therefore be determined to 10. Keywords
Au Al
an overall uncertainty of 62.4% or better.
10.1 absorbed dose; Co-60 irradiators; dose enhancement;
9.2 This method provides a figure of merit usable for
ionization chamber; radiation hardness testing
comparing various source configurations, and for assessing the
relative improvement that is achievable with a lead-aluminum
filter. This method gives no quantitative information about
absorbeddoseenhancementfactorotherthananestimateofits
upper limit.
APPENDIXES
(Nonmandatory Information)
X1. APPLICATION OF THIS METHOD TO HIGH EXPOSURE RATES
−3 −1
X1.1 Thelimitsofapplicabilityofthismethodgivenin1.2 ˙
X = ex
...