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

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 X 10 -6  to 3 X 10 -2  C kg -1  s -1  (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 Appendix X1. Note 1-See Terminology E170 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.
1.4 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: 09-Jun-2000
• 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

• Replaced By: 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
• 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: 10-Jun-2000
• Referred By: ASTM F1190-18 - Standard Guide for Neutron Irradiation of Unbiased Electronic Components
• Effective Date: 10-Jun-2000
• Referred By: ASTM F1892-12(2018) - Standard Guide for Ionizing Radiation (Total Dose) Effects Testing of Semiconductor Devices
• Effective Date: 10-Jun-2000
• Referred By: ASTM E1854-19 - Standard Practice for Ensuring Test Consistency in Neutron-Induced Displacement Damage of Electronic Parts
• Effective Date: 10-Jun-2000

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 1250 – 88 (Reapproved 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
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 Low energy components in the photon energy spectrum 3.1 absorbed dose, D—quotient of d e¯by dm, where d e¯is
ofCo-60irradiatorsleadtoabsorbeddoseenhancementeffects themeanenergyimpartedbyionizingradiationtothematterin
in the radiation-hardness testing of silicon electronic devices. a volume element and dm is the mass of matter in that volume
These low energy components may lead to errors in determin- element.
ing the absorbed dose in a specific device under test. This
D 5 de¯/dm (1)
method covers procedures for the use of a specialized ioniza-
3.2 absorbed dose enhancement factor— ratio of the ab-
tion chamber to determine a figure of merit for the relative
sorbed dose at a point in a material of interest to the
importance of such effects. It also gives the design and
equilibrium absorbed dose in that same material.
instructions for assembling this chamber.
3.3 average absorbed dose—mass-weighted mean of the
1.2 This method is applicable to measurements in Co-60
absorbed dose over a region of interest.
−6
radiation fields where the range of exposure rates is 7 310
−2 −1 −1 3.4 average absorbed dose enhancement factor—ratio of
to3 310 Ckg s (approximately100R/hto100R/s).For
the average absorbed dose in a region of interest to the
guidance in applying this method to radiation fields where the
equilibrium absorbed dose.
exposure rate is >100 R/s, see Appendix X1.
3.5 dosimeter—any device used to determine the equilib-
NOTE 1—See Terminology E170 for definition of exposure and its
rium absorbed dose in the material and at the irradiation
units.
position of interest. Examples of such devices include ther-
1.3 The values stated in SI units are to be regarded as the moluminescence dosimeters (TLDs), liquid chemical dosim-
eters, and radiochromic dye films. (See Practice E668, for a
standard. The values given in parentheses are for information
discussion of TLDs.)
only.
1.4 This standard does not purport to address all of the 3.6 equilibrium absorbed dose—absorbed dose at some
incremental volume within the material in which the condition
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- of electron equilibrium (the energies, number, and direction of
charged particles induced by the radiation are constant
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. throughout the volume) exists. (See Terminology E170.)
4. Significance and Use
2. Referenced Documents
2.1 ASTM Standards: 4.1 AlthoughCo-60nucleionlyemitmonoenergeticgamma
rays at 1.17 and 1.33 MeV, the finite thickness of sources, and
E170 Terminology Relating to Radiation Measurements
and Dosimetry encapsulation materials and other surrounding structures that
areinevitablypresentinirradiatorscancontributeasubstantial
E668 Practice for Application of Thermoluminescence-
Dosimetry(TLD)SystemsforDeterminingAbsorbedDose amount of low-energy gamma radiation, principally by Comp-
tonscattering(1,2). Inradiation-hardnesstestingofelectronic
in Radiation-Hardness Testing of Electronic Devices
E1249 Practice for Minimizing Dosimetry Errors in Radia- devices this low-energy photon component of the gamma
spectrum can introduce significant dosimetry errors for a
tion Hardness Testing of Silicon Electronic Devices Using
Co-60 Sources 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
This method is under the jurisdiction of ASTM Committee E10 on Nuclear
Technology and Applicationsand is the direct responsibility of Subcommittee
E10.07on Radiation Dosimetry for Radiation Effects on Materials and Devices.
Current edition approved May 27, 1988. Published July 1988. The boldface numbers in parentheses refer to the list of references appended to
Annual Book of ASTM Standards, Vol 12.02. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1250
absorbed dose enhancement effects (3, 4). Absorbed dose 5.5 Triaxial Cable, the triaxial cable that connects the
enhancement effects refer to the deviations from equilibrium ionization chamber and the bias supply to the electrometer is
absorbed dose caused by non-equilibrium electron transport usually supplied with the electrometer, and must be of a type
near boundaries between dissimilar materials. that is compatible with the electrometer type used (see Fig. 1).
4.2 The ionization chamber technique described in this
method provides an easy means for estimating the importance 6. Procedure
of the low-energy photon component of any given irradiator
6.1 Assemble the ionization chamber, bias supply, and
type and configuration.
electrometer as shown in Fig. 1.
4.3 When there is an appreciable low-energy spectral com-
6.2 Turn on the bias supply, set the voltage to at least 60 V,
ponent present in a particular irradiator configuration, special
and ensure that there is no appreciable leakage current (I -
leak
experimental techniques should be used to ensure that dosim-
age< 0.1 pA). Turn the bias supply off.
etry measurements adequately represent the absorbed dose in
6.3 Assemble the ionization chamber with the gold/
the device under test. (See Practice E1249.)
aluminum electrodes (the gold sides facing the inside of the
chamber). Place the ionization chamber in the irradiation
5. Apparatus
position of interest. For directional sources, position the
5.1 Ionization Chamber,aspeciallyfabricatedparallel-plate
ionization chamber so that the direction of the main beam is
ionization chamber with interchangeable gold and aluminum
perpendicular to the electrode plates.
electrodes. A specific design is described in Appendix X2.
6.4 Turn on the bias supply and measure the ionization
5.2 Bias Supply, a battery or power supply capable of
current, I , with the gold/aluminum electrodes in place, gold
Au
delivering 60 to 100 V dc at a current up to 1 mA.
side facing inward.
5.3 Electrometer, an electrometer or picoammeter capable
6.5 Repeat steps 6.3 and 6.4 with aluminum electrodes and
of measuring currents as low as 30 pA with a resolution of at
measure the ionization current I . The ionization chamber
Al
least 0.1 pA.
location and orientation shall be the same for both measure-
5.4 Twinaxial Cable, the twinaxial cable that connects the
ments.
ionization chamber to the bias supply and electrometer is an
6.6 Calculate the ionization current ratio a as follows:
integral part of the ionization chamber (see Fig. 1).
a5 I / I (2)
Au Al
This ratio provides a figure of merit for the particular Co-60
irradiator configuration under investigation.
NOTE 3—Since the relationship between ionization chamber current
and exposure rate depends on such environmental factors as temperature,
atmospheric pressure, and relative humidity, it is important to make the
twomeasurementsofI andI asnearlyatthesametimeaspossibleto
Au Al
minimize the influence of environmental factors on the ratio I /I .
Au Al
7. Interpretation of Measurement Results
7.1 Low values of the figure of merit, a ('2 to 2.5) are
indicative of a relatively small low-energy photon component,
and high values of a (>5) indicate a very large low-energy
photon component. Appendix X3 gives a table of measured
values of a for a variety of typical Co-60 irradiator facilities
and experimental arrangements.
FIG. 1 Schematic Diagram of Experimental Setup
NOTE 4—Monoenergetic 1.25 MeV photon radiation would theoreti-
callyproduceavalueofa51.6.Althoughthisvalueisnotattainablewith
any realistic Co-60 irradiator configuration, it is a theoretical lower limit
on a.
NOTE 2—TheionizationchamberdimensionsgiveninAppendixX2are
appropriate to TWC 78-2 twinaxial cable. This cable has the following
7.2 If the measured value of a is >2.5, steps 6.1-6.5 should
physical dimensions (all dimensions given in inches):
be repeated with the ionization chamber surrounded by a filter
Nominal outer diameter 0.242
can or box of 1.5 to 2.0 mm (approximately 0.063 in.) of lead
Conductor spacing (center to center) 0.076
Conductor dielectric outer diameter 0.076
on the outside and 0.7 to 1.0 mm (approximately 0.030 in.) of
Conductor diameter 0.037
aluminumontheinside.Useofsuchafilterwill normallygive
Other equivalent twinaxial cable types can be used, but the applicable
a significant reduction in the low-energy component of the
dimensionsoftheionizationchamberbody,clamp,stem,andcableclamp
spectrum (see Practice E1249).
nut in Appendix X2 must then be adjusted.
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
Available from Trompeter Electronics, 31186 La Baya Dr., Westlake Village,
CA91362-4047. dosimetry errors for the device under test.
E 1250
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
case estimate of the absorbed dose enhancement factor for a silicon-gold
interface.
8.1.3 Theabsorbeddoseenhancementfactorattheinterface
is defined by the following:
F ~Si:Au!5 D ~IF!/D ~eq! (3)
DE Si Si
where:
D (IF) 5 absorbed dose in silicon immediately adjacent
Si
to the silicon-gold interface, and
D (eq) 5 equilibrium absorbed dose in silicon.
FIG. 2 Relationship for Estimating Absorbed Dose Enhancement
Si
Factor in Silicon at a Silicon-Gold Interface From the Ionization
8.1.4 The relationship between the ionization current ratio,
Current Ratio
a, and an estimate of F (Si:Au) is shown in Fig. 2.The basis
DE
for this relationship is discussed briefly in Appendix X4.
NOTE 6—Based on the assumptions inherent in Fig. 2 and Appendix 8.2.1 Except for very soft spectra, the use of a filter box of
X4, monoenergetic 1.25 MeV photon radiation will produce a value of
1.5to2.0mm('0.063in.)ofleadonthesourceside,followed
F (Si:Au) 51.64. Such a low value is not attainable in any practical
DE
by 0.7 to 1.0 mm ('0.030 in.) of aluminum on the test object
Co-60 irradiator configuration.
side, (see Practice E1249), will harden the spectrum suffi-
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
gamma radiation; therefore, the dosimetry error for a device
9. Precision and Bias
under test incurred by neglecting the low energy photon
component would be about 10%. On the other hand, a
9.1 The lowest ionization chamber current to which this
−6
measured ionization current ratio of 7.5 would be considered a
method is applicable is 30 pA (corresponding to 7 310 C
−1 −1
poor figure of merit for another irradiator configuration. In this
kg s [approximately100R/h]),whichcanbemeasuredwith
case, the corresponding estimated absorbed dose enhancement
aprecisionof0.5pAor 61.7%,asspecifiedbytheinstrument
factorwouldbeabout3.0;therefore,neglectingthelowenergy
manufacturer. The ratio I /I can therefore be determined to
Au Al
spectral component would lead to a dosimetry error for a
an overall uncertainty of 62.4% or better.
device under test of as much as a factor of 1.8. For such a
9.2 This method provides a figure of merit usable for
configuration, the use of a lead-aluminum filter box would
comparing various source configurations, and for assessing the
minimize the dosimetry error, and, therefore should be consid-
relative improvement that is achievable with a lead-aluminum
ered (see Practice E1249).
filter. This method gives no quantitative information about
8.2 Selecting a Lead-Aluminum Filter for Spectrum Hard- absorbeddoseenhancementfactorotherthananestimateofits
ening: upper limit.
E 1250
10. Keywords
10.1 absorbed dose; Co-60 irradiators; dose enhancement;
ionization chamber; radiation hardness testing
APPENDIXES
(Nonmandatory Information)
X1. APPLICATION OF THIS METHOD TO HIGH EXPOSURE RATES
−3 −1
X1.1 The limits of applicability of this method given in 1.2 ˙
X 5 exposure rate, R/s (1 R/s 5esu cm s ),
−2 −1 −1
areforexposurerateslessthan3 310 Ckg s (<100R/s).
d 5 electrode spacing, cm (0.3 cm for this method), and
It may be possible to apply this method to exposure rates
V 5 bias voltage, volts.
higher than 100 R/s if the following guidelines are applied.
X1.3.2 Solving Eq X1
...