ASTM E1855-96
(Test Method)Standard Test Method for Use of 2N2222A Silicon Bipolar Transistors as Neutron Spectrum Sensors and Displacement Damage Monitors
Standard Test Method for Use of 2N2222A Silicon Bipolar Transistors as Neutron Spectrum Sensors and Displacement Damage Monitors
SCOPE
1.1 This test method covers how 2N2222A silicon bipolar transistors can be used either as dosimetry sensors in the determination of neutron energy spectra, or as silicon 1-MeV equivalent displacement damage fluence monitors.
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Designation: E 1855 – 96
Standard Test Method for
Use of 2N2222A Silicon Bipolar Transistors as Neutron
Spectrum Sensors and Displacement Damage Monitors
This standard is issued under the fixed designation E 1855; 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 263 Test Method for Measuring Fast-Neutron Reaction
Rates by Radioactivation of Iron
1.1 This test method covers how 2N2222A silicon bipolar
E 265 Test Method for Measuring Reaction Rates and
transistors can be used either as dosimetry sensors in the
Fast-Neutron Fluences by Radioactivation of Sulfur-32
determination of neutron energy spectra, or as silicon 1-MeV
E 720 Guide for Selection and Use of Neutron-Activation
equivalent displacement damage fluence monitors.
Foils for Determining Neutron Spectra Employed in
1.2 The neutron displacement damage is especially valuable
Radiation-Hardness Testing of Electronics
as a spectrum sensor in the range 0.1 to 2.0 MeV when fission
E 721 Guide for Determining Neutron Energy Spectra from
foils are not available. It has been applied in the fluence range
12 2 14 2
Neutron Sensors for Radiation-Hardness Testing of Elec-
between 2 3 10 n/cm and 1 3 10 n/cm and, in theory,
15 2
tronics
should be useful up to 10 n/cm . This test method details the
E 722 Practice for Characterizing Neutron Energy Fluence
steps for the acquisition and use of silicon 1-MeV equivalent
Spectra in Terms of an Equivalent Monoenergetic Neutron
fluence information (in a manner similar to the use of activa-
Fluence for Radiation-Hardness Testing of Electronics
tion foil data) for the determination of neutron spectra.
E 844 Guide for Sensor Set Design and Irradiation for
1.3 In addition, this sensor can provide important confirma-
Reactor Surveillance, E706 (IIC)
tion of neutron spectra determined with other sensors, and
E 854 Test Method for Application and Analysis of Solid
yields a direct measurement of the silicon 1-MeV fluence by
State Track Recorder (SSTR) Monitors for Reactor Sur-
the transfer technique.
veillance, E706 (IIIB)
1.4 This standard does not purport to address all of the
E 944 Practice for Application of Neutron Spectrum Adjust-
safety concerns, if any, associated with its use. It is the
ment Methods in Reactor Surveillance, (IIA)
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3. Terminology
bility of regulatory limitations prior to use.
3.1 Symbols:
2. Referenced Documents F 5 the silicon 1-MeV equivalent fluence (see Practice
E 722).
2.1 The ASTM standards listed in 2.2 from Terminology
h 5 i /i where i is the collector current and i is base current,
E 170 through Test Method E 265 provide a background for FE c b c b
in a common emitter circuit.
understanding how sensors are used in radiation measurements
and general dosimetry. The rest of the standards referenced in
4. Summary of Test Method
the list discuss the choice of sensors, spectrum determinations
4.1 Gain degradation of 2N2222A silicon bipolar transistors
with sensor data, and the prediction of neutron displacement
measured in the test (simulation) environment is compared
damage in some semiconductor devices, particularly silicon.
with that measured in a reference neutron environment. The
2.2 ASTM Standards:
F in the reference environment is derived from the known
1r
E 170 Terminology Relating to Radiation Measurements
reference spectrum and is used to determine a measured F in
1t
and Dosimetry
the test environment (1,2) by the transfer technique. The r and
E 261 Practice for Determining Neutron Fluence Rate, Flu-
t refer to the reference and test environments respectively.
ence, and Spectra Radioactivation Techniques
4.2 The measured F may be used as a sensor response in
1t
a spectrum adjustment code in a manner similar to the use of
reaction foil activities to determine the spectrum (3,4).
This test method is under the jurisdiction of ASTM Committee E-10 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 Dec. 10, 1996. Published February 1997. The boldface numbers in parentheses refer to a list of references at the end of
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 1855
4.3 Spectra compatible with the responses of many sensors 6. Apparatus
may be used to calculate a more reliable measure of the
6.1 A transistor with demonstrated response in agreement
displacement damage.
with calculated F values in widely varied environments is the
silicon bipolar transistor 2N2222A. It is recommended that
5. Significance and Use
three or more of these transistors be calibrated together and
5.1 The neutron spectrum in a test (simulation) environment
used at each location to be characterized. At least three others
must be known in order to use the measured device response in
should be used as temperature correction devices (control
the test environment to predict the device performance in an
devices) during readout. The control transistors should be
operational environment. Typically, spectra are determined by
exposed one time to a calibration exposure of about 1.0 3 10
use of a set of sensors that have response functions that are
n/cm 1-MeV equivalent fluence and then annealed (baked out)
sensitive over the neutron energy region to which the device
at 180°C for 24 h before being used as controls. These control
under test (DUT) responds (see Guide E 721). In particular, for
transistors are not exposed either during the calibration or test
silicon devices exposed in fast neutron spectra, this effective
step, but are read with the exposed transistors to provide
energy range is between 0.01 and 10 MeV. A typical set of
temperature correction.
activation reactions which lack fission reactions from nuclides
6.2 A dry oven for annealing is needed to stabilize the gain
235 237 239
such as U, Np, or Pu, will have very poor sensitivity to
after both the calibration-exposure and gain readout are com-
the spectrum between 0.01 and 2 MeV. For a pool-type reactor
pleted for the reference environment. The oven shall be able to
spectrum, 70 % of the DUT electronic damage response may
maintain the set temperature to within 63.0°C at 80°C and at
lie in this range. Often, fission foils are not included in the
180°C. It would be prudent to have a timer for automatic
sensor set for spectrum determinations because their use must
shutdown and an emergency power system (UPS). Shutdown
be licensed, and they require special handling for health
with a timer will require a door-opening mechanism.
physics considerations. The silicon transistors provide the
6.3 An electronic system is required to maintain appropriate
needed response to define the spectrum in this critical range.
transistor bias and currents and to read the currents for the gain
5.2 If fission foils are a part of the sensor set, the silicon
measurements. It is highly recommended that a programmable
sensor provides an important confirmation of the spectrum
semiconductor parameter tester (such as a Hewlett Packard
shape.
4145A) be used. A programmable tester can operate in pulsed
5.3 The transistors, such as type 2N2222A, are inexpensive,
mode to control heating effects and provide gain values
are smaller than fission foils contained in a boron ball, and are
quickly. The parameter tester determines the common emitter
easy and quick to read provided the proper steps are taken.
current gain by injecting a pulse of current into the base region,
They also can be used directly in arrays to map 1-MeV
measuring the collector current, and determining the current
equivalent fluence. The proper set of steps to take in reading
ratio i /i at a fixed bias of 10 V, where i is the collector current
c b c
the transistor-gain degradation is the primary subject of this
and i is the base current. The bias voltage is measured between
b
test method.
the collector and the base (see Ref (7)).
5.4 Fig. 1 shows the displacement damage function of
6.4 A reference neutron source for calibration of the tran-
silicon compared to two typical activation foil cross
sistors is required. The spectrum shape and magnitude of the
55 56 58 58
sections, Mn(n,g) Mn and Ni(n,p) Co. All three responses
reference source must be known. National Institute for Stan-
are shown to provide comparisons of sensors that respond in
dards and Technology (NIST) (8) and Cross Section Evaluation
widely differing energy regions. Fig. 1 shows that the major
Working Group (CSEWG) (9) benchmark sources are recom-
portion of the response of the silicon transistors will generally
mended for use as primary standards, but for practical reasons
be above 100 keV. See Ref (5) for the silicon cross section
the Fast Burst Reactors (FBRs) at Sandia National Laborato-
evaluation and Ref (6) for the nickel cross section. The
ries, White Sands Missile Range, and Aberdeen Proving
currently recommended silicon damage function is listed in
Ground also are recommended as reference benchmark fields.
Practice E 722.
6.5 If the transistors are exposed on a different run than the
one used to expose foils for spectrum determination, a suitable
monitor such as a nickel foil must be exposed along with the
transistors during calibration to relate the magnitude of the
neutron fluence during the spectrum determination exposure to
that during the transistor calibration exposure (see Section 7).
A photon-sensitive (and neutroninsensitive) detector such as a
CaF thermoluminescent detector (TLD) shall be included in
each test package to monitor the gamma-ray dose in case a
correction must be made for the transistor damage from
gamma-rays.
7. General Description of the Test Method
7.1 2N2222A transistors exhibit a range of initial gain
values and responses, but each responds linearly with 1-MeV
FIG. 1 Response for Typical Sensors equivalent fluence,F , at fixed collector current according to
E 1855
be included with the transistors. This monitor foil should be the same as
the Messenger-Spratt equation (10), if gamma rays do not
one of the sensor set so that a simple ratio of the monitor responses
contribute to the change of gain.
multiplied by the transistor response will provide the proper scaling
1 1
between the runs. This procedure of using the ratio of activities to scale the
2 5 K F~1 MeV! (1)
t
h h
FEF FEO
fluences is valid because the same spectrum is used for both runs.
The term h is the common emitter current gain at some
FEO
7.6 When the D(1/h) is measured in the unknown test
fixed collector current before irradiation in the test environ-
environment, the F can be found in the following manner.
1t
ment, and h is the same quantity measured at the same
FEF
Take the ratio of equations (Eq 1) for the reference and test
collector current after irradiation. K is the damage constant. If
t
environments and rearrange the terms to yield Eq 3 (see Ref
gamma-ray dose contributes to the change in the reciprocal of
(3)).
the gain, then that contribution must be subtracted from the left
side of Eq 1 before the right side is valid for neutrons (see 8.3).
D
S D
t
h 1 1
7.2 A semiconductor parameter analyzer may be used to
F 5 F 5 D (3)
S D
1t 1r
1 K h
t
t
determine h . A basic schematic circuit used by semiconduc-
FE
D
S D
h
r
tor analyzers for measuring h 5 i /i is shown in Fig. 2. Any
FE c b
equivalent method for making the electrical measurement is
7.7 The F is the quantity needed as a sensor value in the
1t
acceptable as long as the currents do not exceed the limits
spectrum determination procedure. The D(1/h) is the change in
t
detailed in 8.1.2 and 8.1.3.
the reciprocal gain induced by the test environment. For
7.3 Since K differs for each transistor, each must be
t neutron damage on 2N2222A transistors, K is a constant for
t
15 2
calibrated. When the technology of manufacture is such that
neutron fluences up to about 10 n/cm . The method described
the K ’s within a batch are the same to within a few percentage
t here provides a direct determination of F . Strictly speaking,
1t
points, a calibration by batch may be satisfactory. A typical
if F is the only quantity desired from the test when the
1t
−15 2
value for K is about 1.5 3 10 cm /neutron for a collector
t
transistor is irradiated, then a monitor is not needed. However,
current of 1 mA.
it is recommended that a monitor be included for possible
7.4 The linearity of response of a given batch of transistors
scaling and for ensuring that the ratio of responses between the
shall be verified by exposure of samples of the batch to at least
transistors and the monitor remain the same at characterized
three levels of neutron fluence covering the range in which the
positions in the neutron field.
devices will be used.
7.5 The calibration is accomplished by exposing the tran-
8. Experimental Procedure
sistors in a reference field for which the spectrum and intensity
8.1 To ensure proper calibration of the sensor, follow the
are known. The 1-MeV equivalent fluence of the reference
steps described in 8.1.1-8.1.9.
environment, F , is obtained by folding the spectrum with the
1r
8.1.1 Step 1—The 2N2222A transistors are inexpensive and
silicon displacement damage response as is described in
Practice E 722. The gain values, h before irradiation, and can be purchased in large lots from electronic supply houses.
FEO
Those purchased from readily available commercial sources
h after irradiation are measured, and the left side of Eq 1 is
FEF
calculated. The following quantity can be defined. have been found to be fairly uniform in electrical properties
and come with initial gains between about 50 and 200. The first
1 1 1
D 5 2 (2)
S D
step is to measure, at 1 mA collector current, the initial gain
h h h
FEF FEO
values of all the transistors in the batch. Throw out all those
This is the change in reciprocal gain. A subscript of r is used
with gain less than 100, and then remove the top and bottom
to denote the reciprocal gain change in the reference calibration
5 % fractions of the remaining set. Thus, if one begins with 100
environment. A subscript of t is used to denote the reciprocal
transistors there may be two with gains below 100, and after
gain change in the test or unknown environment. This mea-
remo
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