ASTM E2450-23

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Designation: E2450 − 16 E2450 − 23
Standard Practice for
Application of CaF (Mn) Thermoluminescence Dosimeters in
Mixed Neutron-Photon Environments
This standard is issued under the fixed designation E2450; 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
1.1 This practice describes a procedure for correcting a CaF (Mn) thermoluminescence dosimeter (TLD) reading for its response
to neutrons during the irradiation. The neutron response may be subtracted from the total TLD response to give the gamma-ray
response. In fields with a large neutron contribution to the total response, this procedure may result in large uncertainties.
1.2 More precise experimental techniques may be applied if the uncertainty derived from this practice is larger than the level that
the user can accept. These more precise techniques are not discussed here. The references in Section 88 describe some of these
techniques.
1.3 This practice does not discuss effects on the TLD reading from neutron interactions with the material surrounding the TLD
and used to ensure a charged particle equilibrium. These effects will depend on the isotopic composition of the surrounding
material and its thickness, and on the incident neutron spectrum (1).
1.4 The values stated in SI units are to be regarded as standard.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E170 Terminology Relating to Radiation Measurements and Dosimetry
E666 Practice for Calculating Absorbed Dose From Gamma or X Radiation
E668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Determining Absorbed Dose in
Radiation-Hardness Testing of Electronic Devices
E720 Guide for Selection and Use of Neutron Sensors for Determining Neutron Spectra Employed in Radiation-Hardness
Testing of Electronics
E721 Guide for Determining Neutron Energy Spectra from Neutron Sensors for Radiation-Hardness Testing of Electronics
This practice is under the jurisdiction of ASTM Committee E10 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 June 1, 2016Jan. 1, 2023. Published July 2016January 2023. Originally approved in 2005. Last previous edition approved in 20112016 as
E2450 – 11.E2450 – 16. DOI: 10.1520/E2450-16.10.1520/E2450-23.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
E2450 − 23
E722 Practice for Characterizing Neutron Fluence Spectra in Terms of an Equivalent Monoenergetic Neutron Fluence for
Radiation-Hardness Testing of Electronics
E1854 Practice for Ensuring Test Consistency in Neutron-Induced Displacement Damage of Electronic Parts
F1190 Guide for Neutron Irradiation of Unbiased Electronic Components
3. Terminology
3.1 Definitions:
3.1.1 absorbed dose—see Terminology E170.
3.1.2 exposure—see Terminology E170.
3.1.3 kerma—see Terminology E170.
3.1.4 linear energy transfer (LET)—the energy loss per unit distance as a charged particle passes through a material.
3.1.4.1 Discussion—
Electrons resulting from gamma-ray interactions in a material generally have a low LET. Heavy charged particles resulting from
neutron interactions with a material generally have a high LET.
3.1.5 neutron sensitivity m(E)—the ratio of the detector reading, that is, the effective neutron dose, to the neutron fluence. Thus,
M~E!
m~E! 5 (1)
Φ~E!
where:
Φ(E) = the neutron fluence, and
M(E) = the apparent dose (light output) in the TLD caused by neutrons of energy E.
4. Significance and Use
4.1 Electronic devices are typically tested for survivability device response to gamma radiation in pure gamma-ray fields. Testing
electronic device response against neutrons is more complex since there is invariably a gamma-ray component in addition to the
neutron field. The gamma-ray response of the electronic device is typically subtracted from the overall response to find the device
response to neutrons. This approach to the testing requires a determination of the gamma-ray exposure in the mixed field. To
enhance the neutron effects, the radiation field is sometimes selected to have as large a neutron component as possible.
4.2 CaF (Mn) TLDs are often used to monitor the gamma-ray dose in mixed neutron/gamma radiation fields. Since the dosimeters
are exposed along with the device under test to the mixed field, their response must be corrected for neutrons. In a field rich in
neutrons, the uncertainty in the interpretation of the TLD response grows. In fields with relatively few neutrons, the total TLD
response may be used to make a correction for gamma response of the device under test. Under this condition, the relative
uncertainty in the TLD neutron response is not likely to drive the overall uncertainty in the correction to the electronic device
response.
4.3 This practice gives a means of estimating the response of CaF (Mn) TLDs to neutrons. This neutron response is then
subtracted from the measured response to determine the TLD response due to gamma rays. The procedure has relatively high
uncertainty because the neutron response of CaF (Mn) TLDs may vary depending on the source of the material, and this procedure
is a generic calculation applicable to CaF (Mn) TLDs independent of their manufacturer/source. The neutron response given in this
practice is a summary of CaF (Mn) TLD responses reported in the literature. The associated uncertainty envelops the range of
results reported,reported and includes the variety of CaF (Mn) TLDs used as well as the uncertainties in the determination of the
neutron response as reported by various authors.
4.4 Should the user find the resulting uncertainties too large for his purposes, the neutron response of the particular CaF (Mn)
TLDs in use during the irradiations must be determined. This practice does not supply guidance on how to determine the neutron
response of a specific batch of TLDs.
E2450 − 23
4.5 Neutron effects on electronics under test are usually reported in terms of 1-MeV(Si) equivalent fluence ((Practice E722).
Neutron effects of TLDs, as discussed here, are reported in units of absorbed dose, since they are corrections to the gamma-ray
dose.
5. Exposure Procedure
5.1 Determine the neutron and gamma-ray environments. Calculate the relative neutron response of the TLDs. If this response is
negligible, document this maximum bound of the TLD response to the neutron environment. No further measurements are required
for the purpose of documenting the neutron sensitivity of the TLDs.
5.2 Expose the TLD along with the device under test (see Practice E1854 and Guide F1190). If there is a non-negligible
fast-neutron or thermal-neutron response, a fast-neutron monitor (for example, nickel) or thermal-neutron monitor (for example,
gold) must also be exposed with the device under test.
5.3 The neutron spectrum must be known (see Guides E720 and E721). This may be determined in a separate exposure. A neutron
monitor should be used on the irradiation along with the device under test (see Practice E1854). The device under test must not
significantly perturb the neutron spectrum.
5.4 Practice E668 provides information on the calibration and use of CaF (Mn) dosimeters for use in X-ray and gamma radiation
fields as well as for electrons in a designated energy range. The guidance in this standard is to adopt, for use in mixed
neutron-gamma radiation fields, these same calibration, handling, and read-out techniques for CaF (Mn) TLDs. In particular, the
CaF (Mn) TLDs that are used in a mixed neutron photon field should only be calibrated in a well-characterized gamma-only
radiation source. See Section 9 of Practice E668.
6. Neutron Sensitivity of CaF (Mn)
6.1 Thermal Neutrons:
6.1.1 Thermal neutron responses of CaF (Mn) ranging from 0.06 to 0.89 Gy[CaF (Mn)] (6 to 89 rad[CaF (Mn)](Mn)]) per
2 2 2
12 2
10 n ⁄cm are reported (2). The sensitivity may depend on several factors, one of the most important parameters being the
manganese doping of the TLD. The sensitivity may also be a function of dosimeter size, since the dosimeter surface-to-volume
ratio affects the portion of the charged particles bornborne within the TLD that deposit their dose outside the TLD. Horowitz (3)
12 2
reported a thermal neutron response of 0.34 Gy(CaF ) (34 rad[CaF ]) per 10 n/cm for CaF (Mn), with 2 % Mn by weight, for
2 2 2
TLD of dimensions 0.165 by 0.165 by 0.083 cm.
NOTE 1—Thermal neutron response is typically reported in terms of TLD response relative to a Co-60 equivalent Roentgen (R)/(n/cm ). For Co-60 decay
gamma rays, the conversion from Roentgen to Gy(air) is 0.00869 Gy(air)/R. For the Co-60 gamma energy, the conversion from Gy(air) to Gy(CaF ) is
0.975. Thus, in a Co-60 source, Gy(CaF ) is 0.0085 times the exposure in Roentgen.
12 2
6.1.2 A value of 0.45 6 0.45 Gy (45 6 45 rad) (1 σ) [CaF (Mn)] per 10 thermal n/cm shall be used for CaF (Mn) TLDs.
2 2
NOTE 2—The variation in measured thermal neutron sensitivities for CaF (Mn) is as large as the average sensitivity.
6.2 Fast Neutrons—A recommended energy-dependent fast-neutron response is displayed in Fig. 1 and listed in Table 1. For the
purpose of this practice, the fast-neutron response is the response due to a neutron with an energy above 0.4 eV. Table 1 is the
Rinard (4) response function multiplied by 1.2. The factor of 1.2 was used to scale the response function to give an optimal fit to
a variety of measured data. See Fig. 2 for the quality of this coverage. Use this response to calculate the fast neutron fast-neutron
response in Gy(CaF ).
Response 5 R E ·Φ E dE (2)
* ~ ! ~ !
-2–2 -1–1
where R(E) is taken from Table 1 and Φ(E) is the neutron spectrum in n·cm ·MeV . Take the 1 σ uncertainty in this response
as 50 % of the calculated value.
E2450 − 23
FIG. 1 Fast-Neutron Sensitivity of CaF (Mn) TLDs
6.3 Subtract the thermal and fast neutron fast-neutron responses from the measured responses to obtain the gamma-ray response
of the TLD:
D 5 D 2 D 2 D (3)
G Meas Thermal Fast
6.3.1 The uncertainties
...