Standard Active Last Updated: Dec 27, 2016
ASTM E2450-16

Standard Practice for Application of CaF2(Mn) Thermoluminescence Dosimeters in Mixed Neutron-Photon Environments

Significance and Use

4.1 Electronic devices are typically tested for survivability 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 CaF2(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 CaF2(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 CaF2(Mn) TLDs may vary depending on the source of the material, and this procedure is a generic calculation applicable to CaF2(Mn) TLDs independent of their manufacturer/source. The neutron response given in this practice is a summary of CaF2(Mn) TLD responses reported in the literature. The associated uncertainty envelops the range of results reported, and includes the variety of CaF2(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 CaF2(Mn) TLDs in use must be determined. This practice does not supply guidance on how to determine the neutron response of a specific batch of TLDs.

4.5 Neutron effects on electronics under test are usually reported in terms of 1-MeV(Si) equivalent fluence (E722). Neutron effects of TLDs, as discussed here, are reported in units of absorbed dose, since they are corrections to the gamma-ray dose.

Scope

1.1 This practice describes a procedure for correcting a CaF2(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 8 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).2

1.4 The values stated in SI units are to be regarded as standard.

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Details
Book of Standards Volume: 12.02
Developed by Subcommittee: E10.07
Pages: 6
DOI: 10.1520/E2450-16
ICS Code: 17.240