Harshaw LiF Research Articles

The applicability of the PTTL dose re-analysis method to the Harshaw LiF:Mg,Cu,P material

The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P material. It is demonstrated that using 254-nm UV light, dose levels as low as 0.2 mGy can be re-estimated. The PTTL efficiency was found to be ∼ 6 % in the dose range of 0.2 mGy-1 Gy, and it appears to be dose-independent. This implies that a simple calibration factor could be applied to the PTTL data for the re-estimation of dose levels. It was demonstrated that with a proper choice of the TL readout parameters, and the UV-light irradiation conditions, dose levels that are relevant to personal or environmental dosimetry can be re-estimated.

Response of 6LiF:Mg,Cu,Si and 7LiF:Mg,Cu,Si TLD Pairs to the Neutrons and Photon Mixtures

Replacement of dopant P by Si in LiF:Mg,Cu,P has provided an improved LiF:Mg,Cu,Si TLD material. Responses of indigenously developed Korean NaturalLiF:Mg,Cu,Si. 6LiF:Mg,Cu,Si and 7LiF:Mg,Cu,Si TLDs to gamma rays and neutrons were evaluated and compared with the commercially available LiF based TLDs. The intrinsic gamma ray sensitivity of NaturalLiF:Mg,Cu,Si was found to be the highest among the studied TLDs. The gamma ray sensitivities of 6LiF:Mg,Cu,Si and 7LiF:Mg,Cu,Si were about 27 and 32 times higher than that of Harshaw LiF:Mg,Ti. The relative neutron sensitivities (ratio of TL/mGy to neutron and gamma rays) of 6LiF TLDs doped with Mg,Cu,P and Mg,Cu,Si were about the same but lower than that of Harshaw 6LiF:Mg,Ti (TLD-600) due to the difference in their LET dependences. The high intrinsic TL sensitivity of 6LiF:Mg,Cu,Si outweighs the higher relative neutron sensitivity of TLD-600. In the testing following ANSI criteria, the performance quotient of the pairs of 6LiF:Mg,Cu,Si / 7LiF:Mg,Cu,Si held in Harshaw neutron TLD badge holders for the dosimetry in the mixed field of neutron and gamma rays was found to be less than 0.1 as against the maximum permitted value of 0.4.

Extensive fade study of Harshaw LiF TLD materials

A comprehensive and extensive fade study was conducted for Harshaw LiF TLD materials. This study covers the well-established LiF:Mg,Ti and LiF:Mg,Cu,P materials in their different isotopes, sizes, forms and time–temperature readout schemes. Two parts of the fade study on the signal loss and the sensitivity loss were carried out in a long-term period of 500 + days at temperatures of 0, 20 and 40 ∘ C using more than 3500 dosemeters. Detailed results are presented and a summary is provided.

Comparison of the effects of exposure to light in Harshaw LiF:Mg,Ti and LiF:Mg,Cu,P

The response of thermoluminescence dosemeters (TLDs) to light, in various conditions, has been studied. TLD cards containing both conventional lithium fluoride (LiF:Mg,Ti) and the high-sensitivity material LiF:Mg,Cu,P were available, so permitting a comparison between the two types. Also available for the tests were Harshaw extremity EXT-RAD (LiF:Mg,Cu,P) dosemeters. The LiF:Mg,Ti body TLD cards and the EXT-RAD extremity dosemeters both showed some response to fluorescent light, while the LiF:Mg,Cu,P cards showed no significant response. It is therefore concluded that LiF:Mg,Cu,P body cards need no special precautions to protect them from the effects of light. For LiF:Mg,Ti cards and extremity dosemeters, effects are small, but steps to avoid excessive light exposure should be considered.

Comparison of time effects, decision limit and residual signal in Harshaw LiF:Mg,Ti and LiF:Mg,Cu,P

The personal dosimetry service of the UK Health Protection Agency--formerly of the National Radiological Protection Board (NRPB)--is currently commissioning a body thermoluminescence dosemeter (TLD) system based on the use of Harshaw 8800 readers and two-element cards. As part of the process, studies have been carried out into the long-term time dependence of response, the limit of detection and the magnitude of the signal remaining after recommended processing. TLD cards containing both conventional lithium fluoride (LiF:Mg,Ti) and the high-sensitivity material LiF:Mg,Cu,P were available, thus allowing a comparison between the two types of material.

Discrimination of photon from proton irradiation using glow curve feature extraction and vector analysis

Two types of thermoluminescence dosemeters (TLDs), the Harshaw LiF:Mg,Ti (TLD-100) and CaF(2):Tm (TLD-300) were investigated for their glow curve response to separate photon and proton irradiations. The TLDs were exposed to gamma irradiation from a (137)Cs source and proton irradiation using a positive ion accelerator. The glow curve peak structure for each individual TLD exposure was deconvolved to obtain peak height, width, and position. Simulated mixed-field glow curves were obtained by superposition of the experimentally obtained single field exposures. Feature vectors were composed of two kinds of features: those from deconvolution and those taken in the neighbourhood of several glow curve peaks. The inner product of the feature vectors was used to discriminate among the pure photon, pure proton and simulated mixed-field irradiations. In the pure cases, identification of radiation types is both straightforward and effective. Mixed-field discrimination did not succeed using deconvolution features, but the peak-neighbourhood features proved to discriminate reliably.

Thermoluminescent response and the effect of exposure order from mixed photon and proton irradiations

Two types of thermoluminescent dosimeters (TLDs): Harshaw LiF:Mg,Ti (TLD-100) and CaF 2 :Tm (TLD-300) were investigated for their glow curve responses to separate, mixed field, and simultaneous X-ray and proton irradiations. All TLDs were exposed to X-rays produced by a 30 keV, 0.2 mA electron beam, X-ray tube source. TLD-100 detectors were exposed to 2.5 MeV protons and the TLD-300 detectors were exposed to 4 MeV protons. The following five separate irradiation schemes were used: only X-ray, only proton, first X-ray then proton, first proton then X-ray, and simultaneous X-ray and proton beam exposures. Computerized glow curve deconvolution based on first order TL kinetics was used to analyze the resulting glow curves for any differences in shape and TL efficiency due to order of exposure. We found no significant differences in glow curve shape or magnitude attributable to radiation exposure order.

Fading Characteristics of LiF and Li2B4O7 TLD Systems Dependent on the Ambient Temperature, the Monitoring Period and the Interval Between Irradiation and Readout

Abstract The change in response of oven-annealed Harshaw LiF:Mg,Ti and Studsvik Li2B4O7:Mn,Si detectors has been investigated as a function of storage periods of up to 100 days at ambient temperatures of -18 oC, 25 oC, 40 oC and 70 oC. Detectors have been irradiated before storage, after storage, and at different times within the storage period of 100 days. In environmental monitoring LiF generally enables determination of field fading correction factors if control dosemeters are used.

Fading Characteristics of LiF and Li2B4O7 TLD Systems Dependent on the Ambient Temperature, the Monitoring Period and the Interval Between Irradiation and Readout

The change in response of oven-annealed Harshaw LiF:Mg,Ti and Studsvik Li2B4O7:Mn,Si detectors has been investigated as a function of storage periods of up to 100 days at ambient temperatures of -18 oC, 25 oC, 40 oC and 70 oC. Detectors have been irradiated before storage, after storage, and at different times within the storage period of 100 days. In environmental monitoring LiF generally enables determination of field fading correction factors if control dosemeters are used.

Optical absorption and thermoluminescence in LiF TLD-100

The thermoluminescent (TL) properties of many LiF samples have demonstrated a strong influence on trace impurities and impurity content on the TL process. Hence, the general validity of any particular model must be tested against its applicability in a standard material such as Harshaw LiF (TLD-100). In this paper the validity of the use of Harshaw LiF(54) by Mayhugh et al. in their model development for the TL process in LiF is demonstrated by comparing the TL and optical properties of LiF(54) with TLD-100. The specific properties of optical absorption bands at 310 and 380 nm, the F band near 250 nm, and the Z3 band near 225 nm are intercompared with observed TL peaks in both materials. Both the gamma and uv-exposure behavior of the Z3 center demonstrates a direct relationship between Z3 and TL peak 10, while no direct conversion between Z3 and the 310-nm band is observed in TLD-100. These results do not support recent models identifying Z3 with TL peak 6 and Z2 with the 310-nm band (and TL peak 5); this is probably due to differences in purity and defect state in the LiF samples used by other investigators, emphasizing the need for standardization of materials in this system.

An extended role for thermoluminescent phosphors in personnel environmental and accident dosimetry using sensitisation, re-estimation and fast fading

This paper summarises some techniques for extending the usefulness of conventional phosphors in personnel, environmental and accident dosimetry. An optimised procedure for utilising radiation sensitisation and UV re-estimation in thermoluminescent LiF is presented. In particular it is shown that optimum performance is achieved by using a UV wavelength of 250 ± 10 nm for both the UV/thermal anneal following sensitisation, and for the UV re-estimation procedure. In the case of Harshaw LiF chips (3×3×0.9 mm 3) the sensitivity is increased by a factor of 4–5 to achieve a minimum detectable dose of ∼ 10 μGy (2 σ) and a minimum re-estimable dose of 50–100 mGy (2σ), dependent on batch. Sensitized LiF also exhibits improved tissue equivalence, extended linearity and improved precision at low doses. The information from fast-fading glow peaks, which is normally rejected, is shown to have a useful application to the evaluation of short-term increases in environmental dose rates such as may occur following accidental releases of radioactivity.

Optical Studies of Alkali Fluorides and Alkaline Earth Fluorides in VUV Region

The results of a series of reflectivity and absorption measurements performed to clarify respectively the excitonic transitions in the intrinsic region to 13.5 eV and the thermal and spectral dependences of absorptions in the tail region of LiF, NaF, KF, CaF 2 SrF 2 and BaF 2 , each being cleaved from Harshaw blocks of single crystal, are presented. The tails of Harshaw LiF, being expressed by exponential functions of energy in the range of 10 0 cm -1 \({\lesssim}A{\lesssim}5{\cdot}10^{2}\) cm -1 and 300°K≤ T ≤573°K, have turned out to be extrinsic to LiF. The present experiments could not provide sufficiently conclusive evidences in clarifying the question whether the tails of Harshaw alkaline earth fluorides, to Urbach rule is applicable for the range of 10 0 cm -1 \({\lesssim}A{\lesssim}10^{2}\) cm -1 and 78°K≤ T ≤573°K, are intrinsic. In the first peak of reflectivity spectra, the fluorine doublet with ∼0.05 eV separation is detected for KF and quintet structure for SrF 2 and BaF 2 . In the latter, th...

Effect of Dislocations on the Thermal Conductivity of Lithium Fluoride

Measurements of the thermal conductivity K of Harshaw LiF crystals were made over the temperature range 2°–100°K. A freshly cleaved crystal exhibited K values in agreement with the measurements of Berman, Foster, and Ziman (1956). Annealing raised the maximum K by a factor of two. Dislocations were added by compression, and the dislocation density was determined by the methods of Gilman and Johnston. The K values below 30°K for the deformed specimens were approximately proportional to T2, in agreement with Klemens' theory, but the reduction in K by introduction of dislocations was much larger than Klemens' predictions. The phonon mean free path when limited by dislocation scattering was found to be approximately (4×106)/DT, where D is the number of dislocation lines/cm2 and T is the absolute temperature.