Book Review

doi:10.1093/rpd/ncr357

OPTICALLY STIMULATED LUMINESCENCE: FUNDAMENTALSAND APPLICATIONS

E. G. Yukihara and S. W. S. McKeever, A John Wiley and Sons Ltd, UKISBN: 978-0470-69725-2, 362 pp

The book ‘Optically Stimulated Luminescence—Fundamentals and Applications’ covers recentadvances in optically stimulated luminescence(OSL). Rapid development in this field is evidentfrom large number of publications (more than 3000in 2010) appearing in a variety of journals. Themain attraction of OSL is its all-optical technologi-cal advantage over the well-established thermolumi-nescence dosimetery (TLD), for not requiringheating of the sample and the ease of associatedequipment. In the recent years, optically stimulatedluminescence dosimetry (OSLD) has emerged as atechnique with a vast potential and has becomefavourite of researchers for studying newer par-ameters and exploring extended applicationsbecause of the possibility of adopting variety ofstimulation sources, recording of different emissionwavelengths in different modes and characterisingdifferent materials (both naturally occurring andsynthesised for the purpose of dosimetry). There aremany similarities between OSLD and TLD, such asphysical forms of the dosemeters, basic mechanismand instrumentation. It now seems that OSL can doalmost all that TLD can do in addition to somenewer areas of applicability beyond the capability ofTLD technique due to the optical nature of stimu-lation. Although another book on this topic wasbrought out about 8 years ago (with one authorcommon in both the books), the need for this bookappears justified to update the rapid progress in thefield in which the authors themselves have made adominating contribution. The potential reader ofthis book expects to get the required, authentic andfirst-hand information because one of the authors isknown to be not only a part of the team of discover-ing pulse optically stimulated luminescence (POSL),an exciting mode of OSL, with a very rich and

continued research experience but also has a largecontribution in the field of TLD and has authored/coauthored several outstanding research papers andbooks on TLD (sole author of his first book on‘Thermoluminescence in Solids’ as early as in 1985which is still very popular).

This book contains 6 chapters (1, introduction; 2,theory and practical aspects; 3, personal dosimetry; 4,space dosimetry; 5, medical dosimetry and 6, otherapplications and concepts) and a large number refer-ences covering18 pages in addition to a brief ‘Preface’,list of contents, subject index and an acknowledge-ment. The first chapter brings out the history of OSLin great detail with several interesting features of therelated discoveries. It starts with the historical develop-ments of TL since 1664 making a foundation for thediscovery of OSL. As per the authors, the early obser-vations of phosphorescence/after glow (which waslater termed as ‘photophosphorescence’) from somematerials after infrared stimulation following exposureto ionising radiation [including the initial observationsof Edmond Becquerel (1843) and Henri Becquerel(1883)] could be considered as part of the history ofOSL. For radiation dosimetry, the work of Antonov-Romanovsy (1955) on the dose dependence ofinfrared-stimulated luminescence from pre-irradiatedsulphides and the work of Albrecht and Mandeville(1956) on the photo-stimulation (410-nm light) ofX-ray-exposed BeO samples leading to ultravioletemission could be considered as the earliest examples.Although, sporadic publications kept coming up in late1960s to early 1980s of the last century, it is clear thatthe major break through responsible for the presentusages of OSL took place in mid-1980s for the geologi-cal dating and later for main stream dosimetry in 1990sthrough careful evaluation of the dosimetric propertiesof Al2O3:C TLD material. Brief introduction to

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applications of OSL in personal, space, medical andsecurity fields with optimistic view of more excitingfuture applications is given in this chapter.

The second chapter on ‘Theory and PracticalAspects’ deals not only with the review of thephysics of luminescence dosemeters, kinetics, basicaspects of solid-state mechanism and the relevantterminology but also provides an overview of thedosimetry materials for OSL and the basic featuresof the required instrumentation for the measurementof OSL signals. It is interesting to note that photo-multiplier tube (PMT) continues to remain the lightdetector of choice in all commercial OSL readers aswell as in prototype reader systems. Limitations ofnon-first-order kinetic OSL processes have been dulystressed and the uses of equations for deconvolutionshave been adequately questioned. There are severalnewer aspects, which have not been covered in theearlier book. Gaps between the present understand-ing of the OSL process and the experimentallyobserved facts have been brought out to emphasisethat much is still needed to be done to bridge thesegaps. It is emphasised that until date Al2O3:Cremains the dosemeter material of choice in allapplications. This also demonstrates the fact that theprogress on the development of OSL materials hasbeen extremely limited. With this inference anattempt has been made to attract the attention ofthe material science engineers and researchers toundertake the challenge of developing bettermaterial than Al2O3:C. This chapter provides suffi-cient material for basic understanding necessary forthe intended readers.

Chapter 3 on ‘Personal Dosimetry’ includesdescription of quantities related to personal dosim-etry and general radiation protection in addition tothe prevalent dosimetry systems and the character-istics of OSL materials. Although the authors havetried to provide sufficient input on the quantitiesand the general considerations necessary for thepurpose, reader interested in detail might have tofollow the original references/reports (available inthe bibliography at the end of the book) and alsostandards relevant to his/her country. This isbecause the changes in the concepts and nomencla-ture of the related quantities appear to have notbeen adopted uniformly in different countries/docu-ments. Indications are apparent from the use ofshallow and deep dose equivalents for Hp(0.07) andHp(10). Reference to original reports may alsobecome relevant if a reader has to deal with doses todifferent organs, especially for the treatment ofremainder tissue (not defined in Table 3.4) for theweighting factors necessary for the limiting quan-tities. On the OSL properties of Al2O3:C, theauthors have meticulously brought out the impor-tant properties in this chapter in such a way that thereader could find the required information in the

book itself. Analogy drawn from TLD has helped inputting the results of OSL in perspective for the easeof the reader. The authors could do this becausetheir command on the characteristics of both TLDand OSL materials. The clarity in the explanation ofthe experimental data for the photon energyresponse of Al2O3:C for different OSL signals(initial intensity and total OSL area or UV and Fcentre emission) and for different forms (singlecrystal and powder impregnated tapes) is one suchexample. The details of newer developments forneutron dosimetry appear quite attractive and thismay lead to adaptation of OSL in routine neutrondosimetry as well.

In a way similar to personal dosimetry, intricaciesof space dosimetry are dealt in Chapter 4 entitled‘Space Dosimetry’. In brief, it covers the details ofthe sources of radiation in space; type, energy andspectral distribution of space radiation; effects ofsolar particles events and earth’s magnetic field;quantities of interest; issues of health risks andNCRP protection limits for astronauts; need forexperimental dose measurements and calibrationrequirements of OSL and TL dosemeters and theirperformance in space dosimetry. In the terminologyof the relevant quantities for the deterministic effects(tissue reaction), the authors have duly brought outthe justification and relevance of ‘Dose Equivalent’for space dosimetry instead of ‘Equivalent Dose’ rel-evant to personal dosimetry. Also, for the determinis-tic effects which could be caused by higher levels ofradiation exposures, a need for the NCRP rec-ommended quantity ‘gray-equivalent’ has beenstressed (International Commission on RadiologicalProtection has termed this quantity for tissue reac-tion as RBE-weighted dose or RBE.D for the high-linear energy transfer (LET) radiation or simplyabsorbed dose for the low-LET radiation, bothexpressed in gray). Dominance of TLD data fordemonstrating the application of OSL is evident inthis chapter also. This may be attributed to not onlyto the similarity between OSL and TLD but more tothe wide spread use of well-established TLD and tothe involvement of the authors in both TLD andOSL. Due attention has been paid to the quality ofradiation (both to high- and low-LET component) inspace. The effect of ionising density on the OSLresponse of Al2O3:C is discussed to complement thephoton energy dependence of the response discussedin the previous chapter. Here, the effect on differentOSL signals, e.g. initial intensity and total OSL areaor UV (SUV) and F-centre OSL emission (SF-centre)has been extensively elaborated for charged particledosimery. For the estimation of LET of the spaceradiation, the use of the difference in the responseSUV and SF-centre OSL signals has been demonstratedin a way similar to HTR (high temperature ratio)method based on the difference in the responses of

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high- and low-temperature glow peaks of LiF:Mg,TiTLD. Performances of both OSL and TLD havebeen shown to be similar in almost all the tests. Theperformance is concluded to be acceptable in low-LET dominated radiation fields and unacceptable inmixed fields of low- and high-LET radiation with sig-nificant (equal) high-LET radiation component or inthe fields dominated by high-LET radiations. Lack ofavailability of appropriate radiation beams for thecalibrations remains the major hurdle in the use ofboth the TLDs and OSLD. It is noted that the valueof SUV/SF-centre ratio of OSL signals changes withLET by less than a factor 2, whereas HTR changesby more than a factor of 6 which goes in favour ofthe use of LiF:Mg,Ti TLDs. It may also be notedthat higher temperature peaks of LiF:Mg,Ti (peaks6/7) exhibit a unique property (among the lumines-cence based known dosemeters till date) of high rela-tive response to high-LET radiation as against thegeneral behaviour of exhibiting a reduction inresponse with increasing LET.

Chapter 5 on ‘Medical Dosimetry’ starts with theusual background on the importance of radiationdosimetry in clinical applications of ionising radi-ation. Brief descriptions of sources of radiations,radiation levels and the required dosimetric accuracyrelevant to diagnostic radiology and radiationtherapy given in this chapter may help the studentsand other readers new to the field of medicalphysics. For demonstrating the applicability ofOSLD by keeping the international trend of the useof protocols for improving the accuracy, formalismdeveloped by the authors would attract medical phy-sicist to adopt OSL technique. It is demonstratedthat the required precision and accuracy can beachieved by adopting different correction factorsand proper calibration. This is possible because ofthe high reproducibility of OSL signal (�0.7 %). Itshould become clear to the reader that unlike anionisation chamber (or a primary dosemeter)wherein ion pairs produced by radiation are directlymeasured to arrive at the dose, in the case of OSLD(or any other dosemeter based on luminescenceproperties of solids) the emission of light is a resultof recombination of holes and electrons at the lumi-nescent centre and there is no way to arrive at thequantity of radiation independently without the useof a pre-established relationship between the emittedlight and the quantity of radiation which ismeasured by a primary or secondary standard dose-meter at that point. Accuracy can never be betterthan the accuracy of calibration and therefore repro-duction of the calibration conditions is important inthe actual measurements. Apart from repeatedreadout from the same dosemeter, one of the mostattractive properties of OSLD is the possibility ofreal-time dosimetry by attaching OSL detector toone end of optical fibre cable of which the other end

goes to a stimulating light source and to a PMT.The discussion on the intricacies of real-time dosim-etry is very lucid and informative. In spite of severalcomplications (e.g. increase in the radioluminescence(RL) signal with total dose), it is demonstrated thatoptical fibre system for recording RL signal andOSL signal provide an acceptable tool for themeasurement of dose and dose rates in clinical appli-cations, especially for in vivo and in-phantom dosim-etry where the dose decreases rapidly with distancefrom a source or from target/treatment volume (e.g.brachytheray and in other in vivo situations). Thechanges in RL signals are considered one of themajor draw back for real-time dosimetry. For X-raycomputed tomography (CT), the success is apparentfrom the availability of a commercial dosimetryservice (like for personal dosimetry) by Landauer,Inc. in which an OSL strip in a special holder isexposed in a CT beam at user institution and sentback to Launders for the evaluation of CTDI fromthe dose profile D(z) determined by scanning thestrip. OSL properties discussed here in this chapter(e.g. non-linearity, fading, irradiation temperature,energy dependence, etc.) are also relevant to otherapplications discussed in earlier chapters. Energydependence of high-energy photons and electronsrelevant to radiotherapy beams is similar to TLDsas expected. Although, the luminescence-based dose-meters are known to exhibit dose rate independentresponses, the results reviewed in this chapter arevery useful in confidence building for the dose rateindependence of OSLD. As concluded by theauthors, applications of OSL in medical dosimetrystill incipient in spite of being widely explored theworld over and it may take time to become popularin routine dosimetry in the near future.

The last chapter (Chapter 6) entitled ‘OtherApplications and Concepts’ is a multidisciplinarychapter dealing with retrospective and accidentdosimetry by using building materials, householdmaterials, electronic components, and dental enameland dental ceramics; environmental monitoring,passive/active devices; UV dosimetry; and somespeculative security applications. As in other chap-ters, TLD continues to occupy major importance forall the applications, but in this chapter, TL and OSLof different materials appear complementing eachother because those materials which cannot beheated can be used only for OSL. In cases where anunstable component of the signal is to be avoided,TL could appear more appropriate by excludinglower temperature glow peaks (by using an appropri-ate pre-heat treatment). Such an obvious distinctionis not possible in OSL because an OSL signal couldbe from multiple traps with higher capture crosssection irrespective of being due to shallow or deeptraps. Application of on-line dosimetry using high-sensitivity Al2O3:C OSLD in addition to passive

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dosimetry like TLD is fascinating for environmentalmonitoring also. The development of integratedsensors appears very attractive but a formidable taskfor applications, such as space dosimetry. A lot moreneeds to be done to make the dreams come true.

Among the noticeable omissions, a discussion on‘Cooled Optically stimulated Luminescence(COSL)’, a variant of photo-transferred TL, appearsto have missed the attention of the authors, in spiteseveral publications on COSL and other historicalpublications on optical readout methods of solid-state dosemeters. From the dominance of TL in abook on OSL, it appears convincing that OSLD isunlikely to displace TLD as a primary luminescencemethod but can supplement and can take lead inseveral applications.

In summary, the authors have done a commend-able job of reviewing the recent literature and bring-ing it out in a form of a book. The review iscomprehensive that is well written and would beuseful to the intended audience of not only studentsor postdoctoral fellows but also researchers and thedosimetry community. Inclusion of additionalcolour photographs of some figures in the middle ofthe book has added to the clarity of descriptions.

A. S. PradhanRtd BARC Scientist, Mumbai,

India and Visiting Scientist,KAERI, S Korea

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