IN9900403I111H

ULTRAVIOLET DOSIMBTRY USING THERMOLUMINESCENTPHOSPHORS - AN UPDATE

byJ. S. Nagpal

Radiation Standards & Instrumentation Division

1998

3 0 - 1 6

BARC/1998/E/007

^ GOVERNMENT OF INDIAo ATOMIC ENERGY COMMISSION

COO

5<CD

ULTRAVIOLET DOSIMETRY USING THERMOLUMBMESCENT

PHOSPHORS - AN UPDATE

by

J.S. NagpalRadiation Standards and Instrumentation Division

BHABHA ATOMIC RESEARCH CENTREMUMBAI, INDIA

1998

BARC/1998/E/007

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BARC External

Technical Report

BARC/1998/E/007

Ultraviolet dosimetry using thermoluminescent phosphors -an update

53 p., 18 figs., 2 tabs., 5 ills.

J.S. Nagpal

Radiation Standards and Instrumentation Division,Bhabha Atomic Research Centre, Mumbai

Bhabha Atomic Research Centre, Mumbai - 400 085

Radiation Standards and Instrumentation Division, BARC,Mumbai

Department of Atomic Energy

Government

Contd... (lb)-la-

30 Date of submission : March 1998

31 Publication I Issue date : April 1998

40 Publisher I Distributor : Head, Library and Information Division,Bhabha Atomic Research Centre, Mumbai

42 Form of distribution : Hard Copy

50 Language of text: English

51 Language of summary : English

52 No. of references : 38 refs.

53 Gives data on :

60 Abstract : Intrinsic response of various thermoluminescent (TL) materials such as CaSO4 (Dy,

Eu, Mn, Sm,Tb or Tm), LiF (Mg, Cu, P), Mg2SiO4:Tb, CaF2:Dy, CaF2:Tb, ThO2:Tb and Al2O3(Si,

Ti); cathodoluminescent phosphors Y3Al6O12:Ce, Y/dfi^: Tb and Y(V,P)O4: Eu; and

fluorescent lamp phosphors Calcium halophosphate (Mn,Sb) and Ce Mg Aluminate (Eu, Tb)

to ultraviolet (UV) radiations has been studied. Intrinsic TL response of most of the phosphors

is rate (radiant flux) dependent. For the first time, UV response of the materials is reported

for a fixed total radiant energy (total UV dose), at a single radiant flux (260 nW.cm'2), for an

appropriate comparison. A wide range of UV sensitivity is observed. Studies conducted

using UV radiation from two unfiltered low pressure mercury lamps show significant

differences in glow curves, as compared to those obtained with nearly monochromatic

UV radiations. Photons of wavelength 365 nm induce bleaching of TL induced by 254 nm

photons, in most of the materials. Sequential/tandem exposures to 254 nm and 365 nm

photons have yielded new but alarming results in CaF2:Tb. Preferential induction and

bleaching of specific TL glow peaks by 365 nm and 254 nm photons are interesting

characteristics discovered in CaSO4:Eu. Photoluminescence studies of Tb3* and Eu3* activated

phosphors have augmented the inferences drawn from the bleaching effects produced by 365

nm photons. Earlier work carried out on phototransferred thermoluminescence of CaSO4:

Dy-teflon dosimeters, TLD-100, Mg2SiO4:Tb and AI2O3(Si, Ti) has also been reviewed.

70 Keywords I Descriptors : PHOSPHORS; ULTRAVIOLET RADIATION;

LITHIUM FLUORIDES; OCCUPTATIONAL EXPOSURE; CATHODOLUMINECENCE;

| TERBIUM; EUROPIUM; PHOTONS; BIOLOGICAL RADIATION EFFECTS;

GLOW CURVE; CALCIUM SULFATES; GAMMA RADIATION; DYSPROSIUM;

PERSONNEL DOSIMETRY; THERMOLUMINESCENT DOSEMETERS

71 Class No. : INIS Subject Category : C5500

99 Supplementary elements:

-lb

CONTENTSTitle

INTRODUCTION

UV SOURCES & BIOLOGICAL EFFECTS

MATERIALS & METHODS

RESULTS & DISCUSSION

A: UV Source Spectra

B: Intrinsic Response to UV Radiations

B 1: CaSO4 based phosphors

B 2: TL phosphors with Tb as Activator

B2.1Mg2Si04:Tb

B 2.2 ThO2. Tb

B 3: Cathodoluminescent Phosphors

B 4: Fluorescent lamp Phosphors

B 4.1: Cerium Magnesium Aluminate (Eu, Tb)

B 4.2: Daylight Calcium Halophosphate

B 5: Li F (Mg, Cu, P)

B 6: Calcium Fluoride based phosphors

B6.1:CaF2:Dy(TLD200)

B 6.2: Ca F2: Tb

B 7: Alumina based phosphors

B7.1:Al2O3(Si,Ti)

B 7.2: a - AI2O3: C

C : Phototransferred Thermoluminescence (PTTL)

C 1: CaSO4: Dy dosemeters

C 1.1: CaSO4: Dy phosphor

C 1.2: CaSO4: Dy - teflon dosemeters

C2: LiF(TLDlOO)

C 3: a - A12O3: C

/ continued on the

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CONTENTS (continued)

Title Pace

Tb 29

D: UV Flux Dependence 29

E: UV Spectral Dependence 33

F: Sequential / Tandem Exposures to 254nm & 365nm photons 35

G: Photoluminescence Studies- Role of Dopants 35

CONCLUSIONS 36

Acknowledgements 37

REFERENCES 38

APPENDIX A: Biological Effects of UV Radiation on Man 41

APPENDIX B: Maximum Permissible Occupational

UV Radiation Exposures 42

APPENDIX C: UV Exposure Limits(EL) &

Spectral weighting Factors S . 43

APPENDIX D: Typical UV Emission from various sources 44

APPENDIX E : Distribution of the Radiant Flux with

wavelength for various UV Lamps 45

List of Figures 47

ULTRAVIOLET DOSIMETRY USING THERMOLUMINESCENT

PHOSPHORS - AN U P D A T E

INTRODUCTION:

Ultraviolet (UV) radiations are used in a variety of applications such as medical therapy,

sterilisation of food, water, air and medical products; and polymerisation of dental fillings.

Excessive exposure to ultraviolet radiations is harmful and it needs to be monitored.

Commercially available UV instruments mostly measure global spectral irradiance with a

typical precision of 10-20 % and can be used for assessing the damaging effects of UV radiation

on biological systems. However, due to lack of standardisation, cross calibration of the

equipments is not possible [1]. It is convenient to have UV dosemeters whose response

approximates to the reference action spectrum. Polysulfone films, on exposure to UV, exhibit

increased absorbance at 330nm, proportional to UV dose [2]. Under controlled etching

conditions, CR-39 plastic has a response approximating to the reference action spectrum. Overall

measurement uncertainty using absorbance of 1 JLWI thick CR-39 film at 400 nm is ± 20 %[3].

For almost three decades, various groups at Bhabha Atomic Research Centre.Trombay have been

engaged in development of TL phosphors and glass dosimeters and the associated read out

systems, mainly with the objective of its application in countrywide monitoring program for

external ionising radiations [4]. UV measurements using thermoluminescence dosimeters (TLD)

has been suggested by many investigators and offers the advantage of being able to place in situ,

without requirements of any special logistics [5]. UV dosimetry based on

Radiophotoluminescence [6] and Thermoluminescence dosimeters [7] was initiated in the

seventies. UV rate dependence of TL phosphors was reported by Nagpal in 1980 [8], This update

on ultraviolet dosimetric studies using thermoluminescence phosphors highlights this aspect and

presents new interesting results from recent investigations carried out by the author.

- 2 -

To appreciate the scope of the UV dosimetry, we need first to discuss various sources and

the biological effects of UV radiations, in brief.

UV SOURCES AND BIOLOGICAL EFECTS :

Electromagnetic spectrum having wavelengths between 100-400 nm is known as

Ultraviolet (UV) radiation. International Commission on Illumination (CIE) has divided it into

three regions [9].

UVA

UVB

UVC

Popular name of the region

Near UV or Blacklite

Erythemal, Tanning

Germicidal

Wavelength (nm)

315-400

280-315

100-280

EnerevfeV")

3.1-3.9

3.9-4.4

4.4-12.4

Vacuum region refers to 100 - 200 nm and is readily absorbed in air and so has little

relevance with respect to the biological damage. It however gives rise to indirect effects such as

the production of ozone (for X < 185 nm) and the oxides of nitrogen (for X < 160 nm ). The

wavelength region 200 -320 nm, which gives rise to most of the known biological effects,

hazards such as sunburn, skin erythema, skin cancer, photokeratitis, cataract and accelerated

ageing, is called the Actinic region.

Sun, Xenon arcs and other artificial sources used in sunbeds for cosmetic tanning and

medical therapy are the main sources of UV radiation. Solar radiation is the strongest source of

incoherent UVA radiation at the earth's surface; its short wavelength limit varies between 305

and 290 nm in the UVB region, depending on the weather, the purity of the air, geographical

altitude, the latitude, the time of the day and the seasonal inclination of the sun.

The biological and photochemical effects of UV radiation are related in part to the

similarity of the photon energy (eV) and the binding energies of most of chemical and biological

molecules. Various biological effects of UV radiation on man are given in Appendix A [9].

- 3 -

To protect the eyes and the skin from acute effects, Threshold Limit Values (TLV) for

occupational exposure to UV radiation were published by the American Conference of

Governmental Industrial Hygienists [10], recommended by International Radiation Protection

Association [11] and later adopted by the UK National Radiological Protection Board and by the

US Department of Health, Education & Welfare [Appendix B and C]. General irradiance levels

and permissible time (t max) for a few commonly used UV sources are given in Appendix D [12].

MATERIALS & METHODS:

Dy-, Eu-, Mn-, Sm-, Tb- and Tm activated CaSO4 TL phosphors were made indigenously

by the acid evaporation method. CaF2: Tb was grown as a single crystal and ground into powder

form. CeMg Aluminate (1.35%Eu,1.8% Tb) and Calcium halophosphate (0.73%Mn, 4.3%Sb)

were supplied by Crompton and Greaves, Mumbai. Y3Al5012:Ce 2% , Y3A15O12: Tb 2%,

Y(V,PP4: Eu 2%, ThO2 :Tb (0.1 %) and A12O3 (10 ppm Si, 300 ppm Ti ) were prepared

indigenously, by fusion method. LiF (20 ppm Cu, 2000 ppm Mg, 5000 ppm P) was prepared by

Physics Department, Nagpur University and Mg2SiO4:Tb(0.1 %) was procured from Dai Nippon

Toryo, Japan. All the phosphors in the polycrystalline form were heat treated for 1 h at 600°C,

before use. UV and gamma irradiations were carried out at RT (25°C) and thermoluminescence

intensity as well as the integrated TL output were measured, after 5 min. delay, at 20°C.sl

between 25°C and 280°C, using a S-l 1 photomultiplier and an indigenously developed TL

reader THELMEDOR, described elsewhere [13]. Sensitivity of the light detection was adjusted

using a 63Ni-plastic scintillator check-light source. A precalibrated l37Cs source was used for

gamma irradiations. For UV irradiations, two low pressure mercury lamps, Lamp 1: Pen ray

lamp (model SCT-1, 4 Watt) of Ultraviolet Products Inc.,California, U.S.A ; and Lamp 2 :

Philips ( model G6T5 GL8, 6 Watt), were employed. A blacklite lamp (4 watt), designated as

Lamp 3, was used for 365nm irradiations. The radiant fluxes, at various distances from the

lamps, were measured using a radiometer / photometer (model 1400 A) of International Light

- 4 -

Inc; Newburyport, Mass.,U.S. A. Interference filters, having maximum transmission around 250 ±

5 nm and 365 ± 10 ran, were employed to obtain specific spectral regions from the lamps.

Photoluminescence studies were made using Hitachi F 2000 Fluorescence Spectrometer.

RESULTS & DISCUSSION :

UV dosimetry using TL phosphors is based on two principles:

(a) Intrinsic TL - virgin phosphors exposed to UV, without subjecting the phosphors to

any gamma irradiation.

(b) Phototransferred thermoluminescence (PTTL): gamma irradiated phosphors

subjected to a partial thermal annealing prior to UV exposures.

A: UVSOURCE SPECTRA -

Emission spectra of the lamps used for the studies, corrected for the detector response,

are shown in Fig.l. Pen ray lamp(Lamp 1, Ultraviolet Products Inc. San Gabriel, U.S.A.) and

microprocessor erasure lamp (Lamp 2, Philips make) are low pressure mercury lamps giving all

the mercury lines 254, 313, 365, 405, 436 and 546 nm, with maximum output ( >90 %) at

254nm. The quantitative light outputs and the relative emission intensities at various

wavelengths are observed to be different in Lamps 1 and 2. Intensity ratio of emission at 254nm

to that around 365 nm is observed to be 21: 1 for lamp 2 (Philips), whereas it is 13: 1 for lamp 1

(Pen ray), showing that lamp 2 is richer in 254 nm emission. In general for the lamps, intensity

ratio in various spectral regions depend on mercury vapour pressure, the lamp envelope and the

operating conditions. Lamp 3, having innerline coated phosphor, has broad emission around

365nm with other wavelengths, as shown in Fig. 1.

B: INTRINSIC RESPONSE TO UV RADIATIONS:

As the list of phosphors being dealt with in this report is large, for the sake of convenience,

the discussion of the phosphors has been clubbed together, suitably on the basis of the matrix, the

activators or having comparable UV sensitivity.

- 5 -

O

o8a

•436 y tin 546 nm

25O 3OO 35O 4OO 4 5O

OO

WAVELENGTH ( nm )

Fig . 1: Emission spectra of the lampsa. Pen ray lamp ( Lamp 1) b. Blacklite lamp ( Lamp 3)

- 6 "

2Or

15TIME(s

Fig. 2 : TL glow curves of CaSO4 based phosphorsUltraviolet radiation ( Pen ray lamp, bare)Gamma radiation

- 7 -

B 1; Calcium Sulfate based phosphors -

Typical TL glow curves of UV ( from bare Lampl ) and gamma irradiated CaSO4 based

phosphors are shown in Fig. 2. Overall, three groups of peaks 80°-100°C, 120°-130°C and 200°-

220°C are observed. Relative peak heights of the three groups vary with the dopant, phosphor

preparation method and the nature of the radiation ( 365nm, 254nm or gamma photons). For

reasons of clarity, glow curves only for bare pen ray lamp and 137Cs gamma radiation are

presented in Fig.2. Generally, UV irradiation gives rise to lower temperature peaks (80°C,

120°C), whereas gamma radiation preferably populates 220°C glow peak, with exceptions in

case of CaSO4.Eu and CaSCVMn. Both gamma as well as UV radiations produce a single glow

peak around 100°C in CaSO4 :Mn; and 120°C glow peak is predominant in CaSO4 :Eu for UV

exposures. Similar observations were reported earlier by Nambi et. al [7]. Table 1 gives the

relative response of the phosphors to UV radiation from the bare Lamp 1. A wide variation in

UV sensitivity of the phosphors is found in literature because of difference in the samples and

also because of incomplete comparisons being made, due to radiant flux values not being stated.

Earlier, Chandra et. al [15] have studied UV response of CaSO4: Dy and reported good intrinsic

response at 210, 250, 300nm with a small inherent response at 350 and 400 nm. Intrinsic TL

response of CaSO4 : Dy-teflon discs at 210 nm, 250 nm and 300 nm using narrow bandpass

filters has been reported in ratio 940 : 30 : 1 at 500 mJ.cm"2, respectively by Calvert et.al [32].

Of the CaSO4 phosphors examined here, CaSO4:Tm has the highest TL response to UV

radiations from bare Lamp 1. This does not agree with the Danby's claim of CaSO4: Eu, having

the highest sensitivity [16].

Extensive studies were carried out on CaSO4 : Eu using various UV lamps and narrow

bandpass filters. Gamma irradiation of CaSO4:Eu produces a glow peak around 120°C, with a

minor signal around 220°C (Fig.3 a). On exposure to blacklite lamp (Lamp 3, main emission

365 nm ) the TL glow intensity is maximum around 120°C (Fig 3 b). Another CaSO4: Eu sample

- 8 -

O

15

1O

,Y: •-••• b'

15TIME(s

O 15 3OTlME(s }

Fig. 3: TL glow curves of CaSCV Eu on exposure toa. gamma radiation (O.I Sv)b. blacklite lamp (mainly 365 nm)b'. blacklite lamp with 365 nm filterc. UV radiation (bare pen ray lamp)d. pen ray lamp with 250 nm filtere. philips lamp (bare)

- 9 -

exposed to blacklite lamp, to almost the same UV dose ( mJ.cm"2), through an interference filter

having a narrow bandpass and 15 % optical transmission around 365nm, a glow curve as shown

in Fig. 3 b'is obtained. This is identical to that of Fig.3b. Thus, it can be inferred that 365nm

induced intrinsic TL in CaSO4:Eu has predominant peak around 120°C with very small

proportion of the charge carriers contributing to 80°C and 220°C glow peaks. Exposure to pen

ray lamp (Lamp 1, without any additional optical filtration) gives rise to a glow curve shown in

Fig. 3 c. This lamp having a lower intensity ratio of emission at 254nm to that at 365nm, as

compared to Lamp 2, produces highest glow peak around 120°C with significant TL emission

around 80°C, 100°C and 220°C. The additional hump around 100°C is clearly identifiable and

very reproducible. On extended exposure of CaSO4:Eu to Lampl, through a 250nm interfererice

filter produces a glow curve, as shown in Fig. 3d. In this case, the TL emission around 220°C is

the highest with minor contributions to 80°C and 120°C peaks. These results indicate that

exposure to 365 nm photons favours trapping of the charge carriers at the defects/locations

responsible for 120°C peak, whereas 220°C peak is favoured by 254 nm photons.

On exposure to bare Lamp 2 (richer in 254 nm emission), CaSO4:Eu gives a glow curve

with maximum TL intensity around 220°C (Fig. 3e). Another virgin sample exposed to Lamp 2

through a 250 nm interference filter to the same UV dose, increasing the exposure time to

correct for the filter transmission, produced a TL output lesser by a factor of 1.8 (radiant flux

dependence!!), thus further strengthening the above stated conclusions.

Similar studies with 254nm / 365nm photons, on CaSO4 : Dy and CaSO4 : Tm yield

somewhat different results, showing that the process is dopant dependent.

TL output for UV exposed CaSO4: Eu is observed to be linear against radiant energy over

1 - 50 mJ.cm"2 for any given radiant flux (mW.cm"2), with or without 250 nm interference filter

(Fig.4). Similar measurements for CaSO4: Tb and CaSO4: Mn are shown in Fig.6.

DCL

h-DO

1O1

to ^

CD a-

•e °n 1O

h-151

162

id1

-10-

I I I3 -• 5

1Oo 3 •• S T S • • 5

1O'UV EXOSURE (mJ.cm5

Fig. 4: TL response of CaSO4: Eu to UV radiationExposure under two different conditionsa : bare pen ray lamp at 90fiW.cm"2

b: philips lamp, with 250 nm filter, at 19u.W.cm"2

-11-

B 2; TL phosphors with Tb as activator -

B 2.1 Me2SiO1: Tb - UV irradiated Mg2SiO4 : Tb has highest TL emission around 200°C

with small peaks around 80°C and 110°C (Fig.5). Its integrated TL output as a function of radiant

energy (mJ.cm*2) for any given radiant flux (mW.cm"2) is linear in the initial stages but becomes

supralinear thereafter (Fig.6 c). This is in agreement with the observations made earlier by

Lakshmanan etal [18] over 1 -103 mJ.cm'2 However, its intrinsic TL response to UV is observed

to be rate dependent.

B 2.2 ThO2: Tb - On UV irradiation, ThO2: 0.1 %Tb (600°C -1 h treated) shows TL peaks

around 85°C and 200°C (Fig.5). Its response is rate dependent and linear over limited radiant

energy range (Fig.6 d ).

B 3: Cathodoluminescent Phosphors -

Cathodoluminescent phosphors like Y3Al5012:2%Ce3+ (YAG:Ce), Y3Al50i2: 2%Tb3+

(YAG:Tb) and Y(V,P)O4: 2% Eu (YVP:Eu), developed at Trombay, have high quantum

efficiency for conversion of UV and electrons to visible light [19]. Fig. 7 gives TL glow curves of

the irradiated phosphors and the integrated TL output as a function of incident radiant energy. On

UV irradiation, using Lamp 1, YAG:Ce exhibits a single TL glow peak around 125°C and the TL

integrated between 25°O250°C is linearly proportional to radiant energy over 0.2-15 mJ.cm"2.

YAG:Tb, on similar UV irradiation, exhibits a single glow peak around 130°C, and the

integrated TL response is linear over radiant energy range 250 jjJ.cm"2 - 60 mJ.cm"2.

YVP:Eu shows two glow peaks around 125°C and 220°C. The integrated TL between

25°C - 280°C is linear over a limited radiant energy range 5-20 mJ.cm*2, becomes sublinear

thereafter and saturates around 500 mJ.cm'2 [20]. Relative TL response of YAG:Ce, YAG:Tb and

YVP:Eu to germicidal wavelength (254 nm) is 85 : 28 : 1.5, taking UV response of CaSO4: Dy

(0.1%) a s l .

- 1 2 -

20DC

Mg SiO :Tby2 4

3Os

ThO2:Tb

CaSO^Tb

3Os

3Os

o 15 3OsTIME

Fig. 5: TL glow curves of U V and gamma irradiated samples

a : gamma b: 365 nm c : 254 nm photons

-13-

Z>CL

O

itfv-

1O'

54 -3

1 #

Mg SI

CaSOjMn

Ca5O:Tb4

100 15 , o 3

RADIANT ENERGY (mJ.cm

Fig. 6: TL output vs. Radiant energy for various phosphors at a fixed UV radiant flux

a:CaSO4:Mn at 260 ^iW.cml c : Mg2Si04:Tb at 19 iW.cm"-.

b : CaSO4: Tb at 260 uW.cm'; d : ThO: :Tb at 40 uW.cm*;

- 1 4 -

o' ocs

5 r

c•3

s

>z, *

4: Eu

$ Y3Al5012:Ce a.

;!iv o_J

O 15 30

TIME(S I

AI5O,2: Tb

: Eu

i i 11 i i 111 i i 111 I

0.1 1 10 loo IOOO

RADIANT ENERGY (mJ/cm2)

Fig. 7: UV response characteristics of Y- based TL phosphors

- 1 5 -

15 3O

T I M E ( s )

Fig. 8: TL glow curves of Ce Mg Aluminate(Eu,Tb),on

irradiation to 60 Co — 365 nm .... 254 nm

-16-

1OO

UJ 75tozO

5) 5OLLJ

rrI- 25

OO O.25 O.5O OJ5 1.OO

2O ^

O1.25

2RADIANT ENERGY (mJ.cm )

Fig. 9: TL response of CeMg Aluminate (Eu,Tb) to

/ 254 nm photons at radiant flux 19 j-iW.cm"2

a : Integrated TL for 30 s at 25°C, without heating

b : TL integrated between 25° -280°C, after 5 min. delay

- 1 7 -

UV response of the three phosphors tested over 80 - 700 iW.cm"2 is observed to be rate

independent, an important characteristic for TL based UV dosimetry. These phosphors are light

sensitive and need to be protected from incandescent as well as fluorescent room lights.

Significant TL is induced even in virgin phosphors.

B 4: Fluorescent Lamp Phosphors -

Cerium magnesium aluminate : Eu,Tb (CMA) and Calcium halophosphate: Mn,Sb

(CHP), two phosphors currently being used for commercial production of fluorescent lamps in

India, have high TL response to UV radiation.

B 4.1 Ce Magnesium Aluminate(Eu,Tb) : On exposure to 365 nm photons (3.4 eV

energy), the phosphor exhibits main glow peak around I25°C with humps around I45°C and

190°C (Fig.8). As the energy of the incident photons is increased to 4.89 eV (254 nm), the glow

peak maximum shifts to 145°C, with a hump at 190°C. In addition to these glow peaks, the

phosphor shows fast decaying TL at room temperature (25°C), immediately after UV

irradiations . It forms nearly 5-7% of the total integrated TL (Fig 9a) and becomes negligible

after 5 min. storage at 25°C. Hence it is advisable to Wait for 5 min., to isolate the uncertain

contribution from the fast decaying TL emission. Intrinsic TL response to 254 nm photons is

high and TL response vs. incident UV radiant energy is linear over an extended range (Fig.9 b) .

Even a few nJ.cm"2 of 254 nm UV can be detected with good confidence. Its UV sensitivity is

20 times of that of Mg2Si04:Tb and 5 times of that of Y3Al5O12:Ce3+ [20].

It is noted that and UV induced peaks occur at lower temperatures than those induced by

ionising radiations. It is similar to observations made earlier by several other investigators.

B4.2 Daylight Calcium halophosphate (CHP):

TL produced by normal room lights is negligible but the germicidal wavelength (254 nm)

produces intense photoluminescence and thermoluminescence in CHP. UV irradiation produces

main TL peak around 125°C (Fig. 10), quite at variance with the glow curves of gamma irradiated

- 1 8 -

125 C

tz

Z

A

O 15 3OTIME(s )

B

O 15 3 OTIME ( s)

Fig. 10: TL glow curves of Ca halophosphates

A : UV irradiation (254 nm) B: l37 Cs gamma (0.01 Sv)

- 1 9 -

samples, which have main glow peaks around 145°C and 185°C, with a small hump around

125°C. In general, UV populates the lower temperature peaks. Intrinsic TL response of the

phosphors for a given UV radiant energy is independent of the radiant flux ( rate independent).

UV response for Blue, Daylight and Red samples in the ratio 20 : 10 : 1, is observed to be

sublinear right from 1 mJ.cm2 and saturates around 800 mJ.cm"2 [TL output equivalent to =5 Gyi.

gamma exposure], UV produced TL signal fades very fast, the integrated TL initially reduces by

50 % in 5 min., 90 % over 2d storage, even in dark [21]. The initial rapid fading is due to a

predominant peak around 60°C and gets depopulated fast, emitting TL at room temperature

itself.

B 5: LiF(Ms,Cu,P) -

TLD-100 as well as LiF : Mg,Ti have low intrinsic UV response but the newly developed

LiF(Mg,Cu,P), having high radiation sensitivity [22], has good UV response [23]. Our

measurements on ceramic material MCP-N (Polish make) supplied by Olko et.al [24] showed

poor UV response even after grinding it into powder form. LiF (20 ppm Cu, 2000 ppm Mg and

5000 ppm P) powder developed by Moharil et.al [25] has high intrinsic UV response. Even

though a strict control is recommended during thermal annealing for 10 min. at 240°C for its

reuse, the phosphor has some interesting characteristics. UV radiation, from a pen ray lamp,

produces a single glow peak around 75°C as compared to the reported five glow peaks at 93°,

137°,202° 236° and 267°C for gamma irradiations(Fig 11). TL output against UV radiant energy,

for a given radiant flux, is linear over a very limited radiant energy range (15 mJ.cm'2) and is

sublinear thereafter. Since the UV induced glow peak is relatively at a lower temperature (75°C),

one reading cycle of 20°C/s for 30 s at T^* of 240°C is sufficient to anneal the phosphor for its

reuse. UV response is, however, rate dependent. Intrinsic response of the phosphor to 365 ran is

very feeble. Preliminary measurements on the phosphor, using narrow wavelength intervals of

the low pressure mercury lamp, indicate that the response to the bare lamp UV radiations is not

- 2 0 -

,nd

D0

H

!D

10

5

' LiF465bare

•

(Mg, Cu, P)nW.cm*2 UV radiation ^-*—»Pen rav lamp J^^

10'

5

D * 3 f Z 3 -f 5 1O2 2. 3 4- 5 1C3- 2 ,

. RADIANT ENERGY (mJ.cm )75 C

15 30TIME(s)

Fig. 11: TL glow curves of UV ( ) and beta ( —) exposed

LiF (Mg,Cu, P)

-21 -

1O2r

1O1

I-

8

O

to

5 -4 -

a -

-2,62

ALO.

i i • i • i i i J I I—L. ' i l l

id1 3A5 3 4 5 10

RADIANT ENERGY (mJ.cm- 2

10

Fig. 12: UV response of various TL phosphors

- 2 2 -

due to the 254 nm line alone. Though still unidentified, other emission lines play an important

role in UV induced TL of LiF (Mg,Cu,P). Some sort of synergistic phenomenon is not ruled out.

B 6: Calcium Fluoride based phosphors -

B 6.1 CaF2:Dv (TLD 200) : UV response of the Harshaw TLD-200 phosphor was studied

after 1 h heat treatment at 600°C. TL glow curves of the UV exposed and gamma irradiated

samples are shown in Fig. 13. For a given radiant flux, its TL output is linear over a limited

radiant energy and becomes sublinear thereafter (Fig. 12). Its response is rate dependent. Earlier

investigators have reported a significant increase in its UV response when the phosphor is heat

treated at 900°C [26].

B 6.2 CaF?: Tb- On UV irradiation, CaF2: Tb crystal and polycrystalline phosphor(Fig. 5),

show TL glow peaks around 90°C, 140°C and 185°C [27]. The material has good UV sensitivity

but its TL response is linear over a very limited range (Fig. 12), similar to that observed for CaF2:

Dy. Its response is rate dependent.

B 7: Alumina based phosphors -

B 7.1 Al2O2(ShTi) - Between RT and 400°C,.Al2O3(10 ppm Si, 300 ppm Ti), on gamma

irradiation shows four glow peaks at 90°C, 125°C, 185°C, 225°C and 320°C [28]. Its response to

365 nm is very feeble but it has high response to germicidal wavelength. On UV irradiation, TL

peaks around 85°C, 120°C and 180°C are observed (Fig. 13). Its UV response is rate dependent.

TL output vs. radiant energy over 0.78 - 156 mJ.cm2 is observed to supralinear (slope 1.19) as

shown in Fig. 12. Growth of individual glow peaks is also supralinear.

B 7.2 a- Al?0v C - recently developed most sensitive TL material for radiation dosimetry,

shows a single glow peak around 180°C, for UV as well as gamma irradiations. Its UV response

is observed to be linear upto 1 J.cm"2 [29]. The material is reported to suffer from the drawback

of light induced fading, heating rate dependence and severe LET dependence.

- 2 3 -

6 r

zLLJ

2

h-

4

3 -

O

lTLD-2 OO

~-4

O 15 3OTIME (s )

4

>

ZLJJ

f-

3

oO 15 3O

TIME ( s )

Fig. 13: TL glow curves of Harshaw TLD-200 (CaF2: Dy)

and A12O3 (Si,Ti) a : gamma irradiation b : UV irradiation

- 2 4 -

C: PHOTOTRANSFERRED THERMOIUMINESCENCE (PTTL) -

Deep traps as well as the dosimetry traps of a TL material are filled with a predose of

beta or gamma radiation and subsequent partial thermal annealing removes the trapped charges

from the dosimetry traps. PTTL involves the production of TL by phototransfer of charge

carriers from deeper, filled traps to empty traps. PTTL response of all the phosphors has been

observed to be rate independent, unlike the case of intrinsic TL. PTTL can be induced and read

many times, after a single high gamma exposure. PTTL intensity, however, depends upon

( i ) level of predose irradiation and UV dose,

( i i ) time and temperature used for partial annealing,

(iii) sample temperature during phototransfer (UV exposure).

Since PTTL depends upon a number of factors, only a few typical studies are discussed here.

C1: CaSO±: Dy dosemeters -

C 1.1 CaSOi : Dv phosphor - Main dosimetry peak ( near 200°C ) of CaSO4 : Dy phosphor

saturates with increasing gamma exposure at about 105R, but PTTL for samples (partially

annealed for 15 min. at 280°C, after gamma exposure) does not saturate upto at least 108R, when

illuminated with 254 nm photons [30]. For short illumination and sample not too dense optically,

PTTL of CaSO4:Dy grows as (Exposure)055 upto at least 108R.

Effect of post gamma partial annealing temperature (400°C-600°C / 6 min. each), the

sample temperature during phototransfer by 365 nm photons and the fading of the PTTL signal at

room temperature(28oC-30oC)) has been studied by Nagpal et.al [31]. Both 120°C and 220°C are

repopulated by 365 nm photons. For partial annealing temperatures upto 480°C, ratio of the

120°C PTTL peak to the 220°C PTTL peak increases, and above 480°C, there is a reversal of

the trend. The integrated PTTL output for the phosphor (gamma exposure 2 xlO4 R, annealed for

6 min. at 460°C) was observed to increase with the sample temperature during phototransfer

(with 365 nm) upto 110°C, after which a decrease was observed. For samples annealed at 380°C

- 2 5 -

h-

LJ

\

a:

1.00-

0.90

0.80

0.70 -

0.600 10 15

TIME (

O

UJ

r-<

UJ

Gamma Exposure : 30 Gy, partial anneal 300°C- 15 min.phototransfer with 310 nm , exposure time varied

Gamma dose : 10 Gy,Partial anneal 300°C- 15 min.Exposure time : 15 min. at various wavelengths

230 310 350 400 480

WAVELENGTH <r\m.)

570

Fig. 14 : PTTL characteristics of CaSO4- teflon dosemeters (6 mm §, 0.8 mm thick,20 mg)TL integrated between 200°C - 360°C

[Reference: Potiens. A.Jr. et al - Ultraviolet and Laser Radiation Dosimetry using PTTL in CaSO^Dy;

Radiat.Protect.Dosim. 66, 1-4 (1966)95-96.]

- 2 6 -

and phototransfer carried out at 90°C, the re-estimation accuracy for 1 R original gamma

exposure was ±20%.

C 1.2 CaSOj:Dy-tefIon dosemeters - Calvert et.al [32] have studied PTTL induced in gamma

irradiated, 266°C annealed CaSO4:Dy-teflon discs for 210 nm and 250 nm photons at 19 and 133

mJ.cm"2 respectively. Net TL produced consisted of intrinsic as well as PTTL. Illumination over

the wavelength region 250 - 405 nm resulted in optical bleaching of the gamma induced TL. No

measurable effect was detected for wavelengths greater than 405 nm.

Integrated PTTL output of CaSO4:Dy-teflon discs between 200°C-360°C has been

reported to be linear between 10 - 65 Gy of gamma radiation and phototransfer duration of 5

min. at 310 nm, by Potiens.Jr. et. al [33]. Studies on 10 Gy samples, using 15 min. phototransfer

over the wavelength range 230 - 570 nm, showed maximum PTTL occuring at 310 nm (Fig. 14).

C2: LiF(TLD - 100) -

A major portion of the individual monitoring all over the world is carried out using tissue

equivalent TLD-100 or LiF( Mg,Ti ). PTTL method has been adopted for re-assessment of the

individual doses. Mason [34] reported that with Con-Rad type LiF, UV produced a broad

intrinsic TL peak around 90°C, whereas PTTL peaks were observed at 120°C, 170°C and 210°C

for samples partially annealed upto 320°C. Gamma doses of 10 rad (0.1 Gy) and above could be

re-assessed. PTTL of TLD-100 crystals was used by Buckman & Payne [35] for germicidal UV

dosimetry. As small as 0.1 i VV.cm2 could be detected, using gamma (5 x 105 R) irradiated

sample, partailly annealed for 1 min. at 300°C after the routine TL read out cycle. PTTL

response, linear with UV exposure upto 7 mJ. cm"2 and sublinear thereafter, increased with the

temperature during UV exposure. It was observed to be exposure rate independent. McKinlay

et.al [36] reported similar temperature dependence of PTTL for LiF:Teflon disc elements and

standardised re-assessment procedure, using 254 nm photons(4 mW.cm"2) at 115°C for partially

annealed (15 s at 300°C) samples over primary gamma exposures 0.2 mGy- 1 Gy.

- 2 7 -

1

HDQ.

or-

QJ

1.1

1.O

o.o1O 1O

RADIANT FLUX - 2 .

Fig. 15: Intrinsic TL response ofC'aSO^ phosphors lo U V nidiations as a

function of radiant dux

Dy : 2.6 mJ.cm"'. Tb : 2.5 mJ.cm'2. Sm : 2.6 m.l.cm"2,

Tm : 2.6 mJ.cm"2. M n : 5 ° mJ-cm'2

- 2 8 -

2.5 r

2.O

h-Da.i -DO\-

1.5

1.O

O.5

1O

LLF(MgCu

:Tb

/CMA

AI2O3(SL,TC)

3 - 4 5 p 2 . 3 4 5 :

• ic r ig-RADIANT FLUX

Fig. 16: UV response of TL phosphors as a function of radiant flux.

- 2 9 -

C3:

Main dosimetry peak around 180°C is observed for UV and gamma irradiations. Deeper

traps, thermally stable upto 930°C, also exist in the material [37]. Colyott et.al have used

dosimeters made of thin layer of a- A12O3: C powder (2.5 mg.cm'2, < 40 nm grain size) on an

aluminium substrate, gamma irradiated to 1-30 Gy at RT and preheated at 600 K for 2 min. to

empty the main dosimetry peak. The system, capable of multiple readouts for PTTL, having

linear response over 102 - 05 uJ.cm"2 of UV spectral region centred at 307 nm, has very little

temperature dependence upto 50°C. It serves as an excellent integrating UVB dosemeter. Field

tests have confirmed its utility and the PTTL response is rate independent [38].

C 4: Me^SlQj: Tb -

PTTL of Mg2SiO4: Tb has been studied by Lakshmanan etal [18] .Intensity of the 200°C

PTTL peak and the sensitization factor S / So have been observed to be proportional to the RTL

peak at 450°C. It has been shown that the phosphor, after a gamma exposure of 2.73 x 102 C.kg"*

and a post anneal of 1 h at 300°C, can be used for UV dosimetry over 5 -103 mJ.cm"2 range.

D: UV FLUX DEPENDENCE -

The intrinsic UV response of most of the TL phosphors is rate dependent [8]. Higher the

radiant flux (mW.cm*2), higher is the TL output even for a constant UV dose (mJ.cm'2). Rate

dependence of the TL phosphors for a fixed dose from bare Lamp 1 is shown in Figs. 15-17. The

factors by which the TL response increases when flux (rate) is increased from 19 to 500 jaW.cm"2

of UV, are given in Table 1. Since some of the phosphors have sublinear or supralinear UV

response, the radiant energy for which the rate dependence has been determined, is also stated in

column 5 of the table. The highest rate (flux) dependence of 7.9 is observed in case of CaSC>4:

Tm. For a total radiant energy of 2.5 mJ.cm2, the intrinsic TL response of the phosphor at 500

uW.cnT2 is 7.9 times higher as compared to that at 19 nW.cm'2. No overall direct correlation

between the flux dependence and the gamma or UV sensitivity of the phosphors can be inferred.

-30-

O.3r

LJ

COLd

a:_J

UJ

<- JUJ

cr:

O.2

1O2 1O3

- 2 , .RADIANT FLUX (yU.W.cm )

Fig. 17: UV response of CaSd: Eu as a function of radiant fluxa: Pen ray lamp (bare) - UV exposure 2.5 mJ.cm'2

b : Philips lamp (bare) - UV exposure 2.6 mJ.cm"2

-31-

TABLE 1

CHARACTERISTICS OF VARIOUS PHOSPHORS FOR IJV DOSIMETRY

PHOSPHOR

CaSO4:Dy 0.1 %

CaSO4:Tm 0.1%

CaSO4:Tb 0 .1%

CaSO4:Mn 0 .1%

CaSO4:Eu 0 .1%

CaSO4:Sm 0 .1%

A12O3 10 ppm Si

300 ppm Ti

CaF2:Tb 0.05 %

CaF2: Dy TLD-200

ThO2:Tb 0 .1%

Mg2SiO4:Tb0.1%

Y3Al5Oi2:Ce 2%

Y3A15O,2: Tb 2%

Y(V,P)O4 :Eu 2%

Calcium halophosphate

0.73%Mn, 4 3 %Sb

CeMg Aluminate

1.35%Eu,1.8%Tb

LiF 20 ppm Cu

2000 ppm Mg

5000 ppm P

Make

BARC

BARC

BARC

BARC

BARC

BARC

BARC

BARC

Harshaw

BARC

Japan

BARC

BARC

BARC

Crompton,

Mumbai

Crompton,

Mumbai

Nagpur

University

Intrinsic UVresponse V / mg[Bare Pen ray lamp

7.8 m J.cm'2 at260 jiW.cm"2|

0.80

3.00

0.27

1.00

1.40

0.84

1.63

0.36

0.10

2.20

16.9

68.0

23.0

1.2

0.14

350

0.40

Radiant Fluxdependence for19-500nW.cm"2

at mJ.cm"2

6.1 2.6

7.9 2.6

5.0 2.5

4.4 5.0

3.6 2.6

4.5 2.6

2.7 2.6

3.0 4.5

1.6 14.0

2.6 1.0

7.0 2.5

1.0

1.0

1.0

1.0

3.5 1.5

3.55 4.65

Effect of 365 nmphotons on 254nm induced TLpeaks

Bleaches

nil

Bleaches

Bleaches

Bleaches

Bleaches

Bleaches

Bleaches

Bleaches

Bleaches

Bleaches

Adds on

Bleaches

Adds on

Bleaches

- 3 2 -

105* \AO*C

O 15TIME ( s )

Fig 18 :TL GLOW CURVES OF CaF2;Tb CRYSTAL ON IRRADIATIONto (a)220nm (b) 260nm (c) 290nm (d) 320rim

(e)350nm (f) 380nm (g) 400nm

- 3 3 -

It is noteworthy to record that the relative peak height ratios for a phosphor, for a given radiant

energy, do not change at different radiant fluxes. Thus the relative probabilities for capture of

various charge carriers, by the respective sites / defects responsible for different glow peaks, do

not change with the radiant flux. Different incident photons such as near visible (365 nra), UV

(254 nm) and gamma do give rise to different peak height ratios, as discussed for various

phosphors.

Intrinsic TL response of CaSO4 : Eu to UV radiation is definitely not rate- independent,

disagreeing with the findings of Madhusoodanan et. al [17]. Results of multiple measurements

with several virgin samples, under specially controlled conditions over 19-725 jxW.cm'2, are

shown in Fig.17. Using Pen ray lamp, when the radiant flux is increased from 19 to 500 jaW.cm"2,

for a fixed total radiant energy of 2.5mJ.cm2, the TL response increases by a factor of 3.6,

whereas a lesser rate dependence of 2.0 is observed for Lamp 2, over the same radiant flux range.

At this stage it is not possible to provide an explanation for the different radiant flux dependence

obtained using the two UV lamps. It looks difficult to enunciate the roles played by the

individual lines, unless experimental results of narrow bandwidth irradiations are examined.

E: UV SPECTRAL DEPENDENCE -

Preliminary measurements on CaSO4: Eu, Y(V,P): Eu and CaF2 : Tb samples using

narrow bandwidth UV radiations have shown that the TL induced in virgin samples is highly

dependent on the incident photon energy (wavelength). Significant differences in the glow curve

structure as well as the relative TL response are observed, as the incident energy is varied

(Fig. 18). To interpret the glow curves and the TL output per unit incident radiant energy in

relation to the kinetics and the defects responsible for the response, studies for each mateial

using narrow band or very nearly monochromatic UV photons might help.

- 3 4 -

TABLE 2

INTRINSIC RESPONSE OF CaF2:Tb CRYSTAL FOR

SINGLE AND COMBINED UV EXPOSURES

S.No:

1

2

3

4

5

EXPOSURE

blacklite 365 nm

2400 mJ.cm 2

pen ray lamp

through 254 nm bandpass filter

15 mJ.cm'2

simultaneous incidence

15 niJ.cm'2 254 nm and 2400 mJ.cm"2 365 nm

15 mJ.cm"2 of 254 nm followed by

2400 mJ.cm'2of 365 nm

2400 mJ.cm" of 365 nm followed by

15 m J.cnf2 of 254 nm

Normalised

response

(arb. units)

0.072

1.000

0.487

0.258

0.984

- 3 5 -

F: SEQUENTIAL /TANDEMEXPOSURES TO 254 nm & 365 nm PHOTONS -

TL response of various phosphors has been studied using low pressure mercury lamps.

Intrinsic TL response (V / mg) for various phosphors given in Table I refers to the integrated TL

output, measured between 25°C - 280°C, after a wait of 5 min. after termination of the UV

exposure from the bare UV lamp having all the characteristic Hg lines 254 nm(>90%), 313nm,

365 nm, 405 nm, 436 nm and 546 nm. When UV sensitivity of the phosphors is to be stated and

compared, it should be read in conjunction with complete information about the source spectra.

Otherwise, it is incomplete. Selected studies using narrow bandwidth spectra (254 ± 5 nm and

365 ±10 nm) with two separate lamps, have given very interesting results. It has been observed

that the incidence of 365 nm photons bleaches the TL induced by 254 nm in some of the

materials. Earlier, somewhat similar observation has been made by Calvert etal in case of of

CaSO4: Dy - teflon discs [32]. In a few cases, it adds onto the TL produced by 254 nm (Table 1).

The extent of bleaching differs from phosphor to phosphor. The sequential order of incidence

also matters. Typical of results obtained for CaF2 : Tb are given in Table 2. For a routine UV

dosimetry from any source which emits a variety of photons, this observation raises an alarm.

G: PHOTOLUMINESCENCE STUDIES- ROLE OF DOPANTS :

Photoluminescence and thermally stimulated studies on rare earth (Tb3+,Ce3+ and Eu +)

dopants in various matrices such as Th62, CaF2, Y3Al50i2 and Y(V,P)O4 have been carried out.

These investigations have indicated that:

(a) For ThO2 and Y(V,P)O4 matrices, reduction in photoluminescence intensity was

observed on continuous irradiation with UV photons corresponding to f-d (of Tb3+) and f-p1

(of Eu3+) bands of the dopant ions in the respective matrices.

- 3 6 -

(b) The reduction in photoluminescence intensity was observed to be reversed, by

365 nm photon illumination, in all the systems where 365 nm photons initiate optical

bleaching in the intrinsic TL induced by 254 nm photons.

(c) Different phosphors have varying intrinsic TL response for 254 nm photons, but

the wavelength dependence studies have revealed that the intrinsic TL response is

maximum for UV photons corresponding to f-d transition band for Tb3+ ions and f-p"1 for

Eu ions.

UV induced TL is predominantly brought about by the absorption of energy in the

respective f-d / f-p'1 bands and subsequent non-radiative energy transfer mode, stabilizing

excited electrons at trapping sites. As f-d / f-p'1 transitions are sensitive to ligand field,

matrix dependence is also observed.

CONCLUSIONS:

UV sensitivity of the phosphors is highly dependent on the method of preparation

and even using the same method, one may obtain batches, differing in sensitivity by a

factor of 2 or 3. Intrinsic TL response of the phosphors, studied for UV radiations at a

single radiant flux (rate) of 260 uW.cm"2, spreads over three orders of magnitude. A wide

variety in choice of sensitivity and usable radiant energy (UV dose, mJ.cm"2) is available.

Intrinsic TL response of most of the phosphors is, however, rate dependent. TL output at

any UV dose (mJ.cm"2) is higher for a higher rate of incidence (uW.cm'2). Highest rate of

dependence of 7.9 is shown by CaSO4: Tm (0.1 %), when the flux is increased from 19 to

500 nW.cm'2. Mg2Si O^Tb shows a rate dependence of 7.0 over the same flux range.

2: Dy (TLD-200) shows the lowest rate dependence of 1.6. Only cathodoluminescent

- 3 7 -

phosphors Y3Al5Ou.Ce3', Y3A15O12: Tb3\ Y(V,P)O4 :Eu3< and Calcium halophosphate

(Mn, Sb) show a UV response which does not depend on the rate of incidence. Intrinsic

TL response of CaSOa: Eu to UV radiation is definitely not rate independent. Materials

such as CaF2:Tb , CaF2:Dy and ThO2:Tb have limited usable range.

Photons of wavelength 365nm (blacklite) bleach the TL induced by 254nm

photons, in a majority of the materials investigated. Photoluminescence studies of Tb3' and

Eu' * activated phosphors have augmented the inferences drawn from the bleaching effects

produced by 365nm photons. Sequential / tandem exposures to 254 ± 5nm and 365

±10nm photons have given interesting results in CaF2:Tb. Preferential population of 120°C

TL glow peak by 365 ±10 nm photons and of 220°C peak by 254± 5nm photons is a

newly discovered characteristic of CaSO4: Eu. These results suggest that TL studies with

nearly monochromatic radiations may be worth pursuing, for all the materials. The studies

will help characterisation of the phosphors and the defects / traps associated with the

individual glow peaks populated by specific wavelengths.

Acknowledgements : The author is grateful to Dr. K.S.V.Nambi, Head, Environmental

Assessment Division, BARC, for critical review of the manuscript and several helpful

suggestions. Thanks are also due to Dr. U.C.Mishra, Director, Health, Safety and

Environment Group, and To Dr. S.C. Misra, Head, Radiation Standards and

Instrumentation Division , Bhabha Atomic Research Centre, Trombay for constant

support and encouragement. It is a pleasure to acknowledge helpful discussions with

Dr.R.K.Kher, Dr.A.G.Page and Dr S.V.Godbole.

-38-

REFERENCES:

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(1997)217-224.

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13. Nagpal J.S. et al - Studies on 63Ni based Check Light Sources for TLD Readers; Radiat.

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Solid Stat.Phys. 7(1974) 4403-4415.

- 3 9 -

REFERENCES (contd.)

15. Chandra B. etal - Ultraviolet Radiation response of CaSO4:Dy; Phys.Med.Biol. 21(1976)

67-73.

16. Danby R.J.- Ultraviolet induced Charge Transfer in CaSO4:Eu; J.Phys.C:

Solid Stat.Phys. 21 (1988)485-494.

17. Madhusoodanan U. et.al -Ultraviolet Radiation Dosemeter based on Intrinsic

Thermostimulated Luminescence in CaSO4: Eu; Proc.National Conf.

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18. Lakshmanan A.R. et. al- Ultraviolet Induced Thermoluminescence and Phosphorescence in

Mg2SiO4:Tb; Phys.Med.Biol. 23,5(1978) 952-960.

19. Alexander G. et.al.- Measurement of Quantum and Cathodoluminescent efficiecies of

inorganic powder phosphors using Silicon Photodiode detector; Indian J. Pure Appl. Phys. 31

(1993)531-538.

20. Nagpal J.S. et .al- Ultraviolet and gamma radiation Induced Luminescence of YA1G:

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21.Nagpal J.S. et. al - Powder from Fluorescent Lamps as an Accident Dosimeter-

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22. ZhaZ. etal - Preparation and Characteristics of LiF: Mg, Cu, P Thermoluminescent

Material; Radiat.Protect.Dosim.47,1/4 (1993)111-118.

23. Osvay M. and Lembo.L.- Comparative Investigations of UV sensitivity of newly developed

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24. Olko P. etal - Microdosimetric Interpretation of the Anomalous photon energy response of

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27. Fukuda Y. et.al - Estimation of Ultraviolet Radiation dose using CaF2: Tb phosphor; Radiat.

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28. Mehta S.K and Sengupta S.-Photostimulated TL of Al2O3(Si,Ti) and its Applications to

UV Dosimetry; Phys.Med.Biol.23 (1978)471-480.

29.Pradhan A.S. et. al - TL response of A12Q3 to UV and Ionising Radiation;Radiat.

Protect.Dosim.64,3( 1996)227-231.

- 4 0 -

REFERENCES (contd.)

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31.Nagpal J.S. et. al - Phototransferred Thermoluminescence Studies in CaSO4:Dy; Phys.

MedBiol. 25,3(1980)549-554.

32. Calvert R.L. et.al - The Effect of UV and Visible Radiation on CaSO4: Dy in Teflon Discs

used for Personnel Monitoring; Health Phys. 46,2 (1984)275-281.

33. Potiens.A.Jr. et al - Ultraviolet and Laser Radiation Dosimetry using PTTL in CaSO4:Dy;

Radiat.Protect.Dosim. 66, 1-4 (1996)95-96.

34. Mason E.W. - Thermoluminescence Response of 7LiFto Ultraviolet Light; Phys.Med.Biol.

16,2(1971)303-310.

35. Buckman W.G. and Payne M.R.- Photostimulated Thermoluminescence of Lithium Fluoride

as an Ultraviolet Radiation Dosimeter; Health Phys. 31 (1976)501-504.

36. McKinlay A.F. et.al - Development of PTTL Technique and Its Application for routine

assessment of absorbed dose in the NRPB automated personal Dosimetry System;

Nucl.Instr.Methods 175(1980)57.

37. Akselrod M.S. and Gorelova E.A.- Deep Traps in Highly Sensitive a- A12CV.C Crystals;

Nuclear Tracks Radiat.Meas. 21,1 (1993) 143-146.

38. Colyott L.E. et.al - An Integrating UV-B Dosemeter using PTTL from a-Al2O3: C;

Radiat.Protect.Dosim.72,2 (1997)87-94.

- 4 1 -

APPENDIX A

BIOLOGICAL EFFECTS OF UV RADIATION ON MAN

From Hughes D. - Hazards of Occupational Exposure to UV Radiation -

Occupational Hygiene Monograph No: 1, 1978 (Science Reviews Ltd.) [9]

11. Early Effects (within hours or days)

(i) Effects on the skin

(a) the darkening of the pigment : (300-400 nm)

(b) the production of erythema (sunburn) : maximum at 297 nm

(c) the increase in pigmentation (suntanning) : migration of melanin granules

to superficial cells

(ii) Effects on the eye

(a) keraititis (inflammation of the cornea) : maximum at 297 nm

UVA causes fluorescence of the lens

(b) conjunctivitis

(iii) On the tissue of the mouth

erythema of skin around the mouth

II. Late Effects (after months or years)

(i) Certainty effects:

(a) on the skin - ageing (dermal tissue degeneration with a

decrease in elasticity)

(b) on die eye - possible cataract formation by UVA radiation

Cornea transmits little radiation below 310 nm

(ii) Stochastic effects:

(a) on the skin - cancer

(b) on the eye - no evidence

- 4 2 -

APPENDIX B

MAXIMUM PERMISSIBLE OCCUPATIONAL UV RADIATION EXPOSURES

Source : IRPA- Guidelines for Protection against Non-Ionising Radiation, 1991 [11]

The International Radiation Protection Association (IRPA) has issued guidelines

on limits of exposure to UV radiation. The limits should be considered absolute limits for

the eye, and 'advisory' for the skin.

For UVA (315 -400 nm), the total radiant exposure of unprotected eye should not

exceed 10 kJ.m'2 (1 J.cm"2) within an 8 h period. For UVB and UVC (180 - 315 nm),

radiant exposure of unprotected skin or eye, within an 8 h period, should not exceed the

values given.

The effective irradiance Ecn(W.m'2) of a broadband source is obtained from the formula

Ecff = E Ex . S).. AX

where Ex is the spectral irradiance

Sx is the relative spectral effectiveness, and

AX is the measurement interval (nm)

Permissible exposure time t max in seconds is given by the equation

tmax = 3 0 / E eff

The lowest value is 30 J.m"2 ( 0.003 J.cm'2 ) for an 8 h period and occurs at 270 nm

wavelength. This corresponds to an average irradiance of 10"3 W.m"2 (0. lu.W.cm'2), over

the eight hour period.

- 4 3 -

APPENDK C

UV radiation exposure limits EL and spectral weighting factors S*Source : IRPA - Guidelines for Protection against Non-Ionising Radiation, 1991 CH J

Wavelength(nm)

180190200205210215220225230235240245250254255260265270275280285290295297300303305308

EL(J.m2)

250016001000590400320250200160130100837060584637303134394756651002505001200

Relative spectraleffectiveness

0.0120.0190.0300.0510.07500950.1200.1500.1900.2400.3000.3600.4300,5000.5200.6500.8101.0000.9600.8800.7700.6400.5400.4600.3000.1900.0600.026

Wavelength(nm)

310313315316317318319320322323325328330333335340345350355360365370375380385390395400

EL(J.m"2)2500500010 00013 00015 00019 00025 00029 00045 00056 00060 00068 00073 00081 00088 000110 000130 000150 000190 000230 000270 000320 000390 000470 000570 000680 000830 0001000 000

Relativespectral

effectiveness

0.0150.0060.0030.00240.00200.00160.00120.00100.000670.000540.000500.000440.000410.000370.000340.000280.000240.000200.000160.000130.000110,0000930.0000770.0000640.0000530.0000440.0000360.000030

- 4 4 -

APPENDIX D

TYPICAL UV EMISSIONS FROM VARIOUS SOURCES(UVA,UVB and UVC irradiances refer to patient surface; Ecir and T ^

are worst case in direct contact with the lamp)From McKinlay A.F. et.al- Hazards of Optical Radiation 1988 (Bristol: Adam Hilger) [12]

Source

Waldmann 8001

PUVA cabinUVA onlyUVB only

Hanovia sunlamp

Kromayer lamp

UVB Fluorescent LampWestinghouse FS20Svlvania F75/85 W

Chromatolite(with filter)UV Sunbed(mean of 8 models)Fluorescent Lamp

bare lampwith clear acrylic

1 diffuserwith opal polycarbonatediffuserHigh pressure sodium,150 VVTungsten Halogen 1 kWHigh pressure mercuryvapour discharge GE 400

with outer bulbwithout outer bulb

Graphic ArtsMetal Halide mercuryHPA2000, 1750 WPrinted circuit boardPhoto etching, UV 180

IrradianceUVA

508.5

25

2.4

0.06

102

0.0220.016

0 . 2 x l 0 3

48

50

UVB

10

22

0.29

3.5 xlO3

2.9 x 103

1.2xl0"7

19

(W.mUVC

0.06

15

4.5

• 2 )

Eeff

3.0

13

1302.9

0.312.7

<W4

0.01

<10"4

<10~4

<10~4

0.02

0.0133.6

Permissibletime

* max

150 s10 s

2s

0.2 s10s

90s10s

> 8 h

48 min.

>8h>8h

>8h

>Sk

25 min.

40 min.9s

Distance

(m)

0.5

0.00.25

0.10.00.0

0.0

1.351.35

1.35

0.5

0.5

2.02.0

1.0

0.0

RELATIVE RADIANT FLUX

2rri C

i OC <

< oc rn

/~> i Z

C zi

Q r

C/3

o

enoco

I

IRELATIVE RADIANT FLUX

to ^ c oo

3Oc_

o •

•5oc

X

aX

id-

rnXT.OCC

*m

rn

RELATIVE RADIANT FLUX

o oo

:i^d

>z ^-_ ^ u>

8 w «

RELATIVE RADIANT FLUX

—

o

2.

c—.tun

>ococ

ztcZ

I

rnOcz73~<GC

z>

to

><m

z/-X o

*>c

Oooc

5'3

<<"

o'o

s.2cqc"2.

Z

3 ~* ^—' V^

E" 53era. —

o ^ i-

• < ~

s ^ 2C »J ^CA M Mm• ^ * ^ «an

—' ^ ?C

8 2g

^ SL ~ ~ —00

c2'0

0 '

<!

c

X"3cc0

<

A*

E.5'

< >k. iir •

^ ^ - MM

2 ^

•«

•<

- 4 6 -

lOOr

80

60

Q

1VE

R

i—'

a:

40

20

0

quartz cooling jacket— glass cooling jacket

I IKil I-PRHSSURH XHNON ARC LAMP_JL_ _J I I I I I

200 300 400 500 600 700 800 900 1000 1100 1200 1300

WAVRLHNGTII(nm)

100

X=> 80

H

^ 60

§ 40<

20

0

DKUTKRJUM LAMi>

200 300 400 500 600

WAVELENGTH (nm)

700 800

- 4 7 -

LIST OF FIGURES

Fig. 1: Emission spectra of the lampsa : Pen ray lamp ( Lamp 1 ) b : Blacklite lamp ( Lamp 3 ). 5

Fig. 2: TL glow curves of CaSO4 based phosphorsUV radiation(Pen ray lamp, bare) — Gamma radiation 6

Fig. 3: TL glow curves of CaSO4: Eu on exposure to 8a. gamma radiation (0.1 Sv)b. blacklite lamp (mainly 365 nm)b'. blacklite lamp with 365 nm filterc. UV radiation (bare pen ray lamp)d. pen ray lamp with 250 nm filtere. philips lamp (bare)

Fig. 4: TL response of CaSO4: Eu on UV irradiation 10Exposure under two different conditionsa : bare pen ray lamp at 90| W.cm"2

b: philips lamp, with 250 nm filter, at 19jxW.cm"2

Fig. 5: TL glow curves of UV and gamma irradiated samples 12a : gamma b: 365 nm c : 254 nm photons

Fig. 6: TL output vs. Radiant energy for various phosphors at a fixed UV 13radiant flux a : CaSO4: Mn at 260 MW.CITI"2.

b : CaSO4: Tb at 260 ^W. cm"2

c:Mg2Si04:Tb at 19 jjW.cm"2

d: ThO2:Tb at 40 nW.cm"2

Fig. 7: UV response characteristics of Y - based TL phosphors 14Fig. 8: TL glow curves of Ce Mg Aluminate(Eu,Tb),on irradiation to 15

60 C o — 365 nm.... 254 nmFig. 9: TL response of CeMg Aluminate (Eu,Tb) to 254 nm photons at 16

radiant flux 19 jjW.cm"2 a : Integrated TL for 30 s at 25°C, without heatingb : TL integrated between 25° -280QC, after 5 min. delay

Fig. 10: TL glow curves of Blue, Red & Daylight Calcium halophosphates 18A : UV irradiation (254 nm) B: " 7 Cs gamma (0.01 Sv)

Fig. 11: TL glow curves of UV ( _ ) and beta ( —) exposed LiF ( Mg,Cu, P) 20Fig. 12: Response, of various TL phosphors as a function of UV exposure 21Fig. 13: TL glow curves of Harshaw TLD-200 (CaF2: Dy)

and AI2O3 (Si,Ti) a : gamma irradiation b : UV irradiation 23Fig. 14 : PTTL characteristics of CaSO4- teflon dosimeters (6 mm <j>, 0.8 mm thick)

TL integrated between 200°C - 360°C 25Fig. 15: Intrinsic response of CaSO4 phosphors to UV radiation as a

function of radiant flux 27Fig. 16: UV response of TL phosphors as a function of radiant flux. 28Fig. 17: UV response of CaSO4: Eu as a function of radiant flux

a : Pen ray lamp (bare) - UV exposure 2.5 mJ.cm"b : Philips lamp (bare) - UV exposure 2.6 mJ.cm"2 30

Fig. 18. TL glow curves of CaF2:Tb crystal on irradiation to(a) 220nm (b)260nm (c) 290nm (d) 320nm (e)380nm (f) 400nm 32

Published by : Dr. M. R. Balakrishnan, Head Library & Information Services DivisionBhabha Atomic Research Centre, Mumbai - 400 085, INDIA.