Nuclear Instruments and Methods in Physics Research A 633 (2011) 31–35

Contents lists available at ScienceDirect

Nuclear Instruments and Methods inPhysics Research A

0168-90

doi:10.1

$Not

No. DE-

Governm

acknow

up, irrev

this man Corr

E-m

journal homepage: www.elsevier.com/locate/nima

Deep UV emitting scintillators for alpha and beta particle detection$

Y. Zhou a, D.D. Jia b, L.A. Lewis b, S.P. Feofilov c, R.S. Meltzer a,n

a Department of Physics and Astronomy, University of Georgia, Athens, GA 30606, USAb Oak Ridge National Laboratory, Oak Ridge, TN 37831, USAc A.F. Ioffe Physical-Technical Institute, St. Petersburg, 194021, Russian Federation

a r t i c l e i n f o

Article history:

Received 13 April 2010

Received in revised form

2 December 2010

Accepted 8 December 2010Available online 7 January 2011

Keywords:

Scintillators

Deep UV

Radiation monitoring

Light yields

02/$ - see front matter & 2011 Elsevier B.V. A

016/j.nima.2010.12.238

ice: This manuscript has been authored by UT

AC05-00OR22725 with the U.S. Department

ent retains and the publisher, by acceptin

ledges that the United States Government re

ocable, world-wide license to publish or repr

nuscript, or allow others to do so, for United S

esponding author.

ail address: rmeltzer@physast.uga.edu (R.S. M

a b s t r a c t

Several deep UV emitting scintillators, whose emission falls in the solar blind region of the spectrum

(200–280 nm), are described and their scintillator properties are characterized. They include LaPO4:Pr,

YPO4:Pr, YAlO3:Pr, Pr(PO3)3, YPO4:Bi and ScPO4. These materials would facilitate the detection of

ionizing radiation in open areas, even during the daylight hours, and could be used to support large area

surveys that monitor for the presence of ionization radiation due, for example, to system leaks or

transfer contamination. These materials can be used in the form of powders, thin films or paints for

radiation detection. They are characterized for both beta radiation using electron beams (2-35 keV) and137Cs and alpha radiations using 241Am sources. Their absolute light yields are estimated and are

compared to that of Y2SiO5:Ce. Their light yields decrease as a function of electron energy but at 10 keV

they approach 8000 ph/MeV.

& 2011 Elsevier B.V. All rights reserved.

1. Introduction

Scintillator materials have been developed for a wide range ofapplications in detecting various sorts of ionizing radiationincluding alpha, beta and neutron particles as well as gammaand X-ray sources [1–3]. These efforts have been directed towardsa number of different goals. In some cases, optimization of lightyield has been of primary importance, especially for maximumenergy resolution and sensitivity. For other applications it hasbeen necessary to minimize the decay time in order to handlehigh counting rates or identify different particles.

The focus of the effort described here is the development ofefficient scintillators which emit in the deep UV region such thatthe emission falls in the solar blind region of the spectrum (200–280 nm). These materials would then facilitate, for example, thedetection of ionizing radiation in open areas, even during thedaylight hours. Such materials could be used, for example, tosupport large area surveys that monitor for the presence ofionizing radiation due to system leaks or transfer contamination.Emphasis in this work is on detection of alpha and beta radiations

ll rights reserved.

-Battelle, LLC, under Contract

of Energy. The United States

g the article for publication,

tains a non-exclusive, paid-

oduce the published form of

tates Government purposes.

eltzer).

which are absorbed in short path lengths within solids, therebyenabling the use of powders, thin films or paints for radiationdetection. In these applications, the most important characteristicof the choice of materials is their light yields. A fast light output isnot important.

There are a number of reported examples of deep UV emittingscintillators. These include predominantly Pr3 +-doped materials[4,5]. Whereas Pr3 + almost always exhibits 4f–4f transitions inthe visible, under certain conditions of the electronic energy levelstructure, the 4f5d level is radiative, resulting in efficient emis-sions in the deep UV. Scintillator action involving the 4f5d levelhas been reported in YAlO3:Pr [6–8], YAG:Pr and other garnets [4][9,10], Pr-doped silicates [4] [11,12] and some concentrated Prphosphates [13,14]. Scintillators producing deep UV intrinsicemission have been reported in a number of materials such asBaF2 [15], MgO [16,17], a-Al2O3 [18] and MgAl4O7 [19]. Themajority of previously reported work is based on single crystalsand involves either X-ray or gamma ray sources. For BaF2, the fastcross luminescence occurs at 220 nm but its light yield isrelatively low. Nd3 +-doped materials have also been reported asgood short wavelength scintillators but their main emissionoccurs in the VUV with only a small portion appearing in thedeep UV region of interest in this work [20].

Here, results are presented for a number of Pr3 +-dopedmaterials including LaPO4, YPO4 and YAlO3, and the concentratedPr(PO3)3. Pr3 + emission falls into two types. For low crystal fieldsites such as for PrF3 [21], the metastable level is the 1S0 state ofthe f2 configuration whose main emission is at about 400 nm. Forhigh crystal field sites, the emission originates from the 4f5d state

Y. Zhou et al. / Nuclear Instruments and Methods in Physics Research A 633 (2011) 31–3532

whose wavelength depends strongly on the crystal field. Thematerials chosen for study here are selected based on this fact. Inaddition YPO4:Bi3 + and undoped ScBO3 are selected for studybased on their emission wavelengths and good light yields.

The scintillating properties of these materials are studiedunder electron beam (2–35 keV) excitation, 137Cs beta radiation(0.51 MeV maximum electron energy) and 241Am alpha radiation(5.1 MeV). Their properties are characterized regarding theiremission spectra under electron beam excitation, and their lightyields relative to a Y2SiO5:Ce (YSO:Ce) standard reference mate-rial. Their absolute light yields are estimated using a (Zn,Cd)S:Agfilm as a reference and the dependence of their light yields onelectron beam energy are presented and discussed. All thesematerials have the major portion of their emission in the 215–280 nm solar blind range. The best of these materials have photonyields that are about 50% of that of YSO:Ce for both low energybeta and alpha radiation. The photon yields of these compressedpowder samples relative to that of YSO:Ce fall off with increase inelectron beam energy.

100

0

100000

200000

300000

400000

ScBO3

YSO:Ce

Emission Spectra under 10 keV e-beam Excitation

Rel

ativ

e qu

antu

m y

ield

(arb

. uni

ts)

Wavelength (nm)200 300 400 500 600 700

YPO4:Bi LaPO4:Ce

LaPO4: Pr 8.5%

YPO4:Pr 5%

YAlO3:Pr 0.5%

Fig. 1. Emission spectra at room temperature of the samples studied under 10 keV

electron beam excitation. All spectra are corrected for the spectral response of the

spectrometer and CCD detector. The relative photon quantum yields are approxi-

mately to scale. The vertical scale of the spectra has been offset for clarity.

2. Experiment

2.1. Sample preparation

All of the phosphate and aluminate samples were preparedwith solid-state chemical reaction. 99.99% or higher purity ofLa(NO3)3, Y(NO3)3, Pr(NO3)3, Ce(NO3)3, Bi(NO3)3, Al2O3 and 85%HPO3 were selected as raw materials. Doping was given as in theexample formula, Y1�xAlO3:xPr, where x is the doping concentra-tion. The dopants were considered to replace larger cation ions inthe host materials. For aluminate, dry mixing was used. Forphosphate, raw materials were mixed as water solutions. Mix-tures were baked at 120 1C to dry water out and then they werepreheated to 900 1C for 2 h to decompose the nitrate. Following asecond grinding and mixing step, the final mixtures were sinteredat 1350 1C for 2 h. For Ce3 + and Pr3 + doped samples, sintering wascarried out in 96%N2+4%H2, forming gas to ensure that theappropriate valence state was obtained. For Bi3 +, the sinteringwas performed in air. The ScBO3 sample was prepared at OregonState University in the laboratory of Dr. Keszler and the procedurehas been described previously [22]. The YSO:Ce reference sampleis the product QBK58/UF-42 obtained from Phosphor Technology,Ltd. Thirteen millimeter diameter compressed pellets of eachsample were formed in a pellet die.

2.2. Optical characterization

Emission spectra were obtained with a 0.15 m spectrometer(Acton, Model 150) using a cooled CCD detector (Santa BarbaraInstrument Group, Model ST-6B). Spectra were obtained in 80 nmincrements and were then spliced together in order to construct acomplete UV/visible spectrum. All spectra were corrected for thewavelength dependent response of the CCD and the monochro-mator using a NIST-calibrated tungsten halogen lamp as areference. Emission spectra were excited with an electron beamsource (Staib Instruments electron gun) operating between 2 and35 keV. Most spectra were obtained at 10 keV.

The dynamics of the emission were obtained under excitationat 157 nm using a molecular laser (GAM Laser, Inc., Model EX5)operating with F2. The PMT signal as a function of time wasobtained using a 1 GHz Textronix TDS 460A digital oscilloscope ora Stanford Research Systems Model SR 430 Multichannel Scaler. Atime resolution of about 10 ns could be obtained, limited by thepulse width of the laser and the temporal resolution of the PMTand the oscilloscope.

2.3. Scintillator characterization

Scintillation detection under electron beam excitation wasobtained using a loosely focused (3 mm) electron beam at about10 nA current. The pellet samples were placed on a long sampleholder whose position could be translated relative to the electronbeam. The pellet samples were oriented with their surfaces at 451to the electron beam. Light was collected at 901 from the electronbeam (also at 451 to the face of the pellet). Using UV grade quartzlenses the emission was either focused onto the entrance slit ofthe CCD spectrometer (emission spectra) or was collimated anddirected onto the 200 diameter photocathode of a Philips XP2254BPMT. Relative photon yields were obtained using the PMT in orderto minimize the variance of the collection efficiency on opticalalignment and therefore provided the least uncertainty in relativephoton yields. PMT photocurrent signals were corrected for thewavelength dependence of the quantum efficiency of the PMTperformance and the optics transmission efficiency, which issignificantly reduced in the deep UV due mainly to reflectionlosses resulting from the many uncoated optical surfaces of thelenses, chamber window, PMT and PMT housing windows.

Scintillation relative photon yields were measured using tworadioactive sources. For beta radiation, a 3.7�105 Bq 137Cs sourcewas used. It provides electrons with a continuous energy distributionpossessing a maximum energy of 510 keV and an average energy of157 keV. The 137Cs source also emits gamma rays but these producednegligible scintillation in our thin samples. For alpha radiation, thesamples were irradiated with a 3.3�104 Bq 241Am source, whichprovides 95% of the particles at 5.1 MeV. These small radioactivesealed sources were located at the center of 100 diameter diskspositioned 100 from the pellet samples, both contained in vacuum.Emissions were detected at right angles to the source beam direction.Light yields were obtained as described for electron beam excitation.

3. Results

3.1. Spectroscopy

The emission spectra under a 10 keV electron beam of 10 nAare shown in Fig. 1. The emission spectra of the samplesinvestigated are compared to those of YSO:Ce, the referencematerial, and LaPO4:Ce, another high-light-yield scintillator. The

1001010.0

0.2

0.4

0.6

0.8Dependence of Relative Photon Yield on Electron Energy

Qua

ntum

Yie

ld R

elat

ive

to Y

SO

:Ce

Electron Beam Energy (keV)

YPO4:BiYAlO3:Pr 0.5%LaPO4:Pr 7%

β (137Cs)

Fig. 3. Relative quantum yield of each of the three samples relative to YSO:Ce

measured at each electron energy as a function of electron beam energy. The data

points at 157 keV were obtained using a 137Cs source.

Y. Zhou et al. / Nuclear Instruments and Methods in Physics Research A 633 (2011) 31–35 33

relative intensities provide a semi-quantitative comparison oftheir relative light yields. All samples provide strong signals inthe solar blind region between 215 and 280 nm. YPO4:Bi andLaPO4:Pr exhibit the largest photon yields under 10 keV electronbeam excitation. A more accurate quantitative comparison isdescribed below. For the Pr3 + samples, the emissions result fromtransitions between the 4f5d and 4f2 configurations [5]. The threebands to the 3HJ and one to the 3FJ states of the 4f2 configurationare best resolved in YPO4, but appear as two broadened bands forYAlO3. Emission from the 3P manifold of the 4f2 configuration isclearly observed for YAlO3 and to a lesser degree in YPO4 andLaPO4. For ScPO4 the emission is intrinsic and arises from a self-trapped exciton [23,24]. For YPO4:Bi3 + the emission results from6s6p-6s2 allowed transitions from the outer unfilled shell ofBi3 + [25]. The emission arises from the 3P0 and 3P1 states of the6s6p configuration, the former spin-forbidden. As a result, thelifetime of the Bi3 + emission is expected to be strongly tempera-ture dependent; it becomes shorter at higher temperatures as the3P1 state becomes populated [26]. The sharp feature locatedbetween 310 and 315 nm in ScBO3 and YPO4:Bi originates fromthe 6PJ emission of a Gd3 + impurity.

The dynamics of the deep UV emission of the Pr3 +-dopedscintillators is known to be very fast as it results from dipole-allowed 4f5d-4f2 transitions and is typically less than 30 ns [4].

3.2. Scintillation

3.2.1. Electron beam excitation

The scintillator outputs were studied as a function of electronbeam energy. The results under constant beam current (10 nA) areshown in Fig. 2, along with the results of the YSO:Ce reference pellet.For YSO:Ce the light output is linear in electron beam energy.However, for all of these deep UV scintillators, the behavior issublinear. In order to better illustrate this observation, the ratio ofthe quantum yield of each of three of the deep UV scintillators to thatof YSO:Ce, obtained at each energy, is plotted in Fig. 3. The drop inrelative light yield with an increase in beam energy is clearly seen.Also plotted are the relative photon yields of the higher-energyelectrons from a 137Cs source. The relative photon yields continueto follow the downward trend observed in the electron beam data.The 137Cs results are discussed below.

Relative Photon Yield vs. Electron Beam Energy

0

10

20

30

40

50

60

0Electron beam energy (keV)

Rel

ativ

e Q

uant

um Y

ield

(a.u

.)

BGOYPO4:BiYAlO3:Pr 0.5%LaPO4:Pr 7%YSO:Ce (x0.5)YPO4:Pr 5%Linear (YSO:Ce (x0.5))

5 10 15 20 25 30 35

Fig. 2. Electron energy beam dependence of the quantum yields of the samples

studied at a 10 nA constant beam current. The relative yields of the different

samples are not to scale. The solid line is a linear fit to the YSO:Ce data.

The question of non-proportionality is a topic of considerablecurrent interest. Measurements on Gd2SiO3:Ce3 + exhibit a lightyield that increases by nearly 28% between 5 and 445 keV [27].For NaI:Tl, the yield increases by about 10% between 5 and 20 keVand then falls from its value at 20 keV by 15% at 444 keV [28].Most studies of non-proportionality utilize transparent singlecrystals. However the samples described here are compressedceramic pellets that raise additional issues regarding non-pro-portionality. The reduced relative output with an increase inbeam energy is attributed, in part, to the strong scattering andpossible residual absorption that may be present in the materials.With increase in energy, the electron energy is deposited deeperwithin the sample. As a result, the light exiting the sample in thedirection from which the beam entered (viewing direction) willundergo additional scattering. The pellets are of sufficient thick-ness that very little light exits at the opposite end of the sample.The increased scattering leads to increased path length of thelight in the pellet, thereby magnifying the affects of residualabsorption. This residual absorption is much more likely in thedeep UV due to material impurities and defects. For the YSO:Cereference sample, the emission is predominantly in the visibleregion and its intensity grows linearly up to 35 keV. It may be thatthe intrinsic increase in light yield seen for Gd2SiO5:Ce3 +, asimilar material, may partly compensate for any decrease due toscattering, resulting in the observed nearly linear behavior.Quenching by surface defects might also play a role, especiallyat low electron energies, but the fact that light yield decreaseswith increase in beam energy seems to argue against theimportance of surface effects. However, since these are ceramicsamples consisting of micron-sized crystallites, surface effectsmay play a role for all beam energies.

The photon yields for low electron energies are about 50% ofthat of the reference YSO:Ce scintillator pellet for both YPO4:Bi(1%) and LaPO4:Pr (5%). However, the relative light yield ofthe LaPO4:Pr pellet (compared to that of YSO:Ce) is better thanthe relative light yield of YPO4:Bi at higher electron energies. Thescintillator output performance of undoped ScBO3 is only slightlybelow that of YPO4:Bi and LaPO4:Pr (5%) at both low and higherelectron energies. The results for all of the materials reported hereare summarized in Table 1.

Table 1Relative photon yield of ceramic pellets of various materials relative to a reference pellet of Y2SiO5:Ce under beta and alpha radiations.

Material k (nm) s (ns) Relative photon yield to YSO:Ce Estimated light yield (ph/MeV) a (5.1 MeV) /b (10 keV)

Range RT b (10 keV) bavg (157 keV) a (5.1 MeV) b (10 keV) bavg (157 keV) a (5.1 MeV)E-beam 137Cs 241Am E-beam 137Cs 241Am

Y2SiO5:Ce 360–650 35,52 [34] 1 1 1 17,000 17,000 5270 0.31

YPO4:Bi 225–270 700 0.51 0.07 0.21 8670 1190 1107 0.13

LaPO4:Pr 7% 220–280 10 (73) 0.48 0.19 0.46 8160 3230 2424 0.30

YPO4:Pr 5% 225–285 17 0.2 0.18 0.26 3400 3060 1370 0.40

Pr(PO3)3 215–270 6.1 [14] 0.09 0.1 0.12 1530 1700 632 0.41

YAlO3:Pr 0.5% 225–325 8 0.28 0.05 0.27 4760 850 1423 0.30

ScBO3 210–300 200 0.42 0.15 0.24 7140 2550 1265 0.18

Y. Zhou et al. / Nuclear Instruments and Methods in Physics Research A 633 (2011) 31–3534

In order to estimate the absolute light yields, we compared thelight output of the YSO:Ce pellet with that of a phosphor screencontaining the phosphor P-20. The screen is composed of(Zn,Cd)S:Ag and is optimized for electron beam conversion intolight with an absolute energy conversion efficiency of 14% [29].Although the screen is very thin (10–15 mm), all the electronbeam energy is totally absorbed in the film. Although a significantfraction of the emitted photons do penetrate out of the screen inthe forward direction, it can be assumed that the photon outputsfrom the backward (viewing) direction is somewhat greater thanthat in the forward direction due to some scattering of theemitted photons. Determining the fraction of photons generatedby the sample pellets in the backward direction is difficult. Due tothe pellet thickness, a significant fraction of the light generated inthe forward direction, deeper into the pellet, will be scatteredbackward in the viewing direction such that a somewhat largerfraction of the light is emitted in the backward direction than forthe reference screen. However, this will be partially counteractedby the increased scattering and absorption in the deep UV.Estimated photon yields relative to YSO:Ce for these deep UVscintillators for 10 keV electrons are presented in column 4 ofTable 1. These values are based on the assumption that (1) therelative efficiency of photon output in the backward direction isthe same for both reference screen and pellets and (2) theefficiency of light conversion in the backward direction is iden-tical in all samples. The result of these assumptions yields anestimate of 17,000 ph/MeV absolute photon yield for YSO:Ce. Thisestimated value is in reasonable agreement with published valuesfor X-rays and gamma rays ranging from 9200 ph/MeV [30] to30,000 ph/MeV [31]. A value of 17,000 ph/MeV is used as areference for estimating absolute light yields for the scintillatorsdiscussed here. These values are given in column 7 of Table 1 for10 keV electrons.

3.2.2. Alpha and beta radioactive sources

These scintillators were also characterized under irradiationby higher energy beta particles (maximum energy 510 keV;average energy 157 keV), using a 137Cs source and alpha particles(5.1 MeV) from a 241Am source. In each case, the light output fromthe scintillators was compared to that of YSO:Ce. All results arecorrected for the wavelength dependence of the optics and filterstransmissions and the PMT response. The relative photon yieldsfor beta particles are shown in column 5 of Table 1. Theperformance of these scintillator pellets is much poorer at thehigher electron energies from the 137Cs source, especially forYPO4:Bi, which was the best performer for lower energy electrons.The maximum relative photon yields are approximately 20% ofthat of YSO:Ce. The poorer performance at these higher energies islikely due to the deeper penetration of the electrons in the pelletsand the greater effects of scattering and residual absorption of the

deep UV photons as discussed for electron beam excitation.Estimated absolute light yields are listed in column 8 of Table 1.

The alpha particle detection performance is the best forLaPO4:Pr (7%), which is almost 50% of that of YSO:Ce. It has twicethe photon yield compared to those of the two next bestcandidates. Since the alpha particle penetration is very small,the effects of scattering and absorption are minimized. Absoluteestimated light yields were determined from these relative lightyields and an estimate of the absolute light yield of YSO:Ce foralpha particles. The ratio of light yield for alpha relative to betaradiation has been determined to be 0.31 for some relatedscintillators [32,33]; this results in an estimated light yield forYSO:Ce under alpha radiation of 5270ph/MeV. The a/b light yieldratio of YSO:Ce was also obtained from the relative signals fromthe 137Cs and 241Am sources, taking into account the relativeactivities and particle energies of the two sources. This yielded anestimated a/b light yield ratio of 0.28. A measurement for BGOusing these same sources yielded a ratio of 0.21, consistent withthat reported previously [25]. The resulting estimated light yieldsfor the scintillators discussed here are then given in column 9 ofTable 1. The last column of Table 1 shows the a/b light yield ratio.For the beta light yield, we use the data for the 10 keV electronbeam which, like the alpha particles, has a very short penetrationdepth (E10 mm). Except for YPO4:Bi, the values fall betweenabout 0.2 and 0.4, a range which has previously been reported fora number of gamma ray scintillators rather than electrons. Thereason for the low value for YPO4:Bi is not known. While it doeswell for low energy electrons, it has a poorer performance foralpha and higher energy electrons.

3.2.3. Concentration dependence of scintillation yield

The results presented above are for samples with dopantconcentrations optimized to maximize light yields. These wereselected based on a study of the concentration dependence of thelight yields for YAlO3:Pr and LaPO4:Pr. The light yields relative toYSO:Ce as a function of Pr3 + concentration are summarized inFig. 4. For YAlO3:Pr (Fig. 4a), the light yield depends strongly onconcentration. The lowest concentration studied, 0.5%, exhibitsthe largest light yield for all three sources; however the concen-tration dependence is much less for the higher energy b particles.For LaPO4:Pr (Fig. 4b), the light yield peaks around 5–7% Prconcentration and falls off slowly at higher concentrations. Theconcentration dependence is similar for alpha and beta (low andhigh energy) particles. Concentration quenching of the emissionfrom the 4f5d state of Pr3 + at room temperature appears to bequite strong in YAlO3 compared to that in LaPO4. Zhuravleva et al.[7] have previously found that the radioluminescence spectrum ismaximized at a concentration between 0.1% and 1% Pr3 + and isreduced by a factor of 10 at 5% Pr3 +, consistent with the currentdata. As a result, the performance of YAlO3:Pr may be furtherimproved at Pr3 + concentrations below 0.5%.

YAlO3:Pr

0

0.1

0.2

0.3

0Pr concentration (%)

Rel

ativ

e Ph

oton

Yie

ld

electron beam (10 keV)

alpha: 5.1 MeV (241Am)

beta: Eavg = 157 keV (137Cs)

0

0.2

0.4

0.6

0Pr concentration (%)

Rel

ativ

e Ph

oton

Yie

ld

LaPO4:Pr electron beam (10 keV)

alpha: 5.1 MeV (241Am)

beta: Eavg = 157 keV (137Cs)

5 10 15

5 10 15

Fig. 4. Concentration dependence of the photon scintillator yields relative to

YSO:Ce for (a) YAlO3:Pr and (b) LaPO4:Pr for 10 keV electrons, 137Cs electrons

(157 keV average energy) and 5.1 MeV alpha particles from a 241Am source.

Y. Zhou et al. / Nuclear Instruments and Methods in Physics Research A 633 (2011) 31–35 35

4. Conclusions

Several new deep UV scintillators with emissions in the solarblind region have been identified and characterized under betaand alpha ionizing radiations. These materials may have specia-lized applications in radiation monitoring under daylight condi-tions because of the very low solar background in the deep UV.With low energy electron radiation, appropriate, for example, inmonitoring for tritium, YPO4:Bi, LaPO4:Pr and ScBO3 appear to bethe best candidates, with photon light yields approaching 50% ofthat of YSO:Ce. We estimate light yields for these materials ofapproximately 8000 ph/MeV. Due to the strong absorption of lowenergy electrons, powder or ceramic scintillator materials wouldsupport alpha or beta detection using powders, thin films andpaints. For higher energy electrons, above 100 keV, LaPO4:Pr,YPO4:Pr and ScBO3 are the best candidate materials with lightyields approaching 20% of that of YSO:Ce based on compressedpellet characterization. For alpha particles, LaPO4:Pr shows thebest performance with light yields almost 50% of that of YSO:Cewith an estimated absolute yield of 2400 ph/MeV. Since the alphaparticles are also absorbed within very short path length, solids,ceramics or powders could be used to support radiation monitor-ing applications. It should be noted that the decreased light yieldas the particles penetrate deeper into the compressed powderpellets should not be a problem with powders since multiple

scattering of the photons among particles will be unimportant.The a/b light yield ratio of the materials described lie in the rangebetween 0.13 and 0.41, values that are typical for oxidescintillators.

Acknowledgements

The research was funded by the Office of Nonproliferation andVerification R&D (NA-22) and was conducted at the University ofGeorgia and the Oak Ridge National Laboratory, ChemicalSciences Division, U.S. Department of Energy. We thank Dr. DougKeszler of Oregon State University for preparing the ScBO3 sampleand Dr. Christophe Dujardin for the YSO:Ce reference material.

References

[1] C.W.E. van Eijk, Nucl. Instr. and Meth. A 460 (2001) 1.[2] W.W. Moses, Nucl. Instr. and Meth. A 487 (2002) 123.[3] S. Shimizu, M. Suzuki, T. Koizumi, H. Ishibashi, S. Kubota, Nucl. Instr. and

Meth. A 537 (2006) 57.[4] J. Pejchal, M. Nikl, E. Mihokova, J.A. Mares, A. Yoshikawa, H. Ogino,

K.M. Schillemat, A. Krasnikov, A. Vedda, K. Nejezchleb, V. Mucka, J. Phys. D:Appl. Phys. 42 (2009) 055117.

[5] A. Srivastava, J. Lumin. 129 (2009) 1419.[6] C. Pedrini, D. Bouttet, C. Dujardin, B. Moine, I. Dafinei, P. Lecoq, M. Koselja,

K. Blazek, Opt. Mater. 3 (1994) 81.[7] M. Zhuravleva, A. Novoselov, A. Yoshikawa, J. Pejchal, M. Nikl, T. Fukuda, Opt.

Mater. 30 (2007) 171.[8] M. Zhuravleva, A. Novoselov, E. Mihocova, J.A. Mares, A. Vedda, M. Nikl,

A. Yoshikawa, Cryst. Res. Technol. 42 (2007) 1324.[9] M. Nikl, H. Ogino, A. Krasnilov, A. Beitlerova, A. Yoshikawa, T. Fukuda, Phys.

Status Solidi A 202 (2005) R4.[10] H. Ogino, A. Yoshiklawa, M. Nikl, A. Krasnilov, K. Kamada, T. Fukuda, J. Crys.

Growth 287 (2006) 335.[11] P. Dorenbos, M. Marsman, C.W.E. van Eijk, M.V. Korzhik, B.I. Minkiv, Radiat.

Eff. Defects Solids 135 (1995) 325.[12] L. Pidol, B. Viana, A. Kahn-Harari, A. Bessiere, P. Dorenbos, Nucl. Instr. and

Meth. A 537 (2005) 125.[13] K. Horchani, J.-C. Gacon, C. Dujardin, N. Garnier, M. Ferid, M. Travelsi-Ayedi,

Nucl. Instr. and Meth. A 486 (2002) 123.[14] J.C. Gacon, K. Horchani, A. Jouini, C. Dujardin, I. Kamenskikh, Opt. Mater. 28

(2006) 14.[15] P.A. Rodnyi, Radiat. Meas. 38 (2004) 343 (references therein).[16] K.A. Kalder, T.N. Kyarner, Ch.B. Lushchik, A.F. Malysheva, R.V. Milenina,

J. Appl. Spectr. 25 (1976) 1250.[17] A. Lushchik, F. Savikhin, I. Tokbergenov, Radiat. Eff. Defects Solids 158 (2003)

305.[18] M. Kirm, G. Zimmerer, E. Feldbach, A. Lushchik, Ch. Lushchik, F. Savikhin,

Phys. Rev. B 60 (1999) 502.[19] A. Lushchik, M. Kirm, A. Kotlov, P. Liblik, Ch. Lushchik, A. Maaroos,

V. Nagirnyi, T. Savikhina, G. Zimmerer, J. Lumin. 102/103 (2003) 38.[20] D. Wisniewski, S. Tavernier, A.S. Wojtowicz, M. Wisniewska, P. Bruyndonckx,

P. Dorenbos, E. van Loef, C.W.E. van Eijk, L.A. Boatner, Nucl. Instr. and Meth. A486 (2002) 239.

[21] E.G. Villora, K. Shimamura, S. Nakakita, M. Nikl, N. Ichinose, Nucl. Instr. andMeth. A. 537 (2005) 139.

[22] S.P. Feofilov, Y. Zhou, J.Y. Jeong, D.A. Keszler, R.S. Meltzer, J. Lumin. 125(2007) 80.

[23] A. Trukhin, L.A. Boatner, Mater. Sci. Forum 239 (1997) 573.[24] Y. Zhou, S.P. Feofilov, H.Y. Jeong, D.A. Keszler, R.S. Meltzer, Phys. Rev. B 77

(2008) 075129.[25] G. Blasse, A. Bril, J. Chem. Phys. 48 (1968) 217.[26] T. Justel, P. Huppertz, W. Mayr, D.U. Wiechert, J. Lumin. 106 (2004) 225.[27] W. Mengesha, T.D. Taulbee, J.D. Valentine, B.D. Rooney, Nucl. Instr. and Meth.

A. 486 (2002) 448.[28] W.W. Moses, W.-S. Ghoong, G. Hull, S. Payne, N. Cherepy, J.D. Valentine, Nucl.

Instr. and Meth. A. 610 (2009) 45.[29] Beam imaging solutions specification for their P20 (Zn,Cd)S:Ag screen.[30] C.L. Melcher, J.S. Schweitzer, C.A. Peterson, R.A. Manente, H. Suzuki, in:

P. Dorenbos, C.W.E. van Eijk (Eds.), Inorganic Scintillators and their Applica-tion, 1995, pp. 309–316.

[31] H. Loudyi, Y. Guyot, J.-C. Gacon, C. Pedrini, M.-F. Joubert, Opt. Mater. 30(2007) 26.

[32] S. Shimizu, M. Suzuki, T. Koizumi, H. Ishibashi, S. Kubota, Nucl. Instr. andMeth. A 537 (2005) 57.

[33] E.V. Sysoeva, V.A. Tarasov, O.V. Zelenskaya, V.A. Sulyga, Nucl. Instr. and Meth.A 414 (1998) 274.

[34] N. Tsuchida, M. Ikeda, T. Kamae, M. Kokubun, Nucl. Instr. and Meth. A. 385(1997) 290.