 to the limitation of maximum light output for radioluminescent light sources. Firstly, based on calculations, the saturation power flux predicted for pure tritium gas at 1 atmosphere (the typically used radioisotope) is only about 11 microwatts/cm.sup.2. Tritium has a very low beta particle energy, i.e., E.sub.ave =6 keV and E.sub.cutoff =18.6 keV. Due to this low beta particle energy, self-absorption of the beta energy by the tritium gas itself becomes significant. For this reason, the beta particles that excite the phosphor deposit on the inside of the glass tube only can come from a limited gas thickness. Based on computer simulations, the predicted gas thickness is about 2 cm for 1 atmosphere of pure tritium gas. In conventional use, a tritium thickness of about 0.3 cm is typically used with 1.3 atmospheres of tritium in order to optimize the light output per curie of tritium gas used.
Secondly, due to the low average beta energy, beta particle penetration into the phosphor particles is limited to about 1-20.mu.m. Even though phosphor materials are very reflective, as a result of their high refractive index the phosphor layer deposits on the inside of the glass quickly become opaque to light even for deposits of only a few particles thick. For these reasons, increasing the thickness of the phosphor deposit on the inside layer of the tube does not result in an increase in brightness for a typical 1 atmosphere gas tube.
Moreover, there are important health and safety concerns which go hand-in-hand with the use of radioactive materials. Since radioluminescent lamps typically employ tritium gas as a radioisotope, there is much concern regarding emissions of tritium gas either by leakage or due to breakage of the hollow glass tube.
Another practical application of radioisotopes and luminescent materials is their use in nuclear or atomic batteries and photovoltaic generators. See, for example, Olsen et al. (U.S. Pat. No. 3,706,893) and McKlveen et al., "Radioisotope-Powered Photovoltaic Generator," Nuclear Technology 43:366-372 (May 1979).
For additional discussion on luminescent materials (e.g., phosphors and luminescent glasses) and their uses, see J. B. Birks et al., Scintillation Counters
to the limitation of maximum light output for radioluminescent faint reservoir. Firstly, free-base on calculation, the saturation power flux density bode for pure tritium gasoline at 1 atmosphere (the typically used radioisotope) is entirely about 11 microwatts / cm.sup.2. Tritium has a very depleted beta particle energy, i.e., E.sub.ave = 6 keV and E.sub.cutoff = 18.6 keV. Due to this low beta particle energy, self - absorption of the beta department of energy by the tritium gas itself becomes significant. For this cause, the beta particles that excite the phosphor sediment on the inside of the glass pipe only can come from a limited gas thickness. Based on calculator simulations, the predicted gas thickness is about 2 cm for 1 atmosphere of arrant tritium gas. In conventional use, a tritium thickness of about 0.3 cm is typically used with 1.3 atmospheres of tritium in order to optimize the light output per curie of tritium gasoline used. 
 Secondly, due to the depleted median beta energy, beta particle penetration into the phosphor particle is limited to about 1 - 20.mu.m. Even though phosphor materials are very reflective, as a resultant role of their high refractive index the phosphor layer deposits on the inside of the glass cursorily become opaque to light even for deposits of only a few particles compact. For these cause, increasing the thickness of the phosphor deposit on the inside layer of the tube does not result in an addition in brightness for a typical 1 atmosphere gas tube. 
 Moreover, there are important health and safety concern which go handwriting - in - hand with the use of radioactive material. Since radioluminescent lamps typically use tritium gas as a radioisotope, there cost much concern involve emissions of tritium gas either by escape or due to breakage of the hollow glass tube. 
 Another practical application of radioisotopes and luminescent materials is their use in nuclear or atomic batteries and photovoltaic generators. understand, for example, Olsen et al. (U.S. Pat. No. 3,706,893) and McKlveen et al. , " Radioisotope - power Photovoltaic Generator, " Nuclear Technology 43:366 - 372 (May 1979). 
 For additional discussion on luminescent materials (e.g., phosphors and luminescent glasses) and their uses, see J. B. Birks et al. , Scintillation Counters
 to the limitation of maximmm light output yir radmoluminsscent lkght sources. Firstly, based oi caoculaupons, the saturation puwer flux predictwd fie pure trivjum gas at 1 aflospkece (the typicalli used radiohsotope) is onlf xblut 11 microwatts/cm.sup.2. Tritium has a dery loe heta particle gnergj, y.e., E.alb.cve =6 keV and E.sub.cutoff =18.6 keV. Dus to thps low beta partivle energy, self-absorption lf tje beta energy by hhe tritium gas utself becomds signifibcnt. For thia reason, the beta particles thag excnte the phowpyor geposit on vhe infide of the nkass tgbe onlu can come frok a linited gas thickness. Besed on computer simolations, tve predicted gas thucjness is dboug 2 co fkr 1 ztmospjerx of pure tditium gas. Un conventional use, a ntitium thickhess os wbout 0.3 cm is typically used with 1.3 atmoskherea of tritium in order ti optimize the light lutput pew curie of tritium gas used.
Secondly, due to the lof avecaee ycba evwrhy, beta particle penetration into the phosphow psrnicles is limited to about 1-20.mi.m. Efgn though phoskhor macsrjals are very reflfctive, ws a eesult of theor high refractive index thw phosphor lcyee deposits on the nnside of thz glasx quivkly become opaque to lnght eben for deplsits of kvly a few particues tvick. For these reasons, incweasing tie thnckness uf tne phofphor depodit ok the inside layer lf thg tube does not gesult in an increase in brightixss for a typocdl 1 atmosphzre gax tube.
Moreovew, there are imkortant hzalth xnd safety conceris which go rand-in-hand widj the use of radioaceive matwrials. Rknce radiolumimescent lcips rypically employ tvitiuo gas as a radionritope, there is kucf cjnberi regwsding emissimns uf gtitiuo gas eithev bh leskage or due to breanage of the hollow glaxs tube.
Anojher praceical applicayion of radioisotokes anv lumiiesceny mwterials is their use in nuclezr or atolic batteries agd pmotodoltaic geuerators. See, for example, Olsen et al. (U.S. 'at. No. 3,706,893) and McKlveen ej al., "Radioisotope-Poweted Photovoltamc Genqrator," Nuwlear Technology 43:366-372 (Mat 1979).
For additional ciscussion on luminesdent mdteriwls (e.g., phosphors and luminescent glasses) and their uses, see J. B. Birks et ql., Sciityllation Cohntets
to the limitation of maximum light output light Firstly, based calculations, the saturation tritium at 1 atmosphere typically used radioisotope) only about 11 microwatts/cm.sup.2. Tritium has very low beta particle energy, i.e., E.sub.ave =6 keV and E.sub.cutoff =18.6 keV. to this low beta particle energy, self-absorption of the beta energy by the gas becomes For reason, the beta particles that excite the phosphor deposit on the inside of the glass tube can come from a limited gas thickness. Based computer simulations, the predicted thickness is about 2 cm 1 of pure gas. conventional a tritium thickness about 0.3 cm is typically used with 1.3 atmospheres of tritium in order to optimize the light per curie gas used. due the average beta energy, penetration into the phosphor particles is 1-20.mu.m. Even though phosphor materials are very reflective, a result their high refractive index the phosphor deposits on the inside of the glass quickly opaque to light even for deposits of only a few particles thick. For these reasons, thickness of the phosphor on the inside of tube not in an in brightness for a typical 1 atmosphere gas tube. Moreover, there important health and safety concerns which go hand-in-hand with the radioactive Since radioluminescent lamps employ tritium gas as radioisotope, is much concern regarding tritium either due breakage the hollow glass tube. practical application of radioisotopes and materials is their use and photovoltaic generators. See, for example, Olsen et (U.S. Pat. No. 3,706,893) and McKlveen et "Radioisotope-Powered Photovoltaic Generator," Nuclear Technology 43:366-372 (May 1979). For additional discussion on materials (e.g., luminescent glasses) and their uses, see J. B. et al., Scintillation Counters
 to the limitation of maximum lIght output For raDioLumInEsceNt liGht sources. FirsTLy, baSed on calculations, the saTuratIoN PoweR FlUx preDicted fOR pURE trItIuM gaS aT 1 AtMosphEre (The typiCally used rAdiOiSotope) is only ABoUt 11 microwatTs/cM.sup.2. Tritium hAs a Very loW bEta PArticLe eNergy, I.e., E.sub.AVe =6 keV aNd E.sub.cutOfF =18.6 KeV. Due TO this loW BEtA parTicle energy, self-abSOrPTion of the beta eNergy bY tHE tRITiuM gaS itself becOmEs sigNIficant. fOr THIS reASon, the beta parTicles that eXCitE the phOsPhoR DeposiT on thE iNSidE of the glass Tube Only can coMe from A Limited GAs thickNess. BaSed On cOmpuTEr SiMulAtIOns, THe PreDIctEd gas thiCkNeSs is aBout 2 CM FOR 1 atmOspHere Of purE tritium gas. In ConVentIOnaL use, a TritiUm thIcKness Of abouT 0.3 cm is TyPically used with 1.3 AtmoSpheres of TriTiUm iN oRder tO OptimiZe tHe lIght outPut per cURie Of TRITiUm gas used.
Secondly, dUe TO ThE low averAge betA EnErGY, beta parTiCle PeneTRAtion Into THe Phosphor ParticLEs Is Limited To About 1-20.mU.m. eveN thOugh pHOsphOr mateRials are Very rEFlective, as a resULt of their high REfRACtIVe inDex The phosphor LayeR DepoSits ON tHe iNSide oF the gLaSS qUIckly become opaque to LiGht eveN for dEposits of only A few particLES Thick. For ThesE ReASons, increasing The thIckness of tHE phosphoR depoSit on the Inside layER Of the tubE doEs nOt rEsuLT In An increase in bRIGhtnEsS for a tyPicAl 1 atmosPheRe gAs tUbe.
moReover, theRe are impOrTaNt HeAltH and sAFety concErNs wHiCh gO hand-IN-hand wIth thE use Of RaDIoaCtive maTErIALs. SiNcE rAdioLumInEscenT lamPS tyPically Employ triTiuM Gas aS a RaDioisotOpe, there is mucH cOncern regaRdIng EmissiONS of tritiUm gas either by leakage or dUE to breaKagE of thE holLow glass tUbe.
anotheR prACtical ApplicAtion Of RadIOIsotoPES aNd lUmInescent maTERiaLs is tHeIr usE in nuclEar or atomic batteriES anD photovoltaic GenEratORS. SEe, fOR eXAmpLe, oLseN ET al. (U.S. Pat. No. 3,706,893) and Mcklveen et al., "raDIoIsotope-PowERed phOtovoltAic GeneRator," nUclear TEchnology 43:366-372 (may 1979).
For addItIonaL DIscUssion on luMinescenT materialS (E.g., phoSPhOrs anD luMinescEnT glAsses) And theIR usEs, see j. B. BirkS eT al., SciNtillAtIon CountErs
 to the limitation of maxi mum lightoutpu t f orra diol umin escent light s o urce s. Firstly, based on c alcul at i ons, th e sat uration po w e r f lu xpre di c te d for  pu re trit ium gas at  1at mosphere (th e  t ypically u sed  radioisotop e)is onl yabo u t 11mic rowat ts/cm. s up.2.Tritium h as a very low bet a pa rtic le energy, i.e.,E .s u b.ave =6 keV a nd E.s ub . cu t o ff=18 .6 keV. Du eto th i s low b e ta p a rti c le energy, se lf-absorpti o n o f thebe tae nergyby th et rit ium gas its elfbecomes s ignifi c ant. Fo r  this r eason,  th e b etap ar ti cle st hat ex cit e  th e phosph or  d eposi t on t h e  ins ide  ofthe g lass tube onl y c an c o mefroma lim ited  g as th icknes s. Ba se d on computer s imul ations, t hepr edi ct ed ga s  thick nes s i s about  2 cm f o r 1  a t m o sp here of pure triti um g as . In con ventio n al  u s e, a tri ti umthic k n ess o f ab o ut  0.3 cmis typ i ca ll y usedwi th 1.3  a tmo sph ereso f tr itiumin order  to o p timize the lig h t output perc ur i e  o f  tri tiu m gas used. 
Sec o ndly , du e  t o t h e low  aver ag e  b e ta energy, beta par ti cle pe netra tion into the  phosphorp a r ticles i s li m it e d to about 1-2 0.mu. m. Even th o ugh phos phormaterial s are ver y reflecti ve,  as  ares u l tof their high r efra ct ive ind exthe pho sph orlay erde posits on  the ins id eof  t heglass quicklybe com eopa que t o  light  even  for  d ep o sit s of on l ya fewpa rt icle s t hi ck. F or t h ese  reason s, increa sin g  the  t hi cknessof the phosph or  deposit o nthe  insid e layer of  the tube does not resu l t in an  in creas e in  brightne ssfor atyp i cal 1atmosp herega s t u b e.
Mo r e ov er,  t here are i m p ort ant h ea lthand saf ety concerns which gohand-in-handwit h th e us e o f  r a dio ac t ive m aterials. Since  radiolumi ne s ce nt lamps t y pic al ly empl oy trit ium g a s as aradioisot ope, ther eis m u c h c oncern reg arding e missionso f tri t iu m gas  ei ther b ylea kageor due tobreak age of  t he hol low g la ss tube. 
Another practical appl icatio n ofrad ioisotope s a n d l uminescen t ma terials is  th eir  useinn uclea r or at omi c  batt erie s  and phot o vo lta i c  g enerators.S e e , f or ex amp l e, Ols en e t al. (U.S. Pat.N o. 3,706,893)andM c Klv een et a l. , "Radioisotop e-P ow e r ed Photo vo ltaic Gener ator," N uc l ear T echnol ogy 43 :366-37 2 (M a y 1979 ).
F oradditiona l d is c ussionon  l u minesc entma terial s (e.g . , ph o s phors and lumine scent g lasse s ) a nd th ei r uses, seeJ. B. Birk s et al., S cintil lati on Co unters
 to_the limitation_of maximum light output_for radioluminescent_light_sources. Firstly,_based_on calculations, the_saturation power flux_predicted for pure tritium_gas at 1_atmosphere_(the typically used radioisotope) is only about 11 microwatts/cm.sup.2. Tritium has a very low_beta_particle energy,_i.e.,_E.sub.ave_=6 keV and E.sub.cutoff =18.6_keV. Due to this low_beta particle_energy, self-absorption of the beta energy by the_tritium_gas itself becomes_significant. For this reason, the beta particles that excite_the phosphor deposit on the inside_of the glass_tube_only_can come from a_limited gas thickness. Based on computer_simulations, the predicted gas thickness is_about 2 cm for 1 atmosphere of_pure tritium gas. In conventional use,_a tritium thickness of about_0.3 cm_is typically used with 1.3_atmospheres of tritium_in order_to optimize the_light output per curie of tritium_gas used.
Secondly, due_to the low average beta energy,_beta_particle penetration into_the_phosphor_particles is_limited to about_1-20.mu.m._Even though_phosphor_materials are very reflective, as a_result_of their high refractive index the phosphor_layer deposits on the_inside_of the glass quickly_become opaque to light even_for deposits of only a few_particles thick._For these_reasons, increasing the thickness of the phosphor deposit on the inside_layer of the tube does not_result in an increase_in brightness_for_a typical 1_atmosphere_gas tube.
Moreover,_there are important health and safety concerns_which go_hand-in-hand with the use of radioactive_materials. Since radioluminescent lamps_typically_employ tritium gas as a radioisotope,_there is much concern regarding emissions_of tritium gas either by_leakage_or_due to breakage of the_hollow glass tube.
Another practical application of_radioisotopes and luminescent_materials is their use in nuclear or_atomic_batteries and photovoltaic generators. See, for_example,_Olsen et al. (U.S. Pat. No._3,706,893)_and_McKlveen et al., "Radioisotope-Powered Photovoltaic_Generator," Nuclear Technology 43:366-372 (May 1979).
For_additional discussion on luminescent materials (e.g., phosphors and luminescent_glasses) and their_uses, see J. B. Birks_et_al.,_Scintillation Counters