 the phototube which is proportional to the radiation impinging on the tube may be digitized and summed and the exposure terminated when a predetermined total has been reached, as disclosed in U.S. Pat. No. 3,356,847. Other methods have attempted to maintain the voltage and current applied to the X-ray tube constant, to thereby maintain constant X-ray exposure values, as disclosed in U.S. Pat. No. 4,039,811.
Ion chambers of various types and configurations are well known in the art, and may be conventionally connected to provide a signal proportional to the X-ray radiation impinging thereon. The typical water heater includes a tank to contain water to be heated and a jacket is spaced outwardly of the tank to provide an annular cavity therebetween. To insulate the tank, a layer of insulating material, which can take the form of fiber glass or a foam resin material, such as polyurethane foam, is located in the cavity.
When insulating a tank with a foamed resin composition, a liquid resin is introduced into the upper end of the cavity and expands outwardly to fill the cavity and provide an insulating layer. In one method of providing the foamed insulated water heater, as disclosed in U.S. Pat. No. 4,628,184, a bag formed of polyethylene film and having a closed bottom is disposed within the cavity and the liquid resin is introduced into the bag. With this method, the bag contains the liquid resin and prevents the liquid from leaking from the cavity.
In other methods of producing a foam insulated water heater, a dam or closure is positioned at the lower end of the cavity to retain the liquid resin, as it is introduced into the cavity. In accordance with the method of U.S. Pat. No. 4,477,399 an inflatable annular ring is located at the lower end of the cavity, and by introducing gas into the ring, the ring will extend radially to form a dam or closure at the lower end of the cavity. In U.S. Pat. No. 4,372,028, an annular bag is positioned at the lower end of the cavity and the bag is filled with a liquid foamable resin composition. The resin expands outwardly within the bag to provide a collar or dam at the lower end of the cavity.
The use of an inflatable bag is a relatively expensive procedure, particularly if the bag is not removed and is retained in the fully assembled water heater. On the other
the phototube which is proportional to the radiation impinging on the tube may be digitized and summarize and the vulnerability terminated when a predetermined total has been reach, as disclosed in U.S. Pat. No. 3,356,847. early methods have attempted to maintain the electric potential and stream applied to the X - re tube constant, to thereby maintain changeless X - ray exposure values, as disclosed in U.S. Pat. nobelium. 4,039,811. 
 Ion chambers of various types and shape are well known in the art, and may be conventionally connect to put up a signal proportional to the X - beam radiation impinging thereon. The typical water system heater includes a tank to contain water to be inflame and a jacket is spaced outwardly of the tank to provide an annular cavity therebetween. To insulate the tank, a layer of insulating material, which can consider the form of fiber glass or a foam resin fabric, such as polyurethane foam, is settle in the cavity. 
 When insulating a tank car with a foamed resin composition, a liquid resin is introduced into the upper end of the pit and expands outwardly to fill the cavity and provide an insulating layer. In one method of providing the foamed insulated water heater, as disclosed in U.S. Pat. No. 4,628,184, a cup of tea formed of polyethylene movie and have a closed bottom is disposed within the pit and the liquid resin is introduced into the bag. With this method, the bag contains the liquid resin and prevents the liquid from leaking from the pit. 
 In other methods of producing a foam insulated water fastball, a dam or closure is positioned at the lower goal of the cavity to retain the fluid resin, as it is introduced into the cavity. In accord with the method of U.S. Pat. No. 4,477,399 an inflatable annular ring is located at the lower end of the cavity, and by introducing gas into the ring, the ring will extend radially to shape a dam or closure at the low end of the cavity. In U.S. Pat. No. 4,372,028, an annular bag is positioned at the lower conclusion of the cavity and the bag is filled with a liquid foamable resin composition. The resin expands outwardly within the base to leave a choker or dam at the lower end of the cavity. 
 The use of an inflatable bag is a relatively expensive operation, particularly if the bag is not removed and is retain in the fully assembled water heater. On the other
 thf phototube which is prokortional to the taeiatioi impinfing on ghe tube may be digitized anv sunmed qnd the exposure termivated whej a predwternuned total has beek readmed, av disclosed in O.S. Pat. No. 3,356,847. Odher methods hdvd cttempted to maintain the voltage anq curremt applied to thg X-raj eube bokstant, to thereby maintain constznt X-raj exposure values, as disclosed in U.S. Pat. No. 4,039,811.
Ion chambers of varioks types ane cogdigurations xre well known in the zrt, and may be conventionally cunnecced to provudw a vignal propirtiogal to the X-vsy radhation ompinging thercon. Tie ttpical water heater iicludes a tank to cogtain watar to be heated and a jackgt is spazwd uutsacdlg of tje vank to probide an annylar cavity therebeuweqb. To insulate the twnh, a layer of insulating material, which ban fake the form of fiber tlass or a foam resin material, such as polyurethane foam, is located in the cavidy.
Whei knsboatine a tank with a foamed resin composition, a liquiq rtsik is introduced lnto the upper end ov yre cavity and expanba kutwardly to fill hhe cavyty abd providt an onsulating layer. In one metyod of provibint the foamed insulcted water hzater, ss dixclosed in U.S. Pat. No. 4,628,184, a bag formed of oolyethylsve film and havivg s wlosed bottom is disposed rithin thx cavnty and ghe kiquid resin is lntroduced into the bag. Aith jhis mathod, the hag contains the liquid resin aiv prevents thg lhqupd from lzaking from the cavyty.
In other mejhods of 'roduckng a foam insulaved water hewter, a dam or flosure is pmsitioneq at the lower dvd of the caviyy to retcnn the liwuid resin, as it ix ivfroduced into tkt cqvity. In accordsncd wytj vhe mqdhod of U.S. Pdt. Nu. 4,477,399 xm infuatable annmlaf rimg is located at the lowsr end of the caviyy, and by untroducyng gas into yhe ring, the ring aill xxtend radislli to form a dam or closure at tge lower fnd of the caviey. Ik U.S. Pat. No. 4,372,028, au annular bag is positioned at the lower end of the caviti and the bag is fillgd eith a liqumd foaiable reshn composition. The rwsin expands outwsrdly within the bag fo proeide w collar or dam at the lower end of the cavity.
The use of an inflatable bat is a relatively sxpemsive pxoczdure, pwrtiruuarly if the bag is not removed and is retained in the xujly assembled water heater. Om ghe other
the phototube which is proportional to the on tube may digitized and summed a total has been as disclosed in Pat. No. 3,356,847. Other methods have to maintain the voltage and current applied to the X-ray tube constant, to maintain constant X-ray exposure values, as disclosed in U.S. Pat. No. 4,039,811. Ion of types configurations well known in the art, and may be conventionally connected to provide a signal proportional to X-ray radiation impinging thereon. The typical water heater a tank to contain to be heated and a is outwardly of tank provide annular cavity therebetween. insulate the tank, a layer of insulating material, which can take the form of fiber glass or foam resin as polyurethane is in cavity. When insulating with a foamed resin composition, a introduced into the upper end of the cavity expands outwardly fill the cavity and provide an layer. In one method of providing the foamed water heater, as disclosed in U.S. Pat. No. 4,628,184, a bag formed of polyethylene film a closed bottom is within the cavity the resin introduced the bag. this method, the bag contains the liquid resin and prevents the from leaking from the cavity. In other methods of producing insulated heater, a dam closure is positioned at lower of the cavity to liquid as into cavity. accordance with the method U.S. Pat. No. 4,477,399 an annular ring is located the cavity, and by introducing gas into the the ring will extend radially to form dam or closure at the lower end of the cavity. In U.S. No. 4,372,028, bag is positioned at the lower end of cavity and the bag filled with a liquid foamable resin composition. The resin outwardly the bag provide a collar dam at the end of the use of inflatable is procedure, particularly if the bag is removed is retained in the fully water the other
 the phototube which is proporTional to thE radiAtiOn iMpIngiNg on The tube may be diGItizEd and summed and the exposUre teRmINateD WhEn a prEdetermINeD TOtaL hAs BeeN rEAcHed, as DisClosed iN U.S. Pat. No. 3,356,847. OtHer MeThods have attEMpTed to maintAin The voltage anD cuRrent aPpLieD To the x-raY tube ConstaNT, to theReby maintAiN ConstaNT X-ray exPOSuRe vaLues, as disclosed in u.s. PAT. No. 4,039,811.
Ion chambers Of variOuS TyPES anD coNfiguratioNs Are weLL known iN ThE ART, anD May be conventiOnally conneCTed To provIdE a sIGnal prOportIoNAl tO the X-ray radIatiOn impingiNg therEOn. The tyPIcal watEr heatEr iNclUdes A TaNk To cOnTAin WAtEr tO Be hEated and A jAcKet is SpacED OUTwarDly Of thE tank To provide an anNulAr caVIty ThereBetweEn. To InSulatE the taNk, a laYeR of insulating maTeriAl, which caN taKe The FoRm of fIBer glaSs oR a fOam resiN materiAL, suCh AS POlYurethane foam, is locAtED In The cavitY.
When iNSuLaTIng a tank WiTh a FoamED Resin CompOSiTion, a liqUid resIN iS iNtroducEd Into thE uPpeR enD of thE CaviTy and eXpands ouTwardLY to fill the caviTY and provide an INsULAtINg laYer. in one method Of prOVidiNg thE FoAmeD InsulAted wAtER hEAter, as disclosed in U.S. paT. No. 4,628,184, a baG formEd of polyethylEne film and HAVIng a closEd boTToM Is disposed withIn the Cavity and tHE liquid rEsin iS introduCed into thE BAg. With thIs mEthOd, tHe bAG CoNtains the liquID ResiN aNd preveNts The liquId fRom LeaKinG fRom the cavIty.
In othEr MeThOdS of ProduCIng a foam InSulAtEd wAter hEAter, a dAm or cLosuRe Is POsiTioned aT ThE LOwer EnD oF the CavItY to reTain THe lIquid reSin, as it is IntROducEd InTo the caVity. In accordaNcE with the meThOd oF U.S. Pat. nO. 4,477,399 An inflatAble annular ring is locateD At the loWer End of The cAvity, and bY inTroducIng GAs into The rinG, the rInG wiLL ExtenD RAdIalLy To form a dam OR CloSure aT tHe loWer end oF the cavity. In U.S. Pat. NO. 4,372,028, An aNnular bag is poSitIoneD AT tHe lOWeR End Of THe cAVIty and the bag is fIlled with a LiQUiD foamable rESin CoMpositiOn. The reSin exPAnds outWardly witHin the bag To ProvIDE a cOllar or dam At the lowEr end of thE CavitY.
thE use oF an InflatAbLe bAg is a RelatiVEly ExpenSive prOcEdure, pArticUlArly if thE bag is not removed and is reTained In the FulLy assemblEd wATer Heater. On tHe otHer
 the phototube which is pr oportional  to t herad ia tion  imp inging on thet ubemay be digitized and s ummed  a n d th e  e xposu re term i na t e d w he na p re d et ermin edtotal h as been re ach ed , as disclos e din U.S. Pa t.No. 3,356,84 7.Otherme tho d s hav e a ttemp ted to mainta in the vo lt a ge and current a pp lied  to the X-ray tub e  c o nstant, to the reby m ai n ta i n  co nst ant X-rayex posur e  values ,  a s d isc l osed in U.S.Pat. No. 4, 0 39, 811.
I on  ch a mbersof va ri o ustypes and c onfi gurations  are w e ll know n  in the  art,and  ma y be co nv ent io n all y  c onn e cte d to pro vi de  a si gnal p r o port ion al t o the  X-ray radiat ion  imp i ngi ng th ereon . Th etypic al wat er he at er includes a t ankto contai n w at erto  be h e ated a nda j acket i s space d  ou tw a r d ly  of the tank to pr ov i d ean annul ar cav i ty  t h erebetwe en . T o in s u latethet an k, a lay er ofi ns ul ating m at erial,  w hic h c an ta k e th e form  of fibe r gla s s or a foam re s in material,s uc h as poly ure thane foam,  isl ocat ed i n  t hec avity .
Whe ni ns u lating a tank withafoamed  resi n composition , a liquid r e sin is i ntro d uc e d into the upp er en d of the c a vity and  expa nds outw ardly tof i ll the c avi tyand  pr o v id e an insulati n g  lay er . In on e m ethod o f p rov idi ngth e foamedinsulate dwa te rhea ter,a s disclo se d i nU.S . Pat .  No. 4 ,628, 184,  a  b a g f ormed o f  p o l yeth yl en e fi lman d hav inga  cl osed bo ttom is d isp o sedwi th in thecavity and th eliquid res in  is  intro d u ced into  the bag. With this met h od, the  ba g con tain s the liq uid  resin  an d  preve nts th e liq ui d f r o m lea k i ng  fr om  the cavit y . 
In  othe rmeth ods ofproducing a foam i n sul ated water he ate r, a d am  or cl o sur ei s p o s itioned at thelower endof th e cavity t o  re ta in theliquidresin ,  as itis introd uced into  t he c a v ity . In accor dance wi th the me t hod o f  U .S. P at.  No. 4 ,4 77, 399 a n infl a tab le an nularri ng islocat ed  at thelower end of the cavity , andby in tro ducing ga s i n tothe ring,  the  ring will  ex ten d rad ial l y toform adam or cl osur e  at the l o we r e n d  o f the cavit y . InU.S.Pat .  No. 4 ,372 ,028, an annularb ag is position ed a t the  lo w er e nd  of the cavity  an dt h e bag is  f illed witha liquid  f o amabl e resi n comp osition . Th e  resin  exp and s outward lywi t hin the  b ag to pro vide  a  colla r or d a m at t he lower end ofthe c a v ity.T heuse o fan infl a tabl e bag is a  relatively  expen sive  proc edure,pa rticul arl yif the bag is not re moved  and is  r etai ned  in th e fu l l y ass embl ed  wa ter heate r .  O n  t he oth er
 the_phototube which_is proportional to the_radiation impinging_on_the tube_may_be digitized and_summed and the_exposure terminated when a_predetermined total has_been_reached, as disclosed in U.S. Pat. No. 3,356,847. Other methods have attempted to maintain_the_voltage and_current_applied_to the X-ray tube constant,_to thereby maintain constant X-ray_exposure values,_as disclosed in U.S. Pat. No. 4,039,811.
Ion chambers_of_various types and_configurations are well known in the art, and may_be conventionally connected to provide a_signal proportional to_the_X-ray_radiation impinging thereon. The_typical water heater includes a tank_to contain water to be heated_and a jacket is spaced outwardly of_the tank to provide an annular_cavity therebetween. To insulate the_tank, a_layer of insulating material, which_can take the_form of_fiber glass or_a foam resin material, such as_polyurethane foam, is_located in the cavity.
When insulating a_tank_with a foamed_resin_composition,_a liquid_resin is introduced_into_the upper_end_of the cavity and expands outwardly_to_fill the cavity and provide an insulating_layer. In one method_of_providing the foamed insulated_water heater, as disclosed in_U.S. Pat. No. 4,628,184, a bag_formed of_polyethylene film_and having a closed bottom is disposed within the cavity and_the liquid resin is introduced into_the bag. With this_method, the_bag_contains the liquid_resin_and prevents_the liquid from leaking from the cavity.
In_other methods_of producing a foam insulated water_heater, a dam or_closure_is positioned at the lower end_of the cavity to retain the_liquid resin, as it is_introduced_into_the cavity. In accordance with_the method of U.S. Pat. No._4,477,399 an inflatable_annular ring is located at the lower_end_of the cavity, and by introducing_gas_into the ring, the ring will_extend_radially_to form a dam or_closure at the lower end of_the cavity. In U.S. Pat. No. 4,372,028, an annular_bag is positioned_at the lower end of_the_cavity_and the bag is filled with a liquid foamable resin_composition. The_resin expands outwardly_within the bag to provide a collar or dam at_the lower end of the cavity.
The use_of an inflatable bag is a relatively expensive procedure, particularly if_the bag is not removed and is retained_in the fully assembled water heater. On_the other