Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the PTB, Germany and the BIPM in medium-energy x-rays

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1 Key comprison BIPM.RI(I)-K3 of the ir-kerm stndrds of the PTB, Germny nd the BIPM in medium-energy x-rys D.T. Burns 1, C Kessler 1, L Büermnn 2 1 Bureu Interntionl des Poids et Mesures (BIPM), Pvillon de Breteuil, F Sèvres 2 Physiklisch-Technische Bundesnstlt, Brunschweig, Germny Abstrct A key comprison hs been mde between the ir-kerm stndrds of the PTB, Germny nd the BIPM in the medium-energy x-ry rnge. The results show the stndrds to be in generl greement t the level of the expnded uncertinty (k = 2) of the comprison of 5.0 prts in The results re nlysed nd presented in terms of degrees of equivlence, suitble for entry in the BIPM key comprison dtbse. 1. Introduction An indirect comprison hs been mde between the ir-kerm stndrds of the Physiklisch- Technische Bundesnstlt (PTB), Germny, nd the Bureu Interntionl des Poids et Mesures (BIPM) in the x-ry rnge from 100 kv to 250 kv. Three cvity ioniztion chmbers of two different types were used s trnsfer instruments. The mesurements t the BIPM took plce in Mrch/April 2014 using the reference conditions recommended by the CCRI (CCEMRI 1972). 2. Determintion of the ir-kerm rte For free-ir ioniztion chmber stndrd with mesuring volume V, the ir-kerm rte is determined by the reltion I W K ir 1 k i (1) V e g ir 1 ir i where ir is the density of ir under reference conditions, I is the ioniztion current under the sme conditions, W ir is the men energy expended by n electron of chrge e to produce n ion pir in ir, g ir is the frction of the initil electron energy lost through rditive processes in ir, nd k i is the product of the correction fctors to be pplied to the stndrd. The vlues used for the physicl constnts ir nd W ir /e re given in Tble 1. For use with this dry-ir vlue for ir, the ioniztion current I must be corrected for humidity nd for the difference between the density of the ir of the mesuring volume t the time of mesurement nd the vlue given in the tble Detils of the stndrds The free-ir chmber stndrd M-01 of the BIPM is of the prllel-plte design, while the PTB Fßkmmer stndrd hs cylindricl geometry in which the inner collector rod nd the outer electrode re concentric nd the entrnce perture is displced from the xis of cylindricl symmetry by 4.5 cm. This ltter design requires the use of n dditionl correction fctor k sh to 1 At the BIPM, for n ir temperture T ~ 293 K, pressure P nd reltive humidity ~50 % in the mesuring volume, the correction for ir density involves temperture correction T / T 0, pressure correction P 0 / P, humidity correction k h = , nd the fctor to ccount for the compressibility of dry ir between T ~ 293 K nd T 0 = K. 1/14

2 ccount for the shdow effect of the centrl electrode. For both chmber types the mesuring volume V is defined by the dimeter of the chmber perture nd the length of the collecting region. The BIPM ir-kerm stndrd is described in Boutillon (1978) nd the chnges mde to certin correction fctors in Burns (2004), Burns et l (2009) nd the references therein. The PTB stndrd ws previously compred with the BIPM stndrd in n indirect comprison crried out in 1999, the results of which re reported in Burns et l (2002). The min dimensions, the mesuring volume nd the polrizing voltge for ech stndrd re shown in Tble 2. Tble 1. Physicl constnts used in the determintion of the ir-kerm rte Constnt Vlue u i ir (BIPM) b kg m ir (PTB) c kg m W ir / e J C b c u i is the reltive stndrd uncertinty. Density of dry ir t T 0 = K nd P 0 = kp dopted t the BIPM. Density of dry ir t T 0 = K nd P 0 = kp dopted t the PTB. Tble 2. Min chrcteristics of the stndrds Stndrd BIPM M-01 PTB Fßkmmer Aperture dimeter / mm Air pth length / mm Collecting length / mm Electrode seprtion / mm Collector width / mm b Mesuring volume / mm Polrizing voltge / V b Difference in rdius between the outer electrode (200 mm) nd the collector rod. Dimeter of the collector rod. 4. The trnsfer instruments 4.1 Determintion of the clibrtion coefficient for trnsfer instrument The ir-kerm clibrtion coefficient N K for trnsfer instrument is given by the reltion K (2) N K I tr where K is the ir-kerm rte determined by the stndrd using (1) nd I tr is the ioniztion current mesured by the trnsfer instrument nd the ssocited current-mesuring system. The current I tr is corrected to the stndrd conditions of ir temperture, pressure nd reltive humidity chosen for the comprison (T = K, P = kp nd h = 50 %). 2/14

3 To derive comprison result from the clibrtion coefficients N K,BIPM nd N K,NMI mesured, respectively, t the BIPM nd t ntionl metrology institute (NMI), differences in the rdition qulities must be tken into ccount. Normlly, ech qulity used for the comprison hs the sme nominl generting potentil t ech institute, but the hlf-vlue lyers (HVLs) my differ. A rdition qulity correction fctor k Q is derived for ech comprison qulity Q. This corrects the clibrtion coefficient N K,NMI determined t the NMI into one tht pplies t the equivlent BIPM qulity nd is derived by interpoltion of the N K,NMI vlues in terms of log(hvl). The comprison result t ech qulity is then tken s k N Q K,NMI RK,NMI (3) NK,BIPM In prctice, the hlf-vlue lyers normlly differ by only smll mount nd k Q is close to unity. 4.2 Detils of the trnsfer instruments Three cvity ioniztion chmbers belonging to the PTB were used s trnsfer instruments for the comprison, the sme sphericl (Exrdin) chmber used in the 1999 comprison nd two Frmer-type (PTW) thimble chmbers new to the present comprison. Their min chrcteristics re given in Tble 3. Chmber type Tble 3. Min chrcteristics of the trnsfer chmbers Exrdin A3 PTW TM30013 PTW TM30013 Seril number Geometry sphericl thimble Externl dimeter / mm Wll mteril C mm PMMA mm grphite Wll thickness cm g cm 2 Nominl volume / cm Reference point centre of sphere on centrl xis, 13 mm from tip Polrizing potentil / V Potentil pplied to the outer electrode. 5. Clibrtion t the BIPM 5.1 The BIPM irrdition fcility nd reference rdition qulities The BIPM medium-energy x-ry lbortory houses high-stbility genertor nd tungstennode x-ry tube with 3 mm beryllium window. An luminium filter of thickness mm is dded (for ll rdition qulities) to compenste for the decrese in ttenution tht occurred when the originl BIPM x-ry tube (with n luminium window of pproximtely 3 mm) ws replced in June Two voltge dividers monitor the tube voltge nd voltge-to-frequency converter combined with dt trnsfer by opticl fibre mesures the node current. No trnsmission monitor is used. For given rdition qulity, the stndrd uncertinty of the distribution of repet ir-kerm rte determintions over mny months is better thn 3 prts in The rdition qulities used in the rnge from 100 kv to 250 kv re those recommended 3/14

4 by the CCRI (CCEMRI 1972) nd re given in Tble 4. The irrdition re is temperture controlled t round 20 C nd is stble over the durtion of clibrtion to better thn 0.1 C. Two clibrted thermistors mesure the temperture of the mbient ir nd the ir inside the BIPM stndrd (which is controlled t 25 C). Air pressure is mesured by mens of clibrted brometer positioned t the height of the bem xis. The reltive humidity is controlled within the rnge 47% to 53% nd consequently no humidity correction is pplied to the current mesured using trnsfer instruments. 5.2 The BIPM stndrd nd correction fctors The reference plne for the BIPM stndrd ws positioned t 1200 mm from the rdition source, with reproducibility of 0.03 mm. The stndrd ws ligned on the bem xis to n estimted uncertinty of 0.1 mm. The bem dimeter in the reference plne is 98 mm for ll rdition qulities. Tble 4. Chrcteristics of the BIPM reference rdition qulities Rdition qulity 100 kv 135 kv 180 kv 250 kv Generting potentil / kv Inherent Be filtrtion / mm Additionl Al filtrtion / mm Additionl Cu filtrtion / mm Al HVL / mm Cu HVL / mm (µ/ ) ir / cm 2 g K BIPM / mgy s During the clibrtion of the trnsfer chmbers, mesurements using the BIPM stndrd were mde using positive polrity only. A correction fctor of is pplied to correct for the known polrity effect in the stndrd. The lekge current for the BIPM stndrd, reltive to the ioniztion current, ws mesured to be round 1 prt in The correction fctors pplied to the ioniztion current mesured t ech rdition qulity using the BIPM stndrd, together with their ssocited uncertinties, re given in Tble 5. The fctor k corrects for the ttenution of the x-ry fluence long the ir pth between the reference plne nd the centre of the collecting volume. It is evluted using the mesured irttenution coefficients given in Tble 4. In prctice, the vlues used for k tke ccount of the temperture nd pressure of the ir in the stndrd. Ioniztion current mesurements (both for the stndrd nd for trnsfer chmbers) re lso corrected for chnges in ir ttenution rising from vritions in the temperture nd pressure of the mbient ir between the rdition source nd the reference plne. 4/14

5 5.3 Trnsfer chmber positioning nd clibrtion t the BIPM The reference point for ech chmber ws positioned in the reference plne (1200 mm from the rdition source), with reproducibility of 0.03 mm. Ech trnsfer chmber ws ligned on the bem xis to n estimted uncertinty of 0.1 mm. The lekge current ws mesured before nd fter ech series of ioniztion current mesurements nd correction mde using the men vlue. The reltive lekge current for ll three trnsfer chmbers ws below 1 prt in For ech trnsfer chmber nd t ech rdition qulity, two sets of seven mesurements were mde, ech mesurement with integrtion time 60 s. The reltive stndrd uncertinty of the men ioniztion current for ech set ws typiclly below 1 prt in 10 4 for the Exrdin chmber nd below 2 prts in 10 4 for the PTW chmbers. Repet clibrtions for PTW chmber 7045 showed short-term reproducibility of round 3 prts in Furthermore, comprison of the Exrdin chmber results with those obtined in 1999 for this chmber showed greement t the level of 2 to 4 prts in 10 4, remrkble long-term stbility. Bsed on these mesurements, n uncertinty component of 3 prts in 10 4 is introduced to ccount for the short-term reproducibility of the chmber clibrtion coefficients t the BIPM. Tble 5. Correction fctors for the BIPM M-01 stndrd Rdition qulity 100 kv 135 kv 180 kv 250 kv u ia u ib Air ttenution k Photon sctter k sc Fluorescence k fl Electron loss k e b Ion recombintion k s Polrity k pol Field distortion k d Diphrgm correction k di b Wll trnsmission k p Humidity k h Rditive loss 1 g ir Vlues for K nd kp; ech mesurement is corrected using the ir density mesured t the time. b Vlues for k e nd k di dopted in September 2009 (Burns et l 2009). The diphrgm correction, described in Burns nd Kessler (2009), is evluted by Monte Crlo clcultion nd includes the effect of photon trnsmission nd sctter in the diphrgm s well s fluorescence nd secondry electron production in the diphrgm. 6. Clibrtion t the PTB 6.1 The PTB irrdition fcility nd reference rdition qulities The x-ry source used for the clibrtions t the PTB is of type MGC41, mnufctured by YXLON Interntionl X-Ry GmbH. The converter-type genertors of type MGG43 nd MGG42 operte t frequency of 40 khz nd yield constnt potentil tht cn be vried 5/14

6 between 20 kv nd 320 kv in steps of 20 V. The bipolr x-ry tube Philips MCN 323 hs tungsten node with n ngle of 22 nd 4 mm beryllium exit window. The high voltge is mesured invsively with frequency compensted voltge divider mnufctured t the PTB nd trceble to the PTB primry stndrd for dc high voltge. A high purity Ge spectrometer ws used to mesure the x-ry spectr from which the chrcteristic bem prmeters shown in Tble 6 were deduced. The mesured x-ry spectr were lso used for the clcultion of men vlues of the correction fctors for the free-ir chmber given in Tble 7. The irrdition re t the PTB is temperture controlled t round 20 C nd is stble over the durtion of clibrtion to better thn 0.1 C. Three thermistors, clibrted with n uncertinty of 20 mk, mesure, respectively, the temperture of the ir inside the PTB stndrd nd of the mbient ir close to the monitor nd trnsfer chmber. The mbient ir pressure is mesured using brometer (Setr cpcitnce-sensing circuit system) clibrted with n uncertinty of 6 P. All ioniztion current mesurements re corrected for ir temperture nd pressure. There is no ir humidity control in the lbortory but the reltive humidity cnnot exceed 60%. Vritions in the humidity re tken into ccount by type B reltive stndrd uncertinty of 4 prts in 10 4 for the PTB stndrd (Tble 7) nd similrly for the trnsfer chmber clibrtion (Tble 9). No humidity correction is pplied to the ioniztion current mesured using trnsfer instruments. Tble 6. Chrcteristics of the PTB reference rdition qulities Rdition qulity 100 kv 135 kv 180 kv 250 kv Generting potentil / kv Additionl Al filtrtion / mm Additionl Cu filtrtion / mm Al HVL / mm Cu HVL / mm (µ/ ) ir / cm 2 g K PTB / mgy s The PTB stndrd nd correction fctors The defining plne for the PTB stndrd ws positioned t 1000 mm from the rdition source, with reproducibility of 0.05 mm. The stndrd ws ligned on the bem xis to n estimted uncertinty of 0.1 mm. The bem dimeter in the reference plne is 80 mm for ll rdition qulities. During the clibrtion of the trnsfer chmbers, mesurements using the PTB stndrd were mde t single polrity. The polrity correction in the stndrd ws mesured previously nd is within 5 prts in 10 4 of unity. The reltive lekge current ws mesured to be less thn 3 prts in The correction fctors pplied to the ioniztion current mesured t ech rdition qulity using the PTB stndrd, together with their ssocited uncertinties, re given in Tble 7. The correction fctor k is evluted using the men mss ttenution coefficients (µ/ ) ir for ir 6/14

7 given in Tble 6. In prctice, the vlues used for k tke ccount of the temperture nd pressure of the ir in the stndrd t the time of the mesurements. Two differences in the PTB nd BIPM correction fctors re noted. The PTB stndrd involves the correction fctor k sh for the shdow effect of the centrl collector in the cylindricl free-ir chmber design. The PTB correction fctor for ioniztion gin k sc includes not only the effect of scttered photons, but lso tht of fluorescence photons (treted seprtely s k fl for the BIPM stndrd). Tble 7. Correction fctors for the PTB Fßkmmer stndrd Rdition qulity 100 kv 135 kv 180 kv 250 kv u ia u ib Air ttenution k b Ioniztion gin k sc c Electron loss k e Ion recombintion k s Polrity k pol Field distortion k d Shdow effect k sh Aperture edge trnsmission k l Wll trnsmission k p Humidity k h Rditive loss 1 g ir b c Component uncertinties below hve been neglected. Vlues for K nd kp; ech mesurement is corrected using the ir density mesured t the time. This corrects for the re-bsorption of scttered rdition nd fluorescence photons. 6.3 Trnsfer chmber positioning nd clibrtion t the PTB The reference point for ech trnsfer chmber ws positioned t the reference distnce (t the PTB 1000 mm from the rdition source), with reproducibility of 0.05 mm. Alignment on the bem xis ws to n estimted uncertinty of 0.2 mm. The lekge current ws mesured before nd fter ech series of five ioniztion current mesurements nd correction mde using the men vlue. The reltive lekge current for ech trnsfer chmber ws less thn 5 prts in The reltive stndrd uncertinty of the smple of five repet current mesurements t ech rdition qulity ws typiclly bout 5 prts in Additionl corrections to trnsfer chmber mesurements 7.1 Ion recombintion, polrity, bem non-uniformity nd field size As cn be seen from Tbles 4 nd 6, the ir-kerm rtes re the sme t the two lbortories nd so no corrections re pplied for ion recombintion. Ech trnsfer chmber ws used with the sme polrity t ech lbortory nd so no corrections re pplied for polrity effects in the trnsfer chmbers. No correction is pplied t either lbortory for the rdil non-uniformity of 7/14

8 the rdition field; ny smll effect of non-uniformity over the dimensions of the trnsfer chmbers is likely to cncel t the two lbortories. The PTB field size of 80 mm is smller thn tht t the BIPM (98 mm). It is known tht trnsfer chmbers respond to chnges in field size in wy tht free-ir chmbers do not, so tht clibrtion coefficients cn show some sensitivity to field size. Mesurements t the PTB under reference conditions (distnce 1000 mm, field size 80 mm) were ugmented by mesurements t distnce of 1200 mm where the field size is 96 mm, conditions close to those t the BIPM. While the results for N K were not different by more thn 5 prts in 10 4, those for the Exrdin chmber were systemticlly higher by round 3 prts in 10 4, while those for the PTW-7045 chmber were lower by round 5 prts in As the net effect is of the order of 1 prt in 10 3, stndrd uncertinty of this mount is included (Tble 10). 7.2 Rdition qulity correction fctors k Q As noted in Section 4.1, slight differences in rdition qulities my require correction fctor k Q. However, from Tbles 4 nd 6 it is evident tht the rdition qulities t the BIPM nd t the PTB re closely mtched in terms of HVL. Even for the Exrdin chmber, whose vlue for N K vries by 4% over the energy rnge, the k Q fctor differs from unity by only 0.05% (for the 100 kv nd 180 kv qulities). For this reson, k Q is tken to be unity for ll chmbers nd qulities, with negligible uncertinty. 8. Uncertinties The uncertinties ssocited with the primry stndrds re listed in Tble 8, those for the trnsfer chmber clibrtions in Tble 9 nd those for the comprison results R K,PTB in Tble 10. The combined uncertinty for the comprison results presented in Tble 10 includes component of 8 prts in 10 4 rising from the different results obtined for the three trnsfer chmbers nd is essentilly the r.m.s. vlue for men of Tble 12. Tble 8. Uncertinties ssocited with the stndrds Stndrd BIPM PTB Reltive stndrd uncertinty u ia u ib u ia u ib Ioniztion current Volume Positioning Correction fctors (excl. k h ) Humidity k h Physicl constnts K std For the PTB, component uncertinties below hve been neglected. The combined stndrd uncertinty u c of the comprison result tkes into ccount correltion in the type B uncertinties ssocited with the physicl constnts nd the humidity correction. Correltion in the vlues for k e nd k sc (including k fl t the BIPM), derived from Monte Crlo clcultions in ech lbortory, re tken into ccount in n pproximte wy by ssuming hlf 8/14

9 of the uncertinty vlue for ech fctor t ech lbortory. This is consistent with the nlysis of the results of BIPM comprisons in medium-energy x-rys in terms of degrees of equivlence described in Burns (2003). Tble 9. Uncertinties ssocited with the clibrtion of the trnsfer chmbers Institute BIPM PTB Reltive stndrd uncertinty u ia u ib u ia u ib K std Positioning of trnsfer chmber I tr Reproducibility N K,std As noted in Section 9, this represents the reproducibility of the pre- nd post-comprison mesurements. Tble 10. Uncertinties ssocited with the comprison results Reltive stndrd uncertinty u ia u ib N N K, PTB K,BIPM Field size Different trnsfer chmbers R K,PTB u c = Tkes ccount of correltions in type B uncertinties. 9. Results nd discussion The clibrtion coefficients determined t the BIPM nd t the PTB before nd fter the BIPM mesurements re given in Tble 11. The trnsfer chmber stbility stb,q for ech rdition qulity is evluted s the reltive stndrd devition of ech pre- nd post-bipm pir. For the two PTW chmbers stbility is 2 to 3 prts in 10 4 (6 prts in 10 4 for chmber 7045 t 100 kv) nd for the Exrdin chmber round 1 prt in 10 3 (4 prts in 10 4 t 250 kv). This pprent instbility of the Exrdin chmber does not pper to be inherent in the chmber sensitivity itself; s the BIPM results for this chmber gree with those mesured in 1999 (corrected for the chnges to the stndrd in the interim period) t the level of 3 prts in Bsed on the results for ll three chmbers, n dditionl uncertinty component of 5 prts in 10 4 is included for reproducibility in Tble 9. The comprison results evluted using ech trnsfer chmber re given in Tble 12. The stbility estimte for ech trnsfer chmber, stb, is the men for the four rdition qulities of the vlues stb,q given in Tble 11. For ech rdition qulity, the finl comprison result (in bold) is tken s the rithmetic men of the results for the three trnsfer chmbers (the resons for not using weighted men re discussed below). The vlue men for ech rdition qulity is 9/14

10 the stndrd uncertinty of this rithmetic men. The r.m.s vlue for men of 8 prts in 10 4 is included in Tble 10 s n uncertinty rising from the results for the different trnsfer chmbers. Tble 11. Clibrtion coefficients for the trnsfer chmbers Rdition qulity 100 kv 135 kv 180 kv 250 kv Trnsfer chmber PTW TM N K,PTB (pre-comp) / Gy C N K,BIPM / Gy C N K,PTB (post-comp) / Gy C Chmber stbility stb,q 0.06% 0.02% 0.03% 0.02% Trnsfer chmber PTW TM N K,PTB (pre-comp) / Gy C N K,BIPM / Gy C N K,PTB (post-comp) / Gy C Chmber stbility stb,q 0.02% 0.03% 0.03% 0.02% Trnsfer chmber Exrdin A3-169 N K,PTB (pre-comp) / Gy C N K,BIPM / Gy C N K,PTB (post-comp) / Gy C Chmber stbility stb,q 0.10% 0.11% 0.10% 0.04% The results show the stndrds to be in generl greement t the level of the expnded uncertinty (k = 2) of the comprison of 5.0 prts in A slight trend with energy of up to 3 prts in 10 3 is observed. The present results cn be compred to those obtined for the PTB in the comprison crried out in These results, updted for the chnges mde to the BIPM stndrd in the interim period (Burns 2004, Burns et l 2009), re shown in the penultimte row of Tble 12. The two sets of results gree t the level of 1 to 2 prts in 10 3, those determined from the 1999 mesurements being closer to unity. The trend with energy observed in the present results is lso pprent in the erlier results, lthough to lesser extent. Common to both comprisons is the Exrdin A3-169 chmber, the updted results from 1999 for this chmber being shown in the finl row of Tble 12. With the exception of the present result t 100 kv, the seven remining results hve men of , the stndrd uncertinty of the distribution being only 7 prts in The results for the PTW chmbers re generlly higher, to (except t 100 kv). In view of the reproducible behviour of the Exrdin chmber over the fifteen-yer period, it is considered tht it should not be given less weight despite its 10/14

11 poorer pre- nd post- comprison stbility ( stb in Tble 12). For this reson n rithmetic men, rther thn weighted men, is used for the finl comprison result. Regrding the difference of round 2 prts in 10 3 in the results obtined for the two chmber types, bout hlf of this could be due to the differences in distnce nd field size t the two lbortories, s noted in Section 7.1. The possibility of ion recombintion differences hs been eliminted by PTB mesurements t series of dose rtes (for the PTW chmbers in 2014 nd for the Exrdin chmber in 1999). Tble 12. Comprison results Rdition qulity 100 kv 135 kv 180 kv 250 kv stb R K for PTW TM R K for PTW TM R K for Exrdin A R K,PTB men Updted R K,PTB from Updted Exrdin R K from Degrees of Equivlence The nlysis of the results of BIPM comprisons in medium-energy x-rys in terms of degrees of equivlence is described in Burns (2003). Following decision of the CCRI, the BIPM determintion of the ir-kerm rte is tken s the key comprison reference vlue, for ech of the CCRI rdition qulities. It follows tht for ech lbortory i hving BIPM comprison result x i with combined stndrd uncertinty u i, the degree of equivlence with respect to the reference vlue is the reltive difference D i = (K i K BIPM,i ) / K BIPM,i = x i 1 nd its expnded uncertinty U i = 2 u i. The results for D i nd U i, expressed in mgy/gy nd including those of the present comprison, re shown in Tble 13 nd in Figure 1, which include the linked results of the corresponding regionl key comprison APMP.RI(I)-K3 (Lee et l 2008). Note tht these dt, while correct t the time of publiction of the present report, become out of dte s lbortories mke new comprisons with the BIPM. The forml results under the CIPM MRA re those vilble in the BIPM key comprison dtbse. When required, the degree of equivlence between two lbortories i nd j cn be evluted by pir of terms: D ij = D i D j nd U ij = 2u ij, its expnded uncertinty (k = 2), both expressed in mgy/gy. In evluting u ij, ccount should be tken of correltion between u i nd u j (Burns 2003). 11. Conclusions The key comprison BIPM.RI(I)-K3 for the determintion of ir kerm in medium-energy x-rys shows the stndrds of the PTB nd the BIPM to be in generl greement t the level of the expnded uncertinty (k = 2) of the comprison of 5.0 prts in The present results gree t the level of 1 to 2 prts in 10 3 with those of the previous comprison in 1999 when ccount is tken of chnges to the BIPM stndrd. Tbles nd grphs of degrees of equivlence, including those for the PTB, re presented for entry in the BIPM key comprison dtbse. 11/14

12 12/14 Metrologi 51 (2014) Tech. Suppl Tble 13. Degrees of equivlence. For ech lbortory i, the degree of equivlence with respect to the key comprison reference vlue is the difference D i nd its expnded uncertinty U i. Tbles formtted s they pper in the BIPM key comprison dtbse; red indictes priciption in BIPM.RI(I)-K3 nd blue in APMP.RI(I)-K kv 135 kv Lb i D i U i Lb i D i U i /(mgy/gy) /(mgy/gy) NPL NPL ENEA ENEA NRC NRC NIM NIM BEV BEV VSL VSL NIST NIST NMIJ NMIJ LNE-LNHB LNE-LNHB GUM GUM ARPANSA ARPANSA MKEH MKEH VNIIM VNIIM PTB PTB INER INER Nuc. Mlysi Nuc. Mlysi DMSc DMSc BARC BARC NMISA NMISA KRISS KRISS IAEA IAEA kv 250 kv Lb i D i U i Lb i D i U i /(mgy/gy) /(mgy/gy) NPL NPL ENEA ENEA NRC NRC NIM NIM BEV BEV VSL VSL NIST NIST NMIJ NMIJ LNE-LNHB LNE-LNHB GUM GUM ARPANSA ARPANSA MKEH MKEH VNIIM VNIIM PTB PTB INER INER Nuc. Mlysi Nuc. Mlysi DMSc DMSc BARC BARC NMISA NMISA KRISS KRISS IAEA IAEA

13 D i / (mgy/gy) kv 135 kv 180 kv 250 kv NPL ENEA NRC NIM BEV VSL NIST NMIJ LNE-LNHB GUM ARPANSA MKEH VNIIM PTB INER Nuc. Mlysi DMSc Figure 1. Degrees of equivlence for ech lbortory i with respect to the key comprison reference vlue BARC NMISA KRISS IAEA 13/14

14 References Boutillon M 1978 Mesure de l exposition u BIPM dns le domine des ryons X de 100 à 250 kv Rpport BIPM-78/3 Burns D T 2003 Degrees of equivlence for the key comprison BIPM.RI(I)-K3 between ntionl primry stndrds for medium-energy x-rys Metrologi 40 Tech. Suppl Burns D T 2004 Chnges to the BIPM primry ir-kerm stndrds for x-rys Metrologi 41 L3 Burns D T, Büermnn L, Krmer H-M nd Lnge B 2002 Comprison of the ir-kerm stndrds of the PTB nd the BIPM in the medium-energy x-ry rnge Rpport BIPM-02/07 Burns D T nd Kessler C 2009 Diphrgm correction fctors for free-ir chmber stndrds for ir kerm in x-rys Phys. Med. Biol Burns D T, Kessler C nd Allisy P J 2009 Re-evlution of the BIPM interntionl stndrds for ir kerm in x-rys Metrologi 46 L21 23 CCEMRI 1972 Qulités de ryonnement Comité Consulttif pour les Étlons de Mesures des Ryonnements Ionisnts (Section I) 2 nd meeting R15 16 KCDB 2014 The BIPM key comprison dtbse is vilble online t Lee J H, Hwng W S, Kotler L H, Webb D V, Büermnn L, Burns D T, Tkeyeddin M, Shh V V, Srimnoroth S, Meghzifene A, Hh S H, Chun K J, Kdni T B, Tkt N nd Msimng Z 2008 APMP/TCRI key comprison report of mesurement of ir kerm for medium-energy x-rys (APMP.RI(I)-K3) Metrologi 45 Tech. Suppl /14