Journal of Research of the National Burea u of Sta nda rds Vol. 62, No.1, January 1959 Resea rch Paper 2924 Preparation of New Solution Standards of Radium W. B. Mann, L. L. Stockmann, W . J. Youden, A. Schwebel, P. A. Mullen, and S. B. Garfinkel New radium-solut ion standards have been prepa red in t he r a nges of 10 micrograms a nd also 10- 9 and 10- 11 gram of r adium element. These h a ve been compa red with thc Nationa l Bureau of Standard's 1940 and 1947 series of radium-solut ion standards and, as a result of t hese compar isons, it has been found t hat t he 1940 10- 9 a nd 10- 11 -gram solut ion standa rds contained som e 2 to 3 percent more r adium element t han cer tified. It has been sho wn t hat t his difference pro ba bly arose in t he dilutio n of t he 1940 standa rds. 1. Introduction out using the NBS radiation balance [4 , 5) . These measurements consisted of three m easurem ents of R adium-solution standards have previously been the rate of energy emission from the new radium prepared at. the National Bureau of Standards in 1940 som'ce alone and also one triad of m easurem ents and 1947. The 1940 series consisted of standards in [1 , 2) of the new source relative to both primary the microgram range, ranging from 0.1 to 100.0 J.1.g of standards (No. XIV and XV). The r esults of these Tadium element in 5 ml of solution, and standards for measurem ents are shown in table 1. radon calibration consisting of 10- 9 and 10- 11 g of radium elemE'nt in 100 ml of the radium-salt and car­ T ABLE l. Radiation-balance results Jor comparison oj new m dium source with the United States primary radium standards I rier solution. The 1947 series consisted only of micro­ 'gram standards ranging from 0.1 to 100.0 J.1. g of ra­ R ate of energy emission in micro· Milligrams I< :l.ium element in 5 ml of solution of the radium watts from- of radium bromide and nitric acid acting as carrier. D ate of measurement element in new source R ecently the stock of 1O- 9_g r adium-solution stand­ No. XIV No. XV New source I ards became so depleted that it was necessary to prepare a new set of standards which has been des­ October 23, 1956. _.. _.. 914.8 6.108 November 1, 1956 ____ . 914.8 6.108 ignated as the 1957 series of tandards and which November 8,1956 _____ _ 914.6 6.107 consists chiefly of 10- 9 and lO- 11 _g standards with a November 28, 1956 .. __ . 5728.0 3000.3 914.1 6. J04 few microgram standards which were prepared for comparison purposes. A new set of "blank solutions" In calcula ting the values shown in table 1 a cor­ was also prepared consisting of 100-ml samplcs con­ rection was m ade for tbe growth of polonium-210 I taining 0.2 percent by weight of B aCb ·2H 20 . in the national standards sin ce June 1934. The mean value of the rate of . energy emission from the 2. Radium Calibration new source is 914.6 J.1.W which corresponds to 6.107 mg of radium elemen t as of N ovember 1956. The A sample of radium chloride containing approxi­ gamma-ray comparison, carried out with the gold­ m ately 10 mg of radium elem ent was retUTned to leaf electroscope, gave an average value from twelve the Radium Chemical Company for a r eseparation measurem en ts equal to 6.08 mg of radium element. from radium D and Its products and for recrystalli- zation. It was requested that the radium salt should Ibe crystallized in such a manner that the grain size 3. Preparation of the New Radium-Solution ,would be of the same approximate dimensions as Standards t hose in the Honigschmid radium standards (which wer e also radium chloride) and that the radium salt The 6.10 7-mg radium source was now completely Is hould be enclosed in a glass tube of about the same shattered at the bottom of a 5-liter thick-bot tomed dimensions (length, diameter, and wall thickness) as glass bottle under 3.052 liters of carrier solution, t he tubes used by H oni gschmid. It would then be determined by weighing and consisting of 0.2-per­ possible to compare this radium SOUTce wi th the two cent BaCl· 2H20 plus 5-percen t Hel, b y imparting a sharp blow to the glass tube by means of a specially United States primary radium standards [1 ,2], 1 using t he BS gold-leaf electroscope [3], without making constructed glass rod with a thickened and elongated any absorption corrections. In such a comparison end which was struck at its other end with a hammer. the sources are supported horizontally and then By this procedure the master solution of radium and carrier , with a concentration of radium elem ent of gen tly tapped so as to spread the grains of salt uni­ 6 formly along the glass t ubes. 2.001 X 10- glml, was prepared. Wbile the radium SOUTce was compared in this The dilutions that were made from this master manner with the two primary standards, this com­ solution are shown diagrammatically in fi gUTe 1. parison was only treated as confirmation for a series These dilutions were carried by two independent of microcalorimetric comparisons which were carried routes, designated as A and B , in order to check the aCCUTacy of dilution. The master solution as well J F igures in b rackets in dicate the literature references at the end of t his paper. as all subsequent dilutions thereof were thoroughly 21 mixed by agitation before aliquots were removed. parison with the 1940 series of 1O-9_g and 10- 11 -g All glassware used was carefully calibrated. radium-solution standards. The nominal values of First of all two lO-ml aliquots were each diluted the dilutions shown by each rou te were: 2 X 10- 7g lml, to 100 ml in a 100-ml volumetric flask using carrier 2 X 10- 9g/ml, 1 X lO- llg/ml, and 1X 10- 13g/ml. solution. Following this, eight 5-ml aliquots were Four of the eight 1957 10-/-Lg radium standards pipetted into glass ampoules and flame-sealed . were now compared in the NBS 41TI'-ionization cham · These eight ampoules each containing 10.163 /-L g of bel' [6 , 7] with four 10-/-Lg radium-solution standards radium-226 per 5.079 ml of solution were set aside of the 1947 series and were found to agree with the for comparison with the microgram range of both 1947 values to within the ± 1 perce nt es timated ac­ the 1940 and 1947 standards by means of the NBS curacy of the 1947 standards. Subsequently three 41T1'- ioniza tion chamber. of the 1940 series of 10-/-Lg radium-solution standards, At this point the r emainder of the master solution the stock of which had been believed to be exhausted, was siphoned off into two 2,500-ml volumetric were found ancl compared with three of the 10-/-Lg flasks and flam e sealed for future possible use. The standards of t be 1947 series and three of the 1957 remaining small volume containing the fragments of series . the glass tube was check ed and found to contain no Due to the quite large calibration correction of more radium per milliliter than one of the 10-fLg the 5-ml pipet (the volumc was equal to 5.079 ml) samples. tbe nominal 1957 10-/-Lg radium-solution standards The further dilutions along routes A and B were have an actual radium content of 10.163 /-Lg. The carried out as shown ill fi gure 1 and gave, by each comparisons of the 1957 standards with the 1947 rou te, fif ty 1O-9_g and fif ty lO-ll_g radium 100-ml standards were carried ou t in April and August solution standards. Of these the first, twenty-fifth, 1957, wbile that of the 1957 with the 1940 10-/-Lg and fiftieth 1O-9_g and 10- 1l-g ampoules in both standards was carried out in August 1957. route A and route B were reserved for later com- The certified values of both the 1940 and 1947 MASTER SOLU TIO N: 6.107 mg Ro - 226 IN 30S2 ml OF CARRIER SOLUTION 10.2% BoCI 2H2 0 + S% HCI ) '2.001 X 10"6 GRAM Ro per ml MASTER SOLUTION 30S2ml 10 mi 10mi ~7~:~,~~.~~,~"~'~10mi STAN DARD AMPOULES FOR 10 ml 4,,1' COMPARISONS ·10.16i X 1<J6 GR AM Ro EACH FIFTY IDO - ml SAMPLE S FIFTY IDO-ml SAMPLES '10" GRAM Ro EACH . NOS. ' IO"GRAM Ro EACH . NOS. IA.2SA AND SOA RESERVED IB.2SB AND SOB RE SER V[O FOR COMPARISON WIT H FOR COMPARISON WITH 1940 STANDARDS 1940 STANDARDS '"o ~0- W 0: 2000 m l FIFTY 100-m! SAMPLES FIFTY 100-ml SAMPLE S '" la-II GRAM Ro EACH ' 10" GR AM Ro EACH FIGU RE 1. Dilution scheme for the prepnration oj 1957 10- 9-g and 10- 1.-(/ radium standards. 22 L "10-Mg" radium-solution standards ~re ] 0 Mg as of four microcalometric comparisons of the 6-mg ra­ August 1940 and lV' ay 1947, respectively.