ILIAS, Jaca, Spain 5 of December 2006 Se-82 purification: distillation and rectification procedures Kornoukhov Vasily INR RAS (Moscow) for IChHPS (Nizhny Novgorod) and IRE (Moscow)

LAL, Orsay, Spain 1 – 2 of June 2006 SuperNEMO: radiopurity requirements Tl-208 ( 232 Th chain) <= 2  Bq/kg (<= 1.5 ppt of Th-232) Bi-214 ( 238 U chain) <= 10  Bq/kg (< = 10 ppt of U-238)

232 Th 1,41·10 10 y 228 Ra 5,75 y 228 Ac 6,15 hours 228 Th 1,91 y 224 Ra 3,64 d 220 Rn 55,3 sec 216 Po 0,158 sec 212 Pb 10,64 h 212 Bi 60,5 min         208 Tl 3,10 min  36,2 % T 1/2 ~ y T 1/2 ~ years T 1/2 ~ days T 1/2 ~< hours

ILIAS, Jaca, Spain 5 of December 2006 SuperNEMO: dangerous isotopes from 232 Th chain Th-232, Ra-228, Th-228 We must remove Th and Ra How to check the procedure: Th: 232 Th (MS), 228 Th (HPGe: 208 Tl  line) Ra: 228 Ra (HPGe: 228 Ac  line)

238 U 4,51·10 9 y 234 Th 24 d 234m Pa 1,18 min 234 U 2,47·10 5 y 230 Th 8,0 ·10 4 y 226 Ra 1602 y 222 Rn 3,824 d 218 Po 3,05 min 214 Pb 26,8 min         214 Bi 19,7 min  T 1/2 ~ y T 1/2 ~ days T 1/2 ~ minutes

ILIAS, Jaca, Spain 5 of December 2006 SuperNEMO: dangerous isotopes from 238 U chain Ra-226 We must remove Ra How to check the procedure: Ra: 226 Ra (Champagne method, HPGe: 214 Bi  line)

ILIAS, Jaca, Spain 5 of December 2006 SuperNEMO: dangerous isotopes and elements 238 U chain: Ra Th cain: Th-232, Ra-228, Th-228 Conclusion: we must remove Ra and Th

ILIAS, Jaca, Spain 5 of December 2006 Industrial scale production of 82 Se At present the only technology for industrial scale production of 82 Se is centrifugation method and only site for ~ 100 kg-scale production is Svetlana (the ECP, Siberia)

ILIAS, Jaca, Spain 5 of December Se transformation at Svetlana (the ECP) (V.Kornoukhov for ILIAS meeting, Orsay, April 2005) Patent #… is “valid” in Russia only nat Se  nat SeF 6  centrifugation  82 SeF 6  82 SeF 6  (glow discharge)  82 Se + …  82 Se washing with H 2 O (to remove F-ions)  Distillation of 82 Se in vacuum “Chemical features” of impurities (chemical forms): fluorine compounds (!)

ILIAS, Jaca, Spain 5 of December 2006 General remarks concerning the problem: ( + ) Se is material for semi-conductive industry: there are many methods for its purification; ( - ) 82 Se is a result of chemical transformation through SeF 6 compound, and behavior of U-, Th-, Ra- impurities presented in such product (fluorine compounds) could be quite different of impurities in selenium produced accordingly to standard technology.

ILIAS, Jaca, Spain 5 of December 2006 Chemical forms of U, Th, Ra impurities in isotopically enriched Se There is no exact information on chemical forms of U, Th, Ra impurities at their low concentration in selenium. There are no data on solubility of U, Th, Ra compounds with oxygen, selenium, fluorine in liquid Se. No data on adsorption ability of U, Th, Ra impurities on heterogeneous particles of submicron size.

ILIAS, Jaca, Spain 5 of December 2006 Some properties of elementary selenium Molecular composition of Se: Vapor (at 700 – 1300 K): Se 2 – Se 8 Melt (at – K): mixture of cyclo-Se 8, katenapoly-Se n (n = 10 2 – 10 3 ), and polycyclo-Se n in chemical equilibrium. Solid: Se α, Se β – Se 8, Se hex. - Se n Melting Point, K. Se  - 443; Se  - 453; Se hex – 494,3 Boiling point, K – Density, g/cm 3 : Se α – 4.46; Se β ; Se hex. – 4.717; Se liq (550 K) – Industrial sources of Se of technical grade (99.0 – 99.7 %): Production of sulfuric acid and non-ferrous metals

ILIAS, Jaca, Spain 5 of December 2006 Distillation procedure & NEMO detector Group from INR RAS (in 1997): 116 Cd distillation for NEMO-3 detector (two portions, 0.15 kg kg): good result!

ILIAS, Jaca, Spain 5 of December 2006 Physical methods of Se purification Distillation methods: 1. One – Stage (Simple) distillation 2. Multi-Stage distillation methods: a. Repeated simple distillation of purified product from previous stages. b. Rectification – multi-stage counter – current method, realized in one apparatus and in one process.

Purification of selenium by distillation method Essence of method: impurity content in equilibrium vapor and liquid is different. х ≠ y Elementary separation process: Influence on the system with initially uniform impurity distribution leading to appearance of spatially divided parts of system with different impurity content. The physical action leading to separation in distillation methods: - evaporation part of liquid - condensation part of vapor. Condition of separation: у α =  ≠ 1 х Conditions of effective separation at distillation: у α =  >> 1 for highly volatile impurities х у α =  << 1 for non-volatile impurities х

Separation coefficient  at the equilibrium “ liquid-vapour” for some impurities in Se at 684 o C Impurity Content, mas.%  S Te As Sb Hg Metals 0,1-1,0 0,01-1,0 0,014-0,3 0,3-2,0 0,04-0,006 0,01-0,001 2,12 2,6 66, , * * ideal separation coefficient

Distribution on size of heterogeneous particles in selenium. Determination method – laser ultramicroscopy Effective separation coefficient of heterogeneous particles in Se as function of evaporation rate

ILIAS, Jaca, Spain 5 of December 2006 Distillation method: One – Stage (Simple) distillation

Multi-Stage methods 1. Repeated simple distillation of purified product from previous stages. 2. Rectification – multi-stage counter – current method, realized in one apparatus and in one process.

ImpurityContentImpurityContent Na 3.00E-08Al<6.00E-04 Fe<4.00E-04Mg<3.00E-04 Mn<1.00E-04P Sn<7.00E-05Ni<7.00E-05 Te<6.00E-05Bi<4.00E-05 Pb<4.00E-05As<2.00E-05 Rb<6.00E-06Sb<2.00E-06 W<3.00E-07Ta<2.00E-07 Ir<2.00E-07Au<4.00E-08 K<1.00E-08Zn<5.00E-09 Cr<4.00E-09Ag<2.00E-09 Co<8.00E-10Cs<2.00E-10 Cd<2.00E-10Hf<1.00E-10 Cu<1.00E-10Sc<6.00E-11 Ga<4.00E-11La<1.00E-11 U<9.00E-12 Impurity content, (at %), in Se, purified by rectification Determination method of impurity content – activation analysis at% - 1 at. ppm at% - 1 at. ppb at% - 1 at. ppt

ILIAS, Jaca, Spain 5 of December 2006 Organizations/institutes could be involved in purification of 82 Se Russia (distillation method): Svetlana (the ECP, Siberia) Kurchatov Institute (Moscow) The IChHPS (Nizhny Novgorod) The Institute of Rare Earths (Moscow) Mendeleev Institute (Moscow) USA (“wet” chemistry): INEEL (Idaho Falls) Coordinator (ILIAS/SuperNEMO): Dominique Lalanne

ILIAS, Jaca, Spain 5 of December 2006 The IChHPS & the IRE: goal and content of work Goal: Foundation and selection of technique for production of high-purity 82 Se according to the requirements of SuperNEMO project; its technological realization for production of ~100 kg. Parameters of the product Elementary selenium enriched with 82 Se isotope with the content of impurities of Th, Ra (U)  at.% (  1 ppt). Requirements to technology - The yield of the product is 90-95% (to be specified during investigations) - Output of technological scheme and equipment is 5-10 kg/cycle - The process instrumentation should preclude the unrecovered losses of 82 Se even in force majeur (destruction of equipment) - To exclude the isotopic dilution during purification procedures

ILIAS, Jaca, Spain 5 of December 2006 The IChHPS& the IRE: content of work 1. Thermodynamic and experimental evaluation of chemical and aggregate forms of the limiting impurities and of their relative volatility in selenium produced from SeF Experimental verification of purity of Se with natural isotopic composition with respect to the limiting impurities purified by multi-stage vacuum distillation and rectification. Verification of abilities of these methods during production of kilograms amounts of Se extracted from SeF Selection of technological process scheme with optimization by numerical methods of the degree of purity, output capacity and reliability. 4. Fabrication of equipment for the process with output capacity of 5-10 kg/cycle. 5. Production of pilot lots, characterization of the product, modifications of the selected scheme and technological modes.

ILIAS, Jaca, Spain 5 of December 2006 Basic stages at development of ultrapurification process 1. Characterization of initial substance (determination of content and nature of impurities). 2. Development of analytical method(s) to control limited impurities with necessary detection limit. 3. Choice of purification method; a priori calculation of apparatus and mode of operation. Fabrication of apparatus. 4. Preliminary experiments on purification. 5. Correction of apparatus construction and mode their operation. 6. Final experiments on ultrapurification. Characterization of high-purity products.

ILIAS, Jaca, Spain 5 of December 2006 Last stage of Se purification and Rn extraction

ILIAS, Jaca, Spain 5 of December 2006 Conclusion At present the only technology for 82 Se production is centrifugation method and only site for 100 kg- scale production is Svetlana (the ECP, Siberia) “Chemical features” of impurities in such a product (chemical forms): fluorine compounds. Multi-stages distillation and rectification methods of purification: the IChHPS and the IRE are ready to start purification of Se in the framework of ILIAS. Quality control with “champagne” method could be easy organize at very last stage of the purification procedure