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Curium-244 alpha-sources for space research
Applied Radiation and Isotopes 53 (2000) 821±824
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Curium-244 alpha-sources for space research V. Radchenko a,*, B. Andreichikov b, H. WaÈnke c, V. Gavrilov a, B. Korchuganov b, R. Rieder c, M. Ryabinin a, T. Economou d a
State Scienti®c Centre of Russia Research Institute of Atomic Reactors Dimitrovgrad 433510, Russia b Space Research Institute of Russian Academy of Sciences, Moscow 117810, Russia c Max-Planck-Institut fuÈr Chemie, Mainz, 6500, Germany d University of Chicago, Chicago, 60637, USA
Abstract Special alpha-proton-X-ray spectrometric complexes (APXS) have been developed in order to perform chemical analyses of the Mars atmosphere and rock surface compounds by alpha back-scattering, alpha-proton measurements, and X-ray ¯uorescence. The sources were prepared by high temperature condensation of metal curium vapour onto silicon substrates. They are silicon disks with curium-244 ®xed on their surfaces as a silicide. The sources have overall dimensions as follows: disk diameter 8 mm; thickness 0.3 mm; and 6 mm diameter active spot. The source activities are 521 mCi and the alpha-line half-widths are equal to (1.7±2.5) and (2.9±4.5)% of full width at 10% of Maximum (Maximum is equal to 5.8 MeV). Thermovacuum (from 196 to 10008C), mechanical, and resource tests were performed and demonstrated that the sources maintained their characteristics. The applicability of the sources for the above-mentioned analytical purposes was con®rmed during NASA Mars Path®nder mission. 7 2000 Published by Elsevier Science Ltd. Keywords: Alpha-proton-X-ray spectrometric complex; Mars Path®nder; Curium-244
1. Introduction The general and detailed analyses of chemical elements contained in the Mars surface material is one of the experiments for Russian±American program of Mars investigation. First, in practice of space research to make chemical analysis of the Mars rock surface compounds, special alpha-proton-X-ray spectrometric complexes (APXS) have been developed, manufactured
* Corresponding author. Tel.: +7-84235-320-21; fax: +784235-356-48. E-mail address: [email protected] (V. Radchenko).
and are being tested as a component of the landing module. These complexes allow obtaining some information about the composition of volatile elements ®xed with the Mars rock and basic rock-forming chemical elements on the planet surface. The experiments are the result of cooperation from Max-Planck Institute for Chemistry (Germany), University of Chicago (USA), Space Research Institute of Russian Academy of Sciences and State Scienti®c Centre Research Institute of Atomic Reactors (Dimitrovgrad, Russia). APXSs were initially used for analysing the Moon surface during 1967±1968. The same devices were installed into ``FOBOS'' project landing modules started in 1988 to the Mars satellite.
0969-8043/00/$ - see front matter 7 2000 Published by Elsevier Science Ltd. PII: S 0 9 6 9 - 8 0 4 3 ( 0 0 ) 0 0 2 6 0 - 8
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V. Radchenko et al. / Applied Radiation and Isotopes 53 (2000) 821±824
Fig. 1. Apparatus spectrum of alpha-sources (activity = 49.5 mCi, DE=E1=2 2:0%, DE=E1=10 3:5%).
The operating principle for the above mentioned devices is based on three processes of alpha-particles, interaction with the substance. 1. The elastic scattering of alpha-particles on the nuclei of chemical elements of analysed substance. 2. Nuclear interaction of alpha-particles with some light elements resulting in proton generation. a, p)proton reaction. 3. Interaction with chemical elements' electron shells resulting in characteristic X-ray generation. These experiments are possible only if the monochromatic alpha-particle source is available. The goal of the work was to develop production technology, produce, and test unsealed curium-244 alpha-sources. Besides providing high analytical characteristics these
Fig. 2. Stability of silicon based sources under vacuum (a) and air (b) 1±4.1 mCi; 2±5.9 mCi; 3±4.3 mCi; 4±4.1 mCi.
sources have been required to provide high resistivity for hard working conditions, such as high mechanical and thermal overloads, long storage periods on the Earth and during the ¯ight, and operating in the Mars surface conditions. 2. Experimental For sources production the preparation of curium244 content was more than 93.31%. Just before preparing sources curium was puri®ed from daughter 240 Pu nuclide by means of extraction using D2EHPA. Puri®cation from cationic impurities was performed by curium oxalate settling. While vacuum distilling metal curium the preparation was additionally puri®ed from americium, microquantities of 252Cf and other impurities of high vapour pressure.
Table 1 Test conditions Source
Activity (mCi)
DE=E (%)
Atmosphere
Temperature (8C)
Time (min)
85a 89a 15 53 80 80
4.6 4.3 4.3 3.8 5.1 5.1
1.7 1.7 3.1 3.1 1.8 1.8
air air air air vacuum air
20 20 1000 1000 1000 ÿ196
± ± 60 60 120 60
a
Vibration (20±2000 Hz), impact (40±500 g), and vibration amplitude (1±10 g) tests were performed.
V. Radchenko et al. / Applied Radiation and Isotopes 53 (2000) 821±824
823
Fig. 4. Proton spectrum of miaskit rock.
Fig. 3. Alpha-spectrum of miaskit rock.
The sources were prepared by high temperature condensation of metal curium vapour onto various substrates. Metal curium was prepared by thermal reduction of curium oxide with metal thorium in accordance with the procedure given below. A de®nite quantity of curium oxide was mixed with excessive thorium saw-dust of spectral purity. Then this mixture was pressed into pellets. The pellets were loaded into a tantalum crucible. The crucible was heated by high-fre-
quency inductor and metal curium vapour was condenced onto tantalum substrates which were further used as a source of curium for preparation of ®nished sources. Polished plates of platinum metals (Pt, Ir, Rh) and silicon were used as substrate. On the basis of preliminary experiments silicon was selected as substrate material due to its high chemical stability and greater availability compared with platinum metals. According to X-ray data condensation of metal curium vapour onto silicon substrate results in formation of various composition curium silicides, as CmSi2, Cm2Si3, CmSi, and Cm5Si3 on the substrate surface. The high speci®c content of curium in these compounds allows preparation of sources of high activity and low alpha-line half-width.
Fig. 5. X-ray spectrum of Allende meteorite.
824
V. Radchenko et al. / Applied Radiation and Isotopes 53 (2000) 821±824
Some sets of these sources have been prepared. The source itself is the silicon disc having curium-244 silicide ®xed in the surface layer. The overall dimensions of these sources are as follows: disc diameter 8 mm, active spot diameter 6 mm, disc thickness 0.3 mm. Source activity is equal to 5 2 1 mCi, alpha-line halfwidth from 1.7 to 2.5%, and alpha-line width at onetenth of peak hieght is from 2.9 to 4.5% of average alpha-particles energy equal to 5.8 MeV. The set of nine of these sources was installed into the collector which at the same time is the source of ionizing radiation within ``Alpha-PXM'' equipment. Metal blinds were open only while the experiment was conducted thus protecting operators and the equipment from direct contact with alpha-radiation (Fig. 1). The sources and their spectral characteristics stability were studied at wide intervals of physical and chemical parameters of the environment simulating real conditions of storage and maintenance (Fig. 2). It was shown that while keeping sources in vacuum DE=E ratio is practically constant over 360 days. When keeping sources in air over the ®rst 200 days alpha-line half-width changes slightly, thereafter increasing gradually. This increase may be caused by chemical interaction of unbonded curium on the source surface with products of radiolysis of air due to 244Cm alpha-decay. While transporting and landing on the Mars surface the sources undergo mechanical loads. The sources
have been tested for vibration, impact, acceleration, and in¯uence of dierent temperatures and atmospheres (Table 1). Inspection after tests showed that spectral characteristics of sources were unchanged. Data on curium sputtering from the surface layer were obtained to estimate surface leakage due to 244 Cm alpha-decay. It was found, that irrespective of keeping conditions (air or vacuum), the curium sputtering rate was 0.1±2.0 atom per decay. After installing sources into devices they were calibrated using special thermal vacuum chambers. Using three dierent detection systems alpha-particles, protons, and X-rays were registered as three dierent spectra of characteristic radiation containing analytical information about the target substance. The results obtained by dierent methods partially complement and re®ne each other because back alpha-scattering is necessary to analyse light elements (C, O), proton emission increases the sensitivity to determine F, Na, Mg, Al, Si and S, while X-ray emission essentially increases the sensitivity for determination of heavy elements (from Na to Fe and above). The combination of these elements allows for determination of all the chemical elements (with the exception of H and He) if their quantity exceeds 0.1%. Figs. 3±5 cover the typical spectra obtained by the aircraft apparatuses. Fig. 3 and 4 are alpha- and proton spectra of igneous rock. Fig. 5 is the X-ray spectrum of Allende meteorite.
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Curium-244 alpha-sources for space research V. Radchenko a,*, B. Andreichikov b, H. WaÈnke c, V. Gavrilov a, B. Korchuganov b, R. Rieder c, M. Ryabinin a, T. Economou d a
State Scienti®c Centre of Russia Research Institute of Atomic Reactors Dimitrovgrad 433510, Russia b Space Research Institute of Russian Academy of Sciences, Moscow 117810, Russia c Max-Planck-Institut fuÈr Chemie, Mainz, 6500, Germany d University of Chicago, Chicago, 60637, USA
Abstract Special alpha-proton-X-ray spectrometric complexes (APXS) have been developed in order to perform chemical analyses of the Mars atmosphere and rock surface compounds by alpha back-scattering, alpha-proton measurements, and X-ray ¯uorescence. The sources were prepared by high temperature condensation of metal curium vapour onto silicon substrates. They are silicon disks with curium-244 ®xed on their surfaces as a silicide. The sources have overall dimensions as follows: disk diameter 8 mm; thickness 0.3 mm; and 6 mm diameter active spot. The source activities are 521 mCi and the alpha-line half-widths are equal to (1.7±2.5) and (2.9±4.5)% of full width at 10% of Maximum (Maximum is equal to 5.8 MeV). Thermovacuum (from 196 to 10008C), mechanical, and resource tests were performed and demonstrated that the sources maintained their characteristics. The applicability of the sources for the above-mentioned analytical purposes was con®rmed during NASA Mars Path®nder mission. 7 2000 Published by Elsevier Science Ltd. Keywords: Alpha-proton-X-ray spectrometric complex; Mars Path®nder; Curium-244
1. Introduction The general and detailed analyses of chemical elements contained in the Mars surface material is one of the experiments for Russian±American program of Mars investigation. First, in practice of space research to make chemical analysis of the Mars rock surface compounds, special alpha-proton-X-ray spectrometric complexes (APXS) have been developed, manufactured
* Corresponding author. Tel.: +7-84235-320-21; fax: +784235-356-48. E-mail address: [email protected] (V. Radchenko).
and are being tested as a component of the landing module. These complexes allow obtaining some information about the composition of volatile elements ®xed with the Mars rock and basic rock-forming chemical elements on the planet surface. The experiments are the result of cooperation from Max-Planck Institute for Chemistry (Germany), University of Chicago (USA), Space Research Institute of Russian Academy of Sciences and State Scienti®c Centre Research Institute of Atomic Reactors (Dimitrovgrad, Russia). APXSs were initially used for analysing the Moon surface during 1967±1968. The same devices were installed into ``FOBOS'' project landing modules started in 1988 to the Mars satellite.
0969-8043/00/$ - see front matter 7 2000 Published by Elsevier Science Ltd. PII: S 0 9 6 9 - 8 0 4 3 ( 0 0 ) 0 0 2 6 0 - 8
822
V. Radchenko et al. / Applied Radiation and Isotopes 53 (2000) 821±824
Fig. 1. Apparatus spectrum of alpha-sources (activity = 49.5 mCi, DE=E1=2 2:0%, DE=E1=10 3:5%).
The operating principle for the above mentioned devices is based on three processes of alpha-particles, interaction with the substance. 1. The elastic scattering of alpha-particles on the nuclei of chemical elements of analysed substance. 2. Nuclear interaction of alpha-particles with some light elements resulting in proton generation. a, p)proton reaction. 3. Interaction with chemical elements' electron shells resulting in characteristic X-ray generation. These experiments are possible only if the monochromatic alpha-particle source is available. The goal of the work was to develop production technology, produce, and test unsealed curium-244 alpha-sources. Besides providing high analytical characteristics these
Fig. 2. Stability of silicon based sources under vacuum (a) and air (b) 1±4.1 mCi; 2±5.9 mCi; 3±4.3 mCi; 4±4.1 mCi.
sources have been required to provide high resistivity for hard working conditions, such as high mechanical and thermal overloads, long storage periods on the Earth and during the ¯ight, and operating in the Mars surface conditions. 2. Experimental For sources production the preparation of curium244 content was more than 93.31%. Just before preparing sources curium was puri®ed from daughter 240 Pu nuclide by means of extraction using D2EHPA. Puri®cation from cationic impurities was performed by curium oxalate settling. While vacuum distilling metal curium the preparation was additionally puri®ed from americium, microquantities of 252Cf and other impurities of high vapour pressure.
Table 1 Test conditions Source
Activity (mCi)
DE=E (%)
Atmosphere
Temperature (8C)
Time (min)
85a 89a 15 53 80 80
4.6 4.3 4.3 3.8 5.1 5.1
1.7 1.7 3.1 3.1 1.8 1.8
air air air air vacuum air
20 20 1000 1000 1000 ÿ196
± ± 60 60 120 60
a
Vibration (20±2000 Hz), impact (40±500 g), and vibration amplitude (1±10 g) tests were performed.
V. Radchenko et al. / Applied Radiation and Isotopes 53 (2000) 821±824
823
Fig. 4. Proton spectrum of miaskit rock.
Fig. 3. Alpha-spectrum of miaskit rock.
The sources were prepared by high temperature condensation of metal curium vapour onto various substrates. Metal curium was prepared by thermal reduction of curium oxide with metal thorium in accordance with the procedure given below. A de®nite quantity of curium oxide was mixed with excessive thorium saw-dust of spectral purity. Then this mixture was pressed into pellets. The pellets were loaded into a tantalum crucible. The crucible was heated by high-fre-
quency inductor and metal curium vapour was condenced onto tantalum substrates which were further used as a source of curium for preparation of ®nished sources. Polished plates of platinum metals (Pt, Ir, Rh) and silicon were used as substrate. On the basis of preliminary experiments silicon was selected as substrate material due to its high chemical stability and greater availability compared with platinum metals. According to X-ray data condensation of metal curium vapour onto silicon substrate results in formation of various composition curium silicides, as CmSi2, Cm2Si3, CmSi, and Cm5Si3 on the substrate surface. The high speci®c content of curium in these compounds allows preparation of sources of high activity and low alpha-line half-width.
Fig. 5. X-ray spectrum of Allende meteorite.
824
V. Radchenko et al. / Applied Radiation and Isotopes 53 (2000) 821±824
Some sets of these sources have been prepared. The source itself is the silicon disc having curium-244 silicide ®xed in the surface layer. The overall dimensions of these sources are as follows: disc diameter 8 mm, active spot diameter 6 mm, disc thickness 0.3 mm. Source activity is equal to 5 2 1 mCi, alpha-line halfwidth from 1.7 to 2.5%, and alpha-line width at onetenth of peak hieght is from 2.9 to 4.5% of average alpha-particles energy equal to 5.8 MeV. The set of nine of these sources was installed into the collector which at the same time is the source of ionizing radiation within ``Alpha-PXM'' equipment. Metal blinds were open only while the experiment was conducted thus protecting operators and the equipment from direct contact with alpha-radiation (Fig. 1). The sources and their spectral characteristics stability were studied at wide intervals of physical and chemical parameters of the environment simulating real conditions of storage and maintenance (Fig. 2). It was shown that while keeping sources in vacuum DE=E ratio is practically constant over 360 days. When keeping sources in air over the ®rst 200 days alpha-line half-width changes slightly, thereafter increasing gradually. This increase may be caused by chemical interaction of unbonded curium on the source surface with products of radiolysis of air due to 244Cm alpha-decay. While transporting and landing on the Mars surface the sources undergo mechanical loads. The sources
have been tested for vibration, impact, acceleration, and in¯uence of dierent temperatures and atmospheres (Table 1). Inspection after tests showed that spectral characteristics of sources were unchanged. Data on curium sputtering from the surface layer were obtained to estimate surface leakage due to 244 Cm alpha-decay. It was found, that irrespective of keeping conditions (air or vacuum), the curium sputtering rate was 0.1±2.0 atom per decay. After installing sources into devices they were calibrated using special thermal vacuum chambers. Using three dierent detection systems alpha-particles, protons, and X-rays were registered as three dierent spectra of characteristic radiation containing analytical information about the target substance. The results obtained by dierent methods partially complement and re®ne each other because back alpha-scattering is necessary to analyse light elements (C, O), proton emission increases the sensitivity to determine F, Na, Mg, Al, Si and S, while X-ray emission essentially increases the sensitivity for determination of heavy elements (from Na to Fe and above). The combination of these elements allows for determination of all the chemical elements (with the exception of H and He) if their quantity exceeds 0.1%. Figs. 3±5 cover the typical spectra obtained by the aircraft apparatuses. Fig. 3 and 4 are alpha- and proton spectra of igneous rock. Fig. 5 is the X-ray spectrum of Allende meteorite.