Search for live 182 Hf in deep sea sediments

Transcription

1 Search for live 182 Hf in deep sea sediments Christof Vockenhuber, Robin Golser, Walter Kutschera, Alfred Priller, Peter Steier, Stephan Winkler Vienna Environmental Research Accelerator (VERA), Institut für Isotopenforschung und Kernphysik, Universität Wien, Austria Chana Feldstein, Michael Paul, Natalia Trubnikov Racah Institute of Physics, Hebrew University of Jerusalem, Israel Max Bichler Atominstitut der Österreichischen Universitäten, Vienna, Austria

2 The discovery that 182 Hf was present live in the Early Solar System... has opened up a great puzzle about r-process nucleosynthesis yields. S. Ramadurai, Abundance of 182 Hf and the supernova model of the solar system. In: Origin of Elements in the Solar System (2000)

3 182 Hf in the Early Solar System Half-life: (9 ± 2) Myr (1961 J. Wing, B.A. Swartz, J.R. Huizenga) Early Solar System abundance: 182 Hf/ 180 Hf = 1.0 x 10 4 Early Solar System chronometer ( 182 Hf 182 W) for the timing of accretion and core formation of planets Check for nucleosynthesis models

4 Early Solar System abundance of short-lived radionuclides (Meyer and Clayton 2000)

5 Possible sources of 182 Hf r-process 'fast' s-process neutrino processes but no natural production on Earth

6 Live 182 Hf today? Was 182 Hf produced continuously, by uniform production? Was the birth of our Solar System a special situation? Was there a nearby supernova in the younger history? Comparison with other short-lived radionuclides ( 60 Fe, 244 Pu,...) with AMS it is possible to search for live 182 Hf

7 Accelerator Mass Spectrometry of 182 Hf high mass resolution and isobar separation

8 Vienna Environmental Research Accelerator Focus 75 kv Preacceleration VERA Vienna Environmental Research Accelerator negative ions Magnetic Quadrupole Doublet Multi Beam Switcher Injection Magnet ME/q²=15 MeV amu r=0.457 m Heavy Isotope Detection E-Detector detection 10 Be Detection y-steerer Einzel Lens x-slits Offset Faraday Cups x/y-steerer Magnetic Quadrupole Doublet Sample material TOF-Detector Gas + Foil Stripper Wienfilter εxb=35 kv/cm x 0.4 T Charging x/y-steerer Chain Electrostatic Quadrupole Triplet Magnetic Quadrupole Doublet with x/y-steerer Gas Absorber + E-Detector E-Detector x/y-slits stripping and molecule dissociation Ion Production and Detection Electrostatic Components Magnetic Components Beamline y-steerer Insertable Faraday Cup Beam Profile Monitor C, Al Detection Analyzing Magnet ME/q²=176 MeV amu r=1.270 m positive ions Offset Faraday Cups Stable Isotope Measurement m

9 Key features of 182 Hf at VERA W suppression ~10 4 using HfF 5 high mass resolution Injector: M/M ~ 900 Analyzer: 2 high resolution components: Magnet and ESA Wienfilter and Switching Magnet Time of Flight total efficiency: 1 x 10 4 ionization yield: 0.5 % stripping yield (4+): 6 % detector efficiency: 30 % measurement at 7 MeV (3+): higher stripping yield 50 nm SiN x entrance window

10 Injector Mass Scan of HfF 4 injector faraday cup current [na] HfFO HfF HfF 2 O HfF 3 HfF 3 O HfF Field of Injector Magnet [Gauss] mass resolution M/M ~ 900

11 First AMS measurements Hf W s of 182 Hf Hf extracted from control rod of nuclear research reactor 182 Hf/ 180 Hf = 3.9 x 10 6 Energy [channels] s W s W s W Counts per channels Time of Flight [channels]

12 182 Hf dilution series measurement 1E-6 1E-7 measured linear fit 1E-8 measured 182 Hf/ 180 Hf 1E-9 1E-10 1E-11 1E-12 1E-13 blank 1E-14 1E-14 1E-13 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 expected 182 Hf/ 180 Hf

13 Deep sea sediment core TRIPOD expedition 17 o 30' N, 113 o 00' W core 7p cm, ~ 0 2 Myr (assumed growth rate 1 mm/kyr) 3763 m water depth ICPMS: Zr 400 ppm Hf 7.7 ppm W 0.2 ppm diameter 5 cm, only ½ used

14 Separation of Pu and Hf from deep sea sediment Chana Feldstein, Michael Paul, Natalia Trubnikov Racah Institute of Physics, Hebrew University of Jerusalem, Israel

15 Deep sea sediment samples samples section time Interval dry weight Bulk3 surface 25 g TRIP7p cm yr 9.15 g TRIP7p cm yr 10.0 g TRIP7p cm yr 25.5 g 2 standard materials ( 182 Hf/ 180 Hf ): Dilu2 ( 4.3 x ) Dilu3 ( 9.4 x ) blank: HfF 4 ( < 5 x )

16 Isotopic ratios

17 Tungsten isotopic ratios

18 Upper limit for 182 Hf from ISM flux

19 Inter Stellar Matter mass flux W.J. Baggaley J. Geophys. Res.105 (2000) flux of 1.8 x 10 8 m 2 s 1 of ISM grains with > 3 x kg

20 Estimation of the expected 182 Hf flux from ISM

21 Comparison to other radionuclides (flux from steady state production)

22 Layout of ATLAS at Argonne Nat. Lab.

23 Isobar separation in gas-filled Magnet

24 182 Hf 182 W separation at ATLAS ECR-Source LINAC (transmission 20%) Gas-filled Enge split pole spectrograph Ionization chamber and position sensitive detector

25 Future combination: negative ions (tandem accelerator) + LINAC and gas-filled magnet improved chemistry (W separation) FeMn crusts (growth rate ~1 mm/myr)

26 Expected 182 Hf counts