Embedding radioactive materials intolow-temperature microcalorimeters
Some preliminary ideas and results
Michael W. RabinLos Alamos National Laboratory
D.A. Bennett4, E. Birnbaum1, E.M. Bond1, R.C. Cantor5, M.P. Croce1, J.E. Engle1, F. Fowler4, R.D. Horansky2, K.D. Irwin, K.E. Koehler1,3, G.J. Kunde1, W.A. Moody1, F.M. Nortier1, D. Schmidt2, W.A. Taylor, J.N. Ullom2, L.R. Vale2, M. Zimmer, M.W. Rabin1
1Los Alamos National Laboratory, Los Alamos, NM, USA2National Institute of Standards and Technology, Boulder, CO, USA
3Western Michigan University, Kalamazoo, MI, USA4University of Colorado, Boulder, CO, USA
5Star Cryolectronics, Santa Fe, NM, USA
Revised Feb 6, 2013
Energy resolution for X- and g-ray spectroscopy
Factor of ten better than conventional semiconductor technology
241Pu/(98.95)
(99.85)
(102.98)
(101.06)
(104.23)
(103.73)
Close look at spectrum for X/g NDA of Pu
Quantitative analysis of isotopic composition
Preliminary results from internal “round robin”— 3 sensors X 4 samples
Microcalorimeter
Conventional sensor
Mcal 0.132 ± 0.006TIMS 0.133 ± 0.003
Atom ratio comparison for spectrum shown
External source
Internal source
External vs. internal for a-decaying isotopes
Decay products are the alpha particle and the daughter atom
External source
Internal source
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Energy(keV)
BranchFraction
Q 5593 1
a 54995456
0.710.29
g 43.599.85
1 x 10-4
7 x 10-5
First high-resolution mixed actinide Q spec
Shows 3X increase in separation between peak centers
238Pu
241Am
8
Large microcalorimeter arrays for spectroscopy
+Embedded radionuclides
+Isotope production facility
10
Some radioactive decays of interest
a, b, electron capture
11Also work by Loidl (CEA)
Some radioactive decays of interest
a, b, electron capture
12
The chemical form and physical microstructure of the combination of absorber and source affects energy thermalization.
Key linking science issue
Some radioactive decays of interest
a, b, electron capture
13
Some possible surrogate isotopes
Use for prototyping methods for isotope encapsulation and sensor designs
Isotopes that decay solely by electron capture to the nuclear ground state of a very long lived or stable product (child) isotope.
High Q is OK for prototyping.
Screening is incomplete and not yet detailed enough.
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Possible methods of deposition and encapsulation
Assuming you start with liquid water-based solution of radioactive material
• Drying of water-based solutionyou get everything that does not evaporatecoffee-ring effectmitigated by extremely very small volumes, ~10 picoliter
• Electrodepositionmore selectivecodeposition of major species (e.g. Cu, Au, Bi) and ultra trace (Fe,
Ho)used for Cu vias in zillions of integrated circuits
• Metalurgyunfavorable phase diagramsrapid freezing from melt common to quench nonequilibrium
concentrationbonding and diffusion techniques based interface metalurgy
(eutectics)
• Surface chemistrycontrolled atmosphere, temperature, time, substratechemical reduction of salts and oxides hard
selective binding to surface with custom ligands
Incorporation of aqueous source and encapsulation
Techniques for analytical picoliter dispensing under development by LANL-HP collaboration
Precise control of dispensed volume, droplet position, and final spot size
Mitigates position-dependent response of sensors
Allows us to control activity per sensor
Control of physical form and chemical composition will affect energy thermalization physics in the sensors
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Examples from 55Fe electrodeposition
17
Recent sensors for ECS of 55Fe
18
Spectral results ECS of 55Fe
commercial 55Fe Taylor-made 55Fe
larger absorber
Taylor-made 55Fe
smaller absorber
~54 eV FWHM
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Improved spectral results ECS of 55Fe
19 eV
s = 5.25 eV l1 = 8.9 eV2.35 s = 12.4 eV l2 = 47 eV
h = 0.37
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New sensors designs
No membrane. Easier to make. More robust.
Concluding remarks
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This is the era for wide-ranging experimentation in for embedding radioactive isotopes into sensors.
Long-range plans for calorimetric spectroscopy for neutrino mass call for
DE = 1-2 eV FWHMA = 1-100 Bq per pixel
which have been not yet been shown for any EC-decaying isotope.
By prototyping with 55Fe, then 163Ho we mean to try.
Large high-resolution arrays + embedded radioisotopes + isotope production
X g a Q b e-
X g a Q b e-
EC
Calorimetric electron capture energy spectroscopy combines many of these.
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END