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

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Some radioactive decays of interest

a, b, electron capture

11Also work by Loidl (CEA)

Some radioactive decays of interest

a, b, electron capture

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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

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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

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Recent sensors for ECS of 55Fe

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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