Embedding radioactive materials into low-temperature microcalorimeters Some preliminary ideas and results Michael W. Rabin Los Alamos National Laboratory D.A. Bennett 4, E. Birnbaum 1, E.M. Bond 1, R.C. Cantor 5, M.P. Croce 1, J.E. Engle 1, F. Fowler 4, R.D. Horansky 2, K.D. Irwin, K.E. Koehler 1,3, G.J. Kunde 1, W.A. Moody 1, F.M. Nortier 1, D. Schmidt 2, W.A. Taylor, J.N. Ullom 2, L.R. Vale 2, M. Zimmer, M.W. Rabin 1 1 Los Alamos National Laboratory, Los Alamos, NM, USA 2 National Institute of Standards and Technology, Boulder, CO, USA 3 Western Michigan University, Kalamazoo, MI, USA 4 University of Colorado, Boulder, CO, USA 5 Star Cryolectronics, Santa Fe, NM, USA Revised Feb 6, 2013

Energy resolution for X- and  -ray spectroscopy Factor of ten better than conventional semiconductor technology

241 Pu/ (98.95) (99.85) (102.98) (101.06) (104.23) (103.73) Close look at spectrum for X/  NDA of Pu

Quantitative analysis of isotopic composition Preliminary results from internal “round robin”— 3 sensors X 4 samples Microcalorimeter Conventional sensor Mcal ± TIMS ± Atom ratio comparison for spectrum shown

External source Internal source External vs. internal for  -decaying isotopes Decay products are the alpha particle and the daughter atom External source Internal source 7 Energy (keV) Branch Fraction Q   x x 10 -5

First high-resolution mixed actinide Q spec Shows 3X increase in separation between peak centers 238 Pu 241 Am 8

Large microcalorimeter arrays for spectroscopy + Embedded radionuclides + Isotope production facility

10 Some radioactive decays of interest , , electron capture

11 Also work by Loidl (CEA) Some radioactive decays of interest , , 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 , , 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.

14 Possible methods of deposition and encapsulation Assuming you start with liquid water-based solution of radioactive material Drying of water-based solution you get everything that does not evaporate coffee-ring effect mitigated by extremely very small volumes, ~10 picoliter Electrodeposition more selective codeposition of major species (e.g. Cu, Au, Bi) and ultra trace (Fe, Ho) used for Cu vias in zillions of integrated circuits Metalurgy unfavorable phase diagrams rapid freezing from melt common to quench nonequilibrium concentration bonding and diffusion techniques based interface metalurgy (eutectics) Surface chemistry controlled atmosphere, temperature, time, substrate chemical 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

16 Examples from 55 Fe electrodeposition

17 Recent sensors for ECS of 55 Fe

18 Spectral results ECS of 55 Fe commercial 55 Fe Taylor-made 55 Fe larger absorber Taylor-made 55 Fe smaller absorber ~54 eV FWHM

19 Improved spectral results ECS of 55 Fe 19 eV  = 5.25 eV 1 = 8.9 eV 2.35  = 12.4 eV 2 = 47 eV  = 0.37

20 New sensors designs No membrane. Easier to make. More robust.

Concluding remarks 21 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  E = 1-2 eV FWHM A = Bq per pixel which have been not yet been shown for any EC-decaying isotope. By prototyping with 55 Fe, then 163 Ho we mean to try. Large high-resolution arrays + embedded radioisotopes + isotope production

X   Q  e -

ECEC Calorimetric electron capture energy spectroscopy combines many of these.

24 END