Gamma-ray microcalorimeter arrays for nuclearmaterials analysis

J. Ullom, NIST Boulder

NIST Boulder:

James BeallRandy DorieseWilliam DuncanLisa FerreiraGene HiltonRob HoranskyKent IrwinBen MatesNathan MillerGalen O’NeilCarl Reintsema

Dan Schmidt

Leila ValeYizi Xu

Denver UniversityBarry Zink

Los Alamos National LaboratoryMike RabinAndrew HooverSteve LamontCliff RudyDuc Vo

OutlineNIST Boulder:

1. Early single pixel results

2. Applications

3. Scaling to arrays

4. Pixel analysis

5. Higher Z absorbers

6. Spectrometer construction

�-ray microcalorimeters

1 mm

160

120

80

40

0

103.30103.25103.20103.15103.10103.05

42 eV FWHM

140

120

100

80

60

40

20

0

Counts

/ 5

eV

bin

1041021009896

Energy (keV)

LANL/NIST Calorimeter #1Gd-153 source with steel attenuator

97 keV and 103 keV gamma-rays

Sn absorber

Mo/Cu thermometer

first detector: spring 2005

record result:42 eV FWHM at 103 keV

On the road to Los Alamos …

(also Randy Doriese)

Applications: analysis of Pu isotopes

current nondestructive analysismethods rely on knowledge ofreactor operating history

ucals may provide Pu measurementwhen operating history is lost orobscured

about 96 % (>600 tons) of the Pu under international safeguards is inspent fuel

Pu mass is a measure of reactor purpose: power vs weapons

Applications: measurement of Pu in spent reactor fuel

fuel in N. Korean cooling pond

Nondestructive assay for plutonium mass in reactor fuel

Spent Fuel XRF Spectrum 12889004

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

170 180 190 200 210 220 230 240 250 260

Channel

Co

un

ts

U K�1

98.43 keV

U K�2

95.65 keV

U K�3110.42 keV

U K�1111.30 keV

U K�2

114.44 keVPu K�1

103.73 keV

Eu-155

105.31 keV

100

2

3

4

5

6

7

8

91000

2

Counts

/ 2

0 e

V b

in

10610410210098

Energy (keV)

155Eu �-ray

Pu K�1 x-ray

U K�1 x-ray

HPGe spectrum of spent fuel from FSU(courtesy LANL)

Simulation of same spectrum with µcal

• ratio of U/Pu x-ray fluorescence measure of Pu mass• resolution of µcal minimizes interference from background, 155Eu

Applications: analysis of Pu isotopes

A 1,000 pixel �-ray spectrometer is feasible

existence proof: 1,280 pixel SCUBA 2

sub-array (for submm)

75 mm

area

count rate

energy resolution

quantum efficiency

1,000 pixels � 1 mm2/pixel

3.2 cm x 3.2 cm

1000 pixels � 100 Hz/pixel

100 kHz

< 42 eV at 100 keV

> 20% at 100 keV

gamma-ray arrays

NIST-LANL �-ray arrays

testbed with all readout circuitry andwiring for 128 pixels

routine fabrication of �-ray arrays

highly parallel micromachiningtechniques

6.25 mm

6.25 mm

mux chip

interface

chips

gamma-ray

arrays

Multiplexed array testing

zoomed view of 128 pixel testbed

6.25 mm

- interface chips for L/R filtering- 4x 32:1 multiplexer chips

muxed spectrum of 153Gd �-ray source

600

500

400

300

200

100

0

counts/5eVbin

103.4103.2103.0

energy (keV)

50.6 eV FWHM at 103.18 keV13 coadded pixels

spread inresolutions

energy resolutionhistogram

13 pixels total

4

3

2

1

0

pix

els

/ 5

eV

bin

120100806040200

energy resolution at 103 keV (eV)

chip 1 chip 2

Homogeneity

new performance record:25 eV FWHM at 103 keV

160

140

120

100

80

60

40

20

0

103102101100999897

energy (keV)

140

120

100

80

60

40

20

0

103.3103.2103.1

More on homogeneity

24

22

20

18

16

14

opera

ting r

esis

tance (

%R

no

rma

l)

43210-1-2

deviation from average Tc (mK)

chip 1 chip 2

why spread in �E ?

common bias and spread in Tc

“ “ complex transition shapes

energy resolution at 103 keV

pix

els

per

5eV

bin

bias chosen for more homogenous �E

14 pixels total

analysis to appear in Appl. Phys. Lett. (B. Zink et al, 2006)

Detailed analysis of device behavior

complex Z reveals absorber and(probably) frame

fitting noise requiresassumption that PN at ends oflink to absorber is uncorrelated

Higher efficiency possible with higher Z absorbers

SnTaMo

82

75

42

73

50

Z

20%250195Sn

94387258Ta

25

100

88

Efficiency100keV

43.8105Pb

1460430Re

1890460Mo

d (µm)�D (K)Material

some insulators andsemiconductors alsointeresting

But … complex behavior in some materials

thermal Decay

athermal

decay

Sn

Time Constant =

1.5 and 12.1 ms

Ta

Time Constant =

1.5 and 80-100 ms

Both Sn and Ta have second, athermal decay

? Ta has anomalous high heat capacity ?

: 6 keV x-ray

: 100 keV �-ray

How can we eliminate athermal decay in Sn ?

mechanical working leads to

smaller grains

cold rolled from supplier

has large grains

200 µm200 µm

• can control (and measure) Sn grain size

• will measure dependence of athermal

decay on grain size

• eliminating athermal decay will allow higher

count rates

!

NIST-designed cryogen-free refrigeratorassembled and tested• push-button operation• 13 hrs to cool from 300K• 7.5 days at 100 mK• < 1 hr to recycle

now available commercially fromHigh Precision Devices, Inc.

Spectrometer under construction for LANL

1 m

60

40

20

0C

ounts

per

8eV

bin

103.30103.25103.20103.15103.10103.05

Energy (keV)

cooler on: 45 eV FWHM at 103.18 keV

cooler off: 48 eV

330 mm

undegraded operation of gamma-ray ucalin electrical environment of pulse tube

TES operation in electrical environment of cryocooler

Conclusions

• there are applications for ucal arrays operating at ~100 keV

- Pu isotopes, spent fuel, HEU, …

• we have developed array-compatible techniques for fabricating �-ray ucals

• under muxed operation

- 50 eV at 103 keV in 13 coadded pixels

- best pixel = 25 eV

• work to understand absorber physics underway

• full spectrometer under development with Los Alamos

- cryogen-free dewar complete

- undegraded ucal operation

- testbed with wiring for 128 pixels complete

Ancient history (LTD11) : TES resolving power vs energy

5

6

7

89

103

2

3

4

5

6

7

89

104

reso

lvin

g p

ow

er

(E/�E

FW

HM

)

103

2 3 4 5 6 7 8 9

104

2 3 4 5 6 7 8 9

105

energy (eV)

STJ

Si thermistormag cal

TES, previous work

TES, this work

?

?

?

? LTD-12

Tc = 100 mK, M = 0

Tc = 100 mK, M = 1

TES resolving power vs energy

5

6

7

89

103

2

3

4

5

6

7

89

104

reso

lvin

g p

ow

er

(E/�E

FW

HM

)

103

2 3 4 5 6 7 8 9

104

2 3 4 5 6 7 8 9

105

energy (eV)

STJ

Si thermistormag cal

TES, previous work

TES, this work

??

??

??

?? LTD-12

Tc = 100 mK, M = 0

Tc = 100 mK, M = 1

Conclusions

• there are applications for ucal arrays operating at ~100 keV

- Pu isotopes, spent fuel, HEU, …

• we have developed array-compatible techniques for fabricating �-ray ucals

• under muxed operation

- 50 eV at 103 keV in 13 coadded pixels

- best pixel = 25 eV

• work to understand absorber physics underway

• full spectrometer under development with Los Alamos

- cryogen-free dewar complete

- undegraded ucal operation

- testbed with wiring for 128 pixels complete