Ultra-pure Copper Electroplating for Background Suppression in - - PowerPoint PPT Presentation

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Ultra-pure Copper Electroplating for Background Suppression in - - PowerPoint PPT Presentation

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news-g.org Ultra-pure Copper Electroplating for Background Suppression in NEWS-G Patrick Knights University of Birmingham P Knights, DM UK Meeting, King's College London 11/04/2019 1 o NEWS-G@SNO o Copper radiopurity o Indirect Pb-210

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SLIDE 1

Ultra-pure Copper Electroplating for Background Suppression in NEWS-G

Patrick Knights

University of Birmingham

11/04/2019 1 P Knights, DM UK Meeting, King's College London

news-g.org

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SLIDE 2
  • NEWS-G@SNO
  • Copper radiopurity
  • Indirect Pb-210 measurements of copper

used for NEWS-G@SNO

  • Development of electroplating of detector

hemispheres

11/04/2019 2 P Knights, DMUK 2019 - London

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SLIDE 3

Spherical Proportional Counter

3 P Knights, DMUK 2019 - London

  • Grounded metallic shell (⌀ ~30-100 cm)
  • Central sphere at high voltage as anode (⌀ ~1-6 mm)
  • Electrons drift to anode and amplified near surface

11/04/2019 !"

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SLIDE 4

NEWS-G@SNO

4 P Knights, DMUK 2019 - London

  • NEWS-G dark matter search next

generation detector – NEWS-G@SNO

  • 140 cm copper sphere to be installed in

SNOLab

  • 4N Aurubis copper (99.99% pure)

– Spun into two hemispheres

11/04/2019

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SLIDE 5

Po 218 84 Pb 214 82 Rn 222 86 Bi 214 83 Po 214 84 Pb 210 82 Bi 210 83 Po 210 84 Pb 206 82

3.8 d 3.1 m 27 m 20 m 160 us 22 y 5 d 138 d Stable

Background Contributions in Copper

  • Copper has no long-lived radio-

isotopes

  • 63Cu(n,⍺)60Co by fast neutrons from

cosmic muon spallation

  • 238U and 232Th decay chain –

naturally found and deposited by

222Rn

– Commercial copper ~1 μBq/kg – Electroformed copper (PNNL*) ~100 nBq/kg

5 P Knights, DMUK 2019 - London 11/04/2019 https://www.nndc.bnl.gov/

  • E. W. Hoppe et al. J. Radioanal. Nucl. Chem. v.277 p.103

*Pacific Northwest National Laboratory, USA

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SLIDE 6

210Pb in Copper

  • 2 measurements of 210Po in our
  • copper. Implied:

– 210Po ~ 80 mBq/kg – 210Pb ~ 60 mBq/kg

  • Geant4 simulation indicates this

gives 4.58 dru < 1 keV – Reduced to 1.96 dru if 500 μm pure copper plated onto surface

6 P Knights, DMUK 2019 - London 11/04/2019

XIA UltraLo-1800

https://www.xia.com/ultralo-theory.html See: XMASS collaboration arXiv:1707.06413 4.58 dru<1 keV 1.96 dru<1 keV 1.59 dru<1 keV 107 decays of 210Pb and 210Bi in Cu Walls in 2 bar Ne+10% CH4 Best Estimate of 210Po & 210Pb from two measurements of 210Po

Preliminary Preliminary

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SLIDE 7
  • Reactions governed by oxidation and

reduction reactions

  • Ions reduced at cathode building up

material – Current supplied to drive reactions – Mass deposited proportional to current supplied: ! = #! ∫ %(') )' *+

7

" – m ass # ! – m olar m ass $(&)– current as function of tim e (– num ber of electrons transferred in reduction reaction ) – Faraday Constant (= + ,- )

Electrolytic Cell and Electroplating

P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 8

Electroplating Ultra-Pure Copper

  • Some ions reduce more readily than
  • thers – reduction potentials
  • Copper benefits from ‘electrowinning’ –

high reduction potential +0.34 V

  • Reduction potential of:

– Uranium: -1.80 V – Thorium: -1.90 V – Lead: -0.13 V – All lower than copper → refined during electroplating

  • Using established techniques, similar to

Majorana Experiment1

8 P Knights, DMUK 2019 - London 11/04/2019 1arXiv:1308.1633

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SLIDE 9

Preparation Procedure

  • Cleaned with detergent
  • Sanded
  • Cleaned again
  • Surface chemically etched with 3% H202,

1% H2SO4 in deionised (DI) water – Shown to be effective etchant while less aggressive than some alternatives

  • Electrolyte of H2SO4, H2O and CuSO4

– Pump and filter to move electrolyte and remove particulates

9 P Knights, DMUK 2019 - London 11/04/2019

  • E. W. Hoppe et al. Nucl. Instrum. Methods Phys. Res v.579 p.486
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SLIDE 10

Electropolishing

  • Electropolishing serves several purposes

– Removes layer from hemisphere without chemical or mechanical attack – Preferentially removes high spots from surface – Increases concentration of CuSO4 in electrolyte

  • First (second) hemisphere 21.20.1 μm

(28.20.1 μm) polished

10 P Knights, DMUK 2019 - London 11/04/2019

Cu Movement in Electropolishing

+

−

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SLIDE 11

Electroplating

11

  • Electroplating performed with pulsed

current

  • 0.27 to 0.3 V amplitude in forward and

reverse directions of plating – Established value for ultra-pure copper electroplating

  • Plating continued for ~15 days
  • In total first (second) hemisphere plated

502.10.2 μm (539.50.2 μm)

  • Passivation with Citric Acid

P Knights, DMUK 2019 - London 11/04/2019

~0.036 mm/day ~1.3 cm/year

Cu Movement in Electroplating

+

−

Preliminary

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SLIDE 12

Result

12

  • Layer of Cu deposited on surface

– Awaiting results of analysis of copper and electrolyte to verify purity

  • Hemispheres to be welded together
  • Final chemical etch to be performed on intact sphere
  • Detector to be installed in LSM for commissioning this year

P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 13

Future NEWS-G Detectors

13

  • Next generation of detector will require

even lower background material

  • Two options:

– 6N copper sphere – Electroformed intact sphere

  • 6N more currently favoured; less pure than

electroformed but commercially available and potentially lower cost – Electroformed copper could be the generation after – demonstrated growth ~ 1.3 cm/year – 10 bar, ⌀ 60 cm sphere requires 4 mm walls - ~ 4 months

  • Currently planned to be ⌀ 60 cm, installed in

NEWS-G@LSM shielding

P Knights, DMUK 2019 - London 11/04/2019

Electroformed copper (PNNL) ~<100 nBq/kg 238U & 232Th

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SLIDE 14

Summary

14

  • Recent indirect measurements of 210Pb in copper show unacceptable

contamination – additional measurements with our copper are ongoing

  • Electroplated ~0.5 mm pure Cu onto internal surface of NEWS-G@SNO

detector to reduce experimental backgrounds – Hemispheres now being welded together

  • Commissioning in LSM later this year

P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 15

29/11/2018 15 P Knights, DMUK 2019 - London

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SLIDE 16

Additional Material

16 P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 17

XIA Counter

UltraLo-1800

17 P Knights, DMUK 2019 - London

From: https://www.xia.com/ultralo-theory.html XMASS collaboration arXiv:1707.06413

11/04/2019

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SLIDE 18

Simulation of Effect of Electroplating

Simulation of 107 decays of 210Pb and 210Bi within the 10.5 mm of thickness of the copper sphere with an inner radius of 67.5 cm. Data processed assuming 4000 V applied on a 3 mm radius sensor and a CREMAT pre-amplifier with !=46 µs. Gas condition: 2 bars of Ne + 10 % CH4 for a mass of 2.03 kg

18 P Knights, DMUK 2019 - London

Assuming 40 mBq/kg: Events with rise time lower than 500 µs and energy lower than 1 keV: No plating : 4.58 dru 500 µm : 1.96 dru (-58%) 1 mm : 1.59 dru (-65%)

11/04/2019

4.58 dru<1 keV 1.96 dru<1 keV 1.59 dru<1 keV

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SLIDE 19

Electroplating Copper

  • Some ions reduce more readily than
  • thers – reduction potentials
  • Voltage between anode and cathode

limits electroplating of some species

  • Copper benefits from ‘electrowinning’ –

high reduction potential +0.34 V

  • Reduction potential of:

– Uranium: -1.80 V – Thorium: -1.90 V – Lead: -0.44 V – All lower than copper; refined during electroplating

19 P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 20

Why don’t impurities plate too?

  • Which reaction proceeds determined by

standard cell potential:

  • Related to Gibbs Free Energy:

– If !"! < $ then reaction is spontaneous – If !"! > $ then need extra energy input

20

&"#$$

!

= &%

! − && !

' " # $ $

!

  • standard cell potential

' %

! - standard cathode reduction potential

' &

! – standard anode reduction potential

!"! = −) * &"#$$

!

P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 21

An Example

  • Example of solution containing U3+ and

Cu2+, with a Cu anode: – U3+ to U

  • !!"## = -2.138 V → Requires energy

– Cu2+ to Cu

  • !!"## = 0 V → In equilibrium
  • Cu2+ reduction will occur at lower

potential

  • Still require a potential difference between

electrodes to overcome energy losses

21

!!"##

$

= !%

$ − !& $

' ! " # #

$

  • standard cell potential

' %

$ - standard cathode reduction potential

' &

$ – standard anode reduction potential

P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 22

Not Quite That Simple…

  • Assumes standard conditions
  • Electrode potentials modified outside of

these conditions: – In theory can have some plating of

  • ther species – heavily suppressed
  • Other effects dominant in contaminant

plating

22

! = !! − $% &' ln ∏" +"

#$

∏% +%

#&

'– Electrode potential '

! – Standard electrode potential

(– M olar gas constant )– Tem perature * " – Chem ical activity of species + , " – Stoichiom etric coefficient of species +

P Knights, DMUK 2019 - London 11/04/2019

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SLIDE 23

Why Pulse-Reverse Plating?

  • Waveform for plating with relaxation

period and/or reverse bias (effectively polishing)

  • Benefits compared to DC plating:

– High points are preferentially removed in reverse bias section – Greater uniformity of plate – relaxation period allows diffusion

  • f ions

– Higher density copper plate

23 P Knights, DMUK 2019 - London 11/04/2019

M . Chandrasekar and M . Pushpavanam , “Pulse and pulse reverse plating - conceptual, advantages and applications,” Electrochim ica Acta, vol. 53, no. 8, pp. 3313 – 3322, 2008.