Nitrogen and argon radiopurity

Grzegorz Zuzel for TG11 MPI-K Heidelberg GERDA General Meeting, Tübingen, 9.-11. November 2005

Outline

   39

Ar,

42

Ar and

85

Kr

- in argon - in nitrogen  222

Rn in nitrogen and argon

- concentrations in different qualities - emanation from the storage tanks - purification tests

Purification system for LN

2

/LAr (?) Conclusions and planned activity

GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

39

Ar,

42

Ar and

85

Kr

Decay mode Source Concentration (STP) 222 Rn 85 Kr 39 Ar 42 Ar    T 1/2 = 3.8 d  ,  ,   T 1/2 = 10.8 y (687 keV) ,  T 1/2  = 269 y (565 keV) T 1/2  = 32.9 y (600 keV) Primordial 238 U 235 U fission (nuclear fuel reprocessing plants) Cosmogenic Cosmogenic 1 - ?00 Bq/m 3 air 1.4 Bq/m 3 1.2 MBq/m 3 air Kr 17 mBq/m 3 1.8 Bq/m 3 air Ar 0.5

µ Bq/m 3 50 µ Bq/m 3 air Ar Q-value of 39 Ar and 85 Kr below 700 keV – relevant in case of dark matter detection Dead-time could be a problem when Ar scintillation is used (slow decay time: ~ 1 µ s) 42 Ar is naturally low Grzegorz Zuzel GERDA General Meeting, Tübingen 09.-11. Nov. 2005

39

Ar and

85

Kr in argon

 Dead time: Assume 10 m 3 – – active volume 39 Ar rate: 15 kHz  85 Kr rate not higher  1.5 %

Fine!

≤ 0.3 ppm Kr required

Results from a 2.3 kg WARP test stand : ~ 0.6 ppm Other measurement possibilities: - mass spectrometry of Kr - direct counting of 85 Kr GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

39

Ar in argon

 39 Ar and dark matter detection (H. Simgen) Grzegorz Zuzel GERDA General Meeting, Tübingen 09.-11. Nov. 2005

39

Ar,

42

Ar and

85

Kr in argon

    39 Ar gives a significant increase of background in the low energy region Ar scintillation used as a veto helps, however...

background index stays at the level of ~ 1 cts/keV rec /kg/y, which limits the ability for dark matter detection Kr present in Ar at the ppm level would give similar contribution (through 85 Kr) Contribution from 42 Ar gives 4  10 -5 events/(kg  y  keV) at Q  and is also negligible for dark matter GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

39

Ar and

85

Kr in nitrogen

Description

MESSER RPN 2 (4.0, used in HD) Air Liquide RPN 2 (4.0, used at GS) Air Liquide HPN 2 Air Liquide 6.0

Linde Worms (7.0) SOL Mantova (6.0) Westfalen AG Hörstel (6.0)

1 ppt Kr = 1 µBq/m 3 (STP) 1 ppm Ar = 1.2 µBq/m 3 (STP)

Ar [ppm]

200 10 10 14

0.015

0.005

0.0005

Kr [ppt]

1 680 40 30 13

0.05

0.04

0.06

If LN 2 is used 39 Ar and 85 Kr should not affect detection of dark matter

GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

Outline

   39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen  222

Rn in nitrogen and argon

- concentrations in different qualities - emanation from the storage tanks - purification tests Purification system for LN 2 /LAr (?) Conclusions and planned activity GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

222

Rn in nitrogen and argon

According to the simulations: 222 Rn in LN 2 /LAr at the level of ~ 0.3 mBq/m 3 → B ~ 10 -4 cts/keV/kg/y 0.3 mBq/m 3 liquid → 0.5 µBq/m 3 gas (STP) Grzegorz Zuzel GERDA General Meeting, Tübingen 09.-11. Nov. 2005

222

Rn concentration in Ar of different qualities (Westfalen AG)

Quality

5.0

6.0

222 Rn concentration [mBq/m 3 (STP)]

8.4 ± 0.2

0.38 ± 0.03

Remarks

At the filling time At the filling time Specification: 0.5  10 -3 mBq/m 3 gas (STP) GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

222

Rn concentration in N

2

qualities of different

Quality

4.0

7.0

222 Rn concentration [mBq/m 3 (STP)]

0.05 – 0.2

~ 0.001

Conclusions: - initial 222 Rn content in nitrogen is lower than in argon of a similar class - however 222 Rn decays (T 1/2 =3.8 d) – emanation from the storage tank limits the final purity GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

222

Rn emanation from storage tanks

Tank description Volume [m 3 ] 2.9

222 Rn emanation rate [mBq] 177 ± 7 Storage tank for argon 5.0 (Westfalen) Storage tank for argon 6.0 (Westfalen) Special storage tank for ultra-pure gases (Linde) 0.66

3 42 ± 2 2.7 ± 0.3

C Rn  1µBq/m 3 Ar (STP) It should be possible to have argon with low enough 222 Rn concentration without purification Grzegorz Zuzel GERDA General Meeting, Tübingen 09.-11. Nov. 2005

Outline

   39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen  222

Rn in nitrogen and argon

- concentrations in different qualities - emanation from the storage tanks - purification tests Purification system for LN 2 /LAr (?) Conclusions and planned activity GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

Nitrogen purification from

222

Rn

Liquid nitrogen purification plant works at GS for Borexino 222 Rn in N 2 before purif. ~50

μBq/m 3

222 Rn in N 2 after purif. < 0.3

μBq/m 3

GERDA General Meeting, Tübingen Red. factor: > 100 Ads. mass: ~2 kg 09.-11. Nov. 2005 Grzegorz Zuzel

Argon purification from

222

Rn

MoREx: Mobile Radon Extraction Unit 222 Rn in Ar before purif. ~200

μBq/m 3

222 Rn in Ar after purif. < 0.5

μBq/m 3

GERDA General Meeting, Tübingen Red. factor: > 400 Ads. mass: ~0.15 kg 09.-11. Nov. 2005 Grzegorz Zuzel

Ar purification from

222

Rn

Purification in gas phase Init. C Rn [mBq/m 3 ] 0.20 ± 0.02

Final C Rn [mBq/m 3 ] < 0.0005 (90% CL) Red. factor R > 400 R/M Ads [1/kg] > 2700 Purification in liquid phase Init. C Rn [mBq/m 3 ] 5.4 ± 0.1

0.10 ± 0.01

Grzegorz Zuzel Final C [mBq/m Rn 3 ] 0.60 ± 0.02

0.006 ± 0.001

Average: Red. factor R 9 17 13 GERDA General Meeting, Tübingen R/M Ads [1/kg] 300 570 ~ 400 09.-11. Nov. 2005

LN

2

/LAr purification from

222

Rn

 It is possible to effectively remove radon from argon / nitrogen  Removal of 222 Rn from liquid phase is somewhat less effective than from gas phase Grzegorz Zuzel GERDA General Meeting, Tübingen 09.-11. Nov. 2005

Outline

   39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen  222 Rn in nitrogen and argon - concentrations in different qualities - emanation from the storage tanks - purification tests

Purification system for LN

2

/LAr (?)

Conclusions and planned activity GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

Purification system for LN

2

/LAr (?)

Having clean storage tanks we do not need a purification system, but it has several advantages:    Operational conditions for the cryo-plant are more relaxed (safety, shorter “access” time)  The same system can be used for LN purification 2 and LAr We know how to build such a plant (Borexino plant) Optimal column size ~200 g (LArGe) / ~1 kg (GERDA) of CarboAct (need some further tests) GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

Purification system for LAr

Grzegorz Zuzel GERDA General Meeting, Tübingen 09.-11. Nov. 2005

Conclusions

       LN 2 allows investigation of 0  2  (and dark matter) 39 Ar limits ability to detect dark matter if LAr is used It is possible to buy „ 222 Rn free“ LN 2 frame of Borexino) (proven in 222 Rn content in fresh argon is higher than in nitrogen of similar quality It should be also possible to have „ 222 Rn free“ LAr without purification – still to be confirmed 222 Rn removal from argon as effective as from nitrogen From the radiopurity point of view for GERDA 0  2  experiment LAr and LN 2 can be used GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005

Planned activity

 Measure 222 Rn content in argon after long storage in the tank of known emanation   85 Kr/Kr measurement in argon Test of a purification system for LArGe (design for GERDA)  Full supply chain test of ultra-pure nitrogen for Borexino – results interesting also for GERDA GERDA General Meeting, Tübingen Grzegorz Zuzel 09.-11. Nov. 2005