Sealed 22 Na source for positron annihilation lifetime spectroscopy

1. The 10th International Workshop on Positron and Positronium Chemistry Sealed 22Na source forpositron annihilation lifetime spectroscopy AIST M. Yamawaki, Y. Kobayashi, K. Ito JRIA M. Matsumoto, H. Ishizu, A. Umino TOYO SEIKO Co., LTD. K. Hattori, Y. Watanabe

2. Background of research To improve the safety of the large-scale systems of the social infrastructure, material inspection techniques to assess the state of fatigue and to evaluate the shot peening performance of materials used for large-scale structures such as nuclear reactors and aircrafts have attracted considerable attention. Usefulness of PALS (Positron Annihilation Lifetime Spectroscopy), which is basically one of nondestructive testing methods. ⇒ http://www.toyoseiko.co.jp/product/product07.html http://www.toyoseiko.co.jp/product/product04.html For Fukushima nuclear plant For inspection system Nondestructive testing in site Shot peening device

3. Sealed 22Na radiation source currently in use Radiation sources on the market is requested to be sealed up safely in law. ⇒22Na radiation sources act on materials like adhesives other than testing objects. This becomes a factor of measurement errors. Effect of adhesive to lifetime histogram, RADIOISOTOPES, 55(8), 469-472 (2006) Part of adhesive Sealed 22Na radiation source of IPLInc. ⇒ To achieve the PALS inspection handily in an arbitrary place, we developed and tested sealed 22Na source not to mix adhesive.

4. sample sample kapton 22Na Type 1 kapton kapton Type 2 22Na scintillator sample Arrangement of Kapton film Purpose of research Development of two types of high performance sealed 22Na radiation sources free from the legal restriction of radiation handling Produced radiation sources Type 1: Kapton/22Na/Kapton sealed sources of 60 kBq and 1 MBq. Type 2: Scintillator/22Na/Kapton sealed sources of 1 MBq.

5. Type 1 Production of Type 1 radiation source It is supposed that in a traditional radiation source the adhesive reaches the radiation source during bonding of Kapton flims Traditional way to seal 22Na by Kapton film currently in use The surrounding of the outside of Kapton films is bonded with the adhesive while suppressing around the radiation source with a cylindrical weight. New way to seal 22Na by Kapton film without contact with adhesive. The apparatus producing radiation sources is due to the idea proposed by professor T. Goworek of Maria Curie Skłodowska University (Poland).

6. Type 1 Type 1 (Kapton/22Na/Kapton) sealed source Sealed 22Na radiation source without positron annihilation in the adhesive was manufactured and tested. Sample : Si single crystal POSK-22 made by IPLInc. (3=1.45 ns, I3=2.6%) Type 1 radiation source (3=1.38 ns, I3=0.21%) intensity/counts Production device to prevent the source from mixing with the adhesive A long life component of Type 1 has almost absent of POSK! Sealed 22Na radiation source of 60 kBq manufactured for trial purpose Time/ns A long life component was mostly decreased by preventing the radiation source from being contaminated with the adhesive.

7. Type 2 Sample setting in usual PALS measurement Positrons emitted from the radiation source must be annihilated in the sample Sample (two boards) Each sample is sandwiched by aluminum foil 22Na source （sealed by Kapton film） Sample setting by sandwich manner Traditional PALS measurement needs the sample cut out from the object to be inspected. We propose the Anti-coincidence method, which does not need the cutting out sample.

8. Type 2 Anti-coincidence (A-C) method PALS measurement method in which cutting out samples is not unnecessary +detector sample scintillator Positron life time detector (conventional) 22Na scintillator PMT 22Na PMT PMT Mirror Mirror PMT sample True signal The event of the simultaneous detection is excluded from counting. e+ e+ e+ e+ Invalid signal remove PMT scintillator not sample Anti-coincidence (Additional circuit) The event of annihilation caused outside the sample area is removed ※patent pending M. Yamawaki, Y. Kobayashi, K. Hattori, Y. Watanabe, JJAP,50 (2011) 086301

9. Type 2 Type2 (Scintillator/22Na/Kapton) sealed source: A-C method Invalid signals are deleted by A-C method ! Positron detector Sample : Si single crystal Red ：Without A-C Blue ：With A-C Green：Sandwich method(traditional) Intensity/counts Experimental device of A-C method Al foil sample kapton Background decreased to half Long life events were removed scintillator 22Na Time/ns PMT With the A-C method, annihilation events in the scintillator, long life components not related with the sample (red dotted line), were removed invalid lifetime data. Configuration of detector （22Na is sandwiched by sample material and scintillator)

10. Type 2 Kapton sealed 22Na radiation source with scintillator Kapton lifetime component was greatly decreased by putting the radiation source directly on the scintillator surface Sample : Si single crystal Red：Case 1 (I2=23.9%) Blue：Case 2 (I2=11.4%) intensity/counts Decreased Kapton component Kapton sealed radiation source with scintillator Time/ns Kapton lifetime component decreases by deleting Kapton film in one side. Case2 Case1 sample sample kapton 22Na kapton kapton Type1 Type2 22Na scintillator scintillator Production of radiation source Arrangement of Kapton film

11. Intensity/counts Time/ns Development of PALS Inspection System Feature of system : No need of cutting out inspected materials : possible only to put sample on inspection stage ※prototype 22Na/sample  detector Dark box PC + detector Sample : Si single crystal Normal system Development system Automatic measurement by program control from calibration to lifetime output DSO The commercialization of PALS inspection system aims to be achieved in two years.

12. Development of portable type System Feature of system : Portable for large-scale structures inspection : Ti sealed source for shading (no need dark box) ※prototype Ti sealed source  detector Positron detector for portable PALS (Ti sealed source for shading) Sample : Si single crystal + detector Normal system Development system Intensity/counts Time/ns The commercialization of PALS inspection system aims to be achieved in two years too.

13. Summary • 22Na sealed radiation source without the handling restriction was made for trial purpose and tested. • It was confirmed that the lifetime component due to the adhesive disappeared in the trial product. • It was confirmed that the sealed radiation source made for trial purposes was appropriate as the radiation source used for the anti-coincident method.

14. At the end of lecture Thank you for listening The present study is done under the consignment business of the supporting industry planned by Chubu Bureau of Economy,Trade and Industryin 2010 fiscal year. Moreover, the apparatus producing radiation sources is due to the idea proposed by professor T. Goworek of Maria Curie Skłodowska University (Poland). We wish to express our gratitude for his cooperation. And thank you for many advices from professor Mohamed F. Hamdy.