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Analysis and Results3.Gamma-ray Spectra of 134Cs
The background subtracted spectra of 605 keV
and 796 keV in multiple hit events, and their coincidence summing peak
1401 keV in single hit events.
4.Beta-ray Spectra of 134Cs
The spectra of beta-rays with the maximum
energies of 658.0 keV (70.23%) and 88.6 keV (27.28%) were obtained on
the basis of corresponding gamma transitions.
5.Asymmetry Distributions of 134Cs
Asymmetry between the charge signals from two PMTs
6.Decay Curve and Calculated Half-life of 134Cs
Measured half-life 2.108 ± 0.3958 Y
Published half-life 2.067 ± 0.0005 Y
(R. H. Martin et al. Nucl. Instr. And Meth. In Physics.
Res. A 390 (1997) 267-273)
Analysis and Results1.Energy Calibration
The energy is calibrated using 59.54 keV
gamma-ray peak from 241Am standard radioactive source, and 605 keV
and 796 keV gamma-ray peaks from 134Cs internal background source.
2.Measured Background Energy Spectra
Figure 6 and Figure 7 show the spectra of the
energy deposited in one crystal, and the sum of the energy deposited in
all 12 crystals, respectively. 605 keV and 796 keV peaks are suppressed
in energy sum spectrum from the multiple hit events, because they are
appeared as their coincidence summing peak at 1401 keV.
Figure 12. Beta-ray spectrum of Max. 658 keV (Avg. 210 keV)
Figure 13. Beta-ray spectrum of Max. 89 keV (Avg. 23 keV)
IntroductionThis study is motivated to understand the properties of 134Cs radioactive
source within the CsI(Tl) crystal. 134Cs decays to a 134Ba by beta emission,
followed by several gamma-ray transitions as shown in Figure 1. The
most dominant gamma-rays are 605 keV and 796 keV (thick red arrows)
with intensities of 97.62% and 85.53%, respectively.
Understanding 134Cs Background in CsI(Tl) CrystalsJ. K. Lee, S. K. Kim, H. C. Bhang, S. L. Olsen, S. S. Myung, M. J. Lee, S. C. Kim, J. H. Choi, J. H. Lee, S. J. Lee, S. Ryu, I. S. Seong, K. W. Kim,
Y. D. Kim1, W. G. Kang1, J. I. Lee1, H. J. Kim2, J. H. So2, Y. J. Kwon3, M. J. Hwang3, I. S. Hahn4, Q. Yue5, J. Li5, Y. J. Li 5
Seoul National University, 1Sejong University, 2Kyungpook National University, 3Yonsei University, 4Ewha Womans University, 5Tsinghua University
AbstractThe purpose of this study is to estimate the 134Cs contamination in CsI(Tl) crystals used in the KIMS experiment. 134Cs is one of the major internal
background sources in the CsI(Tl) detectors for WIMP search. To understand 134Cs background, the gamma and beta spectra of 134Cs have been studied
based on the data taken 12 CsI(Tl) crystals at Yangyang Underground Laboratory. Although 134Cs produces a complex gamma-ray spectrum, our
coincidence tagging technique with 4x3 CsI(Tl) array detectors makes it possible to determine the energy and relative intensity of each gamma-ray
peak. Our preliminary results will be reported.
ConclusionTo estimate 134Cs contamination of CsI(Tl) crystals, gamma and beta
spectra of 134Cs have been studied. And the half life of 134Cs is also
measured and compared with the known value. A more detailed study on
134Cs is in progress.
134Cs
134Ba
1365
802 569
1038 475 242
795
1168 563
605
4+
4+
3+
4+
2+
2+
0+
1969.87
1643.28
1400.55
1167.93
604.70
0.0
E [keV]β-
27.3%
2.50%
70.1%
0.033%
0.10%
Figure 1. Decay scheme of 134Cs
1401 keV gamma from Cs-134 (70%)
1970 keV gamma from Cs-134 (27%)
662 keV gamma from Cs-137 (100%)
1401 keV peak in single hit (pile-up of 605+796 keV)
1365 keV peak in multiple hit
605 keV peak in multiple hit (563 & 569 keV included)
796 keV peak in multiple hit (802 keV included)
Figure 8. Energy sum in all crystalsFigure 7. Energy spectrum in one crystal
Figure 9. Background subtracted 605 and 796 keV peaks
Figure 10. Background subtracted 1401 keV
Figure 16. Decay curves of 134Cs in CsI(Tl) crystal
Figure 11. Energy resolution curve
Figure 14. 2D asymmetry vs. energy (top) and 1D energy spectra of 3 different asymmetry regions (bottom) for single hit events (left) and multiple hit events (right), respectively
Figure 15. 1D asymmetry distributions from 134Cs and 137Cs around 600 keV
Experimental SetupExtreme low-background experiment operated in underground
laboratory (Y2L)
4 x 3 array of 12 CsI(Tl) crystals with 8 x 8 x 30 cm3 dimensions
Each crystal is coupled to 2 PMTs.
Figure 2. Underground Laboratory Figure 3. Array of CsI(Tl) crystals
Y2L
Figure 4. 59.54 keV from 241Am
Figure 5. 605 and 796 keV from 134Cs
Figure 6. Linearity of signal area to energy
605 keV from 134Cs
660 keV from 137Cs660 keV from
137Cs605 keV & 796 keV from 134Cs
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