Search for 2βdecay of¹¹⁶Cd with the help of enriched¹¹⁶CdWO₄crystal scintillators

Abstract

Abstract. Cadmium tungstate crystal scintillators enriched in 116 Cd to 82% ( 116 CdWO 4 , total mass of ≈1.2 kg) are used to search for 2β decay of 116 Cd deep underground at the Gran Sasso National Laboratory of the INFN (Italy). The radioactive contamination of the 116 CdWO 4 crystals has been studied carefully to reconstruct the background of the detector. The measured half-life of 116 Cd relatively to 2ν2β decay is T 2ν2β 1/2 = [2.8 ± 0.05(stat.) ± 0.4(syst.)] × 10 19 yr, in agreement with the results of previous experiments. The obtained limit on the 0ν2β decay of 116 Cd (considering the data of the last 8696 h run with an advanced background 0.12(2) counts/yr/kg/keV in the energy interval 2.7 − 2.9 MeV) is T 1/2 ≥ 1.0 × 10 23 yr at 90% C.L. The sensitivity of the experiment to the 0ν2β process is lim T 1/2 = 3×10 23 yr at 90% C.L. over 5 years of the measurements and it can be advanced (by further reduction of the background by a factor 3−30) to the level of lim T 1/2 = (0.5−1.5)×10 24 yr for the same period of the data taking.

Average and recommended half-life values for two-neutrino double beta decay

“…There are five independent positive results [35,61,63,62,22] that are in good agreement with each other when taking into account the corresponding error bars. Again, I use here the corrected result for the half-life value from Ref.…”

Low background techniques in bolometers for double-beta decay search

“…76 The scintillator is highly radiopure relatively to U/Th ( 228 Th ∼ 0.06 mBq/kg, 226 Ra ≤ 0.005 mBq/kg, total α activity ∼ few mBq/kg) and 40 K (≤ 1 mBq/kg), but still exhibits the residual activity of 113 Cd and 113m Cd (∼0.56 Bq/kg in total) due to not high enough enrichment ( 116 Cd is 82.2%, 113 Cd is 2.1%). 76 The decrease of the 228 Th decay rate in time and the different activity of 238 U and daughters 76,85,86,117 confirm the broken equilibrium in U/Th chains. An evident increase of the residual radioactive contamination along the 116 CdWO 4 crystal boule 76,85,86,117 demonstrates the segregation of U/Th during the CdWO 4 growth.…”

“…76 The decrease of the 228 Th decay rate in time and the different activity of 238 U and daughters 76,85,86,117 confirm the broken equilibrium in U/Th chains. An evident increase of the residual radioactive contamination along the 116 CdWO 4 crystal boule 76,85,86,117 demonstrates the segregation of U/Th during the CdWO 4 growth. This fact has been recently used to improve the radiopurity of one sample by recrystallization, 121 in particular the 228 Th content was reduced by a factor ≈10, down to the level 0.01 mBq/kg.…”

First test of an enriched $$^{116}$$ 116 CdWO $$_4$$ 4 scintillating bolometer for neutrinoless double-beta-decay searches

“…Recently, high-quality radiopure CdWO 4 crystal scintillators were developed from deeply-purified cadmium samples enriched in the isotopes 106 Cd [29] and 116 Cd [30] with the help of the low-thermal-gradient Czochralski crystal-growth technique [31]. These enriched scintillators are currently and succesfully used in the 0ν2β decay experiments with 106 Cd [32,33] and 116 Cd [34,35]. Important advantages of the low-thermal-gradient Czochralski method are a high yield of the crystal boules (≈ 87%) and an acceptable low level of irrecoverable losses of enriched cadmium (≈ 2%).…”