Pulse shape discrimination performance of Inverted Coaxial Ge detectors

We report on the characterization of two inverted coaxial Ge detectors in the context of being employed in future $^{76}$Ge neutrinoless double beta ($0\nu\beta\beta$) decay experiments. It is an advantage that such detectors can be produced with bigger Ge mass as compared to the planar Broad Energy Ge detectors (BEGe) that are currently used in the GERDA $0\nu\beta\beta$ decay experiment. This will result in lower background for the search of $0\nu\beta\beta$ decay due to a reduction of cables, electronics and holders. The measured resolution near the $^{76}$Ge Q-value at 2039 keV is 2.5 keV and their pulse-shape characteristics are similar to BEGe-detectors. It is concluded that this type of Ge-detector is suitable for usage in $^{76}$Ge $0\nu\beta\beta$ decay experiments

Search for α\alpha decay of 151^{151}Eu to the first excited level of 147^{147}Pm using underground γ\gamma-ray spectrometry

The alpha decay of $^{151}$Eu to the first excited level of $^{147}$Pm ($J^\pi = 5/2^+$, $E_{exc}=91.1$ keV) was searched for at the HADES underground laboratory ($\approx 500$ m w.e.). A sample of high purity europium oxide with mass of 303 g and a natural isotopic composition has been measured over 2232.8 h with a high energy resolution ultra-low background n-type semi-planar HPGe detector (40 cm$^3$) with sub-micron deadlayer. The new improved half-life limit has been set as $T_{1/2} \geq 3.7\times 10^{18}$ yr at 68% C.L. Possibilities to improve the sensitivity of the experiment, which is already near the theoretical predictions, are discussed. New half-life limit for $\alpha$ decay of $^{153}$Eu is also set as $T_{1/2} \geq 5.5\times 10^{17}$ yr.Comment: 11 pages, 5 figures, 2 tables, 18 reference

Measurement of anthropogenic radionuclides in post-Fukushima Pacific seawater samples

Following the accident at the Daiichi Fukushima nuclear power plant in 2011, a vast number of Pacific seawater samples from many locations far from Fukushima have been collected by Japanese investigators. Due to dilution, the activities of radionuclides from North Pacific seawater samples are very low, which calls for extraordinary measures when being measured. This study focuses on the metrological aspects of the gamma-ray spectrometry measurements performed on such samples in two underground laboratories; at HADES (by JRC-IRMM in Belgium), and at Ogoya (by Kanazawa University in Japan). Due to many samples and long measurement times, all available HPGe detectors needed to be employed. In addition to single coaxial detectors, this involved multidetector systems and well detectors. Optimization of detection limits for different radionuclides and detectors was performed using Monte Carlo simulations

New information on the characteristics of 1 in. x 1 in. cerium bromide scintillation detectors

In view of highly demanded new and accurate data on prompt gamma-ray emission in nuclear fission a major part of investigations is directed towards the selection of suitable detector systems. Here we have studied a new type of crystal scintillation detectors made from cerium bromide (CeBr(3)). For the first time a full characterization of such a detector is presented in terms of energy resolution, pulse-height linearity, intrinsic activity and intrinsic timing resolution. In particular the latter one is very important for prompt fission gamma-ray studies, because the presence of fast neutrons, emitted in fission too, requires the time-of-flight method for their discrimination. The energy resolution has been found to be comparable to that of cerium-doped LaCl(3):Ce detectors at an efficiency comparable to the one of a LaBr(3):Ce detector of the same size. The intrinsic activity of the CeBr(3) crystal was observed to be much lower compared to lanthanum halide crystals. The intrinsic timing resolution of a coaxial 1 in. x 1 in. sized detector was measured relative to that of a previously characterized LaCl(3):Ce detector and found to be (326 +/- 7) Ps at (60)Co energies, which is in between those of a LaBr(3):Ce and a LaCl(3):Ce detector of same size

New information on the characteristics of 1 in. x 1 in. cerium bromide scintillation detectors

In view of highly demanded new and accurate data on prompt gamma-ray emission in nuclear fission a major part of investigations is directed towards the selection of suitable detector systems. Here we have studied a new type of crystal scintillation detectors made from cerium bromide (CeBr(3)). For the first time a full characterization of such a detector is presented in terms of energy resolution, pulse-height linearity, intrinsic activity and intrinsic timing resolution. In particular the latter one is very important for prompt fission gamma-ray studies, because the presence of fast neutrons, emitted in fission too, requires the time-of-flight method for their discrimination. The energy resolution has been found to be comparable to that of cerium-doped LaCl(3):Ce detectors at an efficiency comparable to the one of a LaBr(3):Ce detector of the same size. The intrinsic activity of the CeBr(3) crystal was observed to be much lower compared to lanthanum halide crystals. The intrinsic timing resolution of a coaxial 1 in. x 1 in. sized detector was measured relative to that of a previously characterized LaCl(3):Ce detector and found to be (326 +/- 7) Ps at (60)Co energies, which is in between those of a LaBr(3):Ce and a LaCl(3):Ce detector of same size

On the use of mercury as a means of locating background sources in ultra low-background HPGe-detector systems

In low-level gamma-ray spectrometry, it is common to measure large samples in order to obtain low detection limits for the massic activity (in mBq/kg). These samples have significant shielding effects. In order to study whether the background sources in three ultra low-background HPGe detectors were located in the detector or in the shield, Marinelli beakers filled with hyperpure mercury were measured. Although the measurements were hampered by the presence of cosmogenically produced 194Hg, information regarding the major background location of 40K, 60Co, 137Cs, 210Pb, 226Ra, 228Ra and 228Th could be obtained