P01 : Hisanori Suzuki
(pdf):Pulse shape analysis of Bi-Po sequential decays with machine learning and estimation of Th/U impurities in GAGG crystal in the PIKACHU experiment

P02 : Tomohiro Tano
(pdf):Measurement of neutron-oxygen interaction cross section using neutron beam

P03 : Takashi Iida
(pdf):Status of the PIKACHU experiment for 160Gd double beta decay search

P04 : Anawat Rittirong
(pdf):Development of Laser Isotope Separation (LIS) for 48Ca toward the Study of Neutrinoless Double Beta Decay by CANDLES

P05 : Ryuta Shirai
(pdf):Evaluation of background reduction efficiency by waveform analysis with CNN in CANDLES experiment

P06 : Keigo Yasuda
(pdf):Evaluation for $gamma$-ray detection efficiency with an activated Tantalum for the half-life measurement of $mathrm{^{180m}}$Ta decay

P07 : Kenta Noda
(pdf): Production of Activated 182Ta for the Half-life Measurement of180mTa Decay

P08 : Mikito Sakuma
(pdf):Gamma-rays detection efficiency evaluation of low background HPGe detector installed in the Kamioka underground laboratory

P09 : Gen Takakusa
(pdf):Half-life measurement of $^{\180m}$Ta with ultra-low background HPGe detector at Kamioka Underground Laboratory

P01 : Suzuki
(pdf):Pulse shape analysis of Bi-Po sequential decays with machine learning and estimation of Th/U impurities in GAGG crystal in the PIKACHU experiment
 In the PIKACHU experiment, which searches for the double beta decay of 160Gd, the issue of U/Th radioactive impurities within GAGG crystals has been a concern. This study focused on the analysis of Bi-Po sequential decay events from the 238U/232Th decay series. The Bi-Po half-lives in these decays are short, with 300 ns for the 232Th series and 164 µs for the 238U series, causing distinctive signal pulse shape (double pulse) with both α and β signals appearing within a single event. Therefore, we used machine learning to distinguish double pulse events from single α and β events, successfully achieving accurate classification of the three event types. Furthermore, by using the count of double pulse events, 232Th/238U impurities within the GAGG crystals was estimated.

P02 : Tano
(pdf):Measurement of neutron-oxygen interaction cross section using neutron beam
 In 2020, Super-Kamiokande started introducing Gadolinium (Gd) for enhancing neutron signal for the first observation of Diffuse Supernova Neutrino Background (DSNB). For the DSNB search, we have to precisely estimate the atmospheric neutrino background, however, it has still large uncertainty because the reaction of neutron with a few hundred's of MeV via oxygen nucleus is poorly understood. We conducted the experiment, named E525, which measure the reaction of neutrons with oxygen, at the Research Center for Nuclear Physics, Osaka University on October 30, and December 16, 2018. In this experiment, 30 MeV and 250 MeV neutrons are irradiated to water target, and gamma-rays emitted from the reaction were measured. In this presentation, the results of 250 MeV experiment will be presented.

P03 : Iida
(pdf):Status of the PIKACHU experiment for 160Gd double beta decay search
 We are promoting the PIKACHU (Pure Inorganic scintillator experiment in KAmioka for CHallenging Underground sciences) experiment to search for double beta decay of 160Gd using Ce:Gd3(Ga,Al)5O12 (GAGG) scintillator crystals. We plan to discover 2nbb of 160Gd by increasing the sensitivity by more than an order of magnitude compared to previous studies using Gd. So far, we have succeeded in developing high-purity GAGG crystals with an order of magnitude reduction in the amount of impurities in the GAGG crystals, and we plan to start experiments at 1000 m underground in Kamioka in 2024. In this presentation, the current status and prospects of the PIKACHU experiment will be presented.

P04 : Rittirong
(pdf):Development of Laser Isotope Separation (LIS) for 48Ca toward the Study of Neutrinoless Double Beta Decay by CANDLES
 This research aims to develop the laser isotope separation (LIS) and production of 48Ca. A successful proof-of-principle experiment was conducted, demonstrating the separation property and production feasibility of the laser deflection method. The first step involves establishing a stable production system from one of the six atomic beam generators utilizing 2W laser units with a stable continuous wave oscillation at a calcium absorption wavelength of 422.7918 nm. This requires a stability of less than 2 MHz rms. We designed an upscale production system consisting of a six-atomic beam generator, a collection system, and a monitoring and control system. The current status of the production unit is discussed, and the first milestone is set at achieving an annual production of 2 mol.

P05 : Shirai
(pdf):Evaluation of background reduction efficiency by waveform analysis with CNN in CANDLES experiment
 The neutrino-less double beta decay (0νββ) is a process that occurs only when neutrinos and antineutrinos are identical (Majorana). This process is very important for the determination of Majorana nature and absolute scale of neutrino mass, but it has not yet been observed. In the 0νββ decay search experiment, the decay rate is quite rare thus it is required to be extremely reduced the background events (BG) near the Q-value of 0νββ. 　In the CANDLES experiment, 96 CaF2 scintillation crystals with natural Ca (containing 350 g of 48Ca) were used to search for 0νββ. The Q-value of 48Ca is 4.27 MeV, which is highest among double beta decay isotopes, so that BG rate is strongly suppressed. One of the major BGs is the pile up waveform, The half-life of 212Po beta decay(T1/2= 299 nsec) is shorter than the decay-time of CaF2 scintillation (1 μsec); hence, the delayed 212Po α-decay piles up the prompt 212Bi β decay (212BiPo event). The 212BiPo event is observed as one event when the time-lag of the decays is relatively short (Double Pulse: DP). This 212BiPo events are difficult to distinguish from the waveform of double beta decay (Single Pulse: SP) by conventional fitting, which reduces the sensitivity to 0νββ. 　We developed the new analysis tool using Convolutional Neural Network (CNN) to identify this pile up waveform and evaluated the BG reduction rate. The reduction efficiency of 212BiPo event by discriminating SP and DP waveforms using machine learning is presented.

P06 : Yasuda
(pdf):Evaluation for $gamma$-ray detection efficiency with an activated Tantalum for the half-life measurement of $mathrm{^{180m}}$Ta decay
 An nuclear isomer, $¥mathrm{^{180m}}$Ta is the rarest isotopes, and the finite half-life has not been measured. The latest result gives a lower limit of $1.5 ¥times 10^{19}$ years. We measured the half-life of $¥beta^{-}$ decay and electron capture of $^{¥mathrm{180m}}$Ta by analyzing the $¥gamma$-ray energy spectra observed with a ultra-low background(BG) HPGe detector installed in the Kamioka Underground Laboratory.To estimate the half-life of $¥mathrm{^{180m}}$Ta decay from the number of $¥gamma$-ray events, we estimated the $¥gamma$-ray detection efficiency of Ge detector. We measured the $¥gamma$-ray energy (93 keV - 351 keV) from the daughter nuclear.We evaluated the detection efficiency at low energies by covering the entire Ge detector with an activated sample of Ta.We used $^{252}$Cf neutron source to activate the Ta sample. Fast neutrons emitted from $¥mathrm{^{252}}$Cf was thermalized with polyethylene moderator and captured by $^{181}$Ta (99.998¥% in natural Ta). By using activated Ta, a uniformly $¥mathrm{^{182}}$Ta which is identical to decaying $¥mathrm{^{180m}}$Ta in natural Ta sample can be produced. The detection efficiency is evaluated by focusing on $¥gamma$-rays with energies of 100.1 keV, 152.4 keV, 222.1 keV, etc. emitted by $^{¥mathrm{182}}$Ta. We will present he results of the evaluation of the detection efficiency.

P07 : Noda
(pdf): Production of Activated 182Ta for the Half-life Measurement of180mTa Decay
 Among various nuclear isomers, 180mTa is considered to have a long half-life but it half-life has not been measured. The current lower limit of the half-life is 1.5 × 1019 years. Using an ultra-low background HPGe detector installed in the Kamioka Underground Laboratory, we measured a natural Tantalum sample (850g) for about 500 days. The γ-rays energy spectrum was analyzed to measure the half-lives of β-decay and electron capture of 180mTa. In order to obtain reliable half-life from the number of observed events, it is necessary to precisely evaluate the detection efficiency for each γ-ray energy. In this study, we experimentally evaluated the detection efficiency using γ-rays emitted from the β-decay of 182Ta. A natural Ta sample, which is an identical sample with that of half-life measurement, was activated by thermal neutron capture reaction (182Ta sample). To increase the activity of the 182Ta calibration sample, the neutron emitted from 252Cf source was efficiently thermalized in the 10cm thick polyethylene, and reflected with 20cm thick graphite. To obtain the accurate efficiency, the uniform activity of 182Ta sample was required. The specimens were also placed with the 182Ta sample to investigate the uniformity of activation. The obtained activity and uniformity of 182Ta sample will be presented. The accuracy of the γ-ray efficiency obtained using the 182Ta sample will be also discussed.

P08 : Sakuma
(pdf):Gamma-rays detection efficiency evaluation of low background HPGe detector installed in the Kamioka underground laboratory
 The nuclide $^{180m}$Ta is considered to be the longest lived nuclear isomer. It undergoes decay processes such as beta decay, electron capture, and deexcitation, but its half-life has not yet been measured. The latest lower limit of the half-life is $\times$ 10$^{19}$ years. Using an ultra-low background HPGe detector installed in the Kamioka Underground Laboratory, $\gamma$-ray emitted from $^{180m}$Ta decay was measured by placing natural Tantalum sample(850 g) for about 500 days. In this research, we evaluated the $\gamma$-ray detection efficiency of the HPGe detector to determine the half-life from the $\gamma$-ray counts, and reproduced the detection efficiency by Monte Carlo simulation (MC). It is particularly important to evaluate the detection efficiency in the energy range of 93 keV to 351 keV, where the $\gamma$-ray energy from $^{180m}$Ta decay is observed. Detection efficiencies are measured for 81 keV-- 356 keV using $^{133}$Ba calibration source. The Ta sample was placed to cover the entire HPGe detector. Since the detection efficiency of such low energy $\gamma$-ray has position dependence, measurements were taken at the head and sides of the HPGe detector irradiating a collimated $\gamma$-ray source of 133Ba in 2mm steps. The obtained results of the position dependence of $\gamma$-ray detection efficiency and the reproduction by MC will be presented.

P09 : Takakusa
(pdf):Half-life measurement of $^{\180m}$Ta with ultra-low background HPGe detector at Kamioka Underground Laboratory
 Among various nuclear isomers, $^{\180m}$Ta is a nuclide with a long lifetime that its decay has not been detected. The main decay processes are considered to be $\beta^{-}$ decay and the electron capture (EC) . The most stringent half-life limit for $^{180m}$Ta decays is $1.5 \times 10^{19}$ years. In this research, we analyzed the data measured for about 500 days using an ultra-low background(BG) HPGe semiconductor detector installed in the Kamioka Underground Laboratory, with a natural Ta sample placed. The half-life of (_ ^180m)Ta was evaluated by identifying $\gamma$-rays emitted from the excited states of $^{180}$W ($\beta^{-}$ decay) and $^{180}$Hf (EC). The search for rare decay events of $^{\180m}$Ta requires a long-term measurement, for which the detector gain often changes. The gain changes deteriorate the detector energy resolution. To overcome this problem, a constant pulse height artificial signal with 1Hz was fed into the pre-amplifier of the HPGe detector during the measurement to make correction of the gain variation. We also tried to separate environmental BG γ-rays from γ-rays emitted by $^{180m}$ Ta decays by analyzing the waveform. The obtained energy spectrum and the sensitivity of the $^{180m}$Ta half-life measurement will be presented.