Direct search for solar axions by using strong magnetic field and X-ray detectors

We have searched for axions which could be produced in the solar core by exploiting their conversion to X rays in a strong laboratory magnetic field. The signature of the solar axion is an increase in the rate of the X rays detected in a magnetic helioscope when the sun is within its acceptance. From the absence of such a signal we set a 95% confidence level limit on the axion coupling to two photons $g_{a\gamma\gamma}\equiv 1/M < 6.0\times 10^{-10}$ GeV$^{-1}$, provided the axion mass $m_a<0.03$ eV. The limit on the coupling is factor 4.5 more stringent than the recent experimental result. This is the first experiment whose sensitivity to $g_{a\gamma\gamma}$ is higher than the limit constrained by the solar age consideration.Comment: 11 pages, REVTeX, 4 eps figures included, submitted to PL

Development of a liquid scintillator containing a zirconium β-keto ester complex for the ZICOS experiment

AbstractA liquid scintillator containing a zirconium β-keto ester complex has been developed for the ZIrconium Complex in Organic Scintillator (ZICOS) neutrinoless double beta decay experiment. We are aiming to develop a detector which has a good energy resolution (4% at 2.5 MeV), a large light yield (60% that of BC505) and a low background rate (0.1 counts/tonne⋅year) with several tonnes of 96Zr isotope, so we have investigated the zirconium β-keto ester complexes tetrakis(isopropyl acetoacetato)zirconium and tetrakis(ethyl acetoacetato)zirconium, which have high solubility (over 10 wt.%) in anisole. We measured the performance of liquid scintillators containing these zirconium β-keto ester complexes and obtained 40% of the light yield of BC505 and energy resolution of 4.1% at 2.5 MeV assuming 40% photo coverage of the photomultiplier in the ZICOS detector. Thus we almost achieved our initial goal. Preliminary investigations indicate that tetrakis(diethyl malonato)zirconium will give us no quenching of the light yield and an energy resolution of 2.9% at 2.5 MeV. This will be a suitable complex for the ZICOS experiment, if it has a large solubility

Development of Liquid Scintillator containing a Zirconium Complex for Neutrinoless Double Beta Decay Experiment

An organic liquid scintillator containing a zirconium complex has been developed for a new neutrinoless double beta decay experiment. In order to produce a detector that has good energy resolution (4% at 2.5 MeV) and low background (0.1 counts/(tonne・year) and that can monitor tonnes of target isotope, we chose a zirconium β-diketone complex having high solubility (over 10 wt.%) in anisole. However, the absorption peak of the diketone ligand overlaps with the luminescence of anisole. Therefore, the light yield of the liquid scintillator decreases in proportion to the concentration of the complex. To avoid this problem, we synthesized a β-keto ester complex introducing -OC3H7 or -OC2H5 substituent groups in the β-diketone ligand, and a diethyl malonate complex. Those shifted the absorption peak to around 245nm and 210nm, respectively, which are shorter than the emission peak of anisole (275nm). However, the shift of the absorption peak depends on the the scintillation solvent. Therefore we have to choose an adequate solvent for the liquid scintillator. The best performance will be obtained by pure anisole scintillator containing a tetrakis diethyl malonate zirconium. We also synthesized a Zr-ODZ complex, which has a high quantum yield (30%) and good emission wavelength (425nm) with a solubility 5 wt.% in benzonitrile. However, the absorption peak of the Zr-ODZ complex was around 240 nm. Therefore, it is better to use the scintillation solvent which has shorter luminescence wavelength than that of benzonitrile

Development of liquid scintillator containing 8-quinolinolate indium complex for measurement of low energy solar neutrinos

An organic liquid scintillator containing indium complex was studied for a measurement of low energy solar neutrinos. The energy of the emitted electrons from those processes could be transferred to the molecular of complex via the organic solvent molecules, and the luminescence from the indium complex would be detected by the photo-multiplier. Here we report some results obtained by photo-luminescence and the γ\u27s inducedenergy spectra of tris (8-quinolinolate) indium (InQ3) complex. Benzonitrile was chosen as a solvent because of good solubility for the quinolinolate complexes (2wt%) and of good light yield for the scintillation induced by γ\u27s irradiation. The photo-luminescence emission spectra of InQ3 of 30 M solution in benzonitrile was measured. The emission maxima for InQ3 is found at 559 nm as excitation wavelength: 397 nm. We prepared InQ3 (50 mg ～ 200mg) of benzonitrile solutions (20mL). Two secondary scintillators, 100 mg of 2,5-diphenyloxazole (PPO) and 10mg of 1,4- bis[2-(5-phenyloxazolyl)]benzene (POPOP), are also dissolved in above solutions and they play a role of wavelength shifter from the UV region emitted by excited benzonitrile molecules to the visible region emitted by InQ3 complex. The energy spectra of electrons emitted by Compton scattering of incident γ\u27s using 60 Co radio isotope was obtained. These results are the first observation of the γ\u27s energy spectra using luminescent metal complexes

Proposal to search for a monochromatic component of solar axions using 57^{57}Fe

An experimental method is introduced to search for almost monochromatic solar axions. In this method, we can search for solar axions by exploiting the axion-quark coupling, not relying on the axion-photon coupling at all. A recent experimental result of Kr\v cmar is presented.Comment: 4 pages, 2 eps figures included, uses espcrc2.sty, to be published in Proc. AXION WORKSHOP, Gainesville, Florida, 13-15 March 1998, ed. by P.Sikivi

A liquid-helium cooled large-area silicon PIN photodiode x-ray detector

An x-ray detector using a liquid-helium cooled large-area silicon PIN photodiode has been developed along with a tailor-made charge sensitive preamplifier whose first-stage JFET has been cooled. The operating temperature of the JFET has been varied separately and optimized. The x- and $\gamma$-ray energy spectra for an \nuc{241}{Am} source have been measured with the photodiode operated at 13 K. An energy resolution of 1.60 keV (FWHM) has been obtained for 60-keV $\gamma$ rays and 1.30 keV (FWHM) for the pulser. The energy threshold could be set as low as 3 keV. It has been shown that a silicon PIN photodiode serves as a low-cost excellent x-ray detector which covers large area at 13 K.Comment: 6 pages, and 3 figures, Elsevier macros elsart.sty and elsart12.sty are neede

Performance of a liquid scintillator containing a zirconium β-keto ester complex developed for the ZICOS experiment

A liquid scintillator containing a zirconium β-keto ester complex has been developed for the ZIrconium Complex in Organic Scintillator (ZICOS) neutrinoless double beta decay experiment. We are aiming to develop a detector which has a good energy resolution (4% at 2.5 MeV), a large light yield (60% that of BC505) and a low background rate (0.1 counts/tonne・year) with several tonnes of 96Zr isotope, so we have investigated the zirconium β-keto ester complexes tetrakis (isopropyl acetoacetato) zirconium and tetrakis (ethyl acetoacetato) zirconium, which have high solubility (over 10 wt.%) in anisole. We measured the performance of liquid scintillators containing these zirconium β-keto ester complexes and obtained 40% of the light yield of BC505 and energy resolution of 4.1% at 2.5 MeV assuming 40% photo coverage of the photomultiplier in the ZICOS detector. Thus we almost achieved our initial goal. Preliminary investigations indicate that tetrakis (diethyl malonato) zirconium will give us no quenching of the light yield and an energy resolution of 2.9% at 2.5 MeV. This will be a suitable complex for the ZICOS experiment, if it has a large solubility

Discrimination of Cherenkov light in Liquid Scintillator for Neutrinoless Double Beta Decay Experiment

　A liquid scintillator containing a tetrakis（isopropyl acetoacetato）zirconium has been developed for ZICOS experiment. We will use 180 tons of liquid scintillator containing 75 kg of 96Zr in the inner balloon（45 kg in fiducial volume）surrounding 64 % photo coverage of 20 inch photomultiplier. In order to reach the sensitivity ≥1027 years, we have to reduce 95 % of 208Tl decay backgrounds at least. Using Monte Carlo simulation, we could demonstrate new method using the hit pattern of PMT which received Cherenkov light, and could reduce 93 % of 208Tl background with 78 % efficiency for 0νββ signal. For the discrimination of Cherenkov light, we measured the timing pulse shape of Zr loaded liquid scintillator using FADC digitizer, and we found an inconsistent pulse shape at the rise timing with the template of scintillation. Also the event with an inconsistent pulse shape seems to have a directionality

Direct measurement of spectral shape of Cherenkov light using cosmic muons

The spectral pulse shape of Cherenkov lights was directly measured by using cosmic muons. The observed decay times for early and late timing were 5.0 and 5.2ns, respectively. They were actually shorter than the time of scintillation lights which were also measured as 9.3ns and 9.2ns, respectively. However we could not see the difference of the rise time between scintillation and Cherenkov lights. This was due to the slow response of our DAQ equipment, photomultiplier and FADC digitize