Correlation of atomic hydrogens with radiation-induced phenomena

Abstract

The behavior of Blue Thermoluminescences (BTL) from quartz minerals irradiated with gamma-ray radiation has been studied paying much attention to the OH impurities in quartzes. The 11 samples of differently originated quartz have been examined by using Electron Spin Resonance (ESR) spectroscopy and Instrumental Neutron Activation Analysis (INAA). The samples were irradiated with gamma-rays at a dose rate of about 15 kGy/h at 77 K. The ESR measurements for the samples have been carried out twice, first at 77 K and second also at 77 K after warming them once up to room temperature. BTL has been measured for the annealed quartz samples. It was revealed for the sample from Madagascar that the existence of an atomic hydrogen besides intense Al-center has been detected in the ESR spectrum measurement at 77 K. The remarkable decrease of the Al-center signals has been observed after warming once up to room temperature associated with the increase of the atomic hydrogen. It was supposed that atomic hydrogen derived from radiolysis of OH impurities operated as a killer of radiation induced Al-centers. In the annealing experiments, it was found that atomic hydrogen and Al-centers tend to increase simultaneously up to 800 C. However, that atomic hydrogen signals have suddenly disappeared beyond 850 C. This suggests that water vapor in quartz is easily evolved at the tridymite/beta-quartz phase transition temperature.

γ線放射で照射した石英鉱物から発光される青色熱ルミネセンス(BTL)の挙動を石英中のOH不純物に注目して研究した。産出地の異なる11種の石英試料を電子スピン共鳴(ESR)分光法および中性子放射化分析(INAA)を用いて試験した。約15kGy/時間の線量率でγ線により温度77Kで試料を照射した。試料に対するESR測定は2回行い、最初は77Kで、2回目は試料を一度室温まで加温後再び77Kで測定した。BTLは焼鈍石英試料に対して測定した。マダガスカルからの試料について、77KにおけるESRスペクトル測定で強いAl中心の他に原子状水素の存在が検出されたことが明らかになった。また、原子状水素の増加に伴い、一度室温まで加温後試料のAl中心信号に著しい減少を観測した。OH不純物の放射線分解から派生する原子状水素が放射線誘導Al中心のキラーとして作用すると推測した。焼鈍実験では、原子状水素およびAl中心は800度Cまでは同時に増加する傾向を示すが、850度Cを超えると原子状水素の信号は突然消滅した。これは石英がリン珪石/β-石英相転移温度で水蒸気を容易に放出することを示唆している。