A STUDY ON THE PRODUCTION TECHNIQUE OF PLUTONIUM TRACER AS THE STANDARD FOR THE ENVIRONMENTAL ANALYSIS

研究了一种生产^<236>Pu的方法，该方法可作为分析环境中Pu的尖峰同位素。利用京都大学反应堆研究所的电子-LINAC电子轫致辐射，研究了^<237>Np(γ, n)^<236m>Np * ^<236>Pu的生产方法。为了降低热中子通量以避免（n, γ）反应，采用尺寸为4cmX4cm的水流式冷却塔进行了三次辐照试验，得到了以下结果：验证了Np.2双密封石英靶的辐照性能安全可靠。在120mA/30MeV电子束条件下，^<237>Np(γ, n)^<236m>Np的核反应速率为约3.6 X 10^<-12> (1/sec)。在此条件下，1mg Np照射5小时可产生0.65 kBq的^<236>Pu.3。作为干扰副产物的^<238>的Pu含量在放射性比中小于^<236>的0.06%，表明该方法具有较高的放射化学纯度。报道的^<236m>Np的衰变数据与观测到的^<236m> Pu.5的产率吻合得很好。据认为，一次^<237>Np（10mg， 30小时）的辐照产生约35kbq的放射性化学纯度^<236>Pu是可行的，这对应用是足够的。本研究结果证实了在京都大学反应堆研究所利用轫致辐射成功生产高纯度^<236>的Pu。该方法的靶制备和辐照技术相对简单，为环境中痕量Pu的评价提供了安全可靠的保证。

A production method of ^<236>Pu that is useful as a spike isotope for the analysis of Pu in the environment was studied. A production method by ^<237>Np(gamma, n)^<236m>Np * ^<236>Pu using e-bremsstrahlung of electron -LINAC of Research Reactor Institute, Kyoto University was studied. On the purpose of reducing the thermal neutron flux to avoid the (n, gamma) reaction, three irradiation tests were performed using water-flow type cooling column of 4cmX4cm dimension, and the following results were obtained.1. Safe and reliable irradiation performance was confirmed for the double-sealed quartz target of Np.2. The nuclear reaction rate of ^<237>Np(gamma, n)^<236m>Np was revealed to be c.a. 3.6 X 10^<-12> (1/sec) on the electron beam condition of 120mA/30MeV.With this condition, 5 hours irradiation of 1mg Np resulted in the production of 0.65 kBq of ^<236>Pu.3. The content of ^<238>Pu which is an interfering by-product was found to be <0.06% of ^<236>Pu in the radioactivity ratio, which suggests that this method ensures quite high radiochemical purity.4. Reported data of decay of ^<236m>Np agreed well with the observed production rate of ^<236>Pu.5. It is considered to be feasible that one irradiation of ^<237>Np(10mg, 30 hours) produces about 35 kBq of 236 radiochemically pure ^<236>Pu which will be sufficient for the application.As a result of this study, we confirmed that the successful production of highly-pure ^<236>Pu by the bremsstrahlung irradiation at Research Reactor Institute, Kyoto University. By this method consisting of rather easy techniques for target preparation and irradiation, we believe that the safe and reliable production of pure ^<236>Pu will be ensured for the assessment of trace Pu in the environment.