A survey meter is a detector indispensable to inspection of the surface contamination in the nuclear accident or radiation accident. It is also a typical device used for daily management at nuclear or radiation facilities. The time of about 30 seconds is necessary for an accurate measurement when the time constant is set to be 10 seconds. A lot of time is needed to measure a lot of areas, and heavy labor will be compelled to the worker in the emergency or the daily management. Moreover, a prompt measurement is strongly required for the emergency case. The method of forecasting the final value at the initial stage of response regardless of geostationary or moving was proposed and examined by using small sealed sources. This paper introduces the improved method with higher accuracy than the previously reported method in practical fields such as a controlled area at a nuclear plant where the low activity of 0.8Bq/cm2 of 60Co is the critical level. The improved method has been estimated by experiments and proved to be effective for such low activity measurements.
On the highly sensitive and on-line detection for the contamination of artificial nuclides, much attention has been paid to the elimination of significant problem due to 222Rn-progenies. A phosfich-type α- and β-ray radiation counter, which was fixed just above the dust-collecting filter paper within a space in a few mm, provides both α- and β-ray pulses during continuous collection of air-borne dust. Both pulse input times were registered into the memory buffer in a pulse time interval analyzing (TIA) system, followed rapidly by the data processing using MTA (multiple TIA) method. Resultant β-α TIA-spectrum (or decay-curve of β-α correlated events) and changes of α- and β-counting rates were displayed instantly on a PC-display with 1μs time resolution using installed softwares. Thus, three practical values, including β-α correlated event rates (nαβ), α-(nα), and β-ray counting rates (nβ) were available from the present TIA-measurement system. A uranium deposited source (as mixture of α- and β-ray emitters), uranium mineral powder sample, and 226Ra-source (as β-source) showed negligible contribution to β-α correlated events in TIA-spectrum, giving constant α/β counting ratios. In the case of air-borne dust samples, the β-α correlated events in TIA-spectrum showed certainly a presence of 164μs decay-curve due to 214Po, based on successive decay process such as 214Bi(β)→214Po (α: T1/2=164μs)→. By using three measuring values, new parameters, Rα and Rβ[equal to (nα or nβ)*(nα+nβ)/nαβ], have been introduced for the highly sensitive and real-time indicators of contamination owing to artificial nuclides, even under the inevitable existence of 222Rn progenies in the air-borne dust sample. The present radiation measurement system, combined with β-α correlated events, has been proved to be useful for the detection of extremely small contamination with artificial α-nuclides as well as β-nuclides; the detection limit was estimated to be several percents of radioactivity against natural α-nuclides. The present method will be preferable to the in situ or remote monitoring of artificial radionuclides from nuclear facilities and so on.
A prototype GSPC without the gas purification system was developed in China Institute for Radiation Protection(CIRP). Xenon filled GSPC has many advantages, including high energy resolution, large detection area, ability for implementing position sensitive detection, etc. It may find a wide application in low energy X-ray and γ-ray fields, e.g., astronomy X-ray detection, medical imaging. Further applications in neutron and charged heavy particle detection are also possible. Several tests for 241Am and 55Fe have been carried out to check out its preliminary performance. Currently the energy resolution is still far from expectation, nevertheless, the concept is proved to be promising and the experimental results suggest the way for further improvements. The possible ways for improvement of the detector performance are discussed in conclusion. This work was funded by National Natural Science Foundation of China. Authorization number:10375054(National Natural Science Foundation of China).
A method for fabricating a disk-shaped radiation source from material containing natural radioisotopes was developed. In this compression and formation method, a certain amount of powdered material is placed in a stainless steel formwork and compressed to form a solid disk. Using this method, educational radiation sources were fabricated using commercially available chemical fertilizers that naturally contain the radionuclide, 40K, which emits either beta or gamma rays, at each disintegration. The compression and formation method was evaluated by inspecting eleven radiation sources thus fabricated. Then the suitability of the fertilizer radiation source as an education aid was evaluated. The results showed that the method could be used to fabricate radiation sources without the need for learning special skills or techniques. It was also found that the potassium fertilizer radiation source could be used to demonstrate that the inverse-square law can be applied to the distance between the radiation source and detector, and that an exponential relationship can be seen between the shielding effectiveness and the total thickness of the shielding materials. It is concluded that a natural fertilizer radiation source is an appropriate aid for demonstrating the characteristics of radiation.
Lead isotope ratio method was applied to the provenance study of lead and bronze objects excavated from the Ootomo site at the end of 16th century in Ooitashi, Ooita prefecture. Several objects among them showed completely different lead isotope ratios from the East Asian objects such as Chinese, Korean and Japanese objects. The lead values were also found in the samples from the sites of Harajo castle of Nagasaki, Tanakajo fort of Kumamoto in the 16th to 17th centuries and the King Muryeong's tomb in Korea in 6th century. The same lead values were also discovered in the samples from Phun Snay sites in Cambodia around 1st to 5th century. The agreement of lead isotope ratios in the objects excavated from different area and at different time might be the result of an accidental chance but would be explained by the circulation and exchange of materials from one of the lead mines in that area. An assumption suggested that bronze and glass making techniques were developed after BC400 in East-South Asia. The glass objects produced were transported along the coast of China to Korea around 5th to 6th centuries. Then in 16th or 17th century, European people stopped at some ports in East-South Asia and obtained the lead, gunpowder and others to bring them to Japan.