High-sensitivity Environmental Neutron Dose Meter Optimization Of Design And Experimental Verification

In the field of radiological protection, it has always been paid attention to the methods for measurement of neutron like other rays. Firstly, because of its characteristics resulting in a series of problems, it is required for consideration cautiously on the measurement of neutron radiation dose, for example, it is with a wide energy range of neutron spectrum from thermal neutron to fast neutron and often accompanied someγrays in neutron radiation field. Secondly, the conversion coefficient between neutron fluence and ambient dose equivalent varies widely with a difference almost about one hundredfold. Thirdly, the most of neutron detector is sensitive to thermal neutron but the less to fast neutron, or it is sensitive to fast neutron but not to thermal neutron. In case of neutron monitoring in the environment, it should be needed a more high requirement on neutron dose meter, such as properly response to a wide range of neutron energy, highly sensitive to neutrons but low to photons, and more cheaper, ect. At present, it is still an interesting problem mentioned above and more attention should be paid to it.With the fast developing of national economy, the scale and quantity of nuclear facilities and nuclear installations are still extended. In order to assure the safety and security of these facilities and their surrounding environment, it should be provided for some more effective means to have a rigorous monitoring of radiation(n, y, etc) resulted from these nuclear facilities and that in the environment around these facilities. Especially, at present the question is that more attention should be paid to the increasingly changing of the international circumstance and it brings us at any moment to be ready to deal with nuclear accident and nuclear terrorism event. At the same time, in order to evaluate the background radiation level of neutron dose in the environment, it is also required that the detecting system is with the characteristic of wide response to neutron energy spectrum, high sensitivity and high capability of anti-jamming. So that it looks very important to the neutron monitoring of low radiation fields.So the major task of my theme is to design and make a high sensitivity neutron dose equivalent meter.In this theme it has taken an introduction of the development and its present situation of neutron dose meters. By Monte Carlo Code MCNP4C, the parameters of neutron probe design and its optimum selection were simulated. It was put forward a design scheme of neutron dose equivalent meter with high sensitivity to neutron in the environment. By verified experiment, the experimental results are primarily tallied with those by theoretically calculated.In this paper, it is divided into five parts to introduce the optimum design and verified experiment of a high sensitivity neutron dose meter as follows.The first section is an introduction. It mainly introduces the purpose of developing a high sensitivity neutron dose equivalent meter, its working principle and present situation of development of neutron dose meters in the world.The second section is mainly introduced the relative parameters of neutron detector probe simulated by MCNP4C, including: a) The geometrical parameters, such as diameter, length of ³He proportional counter, and air pressure of counter, etc. b) The thickness of polythene moderator, the hole's area of cadmium absorber, and its position within the moderator. c) The sensitivity of ²⁵²Cf and ²⁴¹Am-Be neutron source. d) The estimation of fluence energy response and angular response. It is carried out the calculation and theoretical analysis of the relative parameters by Monte Carlo simulation method, and the design of the detector is optimized.The third section is mainly introduced the collectivity design of the detector probe and its electronic parts of the neutron dose equivalent meter.The fourth section is mainly introduced the verified experiment of its design and the detector manufactured, including: a) the sensitivity measurement, b) the angular response measurement, and c) comparative testing experiment.The last section is the conclusion and discussion.In this paper, by calculation of MCNP Code simulation and optimum selection of detector parameters, the sensitivity of the designed neutron dose meter reaches 42.4cps perμSv h^-1, its energy response range is 2.5×10^-8—20Mev. By comparison between the experimental results and the calculated values, they are primarily tallied within the allowed range of error in which the relative error is 28%. So that it is not only to prove the reasonableness of the detector design, but also to provide bases on validation experiment. The performance of the designed neutron dose meter here is superior to that of the present commercial ones which are used to measure the neutron dose in environmental level. It is also to provide one of the monitoring means and methods for responding to a nuclear terrorism event and nuclear emergency.