Research On A Portable Alpha-ray Spectrometer For Measuring Wiping Samples

With the nuclear science and technology is widely used in the field of medicine, medical radiation measuring instruments has become one of the key developing directions in medical equipment.However,due to the high-speed nuclide transformation,it's difficult to make an absolute measurement of the content and check the results at any time.As the measurement results have a direct impact on medical diagnosis,measuring instruments applies to medical testing are called for the abilities of rapid measurements at the scene,accurate analysis and so on.In this paper, "a portable alpha-ray spectrometer for measuring wiping samples" is developed to meet the require of a military medical institution in China.The research project aimed at developing a set of instrument with multi-channel spectrometer,information processing and alpha-ray spectrum analysis technologies,specifically for measuring medical cotton swabs which collected wiping samples from nasal passage.The instrument is light and has high precision,good stability,flexibility and intuitive intelligence.Theαenergy spectrum is the distribution ofα-ray intensity with energy.α-ray energy released by radionuclide is normally between 4 to 10MeV.It is the discrete spectrum,hence the energy spectrum measurement and analysis is relatively simple.α-ray spectrometer is a kind of instrument which used to measure the spectrum ofαradiation.Its working principle is:when the different elements subject to the same intensity of excitation sources,they will produce different characteristics of energyray or fluorescence spectroscopy,and it's almost nothing to do with the material in which they are physical or chemical state.We can complete the qualitative and quantitative analysis of the material composition through the energy and intensity measurements.This kind of spectrometer is usually made up by a linear function of radiation detector and other electronic modules.The structure of the mainstream is: detector signals→pre-amp→pulse shaping and amplifiers→range Analysis→calibration or records.With the demand for site analysis and the development of micro-electronic technology,the research on the whole spectrometer is towards the directions such as strong performance compatibility and long-term job stability,the expansion of a high degree of flexibility and portability.In this paper,we introduced the hardware and software of different functions and related techniques of the alpha-ray spectrometer.In the principle of high-precision, low-power,small size and simple design,we selected the PIPS(Passivated Implanted Planar Silicon) detector as the detector and the embedded single-chip microcomputer as the control platform,and carried out the research of the core circuits system.The hardware system includes:the installation of the samples,signal acquisition, signal amplification,pulse amplitude analysis,the display of spectral lines,and so on. The front-end part of the hardware including the sample holder,the preamplifier circuit of a small size and the detector which constitute the whole measurement apparatus;signal acquisition module based on high-performance C8051F series single-chips is composed of three parts,that is,the analog circuits,the pulse height analysis circuits and the serial communication circuit.This module realized the functions of forming the main signal,amplification,filtering,AD conversion,spectral data acquisition,etc.,and accessed to transform the nuclear radiation detector signals into digital signals at the same time.The control module completed the main task of human-computer interaction,including display of spectral lines,real-time display of the measurement results,and set up other parameters.The liquid crystal display and keyboard are used to control the signals to start and stop modules,to achieve a variety of parameter settings,to analysis,preservation,read,delete and other related control operations of the spectrum.In addition,the op-amp circuits are using single power supply devices which reduce the size of the spectrometer.The software system is composed of the single-chip software and energy spectrum analysis software.Single-chip software system has two main parts,one is the signal obtain module,the other is the control module.The signal obtain module is used to obtain data and form spectral lines during the interruption of the ADC conversion, and a one-second timer is designed to ensure the accuracy of each measurement,and then transmit data to the control module through the serial port communication.The control module has to complete the functions like ADC data acquisition,LCD display and serial port communications.Spectrum analysis software is based on Windows XP platform and applied Visual C + + 6.0 as its tool to build the framework of the whole analysis system.Through in-depth study on spectral analysis,we selected the right methods to smooth the spectrum,search the peaks,calculate peak areas,and so on. The spectrum analysis software which we designed is user-friendly,easy to operate and can achieve a certain degree of accuracy.When the hardware and software of the spectrometer are established,the performance of the system is tested.Initial tests include power consumption test,the energy resolution test and accuracy test.After the installation of the system,a group of measurements were carried out in a row to two samples(original 239Pu source samples marked the activity of 3230/2π·min and 220.7/2π·min).A good experimental test results verified the stability and accuracy of the spectrometer.Through the one-year research work,the architecture of hardware and software system has developed into the machine molding and testing phase.Preliminary test results showed that:The portable alpha-ray spectrometer for measuring medical wiping samples in line with the high-precision,low power,small size,rapid analysis, and suitable for site measuring,and has wide application prospects.