Development Of A New Nuclide Activity Measurement System Based On 4πγ Ionization Chamber

In the clinical diagnosis and treatment of malignant tumors,radioactive drugs have been widely used.As increasing short half-life radionuclides(e.g.,¹⁵O,¹³N,etc.)are used to diagnose or treat,these short-life rapid measurement value is increasingly important.Nuclide activity measuring system（referred to as activity meter）is one of an important equipment for accurate measurement of radioactive drug activity,and is widely used in nuclear medicine.Compared with foreign similar equipment,there is still a certain gap in measurement accuracy,measurement activity range,stability,etc.,which require further mention.Developing miniaturization,fast measurement,high precision,and width reach.This article relies on the"National Key R&D Plan"sub-subject"Electronic Instruments"Transferring Nucomycological Value Value."Based on the 4πγhigh-voltage electricity off chamber detector,a portable activity meter applied to the spot and accurate measurement of the radioactivity activity was developed.This paper develops the actual meter hardware system and the host computer measurement software.The capacity meter current measurement is less than 100f A,the upper limit is higher than 1μA,the maximum measurement time is 3 seconds.In terms of hardware,based on improved I-V circuitry,a very weak current detecting device（current meter）is designed to achieve f A-level resolution current detection in combination with high precision analog-to-digital conversion,hardware filtering,electromagnetic shielding,Guard-Ring protection.The current signal output by the 4πγionization chamber is converted into a voltage signal by the modified IV circuit of the built-in multi-range switch.The data is completed by the high resolution ADC,and the data is read and stored by the MCU through the SPI bus,and passed RS-485.The bus is transmitted to the host computer;the software has developed the lower computer embedded control program and the host computer data acquisition and handler.Among them,the lower machine program implements the range of rapid switching,A/D conversion control,data preoperation,range calibration,data uploading and other functions;the host computer software implements the data acquisition control,activity scale,this deduction,activity measurement Function.In this paper,the effective range of the internal current meter of this paper is 50f A to 0.5m A,the resolution is 1f A,and the absolute deviation is less than 3f A when the current is measured below,and the relative deviation is less than 0.85%when the current of 500f A is measured.The final current noise of the measured ionization chamber is about 40f A.In a consecutive 9 days of activity measurement,the maximum deviation of the active meter is less than 1.7%,and the measurement response time is less than 3s.The above performance indicators have reached the topic requirements.The developed activity meter can meet the rapid and accurate measurement of the radioactive nucleus activity.