Patent Number: 
Section: claims

1. A radiation monitor comprising:a radiation detector which detects a γ ray emitted from a measurement target nuclide and outputs an analog voltage pulse; anda radiation measuring instrument which receives the analog voltage pulse output from the radiation detector, and measures and outputs radiation in a measurement energy range,wherein the radiation measuring instrument includesa pulse amplifier which amplifies the input analog voltage pulse and removes superimposed high frequency noise,a high-energy count-rate-measuring instrument which discriminates the analog voltage pulse output from the pulse amplifier by a high-energy window and a low-energy window which are set so as not to be superimposed on each other in accordance with a voltage level, respectively, measures and outputs a high-energy count rate by performing a time constant process of the pulses entering the high-energy window so that a standard deviation becomes constant, and outputs an alert, when the high-energy count rate is increased beyond an acceptable set value,a low-energy count-rate-measuring instrument which measures and outputs a low-energy count rate by moving and averaging the pulse entering the low-energy window at a constant measurement time,an alert-diagnosis device which determines whether or not the low-energy count rate is in a set acceptable range, when an alert is output from the high-energy count-rate-measuring instrument, determines that the alert is caused by fluctuation, when the low-energy count rate is in the set acceptable range, determines that the alert is caused by any one of an increase in the γ ray which is a measurement target or enter of noise, when the low-energy count rate increases beyond the acceptable range, and outputs a result of the determination, anda display/user-operation device which displays each output and performs operations and settings of each unit. 2. The radiation monitor according to claim 1,wherein measurement time of the low-energy count-rate-measuring instrument is set to be 1 time to 3 times the time constant which is unequivocally determined from a background level and a standard deviation of the high-energy count rate of the high-energy count-rate-measuring instrument. 3. The radiation monitor according to claim 1,wherein, in a case where an alert is output from the high-energy count-rate-measuring instrument and it is determined that the alert is caused by any of an increase in the γ ray which is a measurement target or enter of noise, the alert-diagnosis device determines that the alert is caused by the noise, in a case where a ratio of a net increased amount from each background level is equal to or greater than a set value, regarding the low-energy count rate of the low-energy count-rate-measuring instrument and the high-energy count rate of the high-energy count-rate-measuring instrument. 4. The radiation monitor according to claim 1,wherein the high-energy count-rate-measuring instrument includesan up-down counter which receives a shaping pulse corresponding to the pulse entering the high-energy window through an up input,a negative feedback pulse generation circuit which generates a feedback pulse at a repetition frequency so as to respond the output of the up-down counter with a primary delay of the time constant and inputs the feedback pulse to a down input of the up-down counter, andan integration control circuit which performs weighing when the up-down counter performs the counting in accordance to the standard deviation of the count rate, anda count rate is operated so that the standard deviation becomes constant based on an addition/subtraction integrated value of the up-down counter. 5. A radiation monitor comprising:a radiation detector which detects a γ ray emitted from a measurement target nuclide and outputs an analog voltage pulse;a first radiation measuring instrument which receives the analog voltage pulse output from the radiation detector, measures radiation in a measurement energy range on a high energy side, outputs a result of the measurement, and outputs an alert, when the result of the measurement is increased beyond an acceptable set value;a second radiation measuring instrument which receives the analog voltage pulse output from the radiation detector, measures radiation in a measurement energy range on a low energy side, and outputs a result of the measurement; anda diagnosis apparatus which receives the output of the first radiation measuring instrument and the output of the second radiation measuring instrument, performs moving and averaging of a result of the measurement of the second radiation measuring instrument for a constant time, determines whether or not the moved average value is increased beyond a set acceptable range, determines that the alert is caused by fluctuation when the value is in the acceptable range, determines that the alert is caused by any of an increase in the γ ray which is a measurement target or enter of noise, when the value is increased beyond the acceptable range, and as a result of the determination, displays a trend of the result of the measurement of the first radiation measuring instrument and a trend of the moved average value,wherein measurement energy ranges of the first radiation measuring instrument and the second radiation measuring instrument are set not to be superimposed to each other. 6. The radiation monitor according to claim 5,wherein the measurement energy range of the second radiation measuring instrument is set so as to contain peak spectra of radioactive rare gas which is an emission management target and main Compton scattering spectra. 7. The radiation monitor according to claim 5,wherein a moving average time of the diagnosis apparatus is set to be 1 time to 3 times the time constant which is unequivocally determined from a background level and a standard deviation of the first radiation measuring instrument. 8. The radiation monitor according to claim 6, wherein a moving average time of the diagnosis apparatus is set to be 1 time to 3 times the time constant which is unequivocally determined from a background level and a standard deviation of the first radiation measuring instrument.