Digital logarithm gamma energy spectrometer

Abstract

The invention discloses a digital logarithm gamma energy spectrometer, which comprises a NaI crystal, a photomultiplier, a high-voltage power supply module, a preamplifier, a logarithmic amplifier, a gain-programmed amplifier, an anti-aliasing active filter, a high-speed analog-digital converter (ADC) and a CPLD programmable logic device, wherein the logarithmic amplifier performs logarithmic operation on received nuclear pulse signals to acquire a high energy section spectral line and a low energy section spectral line; the high-speed analog-digital converter (ADC) performs analog-digital conversion on filtered signals; and the CPLD programmable logic device realizes pulse amplitude analysis, baseline restoration and filtering de-noising to digital signals, and obtains information on corresponding nuclear pulse peak values. The logarithmic amplifier performs logarithmic compression on the nuclear pulse signals to ensure the resolution of the high energy spectral line and the low energy spectral line; and the high-speed analog-digital converter and the CPLD programmable logic device are adopted to realize a digital energy spectrometer and ensure the high counting pass rate and the energy resolution of the energy spectrometer.

Description

technical field [0001] The invention relates to a gamma energy spectrometer, in particular to a digital logarithmic gamma energy spectrometer. Background technique [0002] Gamma ray is a kind of strong electromagnetic wave, its wavelength is shorter than X-ray, generally the wavelength is less than 0.001 nanometer. In the nuclear reaction, when the nucleus undergoes α and β decay, it often decays to an excited state, and the nucleus in the excited state is still unstable, and will transition to a stable state by releasing a series of energies, and these The release of energy is achieved by ray radiation, and this ray is gamma ray. [0003] Gamma rays were first discovered by French scientist P.V. Villard, and they are the third nuclear rays discovered after alpha and beta rays. Gamma rays are produced by transitions between nuclear energy levels, and both nuclear decay and nuclear reactions can produce gamma rays. Gamma rays are more penetrating than X-rays. When γ-rays...

AI Technical Summary

Problems solved by technology

[0007] 1. The use of analog circuits to form a peak sample-and-hold circuit leads to a decrease in the obtained energy resolution, especially in the case of high technology rates, which is even more serious

Since the analog peak sample-and-hold circuit samples the analog voltage by charging and discharging the capacitor, and the dielectric absorption effect of the capacitor itself, there is an error in the collected analog voltage, and the error changes with the peak value of the analog signal. brings about the nonlinearity of the spectral line

At the same time, the capacitance, resistance and other parameters of the analog circuit change greatly with the influence of temperature, which also brings problems in debugging and production.

[0008] 2. The minimum pulse width that the analog peak sample-and-hold circuit can handle is generally around tens of microseconds, and the device working in the low-speed analog converter cannot handle the new incoming nuclear pulse signal, which leads to the problem of dead time and makes the allowable maximum The count rate is low, usually around tens of K, which cannot meet the detection requirements of large crystals

[0009] 3. Due to the use of linear amplifiers, in order to simultaneously detect high-energy nuclear pulse signals (above 3Mev) and low-energy nuclear pulse signals (below 30Kev) under the condition that the effective resolution of the analog-to-digital converter is fixed, the system gain must be reduced, so that The peak value of the low-energy nuclear pulse signal is very low, usually less than tens of Mv. Affected by noise and ADC resolution, the resolution of the low-energy spectral line will deteriorate sharply, and the low-energy spectral line has more spectral peaks. And it is compressed, no useful information can be obtained, and the high-energy spectral line has fewer spectral peaks, but occupies a large input range of the ADC, which becomes a waste

Images