Gamma-Ray Spectrum Stabilization in a Borehole Probe Using a Light Emitting Diode

Abstract

A borehole probe which has a Light Emitting Diode (LED) implanted in a Nal detector has been constructed to collect spectral gamma-ray data for uranium exploration. The LED is pulsed to simulate light from gammaray interactions in the detector, and the resulting light is used as a reference to gain stabilize the detection system. The LED allows optimum gain sensitivity by producing a peak higher in the energy spectrum than the natural gamma-ray peaks, and the LED has no Compton scattering to interfere with the natural spectrum as do isotopic gamma-ray sources used in gain stabilization. A temperature-sensitive resistance network is used to compensate the LED for the extreme temperature variations encountered in the borehole environment. Diagrams of the probe and LED system are given along with test results.

A New Temperature Correction Method for NaI(Tl) Detectors Based on Pulse Deconvolution

“…Although there was some deviation between the pulse model and the actual response, the consistency of pulse shapes after deconvolution and trapezoidal shaping at different temperatures shown in Figure 4 reflects the effectiveness of this method in pulse shape correction. Compared with previous temperature correction methods [5][6][7][8][9][10][11][12], this method can be used at high count rate due to the correction of pulse shape and adjustable trapezoid width.…”

“…In Equation (7), A is the pulse area, τ0 is the rising time constant, τ1 and τ2 represent the time constant of the fast component and the slow component respectively, and φ is the proportion of the fast component.…”

“…Temperature correction for NaI(Tl) detectors has generally been treated by three types of spectra stabilization methods. The first is to stabilize the position of some reference peaks by adjusting the high voltage of the photomultiplier tube (PMT) [5] or the gain of the amplifier [6,7]. The second is correcting continuously the spectra in time series [9][10][11] based on the reference peak [5,8] or the reference spectrum [9,10].…”

A New Temperature Correction Method for NaI(Tl) Detectors Based on Pulse Deconvolution

“…D(z) is the deconvolution filter, and depends on the temperature, T. a k is the polynomial coefficient determined only by model parameters τ i , λ j , ϕ i and φ j . When M = 2, N = 1, δ is very close to 0, and a simplified model such as (7) can be obtained. It is the convolution between an exponent function and the sum of two exponent functions.…”

“…Temperature correction for NaI(Tl) detectors has generally been performed using three types of spectra stabilization methods. The first is to stabilize the position of some reference peaks by adjusting the high voltage of the photomultiplier tube (PMT) [5] or the gain of the amplifier [6,7]. The second is to continuously correct the spectra in time series [8][9][10] based on the reference peak [5,11] or the reference spectrum [8,9].…”