Ametek Ortec radEAGLET-R Series User Manual page 147

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C Technological Background, Limitations

C.1 Stabilization

The primary spectroscopic detector of radEAGLET-R is the scintillation crystal. This crystal

produces light pulses whenever gamma photons interact with the crystal material. The

light pulses are very weak so they must be amplified. Therefore, the crystal requires a

photo-multiplier tube (PMT) which is coupled to the crystal. This assembly allows the in-

cident gamma photons to be digitized by the internal electronics, and the pulses (which are

proportional to the energy of the incident gamma rays) form a histogram or gamma spec-

trum. This spectrum is stored in the embedded multi-channel analyzer.

The response of both the detector and the PMT may vary based on measurement conditions

such as temperature or magnetic field. The peaks in the gamma radiation spectrum may

shift due to these temperature variations. As temperature changes are encountered, mod-

ern scintillation based instruments must apply some means of stabilization. Shown below is

the procedure the radEAGLET-R uses to correct for peak shifts and to adjust the peaks in

the spectrum to their scientifically correct positions.

C.1.1 Initial Stabilization

Each time the system is turned on, during the start-up the radEAGLET-R performs an initial

stabilization. It runs temperature checks and searches for known peaks in the spectrum. It

is strongly advised not to have check sources in the immediate area during this initial phase,

because this can confuse the process.

C.1.2 Continuous Temperature Monitoring

During the manufacturing process, each radEAGLET-R is tested in a climate chamber to

learn the individual temperature dependencies of crystal and PMT. Both the absolute value of

the temperature as well as the temperature gradients are used in this process. In the field,

the instrument continuously monitors and adjusts the gain by measuring the temperature.

It also distinguishes between slow temperature drifts and quick temperature shocks.

C.1.3 Continuous Spectroscopic Adjustments

Although there is not always an actual source present, the natural background spectrum

often contains valuable information. The radEAGLET-R uses the natural background peaks

for an advanced stage of self-stabilization. When turned on, the radEAGLET-R is automat-

ically taking background spectra and analyzing them. All this happens automatically in the

Software 3.2.12r • Document 3.3.3b4o

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