Model 599 Loss Free Counting Module

Features

• Statistically corrects for detector pulses lost when system electronics are busy
• Usable in both variable and high count rate situations
• Uses the Virtual Pulse Generator (VPG) technique developed by Dr. G.P. Westphal, Univ. of Vienna¹
• Real time correction of system counting losses
• Precision live time correction for statistically accurate peak areas
• Dual spectra collect mode allows accurate calculations of peak area uncertainties

1. US Patent 4,476,384.

Description

The Model 599 Loss Free Counting (LFC) module provides the ability of performing real-time correction of system counting losses. This feature is particularly useful when measuring short-lived radionuclides or stack emissions, or any measurements where spectral distribution is changing. LFC can also be used to obtain significant improvements in the live time accuracy of the spectroscopy system.

LFC provides the capability of dynamically adding the fractional counting losses to the spectrum as they occur, rather than extending the measurement duration as in live time correction. Several techniques for computing the short term counting losses have been implemented and can be selected by the user.

The Model 599 is compatible with the CANBE RRA Model 556A MCA. The MCA and ADC must be equipped with the standard 34-pin ribbon cable connections to allow the Model 599 used to plug in directly.

To achieve maximum throughput rate, the MCA, such as the Model 556A, must be equipped with a REA D-ADD-N weighting factor feature which allows the MCA to add numbers 1 to 255 to the contents of a channel. Without this feature, multiple REA D-ADD-1 memory cycles must be performed for each event, thereby limiting the system throughput rate.

The accuracy of the results obtained with either mode is the same; only the maximum detector input rate is affected. If detector input rates in excess of 50 kHz are expected, the MCA should be equipped with the READ-ADD-N option. An internal jumper in the Model 599 selects the transfer mode.

Dual LFC Option

The Dual LFC Mode accumulates a loss-free corrected spectrum simultaneously with an uncorrected spectrum. Analysis of the two spectra together allows more accurate quantification of the data than analysis from a single spectrum.

Peak centroid (energy), net area, background and counts per second are computed from the corrected spectrum, while the uncertainty in the computed peak area is derived from the uncorrected spectrum. This results in a better estimate of the error than if the computation were performed using the corrected spectrum (due to the non-Poisson nature of the corrected spectrum).

To use the Dual LFC Mode, a contiguous band of MCA spectral memory must be allocated which is equal to at least twice the desired conversion. The analysis software required to quantify the tandem spectra is contained in the Model 480198 Genie-ESP Spectroscopy Applications software. Additional analysis software, such as the Model 480201 Genie-ESP Nuclide Identification software, may be required, depending on the application.