The E-600 V2.XX programming has added the capability for active crossover correction to enable the instrument to reduce the effects of window to window crossover which is always present to some extent when alpha/beta probes are used. If you have not upgraded your E-600 and WinE600 software to Version 2.00 or higher you cannot take advantage of this capability.

Beta to alpha crossover is seldom more than about 1% of the beta count rate; however, alpha to beta crossover (alpha induced counting pulses which show up in the beta window) can exceed 30% of the alpha induced pulses in some cases causing misleading beta information to be presented to the user when the beta channel is selected on the E-600 and an alpha source is presented to the probe.

Alpha to beta crossover occurs when alpha particle energy (and thus pulse height) is degraded through alpha particle interactions in air, the probe face and other interactions which result in alpha particle pulses below the alpha threshold.

The crossover correction feature of the E-600 provides an effective means of greatly reducing unwanted crossover. This application note discusses the methods used to properly setup the crossover correction factors.

Setting the Crossover Factor - Method 1

The WinE600 software provides two methods which may be used to adjust the crossover factors. The simplest method is to follow the following steps.

1. Place the instrument in ratemeter mode with the alpha/beta detector connected

2. Turn the speaker on and select either the alpha or beta channel

3. Expose the detector to a source which emits particles of the opposite type (alpha if the beta channel is selected, beta if the alpha channel is selected)

4. Using the WinE600 software select edit channel parameters and edit the crossover factor in small steps until very little crossover of the incorrect radiation type is present

As an example, to edit the crossover factor for the beta channel, select the beta channel and expose the detector to an alpha source such as ²³⁹Pu. Adjust the Upper to Lower XOver factor until alpha induced counts rarely occur in the beta channel.

Caution! Make sure you do not over-compensate for the crossover. Using too large a crossover correction factor will cause over-compensation and artificial suppression of the reading for the target channel. It is best to stop just short of total suppression when adjusting the crossover factor.

An important point to remember when adjusting the crossover factor is that the crossover factor is a fractional value representing the amount of the undesired count rate information which crosses over into the other channel. For example, if you place an alpha source under the detector and you measure 10,000 ncpm (net counts/min) in the alpha channel and 1,000 ncpm in the beta channel you will use a Upper to Lower XOver factor of 1,000/10,000 or 0.10 to remove the unwanted information from the beta channel. Due to the nature of this factor, values outside the range of 0.00 to 0.50 (50% crossover) should be highly suspected as incorrect values.

Note: The Upper to Lower XOver factor need only be edited in the channel parameters for the beta channel although it does no harm to enter the same factor in all three (alpha, beta and alpha/beta) channels assuming the thresholds and operating voltage are set the same for all channels.

Setting the Crossover Factor - Method 2

The second method for setting the crossover correction factor is more automatic, but not nearly as much fun. The WinE600 software will automatically calculate the crossover factor during channel calibration if selected.

To determine the crossover factor for a specific source, determine the calibration constant as you normally would but make sure and click on the Do XOver check box before starting the calibration constant determination.

At the end of the determination the crossover from the calibrated window to the other window is displayed and stored in the channel parameter file.


Take the calculated crossover factor and enter it in the channel for which it will do some good. For example, when you perform an alpha source calibration on your alpha channel, the upper to lower window crossover factor is calculated and stored in the channel parameters for the alpha channel. Since the alpha channel does not need upper to lower correction because it is an upper window channel, enter the calculated upper to lower correction factor into the channel parameters for the beta channel since it does need upper to lower crossover correction as protection against alpha pulse spillover into the lower window. 

Crossover Correction Limitations

While the crossover correction factor is a tremendous tool when using combination alpha/beta probes with systems of this type, the crossover correction is not guaranteed to be a perfect solution in all cases.

The most important use for the crossover correction is alpha channel to beta channel crossover. As long as the alpha source type and the source to probe distance are consistent with that used during determination of the Upper to Lower XOver factor, the correction works very well. If the source to detector distance changes, the correction does not work as well.

It is because of these limitations that it is recommended that the Upper to Lower XOver factor be determined with an alpha source in as close a counting geometry to the detector as is likely to ever be achieved in the field. Determining the factor in this fashion assures that a conservative correction will always be applied since as the alpha source to detector distance increases above that used to determine the factor, the alpha to beta crossover will be greater and the correction will be under-applied.