Dear Muhammad,

you will never be able to detect lead K alpha with 12 keV excitation: The lead K edge is at 88 keV, so you'll need at least 88 keV to excite Pb K alpha. Even for the lead L lines, you need at least 13,035 keV, i.e. more than your gun supplies!

Using the threshold of your spectrometer (I suppose you have an energy dispersive apparatus, with a solid state detectors, a pulse processor and a multichannel analysor), you usually suppress electronic noise and thermal noise of the detector - but this normally gives you contributions below say typically 1 keV... But not a higher energies.

So if you start in setting up the spectrometer, start without any threshold, and if you only see noise, then increase slightly the level of the threshold to a physically senseful value.

Good luck, Dirk

thanks for kind information but i am still facing same problem... means 12kV is applied energy and within the plasma focus, we achieved the electron beam energy more than 500 keV and it is much greater than the Lead K alpha (74kev) and I have seen the 12 keV Lead L apha2.

now , what will you suggest more regarding this problem.

What kind of spectrometer do you have - it might be that the amplification of your pre-amp in the spectrometer is set too high, then the K alpha peak might be to high in voltage, and could not be counted properly. Try to decrease the amplification (of your spectroscopy amp.). And - additionally - what is the maximum peak energy that you have measured, and in which channel of your MCA is this peak detected? Then you can scale and see whether you may expect the Pb L alpha on your MCA.

XR100CR X-ray Spectrometer , its range is maximum upto 45 keV. but some other CdT spectrometer, not sure actuall name, has range more than 100keV, so it is better for meausrement but we haven;t this spectrometer in the Lab. ... so other solution, if you have to share to me, will kind help to me...regards

We have the same, if you reduce the amplification at the potentiometer stepwise down, then you should be able to measure up to more than 100 keV. We measured radioactive gamma-sources (Am241 and Co57) with this set-up, and accordingly higher energies between 60 and 130 keV ... See the charts enclosed.

This must definitely work also in your lab. So reduce the amplification either by soft or hardware (which interface to you have, the USB with the PX4 or PX5 or the older one with the serial interface?) and then it should function, try out reducing the amplification step by step! The lead K alpha should be quite intense.

Good luck, Dirk

how may i reduce the amplification by soft or hardware and PX4 or PX5 with serial interface?

I have no idea about this things which have you told me But i will try first and then again i will communicate to you regarding my progress on that way.... thanks, Zubair

If you have the old interface with serial interface to the computer, see enclosed Figure, than you have a dial on the upper right corner (Gain), there you can adjust the gain. Turning anti-clockwise will reduce.

With the new interface (PX4/PX5 with USB interface to computer) you have to do everything by software. Find the menu "Gain settings", there you can adjust the amplification ("gain") by software from 0.5 to several hundred. If you increase this value, the spectrum will more and more be spreaded, i.e. the peaks will appear at larger channels in the multichannel analyzer. Decreasing this number will shrink the spectrum, so that high energy peaks will appear at higher channel numbers.

I currently only have the old software for the serial interface on my PC, so I cannot create a screen-shot for this ...

Good Luck, Dirk

thanks i will check and then again communicate with you , thanks, Zubair

This is from the Amptek homepage:

All hardware parameters can be accessed by clicking the “Acquisition Setup” toolbar button. Controls are grouped by tabs. “MCA” tab controls acquisition presets, number of channels, LLD (threshold), setup of single channel analyzers (SCA’s), etc. “Shaping” tab controls peaking time, flat top, baseline restoration, pile-up rejection, and risetime discrimination. Common controls also set by shortcuts. Gain can be controlled by increment and decrement buttons on the toolbar, or by setting a specific value in the Setup display. “AutoTune” controls are available to automatically tune key parameters, such as the input offset and the fast and slow thresholds. Customized hardware configurations may be stored as .cfg files. DPPMCA is shipped with a library of .cfg files for the common configurations of Amptek’s detectors.

...

A common task is to change the energy range of a system. This is done by adjusting the gain of the amplifier. A lower gain corresponds to a higher energy range, and a higher gain to a lower energy range. For example, in Amptek’s digital systems a gain of x100 may correspond to a 15 keV full scale and a gain of x50 to a 30 keV full scale. To adjust the energy range it is always the gain of the system that must be changed. It is not enough to change the software calibration only. The software calibration is only in software. If the software’s calibration is changed without the amplifier’s gain changing appropriately, the software will be displaying the wrong energy range and peaks will be incorrectly identified.

If you are using one of Amptek’s digital processors (DP5, X-123, Gamma-Rad5 etc.), the gain is adjusted through the DPPMCA software on the Gain & Pole Zero tab of the DPP Properties, or by using the gain buttons on the toolbar It is necessary to readjust the thresholds whenever the gain is changed. This can be done automatically by starting an acquisition (pressing space bar) and clicking the “Tune Slow/Fast Thresholds” button on the toolbar of the DPPMCA application with no source exciting the detector. See the quick start guide of the appropriate product for more information.

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Hope this helps now! Dirk