See this article – https://www.berkeleynucleonics.com/december-23rd-2020-how-gamma-ray-spectroscopy-has-evolved

Our SAM III series of equipment (SAM 950, SAMpack and SAMmobile 150) is compatible with FEMA’s RadResponder network at no additional cost to the end user.

BNC generally recommends a 2x4x16 inch detector unless greater efficiency is needed at high photon energies.  For energies that include photons from U-235 and Pu-239 there is negligible difference between the two sizes.  This means that the photons from both U-235 and Pu-239 are fully absorbed in either size detector.  For isotopes like Cs-137 and U-238 some differences begin to show.  The photon energy at 2615 keV (which is an indication of highly enriched material) is still easily detected in the 2x4x16 inch detector because the background is quite low in this region.  Contact the factory for application specific support. The data for several common isotopes is shown below:

2x4x16

• 100% absorption (abs) at 186 keV (includes all energies of U-235)
• 87% abs at 414 keV (includes Pu-239 at 332, 375 and 414 keV)
• 75% abs at 662 keV (Cs-137)
• 67% abs at 1000 keV (U-238)
• 52% abs at 2615 keV

4x4x16

• 100% abs at 186 keV (includes all energies of U-235)
• 98% abs at 414 keV (includes all energies of Pu-239)
• 95% abs at 662 keV (Cs-137)
• 89% abs at 1000 keV (U-238)
• 76% abs at 2615 keV

The Model SAM 950 has a highly upgraded power source with rechargeable lithium-ion batteries. These batteries give reliable operation for over 8 hours before requiring recharge.

The smart phone technology lends itself to spectroscopy with a simplified and intuitive operation. The advantages are many fold:

1. Smart phone operation is wide spread allowing the user to quickly adapt to touch screen use and utilizing many cell phone features.
2. The device (PDA) is a quality product which gives the SAM III products reliable operation with many first-ever capabilities. The display has excellent linearity and resolution with color coded spectra and one-finger operation of the cursor. Many features are automated, for example, auto calibration and stabilization which are clearly displayed.
3. Detaching the PDA (SAM 945, RD120) allows convenient control of the instrument from a distance (bluetooth control). With the RD120 SAMpack monitoring can be clandestine with or without earphones.
4. When monitoring waste or highly active material the user can be at a safe distance (20 feet or more) and have complete control of the spectrometer which includes making measurements, taking multiple acquisitions, manipulating the spectrum, etc. Therefore, the ALARA safety practices are easily accomplished.
5. General cell phone features are incorporated into the operation of the SAM. For example, taking a picture and adding text or video describing details of the source being measured. This added information is included with the report and spectrum.

The SAM III instruments have a maximum count rate of 100,000 CPS and 150,000 CPS depending on the amount of background and the number of energy peaks being processed.

The sigma trigger allows a low threshold for sensing a radioactive source while being unaffected by false triggering due to changes in background (sigma indicates standard deviations over background).  This provision automatically updates the current background which yields higher sensitivity while eliminating false triggers due to changing ambient background.  This feature allows the user to survey a large area without needing to continuously stop and store a new and different background.  A sigma setting of 4 is recommended.

Berkeley Nucleonics provides the standard ANSI N42 compliant libraries for SNM, Medical, Industrial and NORM. Also a user defined library is provided. Finally, an expanded ANSI compliant library is available for CeBr and LaBr detector upgrades. New medical libraries and isotopes are updated through the product’s free apps, PeakGo and PeakAbout.

The example given here is for a typical background of 7 urem/hr (70 nSv/hr) which corresponds to about 250 gamma counts per second (cps).    When a Ra-226 source is detected there will be an alarm at background levels but a firm ID will not occur until the cps reaches about twice the background level (500 – 600 cps for this example).  This higher cps level for ID is expected since Ra-226 has many peaks and many are very low in abundance (sometimes referred to as Branching Ratio, Branching intensity or intensity of peaks.)

In addition Ba-133 has similar peaks with much higher branching intensities (about 20 times higher) which add to the complexity of identifying Ra-226 especially at low cps.  The library is carefully designed to take this into account but moving closer to the source or waiting a little longer for a solid ID is always important (Ba-133 ID may be seen momentarily but will cease as statistics improve).  Identifying two or more isotopes each with low abundant lines (peaks) may also require moving closer to the source and possibly waiting longer to obtain good performance.

U-238 is another example of a source with low abundant lines and may take up to 30 seconds or more to identify at minimum count rate (<500 cps).  Users must realize that the basic specifications which are given for the Cs-137 standard is the result of a very high branching intensity (>85%) – whereas the branching intensity of U-238 lines are less than 1% of Cs-137.  It is therefore expected that acquisitions on some sources will take a little longer but it is common practice to use acquisitions of at least 1 minute and to move closer to the source if possible.

When using the Variable Alarm Mode (as opposed to Fixed Alarm Mode) a low threshold can be set to start the acquisition during a search for radionuclides.  A low threshold which triggers the start of an acquisition is important for achieving high sensitivity.  However, changes in the background during surveillance can cause false triggers that may result in false identification of isotopes.  To prevent false triggers from happening BNC uses a scheme called “Auto Variable Trigger”. This is a threshold adjustment that continuously optimizes the threshold setting automatically.  Those performing environmental surveillance will find this mode especially valuable as it allows identification of NORM isotopes with the highest sensitivity possible during changes in NORM.

See this article: https://www.berkeleynucleonics.com/december-3th-2020-history-neutron-detection