The Model SF-TF-6 is a small portable gas proportional counter with a shielded drawer system for measuring surface contamination collected on wipes, filter papers, or other thin samples. It is suitable for measuring any alpha or beta emitter, but is designed for measuring low energy beta emitters such as tritium and C-14. Contaminated wipes are inserted into a 2” wide metal drawer system with two sample cavities of 1.25” (31mm) diameter and 0.18” (4.5mm) depth and surrounded by 1” lead shielding. Two cavities allow the user to save time unloading and loading samples. Usable sample diameter is limited by the 1” (25mm) diameter of the detector face.
The detector is a low background windowless gas flow proportional detector with a nominal outside diameter of 1.38” (35mm) and an inside diameter of 1” (25mm). P-10 or similar counting gas is required for use of the instrument. Steady-state gas usage is about 250cc/min, and some users turn the flow rate up to 600cc/min between samples as a purge. Six feet of ¼” tubing is supplied with the instrument for connecting to a P-10 gas supply. The instrument body is a lead shield approximately 3.87” x 3.5” x 3” (98x87x76mm) to reduce background radiation in the detector cavity, and a carrying handle attaches to the shield block for easy carriage.
Includes PRS-7 scaler/counter/analyzer, which is a digital display pulse counter that covers a 6-decade range (1-100,000 CPS or other unit of choice). The PRS-7 is battery-powered, with an internal lithium cell and charger, and an external 12V AC power input. The PRS-7 has a preamplifier with a built-in single-channel analyzer so that pulses may be selected by their pulse height and cancel out other noise. It can also scale the counter display by a multiplier over a wide range, and the display can show both pulse rate and total pulse count, with a timer that will stop the counter after a preset interval. Includes an adjustable high voltage power supply with a range of 200-2500 Volts, audible/visible alarms, and RS-232 data output.
Gas proportional probes generate signal pulses of heights proportional to the energy of the detected radiation events. The single-channel analyzer (SCA) in the PRS-7 consists of two comparators with adjustable thresholds. The thresholds are called “discriminator” and “window” and are controlled by 10-turn potentiometers on the front panel. The SCA selects which pulses to pass along to the counter based on the two thresholds and the mode setting.
Discriminator Mode: Only the discriminator threshold is used and all pulses with heights exceeding the threshold are passed then counted. A dial setting of 100 is typically used to block low-level pulses which are predominately noise. Note: A 3-way toggle switch allows you to select from 3 different adjustable preset discriminator levels for convenience when measuring different isotopes.
Window Mode: Both the discriminator threshold and window threshold are used, and only pulses that are above the discriminator and below the window will be passed then counted. When performing measurements where there is significant background or the possibility of more than one radioactive emitter, use window mode to eliminate higher energy from the counted pulses.
|MEASUREMENT RANGE||6 decades, 1 to 100,000 CPS or other measurement unit of choice|
|DRAWER (SAMPLE SIZE)||2” wide drawer with two sample cavities 1.25” (31mm) diameter and 0.18” (4.5mm) depth|
|DETECTOR||Windowless gas flow proportional counter with 1” diameter (25mm) sensitive area|
|SHIELDING||1” lead shielding around detector and sample cavity|
|SENSITIVITY||0.5 nCi (18.5 Bq) / sample|
|TIMER||Crystal controlled, 1 to 10,000 seconds, user settable|
|DISPLAY MODES||Rate or Integrate|
|ALARMS||Visible: orange light on front panel, Audible: piezoelectric sounder with volume control|
|CALIBRATION||4 range pots and 1 overall control, internal|
|INDICATORS||Pilot light: Green indicator that the power is on|
Panel meter: Red Lion CUB5 LCD digital display
Sonalert: Acoustic click for each pulse detected
Alarm: Orange light indicating an alarm condition, if the alarm is enabled
On-Off, Show HV, HV Set, Alarm On or Mute
Time Interval Controls:
Auto or Singe Shot Mode, Start, Stop
In auto mode, the measurement time is repeated continuously, versus only once in single shot
Energy Window Controls:
Discriminator Level: 10-turn lockable dial adjusts discriminator threshold
Window Level: 10-turn lockable dial adjusts window threshold
Presets D, A, B: 3-position toggle switch to select one of 3 values for the discriminator threshold
Position D is the 10-turn dial on front panel. A and B are alternative internal 10-turn potentiometers
|CONNECTORS||The connector for the probe is on the front panel, all other connectors are on the left side of case|
Power: 2.5mm round socket, 12V DC from an AC powered converter
MHV: Coaxial cable connection to probe (MHV on instrument, BNC on probe end)
HV Output: Separate HV connection that may be used instead of the HV on the MHV
Alarm: 3-pin Philmore: Isolated connections for a remote alarm: common, NO, NC
|SIZE AND WEIGHT||Probe and shield assembly:|
3.87” L x 3.5” W x 12” H including handle, 6.4 kg (14 lbs)
Electronics (NEMA-4X polycarbonate gasket sealed enclosure):
10″ L x 4.1” W x 7″ H including handle, 2.5 kg (5 lbs) including batteries
|Accessories included||• Cables|
• Six feet of ¼” tubing for connecting to P-10 supply