Model 12-4 Neutron Counter
The neutron "remball" detector has been the standard for measuring neutron fields for more than 50 years.
At about 23 pounds, it is not a well-loved detector, especially at the end of a long day. However, thousands
of these detectors still exist and are heavily relied upon today. Currently IATA (International Air Transport Association) regulations prohibit the shipping of these detectors due to the poisonous nature of the BF3. The result is that the international shipping of these detectors has become very expensive or practically impossible.
Ludlum Measurements now offers two alternatives to this problem: 1) a Model 42-41 PRESCILA detector
(see: www.ludlums.com/product/m42-41.htm ), or 2) replacement of the tube inside your existing detector
with an identically sized 3He tube. The remainder of this article clarifies the second alternative.
The following is a list of differences and similarities between BF3 and 3He tubes:
- Pressure: Replacement 3He tubes have less than 2.7 atmospheres of
pressure and are therefore exempt
from any shipping requirements.
- Energy Response: There is no change in energy response which still follows
the inverse-RPG curve.
- Crosstalk: Gamma interference or “crosstalk” is the same
for both the BF3 and 3He tubes. Crosstalk
is less than 10 counts per minute at 10 R/hr (137Cs).
- High Voltage: Operating HV is normally about 1100 Vdc for the 3He
tube, where the BF3 tube
requires about 1700 Vdc.
- Count rate: The 3He tube has approximately four times
the count rate of the BF3 tube at a given
neutron dose rate. This difference is mostly beneficial because it reduces statistical error. However,
a resistor change-out is needed in some of our older electronics in order to calibrate the top range.
the following actions:
- New detectors will have a new model number and model name that
includes an "H", as in
the Model 42-30H, and the Model 42-31H. For the Model 5, the new detector model number is Model 42-14H.
- Modified detectors and electronics will have a small circular label with
an "H" placed in a highly
visible location.
- Modified detectors will receive a new serial number label with the new
model number.
Before shipping your detector internationally to Ludlum Measurements
for modification, the BF3 tube will need to be removed. Download the instructions
on the removal of the BF3 tube by clicking BF3 Tube Replacement Instructions or
contact Ludlum Measurements’ Sales Department.
| Tube (Part No.: 01-5793) Cost | $500.00 | |
|---|---|---|
| Recalibration | $90.00 | |
| Labor | $90.00 |
Prices subject to change without notice.
