BF3 counter

Gas-filled detectors are used, for the most part, to measure alpha and beta particles, neutrons, and gamma rays. The detectors operate in the ionization, proportional, and G-M regions with an arrangement most sensitive to the type of radiation being measured. Neutron detectors utilize ionization chambers or proportional counters of appropriate design. Compensated ion chambers, BF3 counters, fission counters, and proton recoil counters are examples of neutron detectors. 

Proportional counters can also count neutrons by introducing boron into the chamber. The most common means of introducing boron is by combining it with tri-fluoride gas to form Boron Tri-Fluoride (BF3). When a neutron interacts with a boron atom, an alpha particle is emitted. The BF3 counter can be made sensitive to neutrons and not to gamma rays. 

The detectors generally used for the y area monitors are GM counter and Nal(Tl) scintillator for lower dose rate regions and ion-chamber for higher dose rate regions. For the neutron, a BF3 counter with or without moderator is used. 

The BF3 counter is a proportional counter filled with BFj gas, usually enriched to more than 90 percent in °B (about 20 percent of natural boron is B the rest is B). The BF3 counter detects the alpha and the lithium particles produced by the reaction... 

The specifications of commercial BF3 counters consist of sensitivity, dimensions, composition of the filling gas, operating voltage, and maximum operating temperature. 

Another technique for neutron detection uses a fission chamber. One design contains a stack of alternate anodes and cathodes, one of the electrodes being covered by a thin layer of uranium enriched in The fission fragments produce large ionization even though the gas multiplication is quite low. This detector is more sensitive to fast neutrons than the BF3 counter, and can be used for fast neutron fluxes up to 10 n s with a backgroimd of a few cps. 

Descending coke profiles were observed experimentally by Van Zoonen in the hydroisomerization of olefins [1965]. Hughes et al. [1987] observed a decreasing coke profile when xylenes reacted over a silica/alumina bead catalyst around 460°C. The profile was measured by a noninvasive technique neutron beam attenuation coupled with a BF3 counter. 

PC-BF3 Counter - a Proportional Counter tube filled with B oron-Trifluorlde gas so that wnen a neutron enters the tube an n-oc reaction emits enough energy to form a pulse which will then activate a scaler. By combining amplification and a discriminator into the system a controlled portion of radiation can be counted. 

Scintillation methods offer the possibility of high-efficiency detectors with a more rapid time response than the BF3 counter. As mentioned in the previous section, the basis of the scintillation detector is the conversion, in a suitable crystal, such as thallium-activated sodium iodide, Nal(Tl), of the kinetic energy of the charged particle to light, which can be amplified by a photomultiplier tube to provide an electrical pulse. Again, the neutron has to interact to produce either a charged particle or a 7 ray, the latter of which may in turn interact to produce ionizing particles. 

Channel 3. Linear micromicroammeter, and Channel 4. BF3 counter (placed in access port 4). 

The exact stable period of the reactor is determined by the external BF3 counting system. The BF3 counter is placed at a desired location in access port number four. The counts per fraction of a minute are then taken periodically, A plot of the counting rate versus time is made on semilog paper. The plotting should commence when the first count is taken, this will enable the participant to determine whether or not the reactor is rising on a stable period. The stable reactor period will be determined from the semilog plot and recorded along with the control rod position and temperature on the data sheet. 

A Lucite blank is then placed at the center of the glory hole in place of the boron sample A. Caution is again stressed in this operation, since positive reactivity is being inserted. The coarse control rod is then raised to its previously recorded position. Once the reactor has reached its stable period, a period measurement should be made with the external BF3 counter as described above. The reactor period should, of course, be shorter since the boron absorber has been removed from the core. Record control rod settings, period and temperatures. 

The MPC unit serves as the high-voltage source to the BF3 counter, and low-gain amplifier, and as a pulse inverter. The MPC switch is a convenient method of suddenly removing or restoring, the signal input to the multichannel analyzer for the time-versus-channel number calibration. 

With the equipment used in this experiment, pulsed-neutron generator AL-ZOl, BF3 counter, TMC analyzer, and the ambient natural background present, we can obtain the value of a for > 0.1 cm directly and for B < 0.1 cm" through harmonic analysis. 

B. Vertical Distribution The BF3 counter is connected to the same type of a drive unit described above and positioned with identical controls. 

The BF3 counter used is encapsulated in a Lucite tube. Why was this material used, and what other material could be used ... 

What could you suggest to eliminate the gamma counting registered by the BF3 counter ... 

What is the sensitivity of a BF3 counter Must it be known before the neutron-flux distribution can be determined ... 

This instrument uses a REM/n counter as a detector, and normally has 3 logarithmic ranges extending from 10 to 10 Sv/hr (1 mRem/hr to 100 mRem/hr). The basic detector is a BF3 counter surrounded by a moderator/attenuator assembly (rich in hydrogen) to provide a weighted dose response from. 025 eV to 14 MeV of neutron energy. 

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