Very Large Boron Trifluoride Proportional Counters

Abstract

More than 50 very large BF3 counters, each approximately 6 ft (180 cm) long and 6 in. (15 cm) in diameter have been made for cosmic-ray monitors. During the fabrication of these counters, the characteristics at varying gas pressures have been studied and the alpha backgrounds of the various metals used for cathodes have been determined. The counters have excellent characteristics at pressures up to 30 cm Hg and perfectly acceptable characteristics to 60 cm Hg pressure. With anode diameter 0.008 in. (0.2 mm) and gas amplification 35, the operating voltage for a filling of 20 cm Hg pressure of pure BF3 is 2800 V; at 30 cm Hg it is 3400 V. Counters with copper cathodes have backgrounds due to residual alpha contamination of about 2 counts/min, and with stainless steel cathodes, about 5 counts/min. Using a BF3–Ar filling a value of 6.30±0.05% has been obtained for the branching ratio of the B10(n,α)Li7 reaction.

Long‐term decline of South Pole neutron rates

“…The resulting count rate was 50 per minute, but pulse height analysis indicated that these counts were still predominantly due to neutrons. This is consistent with the finding of Fowler [1963] that the typical background due specifically to alpha particles from radionuclides in the detector itself is about 5 per minute. In the Pole monitor at solar minimum (1997 epoch), the count rate of this detector would be about 6400 per minute per tube, so background is at the 0.8% level at worst (and probably much less), which is not enough to impact our conclusions.…”

Effect of adding Ar gas on the pulse height distribution of BF3-filled neutron detectors

“…The branching ratio is obtained by taking ratio of the sums of the number of pulses in the 2.78 MeV peak to the total number of pulses collected. The value obtained is 6.1 ± 0.2, which agrees with values reported in the literature [1,4]. Figure 2 shows gas gain as a function of applied anode voltage for detectors filled with pure BF 3 and BF 3 + Ar mixture.…”

“…But BF 3 is not an ideal proportional counter gas. Worsening of plateau characteristics results with increase in cathode diameter and it is not possible to obtain good characteristics in counters with gas filled at 60 cm Hg and diameters more than 3.8 cm [1,2]. This may be due to fluctuations of the number of initial ion pairs produced due to wall effects and fluctuation of the gas amplification due to electron capture by the impurities in the gas or to saturation effects because of the space charge at the anode wire [3].…”

“…The dilution of BF 3 with argon causes a decrease in detection efficiency, but the pulse height spectrum shows sharper peaks and more stable plateau characteristics than counters filled with pure BF 3 . Large dimension detectors filled with various high pressures of BF 3 +Ar mixtures have been used for cosmic ray monitoring [1]. Low pressure counters filled with up to 5 cm Hg pressure of BF 3 with sufficiently high argon pressure have been used for neutron beam applications [4].…”

Performance of Chemical Vapor Deposited Boron-Doped AlN Thin Film as Thermal Interface Materials for 3-W LED: Thermal and Optical Analysis

“…BCl 3 is of great importance in chemical physics due to their nonpolar and highly plane symmetric (D 3h ) geometry. For this reason, BCl 3 is extensively used in deposition and doping of boron [22].…”