Proportional counter particle

The variations in the background, the sensitivity to moisture, the alpha activity of the chamber itself and the influence of recombination were discussed by Hultqvist. The standard deviation due to counting statistics was estimated to be about 3 % (in a few measurements 6 %). The calibration was made by counting each alpha particle by a proportional counter specially designed at the Department for this purpose. The statistical uncertainty of the calibration of the equivalent radon concentration was estimated to be 12 %. 

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 are extremely sensitive, and the voltages are large enough so that all of the electrons are collected within a few tenths of a microsecond. Each pulse corresponds to one gamma ray or neutron interaction. The amount of charge in each pulse is proportional to the number of original electrons produced. The proportionality factor in this case is the gas amplification factor. The number of electrons produced is proportional to the energy of the incident particle. 

Proportional counters measure the charge produced by each particle of radiation. To make full use of the counter s capabilities, it is necessary to measure the number of pulses and the charge in each pulse. Figure 9 shows a typical circuit used to make such measurements. 

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 proportional counter measures the charge produced by each particle of radiation. 

Neon is also used in scintillation counters, neutron fission counters, proportional counters, and ionization chambers for detection of charged particles. Its mixtures with bromine vapors or chlorine are used in Geiger tubes for counting nuclear particles. Helium-neon mixture is used in gas lasers. Some other applications of neon are in antifog devices, electrical current detectors, and lightning arrestors. The gas is also used in welding and preparative reactions. In preparative reactions it provides an inert atmosphere to shield the reaction from air contact. 

Radioactivity of uranium can be measured by alpha counters. The metal is digested in nitric acid. Alpha activity is measured by a counting instrument, such as an alpha scintillation counter or gas-flow proportional counter. Uranium may be separated from the other radioactive substances by radiochemical methods. The metal or its compound(s) is first dissolved. Uranium is coprecipitated with ferric hydroxide. Precipitate is dissolved in an acid and the solution passed through an anion exchange column. Uranium is eluted with dilute hydrochloric acid. The solution is evaporated to near dryness. Uranium is converted to its nitrate and alpha activity is counted. Alternatively, uranium is separated and electrodeposited onto a stainless steel disk and alpha particles counted by alpha pulse height analysis using a silicon surface barrier detector, a semiconductor particle-type detector. 

Some practical designs for proportional counters are shown in Figure 18.5. In the cylindrical detector, a very thin window of split mica or Mylar plastic covers one end of the tube. It can be so thin (down to 150 p.g/cm3) that the absorption of a particles by the window is not extensive. An even more efficient arrangement is found with the hemispherical detector, where the radioactive sample can be introduced directly into the detector chamber. In the hemispherical detector, one detects 50% of all the... 

Gas-flow proportional counter (beta and alpha particles) 2,4, 6, 13 and 14... 

In Part 2A, the student will calibrate a gas-flow, end-window, anti-coincidence proportional counter for beta-particle counting efficiency as function of energy with certified standard solutions, and perform quality assurance (QA) counting tests. 

Alpha-particle detector Beta-particle detector Gamma-ray detector proportional counters silicon (Si) diode with spectrometer proportional counters Geiger-Muller counters liquid scintillation (LS) counters thallium-activated sodium iodide (Nal(Tl) detector with spectrometer germanium (Ge) detector with spectrometer... 

Beta particle calibration sources span energies from about 100 to 3,000 keV for proportional counters, and down to a few keV for liquid scintillation counters. In this experiment, a low-background, gas-flow, end-window proportional counter with automatic sample changer for alpha- and beta-particle counting is calibrated. Beta-particles sources are counted with pulse-height discrimination to eliminate interference from alpha particles the discriminator may be turned off when no alpha particles are present. 

Step 1. Place 10 blank planchets in the proportional counter system and count each for 50,000 s at settings (a) and (b) to determine the beta-particle background count rate. 

Step 2. Prepare sources in duplicate for the proportional counter by pipetting the appropriate volume - typically 100X - specified by the instructor of each of 3 standard solutions and the unknown solution onto the center of a separate planchet. You will have a total of 8 planchets 2 each for the beta-particle standards and the unknown beta-particle sample. Dry under heat lamps placed at sufficient distance over the planchets for slow drying. 

Count the alpha particles in each tracer sample for a time period sufficient to accumulate at least 1000 counts. An initial estimate of the sample counting period is based on the activity of the tracer and the known counting efficiency. Count all disks for the same period of time. The samples may be counted more than once. Count the spectral analysis background for approximately 200,000 s and the proportional-counter alpha-particle background at least 30,000 s. Record data in Data Table 6.2. 

Compare the activity reported for the tracer solution with the activity obtained with the proportional counter and the alpha-particle spectrometer based on their respective counting efficiency (s) values, adjusted for sample volume and radioactive decay. Discuss whether the differences in activity are significant and decide which values are more reliable and should be associated with the tracer solution for subsequent measurements of plutonium. 

Step 4. Disassemble the filtering apparatus and remove the filter with forceps. Fix the filter to a planchet with 2-sided tape. Count the sample three times with a proportional counter for alpha particles and beta particles for 3,000 s. Record mid-point of counting time. Record counting data in Data Table 7.1. Also measure detector background data for at least the same period and record in Data Table 7.1. 

Step 5. Pipette 100 X of the uranium solution each onto the centers of two planchets and dry under a heat lamp. Count one with the proportional counter and then with the alpha-particle spectrometer. Save the second planchet for Part 1C, Step 8. 

Determine counting efficiency of the proportional detector in Step 5 for three 3,000-s periods to measure alpha particles and beta particles. Record in Data Table 7.2. Also perform overnight count (50,000 s) for alpha-particle spectral analysis of the planchet to identify the uranium isotopes and any other radionuclides and to determine their relative amounts from their alpha-particle energy spectra and record results in Data Table 7.2. Count alpha- and beta-particle background in proportional counter and alpha-particle spectral background in spectrometer for at least the same periods. 

Average proportional counter net a-particle and beta-particle rate (R) of three counts (alpha) cps (beta) cps... 

Step 7. Count the sample three times for 3,000 s each with a proportional counter for alpha and beta particles and record in Data Table 7.4. Record the time. 

Step 8. Evaporate 10 ml 0.5 M oxalic acid to about 2 mL and pour onto the second planchet with dried 100-A. sample of the initial uranium solution (see Part 7A, Step 5). Evaporate to dryness under the heat lamp. Flame the planchet as in Step 6. Count three times for 3,000 s each with proportional counter for alpha and beta particles. Record in Data Table 7.5... 

Scheme 2. Count the sample immediately with an a and (3 counter (e.g., the proportional counter) for 200 minutes. Repeat the count each day for 14 days or until the count rate equals or nearly equals the background. Obtain background counts for both alpha-particle and beta-particle counting modes. Subtract respective backgrounds for each count period and record in Data Table 8.7...

Step 13. Count the sample for beta particles with proportional counter for 6,000 s and record results in Data Table 10.1 Measure the background count rate for 6,000 s immediately before or after the sample measurement. To check radioactive decay rate, repeat counting under identical conditions every second or third day for at least two weeks. 

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