Radiant energy – Automatic/serial detection of similar sources
Patent
1992-05-29
1994-06-28
Fields, Carolyn E.
Radiant energy
Automatic/serial detection of similar sources
250362, 250364, 250369, G01T 1204
Patent
active
053249437
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method and an apparatus for determining the amounts of a radioactive isotope in scintillation samples. More particularly this invention relates to a determination of quench level and quench correction in a scintillation counter.
BACKGROUND OF THE INVENTION
Scintillation counting of soft beta-emitters like tritium and carbon-14 is a very common analytical technique in life sciences. The aim of this technique is to accurately determine the activity of one or several radioactive isotopes dissolved in a special scintillation liquid held in a transparent vial. The scintillation counter can normally count several hundreds of vials (samples) in an automatic manner without attendance.
The standard scintillation counter comprises a detector compartment for sequentially holding each sample at a time. Normally the detector comprises two photomultiplier (pm) tubes simultaneously converting photon pulses that are emitted from the sample into electrical pulses. The pm tubes normally work according to the coincidence technique. In this technique, the electrical pulses from both tubes are fed into an electronic circuit, called the coincidence analyzer, which passes pulses on to pulse height analyzers and scalers only if there is a pulse in both of the two photomultiplier tubas within a certain time period, called the coincidence resolving time. The function of the coincidence analyzer can shortly be described as follows: assume that a scintillation pulse causes an analog output pulse at the output of one of the two pm tubes. At a certain time, the analog output pulse exceeds a certain threshold and sets a logic signal that will prevail for a finite time period, equal to the coincidence resolving time. Normally, the coincidence resolving time is quite short, typically in the order of about 15 ns. If during the coincidence resolving time an analog output pulse from the other pm tube triggers the coincidence analyzer, the analyzer sets its output gate signal to indicate a coincidence pulse. This output gate signal causes the analog pulse height analyzer to accept the two analog pulses from the two pm tubes. Normally the two analog pulses are summed before further analysis by pulse height analyzers and scalers or a multichannel analyzer.
A radioactive disintegration is a fast phenomenon in itself, but the process, in which the disintegration energy is transformed into photons, may extend over a considerable time period, e.g. up to a few microseconds. The characteristics of this scintillation pulse, the intensity and its decay rate, depends on the scintillation medium. In most media, the decay consists of two parts: the prompt part, which is the major part, and the slow, or delayed part. The prompt part, which originates from the lower excited singlet states immediately formed at the disintegration, is so short and instant that most of the photons can be observed during the first 20 ns after the disintegration. A typical scintillation pulse is shown in FIG. 1. The slow part, which is dependent on the formation of higher excited and ionized states, may extend over a considerable time period and photons in this part may not be noticed by the coincidence analyzer. This fact is of no concern when the total number of photons is high, as in that case there be many photons in the prompt part and a high probability that both pm tubes will receive photons within the coincidence resolving time. But if only a few photons are emitted, the first photon has a high probability to occur within the prompt part, and the next may occur much later, or within the slow part, after the coincidence resolving time. In this case the coincidence analyzer will not accept this pulse. Thus, if the coincidence resolving time is short in comparison to the decay rate of the slow part, there is a certain chance that a disintegration resulting in only two or three detected photons will not cause a coincidence condition. This situation arises typically with low energy isotopes like tritium in certain scintil
REFERENCES:
patent: 4652751 (1987-03-01), Rundt et al.
patent: 5120962 (1992-06-01), Rundt et al.
Oikari Timo
Rundt Kenneth
Fields Carolyn E.
Wallac Oy
LandOfFree
Method for scintillation counting and a scintillation counter wi does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for scintillation counting and a scintillation counter wi, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for scintillation counting and a scintillation counter wi will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2378830