gamma counter
{{Short description|Instrument to measure gamma activity}}
{{CSS image crop |Image=Two medical technologists use a gamma counter to measure hormone concentrations in the blood.tif|bSize=300||cHeight=345|cWidth=250|location=right|Description=Technologists use a gamma counter to measure hormone concentrations in the blood and pituitaries using such methods as radio-immuno assays and competitive protein-binding assays.}}
A gamma counter is an instrument to measure gamma radiation emitted by a radionuclide. Unlike survey meters, gamma counters are designed to measure small samples of radioactive material, typically with automated measurement and movement of multiple samples.
Operation
Gamma counters are usually scintillation counters. In a typical system, a number of samples are placed in sealed vials or test tubes, and moved along a track. One at a time, they move down inside a shielded detector, set to measure specific energy windows characteristic of the particular isotope. Within this shielded detector there is a scintillation crystal that surrounds the radioactive sample. Gamma rays emitted from the radioactive sample interact with the crystal, are absorbed, and light is emitted. A detector, such as a photomultiplier tube converts the visible light to an electrical signal.{{cite journal|last1=Jakowiuk|first1=Adrian|last2=Filipiak|first2=Paweł|last3=Bartak|first3=Jakub|last4=Pieńkos|first4=Paweł|last5=Kowalska|first5=Ewa|title=Laboratory automatic measuring system for gamma specimens|journal=Nukleonika|date=2012|volume=57|issue=4|pages=633–635|url=http://www.nukleonika.pl/www/back/abstract/vol57_2012/v57n4p633.htm}}{{cite journal|last1=Lubran|first1=MM|title=Quality control of gamma counters. I. Experimental evaluation of sources of error.|journal=Annals of Clinical and Laboratory Science|date=1977|volume=7|issue=1|pages=57–67|pmid=836003|url=http://www.annclinlabsci.org/content/7/1/57.full.pdf}} Depending on the half-life and concentration of the sample, measurement times may vary from 0.02 minutes to several hours.
If the photon has too low of an energy level it will be absorbed into the scintillation crystal and never be detected. If the photon has too high of an energy level the photons may just pass right through the crystal without any interaction. Thus the thickness of the crystal is very important when sampling radioactive materials using the Gamma Counter.{{cite web|title=Gamma Counter|url=http://www.radiationanswers.org/radiation-introduction/detecting-measuring/gamma-counter.html|website=Radiation Answers|publisher=RadiationAnswers.org|access-date=15 June 2016}}{{cite book|last1=Phelps|first1=Simon R. Cherry, James A. Sorenson, Michael E.|title=Physics in nuclear medicine|url=https://archive.org/details/physicsnuclearme00phds|url-access=limited|date=2012|publisher=Elsevier/Saunders|location=Philadelphia|isbn=978-1-4160-5198-5|pages=[https://archive.org/details/physicsnuclearme00phds/page/n200 179]|edition=4th|chapter=Counting Systems}}
Applications
Gamma counters are standard tools used in the research and development of new radioactive compounds used for diagnosing (and treating disease) as in PET scanning. Gamma counters are used in radiobinding assays,[http://las.perkinelmer.ca/content/manuals/man_antidsdnaradiobindingassay.pdf Anti-dsDNA [I-125] Radiobinding Assay Kit]{{Dead link|date=May 2024 |bot=InternetArchiveBot |fix-attempted=yes }} At PerkinElmer Life Sciences, Inc. Retrieved Jan 2011 radioimmunoassays (RIA){{cite book|last1=Stanley|first1=Jacqueline|title=Essentials of immunology & serology|date=2002|publisher=Delmar, Thomson Learning|location=Australia|isbn=9780766810648|page=[https://archive.org/details/essentialsofimmu0000stan/page/142 142]|url=https://archive.org/details/essentialsofimmu0000stan|url-access=registration}} and nuclear medicine measurements such as GFR{{cite journal|last1=Fleming|first1=JS|last2=Zivanovic|first2=MA|last3=Blake|first3=GM|last4=Burniston|first4=M|last5=Cosgriff|first5=PS|last6=British Nuclear Medicine|first6=Society|title=Guidelines for the measurement of glomerular filtration rate using plasma sampling.|journal=Nuclear Medicine Communications|date=August 2004|volume=25|issue=8|pages=759–69|pmid=15266169|doi=10.1097/01.mnm.0000136715.71820.4a|s2cid=6657901 }} and hematocrit.{{cite web|last1=Williams|first1=Scott|title=Blood Volume Determination|url=http://www.auntminnie.com/index.aspx?sec=ser&sub=def&pag=dis&ItemID=62855|website=auntminnie.com|access-date=15 September 2016|date=3 April 2002}}
Some gamma counters can be used for gamma spectroscopy to identify radioactive materials based on their output energy spectrum, e.g. as a wipe test counter.{{cite book|last1=Lombardi|first1=Max H|title=Radiation Safety in Nuclear Medicine.|date=2006|publisher=CRC Press|location=Hoboken|isbn=9780849381799|page=129|edition=2nd|url=https://books.google.com/books?id=2Q3NBQAAQBAJ&pg=PA129}}