On November 8, 1895, at the Universityof Wurzburg….Glowing fluorescent screen on a nearbytable.fluorescence was caused by invisible raysoriginating from the partially evacuatedglass Hittorf-Crookes tube he was usingto study cathode rays (i.e., electrons).
Surprisingly, these mysterious rays penetratedthe opaque black paper wrapped around thetube. Roentgen had discovered X rays.However, prior to his first formal correspondenceto the University Physical-MedicalSociety, Roentgen spent two months thoroughlyinvestigating the properties of X rays.Silvanus Thompson complained that Roentgenleft "little for others to do beyond elaborating hiswork."
For his discovery, Roentgenreceived the first Nobel Prize inphysics in 1901.
As a student in Holland, Roentgen wasexpelled from the Utrecht Technical Schoolfor a prank committed by another student.Even after receiving a doctorate, his lack ofa diploma initially prevented him fromobtaining a position at the University ofWurzburg.He even was accused of having stolen thediscovery of X rays by those who failed toobserve them.
He rejected a title (i.e., von Roentgen) that wouldhave provided entry into the German nobility.Donated the money he received from the NobelPrize to his University.Roentgen did accept the honorary degree ofDoctor of Medicine offered to him by the medicalfaculty of his own University of Wurzburg.At the time of his death, Roentgen was nearlybankrupt from the inflation that followed WorldWar I.
Henri Becquerel was born into a family of scientists. Hisgrandfather had made important contributions in the fieldof electrochemistry while his father had investigated thephenomena of fluorescence and phosphorescence.Becquerel not only inherited their interest in science, healso inherited the minerals and compounds studied by hisfather.And so, upon learning how Wilhelm Roentgendiscovered X rays from the fluorescence theyproduced, Becquerel had a ready source offluorescent materials with which to pursue hisown investigations of these mysterious rays.
The material Becquerel chose to work with waspotassium uranyl sulfate, K2UO2(SO4)2, which heexposed to sunlight and placed on photographicplates wrapped in black paper.When developed, the plates revealed an image ofthe uranium crystals. Becquerel concluded "thatthe phosphorescent substance in question emitsradiation which penetrates paper opaque tolight." Initially he believed that the suns energywas being absorbed by the uranium which thenemitted X rays.
Further investigation, on the 26th and 27th ofFebruary, was delayed because the skies overParis were overcast and the uranium-coveredplatesBecquerel intended to expose to the sun werereturned to a drawer.
On the first of March, he developed thephotographic plates expecting only faint imagesto appear. To his surprise, the images were clearand strong.This meant that the uranium emitted radiationwithout an external source of energy such as thesun.Becquerel had discovered radioactivity, thespontaneous emission of radiation by amaterial.
For his discovery of radioactivity,… Becquerel was awarded the 1903Nobel Prize for physics.
In 1880, he and his brother Jacques haddiscovered piezoelectricity whereby physicalpressure applied to a crystal resulted in thecreation of an electric potential.He also had made important investigations intothe phenomenon of magnetism including theidentification of a temperature, the curiepoint, above which a materials magneticproperties disappear.
Together, they began investigating the phenomenon ofradioactivity recently discovered in uranium ore.Although the phenomenon was discovered by HenriBecquerel, the term radioactivity was coined by Marie.After chemical extraction of uranium from theore, Marie noted the residual material to be more"active" than the pure uranium.She concluded that the ore contained, in addition touranium, new elements that were also radioactive. Thisled to their discoveries of the elements of poloniumand radium.
For their work on radioactivity, the Curieswere awarded the 1903 Nobel Prize inphysics.Tragically, Pierre was killed three years laterin an accident while crossing a street in arainstorm.Pierres teaching position at the Sorbonnewas given to Marie. Never before had awoman taught there in its 650 year history!
Her first lecture began with the verysentence her husband had used to finish hislast.In his honor, the 1910 Radiology Congresschose the curie as the basic unit ofradioactivity: the quantity of radon inequilibrium with one gram of radium(current definition: 1 Ci = 3.7x1010 dps).
A year later, Marie was awarded the Nobel Prizein chemistry for her discoveries of radium andpolonium, thus becoming the first person toreceive two Nobel Prizes.For the remainder of her life she tirelesslyinvestigated and promoted the use if radium as atreatment for cancer.Marie Curie died July 4, 1934, overtaken bypernicious anemia no doubt caused by years ofoverwork and radiation exposure.
Father of nuclear physics.Particles named and characterized by himinclude the alpha particle, beta particle andproton.Even the neutron, discovered by James Chadwick, owesits name to Rutherford. The exponential equation usedto calculate the decay of radioactive substances wasfirst employed for that purpose by Rutherford and hewas the first to elucidate the related concepts of thehalf-life and decay constant.
Rutherford won the 1908 Nobel Prize inchemistry.In 1909, now at the University ofManchester, Rutherford was bombarding athin gold foil with alpha particles when henoticed that although almost all of themwent through the gold, one in eightthousand would "bounce" (i.e., scatter)back.
From this simple observation, Rutherfordconcluded that the atoms mass must beconcentrated in a small positively-chargednucleus while the electrons inhabit the farthestreaches of the atom. In 1919, Rutherford returned to Cambridge to become director of the Cavendish laboratory where he had previously done his graduate work under J.J. Thomson. It was here that he made his final major achievement, the artificial alteration of nuclear and atomic structure.
By bombarding nitrogen with alphaparticles, Rutherford demonstrated theproduction of a different element, oxygen."Playing with marbles" is what he called; thenewspapers reported that Rutherford had "splitthe atom."After his death in 1937, Rutherfords remainswere buried in Westminster Abbey near thoseof Sir Isaac Newton.
The radioisotopes have numerousapplications inmedicine, agriculture, industryand pure research.
Many applications employ a specialtechnique known as “ tracertechnique”.A small quantity of a radioisotope isintroduced into the substance to bestudied and its path is traced bymeans of a Geiger-Muller (G. M.)counter.
What are radioisotopes?Many of the chemical elements have anumber of isotopes.The isotopes of an element have the samenumber of protons in their atoms (atomicnumber) but different masses due todifferent numbers of neutrons.
In an atom in the neutral state, the number ofexternal electrons also equals the atomicnumber.These electrons determine the chemistry of theatom.The atomic mass is the sum of the protonsand neutrons. There are 82 stableelements and about 275 stable isotopes ofthese elements.
When a combination of neutrons andprotons, which does not already exist innature, is produced artificially, the atomwill be unstable and is called a radioactiveisotope or radioisotope.There are also a number of unstablenatural isotopes arising from the decay ofprimordial uranium and thorium. Overallthere are some 1800 radioisotopes.
Radioisotopes in MedicineNUCLEAR MEDICINEThis is a branch of medicine that uses radiation toprovide information about the functioning of apersons specific organs or to treat disease. Thethyroid, bones, heart, liver and many other organscan be easily imaged, and disorders in theirfunction revealed. In some cases radiation can beused to treat diseased organs, or tumours.
Diagnostic techniques in nuclear medicine useradioactive tracers which emit gamma rays from withinthe body.They can be given by injection, inhalation or orally.The first type are where single photons are detected bya gamma camera which can view organs from manydifferent angles.The camera builds up an image from the points fromwhich radiation is emitted; this image is enhanced by acomputer and viewed by a physician on a monitor forindications of abnormal conditions.
In a similar way, the passage of a particularelement in the body and the rate at whichit accumulates in different organs can bestudied.
A positron-emitting radionuclide isintroduced, usually by injection, andaccumulates in the target tissue. As itdecays it emits a positron, which promptlycombines with a nearby electron resultingin the simultaneous emission of twoidentifiable gamma rays in oppositedirections.These are detected by a PET camera andgive very precise indication of their origin.
PETs most important clinical role is inoncology, with fluorine-18 as thetracer, since it has proven to be the mostaccurate non-invasive method of detectingand evaluating most cancers. It is also wellused in cardiac and brain imaging.
Positron emission tomography (PET) is nuclearmedicine imaging technique that produces athree-dimensional image or picture offunctional processes in the body.The system detects pairs of gamma rays emittedindirectly by a positron-emitting radionuclide (tracer), which isintroduced into the body on a biologically activemolecule.
Three-dimensional images of tracerconcentration within the body are thenconstructed by computer analysis.In modern scanners, three dimensional imagingis often accomplished with the aid of a CT X-rayscan performed on the patient during the samesession, in the same machine.
Gamma imaging by either method described provides aview of the position and concentration of theradioisotope within the body. Organ malfunction can beindicated if the isotope is either partially taken up inthe organ (cold spot), or taken up in excess (hot spot). Ifa series of images is taken over a period of time, anunusual pattern or rate of isotope movement couldindicate malfunction in the organ.A distinct advantage of nuclear imaging over x-raytechniques is that both bone and soft tissue can beimaged very successfully. This has led to its commonuse in developed countries where the probability ofanyone having such a test is about one in two andrising.
RADIOTHERAPYRapidly dividing cells are particularly sensitive todamage by radiation. For this reason, somecancerous growths can be controlled oreliminated by irradiating the area containing thegrowth.
External irradiation can be carried out using agamma beam from a radioactive cobalt-60source, though in developed countries the muchmore versatile linear accelerators are now beingutilised as a high-energy x-ray source (gammaand x-rays are much the same).
Internal radiotherapy is by administering or planting asmall radiation source, usually a gamma or betaemitter, in the target area.Iodine-131 is commonly used to treat thyroidcancer, probably the most successful kind of cancertreatment. It is also used to treat non-malignant thyroiddisorders. Iridium-192 implants are used especially in thehead and breast.They are produced in wire form and are introducedthrough a catheter to the target area. After administeringthe correct dose, the implant wire is removed to shieldedstorage. This brachytherapy (short-range) procedure givesless overall radiation to the body, is more localised to the
Targeted Alpha Therapy (TAT): especially for the controlof dispersed cancers.The short range of very energetic alpha emissions intissue means that a large fraction of that radiativeenergy goes into the targeted cancer cells, once a carrierhas taken the alpha-emitting radionuclide to exactly theright place. Laboratory studies are encouraging andclinical trials for leukaemia, cystic glioma and melanomaare under way.
An experimental development of this is BoronNeutron Capture Therapy using boron-10 whichconcentrates in malignant brain tumours.The patient is then irradiated with thermalneutrons which are strongly absorbed by theboron, producing high-energy alpha particleswhich kill the cancer. This requires the patient tobe brought to a nuclear reactor, rather than theradioisotopes being taken to the patient.
BIOCHEMICAL ANALYSISIt is very easy to detect the presence or absence of someradioactive materials even when they exist in very lowconcentrations. Radioisotopes can therefore be used tolabel molecules of biological samples in vitro (out of thebody). Pathologists have devised hundreds of tests todetermine the constituents ofblood, serum, urine, hormones, antigens and many drugsby means of associated radioisotopes. These proceduresare known as radioimmuno assays and, although thebiochemistry is complex, kits manufactured for laboratoryuse are very easy to use and give accurate results.
DIAGNOSTIC RADIOPHARMACEUTICALS:Every organ in our bodies acts differently from achemical point of view. Doctors and chemistshave identified a number of chemicals which areabsorbed by specific organs.The thyroid, for example, takes up iodine, thebrain consumes quantities of glucose, and so on.
With this knowledge, radiopharmacists are ableto attach various radioisotopes to biologicallyactive substances.Once a radioactive form of one of thesesubstances enters the body, it is incorporatedinto the normal biological processes andexcreted in the usual ways.
Diagnostic radiopharmaceuticals can be used toexamine blood flow to the brain, functioning ofthe liver, lungs, heart or kidneys, to assess bonegrowth, and to confirm other diagnosticprocedures.Another important use is to predict the effectsof surgery and assess changes since treatment.
A radioisotope used for diagnosis must emitgamma rays of sufficient energy to escape fromthe body and it must have a half-life shortenough for it to decay away soon after imagingis completed.The radioisotope most widely used in medicineis technetium-99m, employed in some 80% of allnuclear medicine procedures.
Myocardial Perfusion Imaging (MPI) usesthallium-201 chloride or technetium-99m and isimportant for detection and prognosis ofcoronary artery disease.For PET imaging, the main radiopharmaceuticalis Fluoro-deoxy glucose (FDG) incorporating F-18- with a half-life of just under two hours, as atracer.The FDG is readily incorporated into the cellwithout being broken down, and is a goodindicator of cell metabolism.
THERAPEUTIC RADIOPHARMACEUTICALS:For some medical conditions, it is useful to destroy orweaken malfunctioning cells using radiation. Theradioisotope that generates the radiation can belocalised in the required organ in the same way it isused for diagnosis - through a radioactive elementfollowing its usual biological path, or through theelement being attached to a suitable biologicalcompound.
In most cases, it is beta radiation whichcauses the destruction of the damagedcells. This is radiotherapy.Short-range radiotherapy is known asbrachytherapy.
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