Introduction: Radiation can be defined as the extension of energy through affair or infinite. It can be in the signifier of electromagnetic moving ridges or energetic atoms.
Ionizing radiation has the ability to strike hard an negatron from an atom. i. e. to ionise. Examples of ionising radiation include: • alpha atoms • beta atoms • neutrons • gamma beams • x-rays Non-ionizing radiation does non hold plenty energy to ionise atoms in the stuff it interacts with. Examples of non-ionizing radiation include: • microwaves • seeable light • wireless waves • Television moving ridges • Ultraviolet radiation ( except for the really shortest wavelengths ) The Earth has been radioactive of all time since its formation into a solid mass over 4? billion old ages ago. However. we have merely known about radiation and radiation for merely over one hundred old ages. [ One hundred and four old ages and 10 months to be exact. ] You are likely familiar with the radiation warning mark. the “trefoil” . See http: //www. orau. com/ptp/articlesstories/radwarnsymbstory. htm for a history of the symbol.
A Brief History of the Discovery of Radiation and Radioactivity The History of the Discovery of Radiation and Radioactivity
1895: The Discovery of the X-ray Radiation was discovered by Wilhelm Conrad Roentgen on November 8. 1895. hypertext transfer protocol: //www. orcbs. msu. edu/radiation/radhistory/wilhelmrontgen. hypertext markup language Roentgen. like many other physicists at that clip. had been experimenting in his research lab with the discharge of electricity in “vacuum tubes” . The glass tubings were evacuated ( and made airtight utilizing Bank of England sealing wax ) and had metal home bases sealed at the terminals. The metal home bases could be connected to a battery or an initiation spiral. This flow of electricity was necessary in order for the tubing to glow.
The freshness emerged from the negative home base ( the cathode ) and disappeared into the positive home base ( the anode ) . If a round anode was sealed into the center of the tubing. the freshness ( the cathode beams ) could be projected through the circle and into the other terminal of the tubing. If the beam of cathode beams were energetic plenty to hit the glass. the glass would glow ( fluoresce ) . The glass tubings were given assorted names. e. g. Crookes tubing ( named after William Crookes ) or Hittorf tubings ( Johann Hittorf ) based on the single able to plan a tubing better able to bring forth or keep vacuity. Roentgen’s work was carried out utilizing a Hittorf tubing. [ See www. chem. uiuc. edu/demos/cathode. hypertext markup language for a demo of an early cathode beam tubing in operation. ]
It had already been demonstrated that the emanation coming from the cathode. the “cathode rays” . were non really perforating. On the eventide of November 8. 1895. Roentgen had covered the tubing wholly with black composition board. The research lab was wholly dark. Several pess off from the tubing was a piece of paper. used as a screen. covered with barium-platinum nitrile. In the darkened room. Roentgen noticed the screen fluorescing. breathing visible radiation. Something must hold hit the screen if it reacted by breathing visible radiation.
However. since the Hittorf tubing was covered in composition board. no cathode rays or visible radiation could hold come from Hittorf tubing. Very surprised. Roentgen began look intoing this unusual happening. He turned the paper screen so that the side without Ba platinum-cyanide faced the tubing – still the screen fluoresced. He moved the screen further from the tubing and still the screen fluoresced. Then he placed several objects between the tubing and the screen but all appeared to be crystalline. When he put his manus in forepart of the tubing he saw his castanetss on the screen.
Roentgen experimented with these “new rays” . entirely in his research lab. for many hebdomads. He found that objects were crystalline to these beams in different grades. Photographic home bases were sensitive to X raies. He could non observe any appreciable contemplation or refraction of the beams. nor could he debar them with a magnetic field. The beams originated in the country of the discharge tubing where the cathode rays impinge on the wall of the glass tubing. On December 28. 1895. Roentgen delivered a preliminary paper to the secretary of the Physical-Medical Society of Wurzburg. It was printed instantly and by early January of 1896 it was being distributed. The paper caused a great splash ( as can be imagined ) and may hold been ignored as incredible had he non besides included x-ray exposure of custodies ( taking 3-10 proceedingss to get ) . This grounds could non be easy dismissed. The response to this new find was enormous.
Roentgen was invited to talk all over the universe. nevertheless he declined all invitations ( except one – he made a presentation to the Kaiser on January 13. 1896 ) in order to go on his probes. In the twelvemonth 1896 there were over 1. 000 documents written on the topic of X raies. Roentgen himself wrote merely two more documents on X raies. in 1896 and 1897. He so went back to working on his former involvements but received the first Nobel Prize for natural philosophies in 1901. What Happens in the Crookes/Hittorf Tube? 1. Phosphorescence/ Fluorescence: The freshness from the tubing Electrons exist in distinct orbits in the atom.
Electrons can leap to a higher orbit merely by soaking up of energy or to a lower orbit by emanation of energy. The energy is equal to the difference in energy degree between the two orbits. In the illustration below. an negatron in the outer shell ( Ei ) drops into the inner shell ( Ef ) . In doing this passage. a photon is given off. The energy of the photon is equal to Ei-Ef. If the emanation of a photon ( following energy soaking up ) is really speedy ( eg 10-8 – 10-9 s ) . the phenomenon is called “fluorescence” . If the emanation is slow to happen. the phenomenon is referred to as “phosphorescence” .
Since the energy degrees of each atom are alone to that atom. the photons emitted during fluorescence are really typical and act as ‘fingerprints’ for that peculiar component. This fact is frequently used in the designation and quantification of elements in a sample. Because the fluorescent ( or phosphorescent ) photons are alone to the atom. these photons are sometimes referred to as “characteristic radiation” . Bremsstrahlung ( X-rays ) : The Mysterious Rays: What Roentgen discovered was the phenomenon we now know as “bremsstrahlung” . He himself didn’t know what the beams were – they were new. penetrating and cryptic. For deficiency of a better name he called them “x-rays” . The cathode beams generated in the Hittorf tubing. the negatrons. struck the glass wall of the tubing. When negatrons interact with affair they typically do one of two things.
They ( 1 ) dislodge orbital negatrons in the stuff ( via elastic hits ) ; these negatrons make an ionisation path themselves in the stuff ; finally the energy is given to the stuff as heat. Orbital vacancies are filled from negatrons dropping in from higher shells and characteristic radiation ( fluorescence ) may be given off. Or. they ( 2 ) are decelerated in the field of the karyon in the glass tubing. Remember that the negatrons are negatively charged and will be attracted to the positively-charged karyon. The flight of the negatron will alter. flexing toward the karyon and decelerating down. Classical theory Tells us that when any charged atom undergoes a alteration in acceleration. electromagnetic radiation ( an X ray ) is emitted. This phenomenon is called bremsstrahlung. which is German for ‘braking radiation’ . and is the phenomenon observed by R. [ This procedure. which is the footing for all x-ray tubings in usage today. will be item with in more item later in the course. ] 2.
1896: The Discovery of Radioactivity The find of radiation followed the find of X raies by merely two-anda-half months. Henri Becquerel. a 3rd coevals expert on fluorescence and phosphorescence. heard a study ( and saw radiogram ) of Roentgen’s work at the hebdomadal meeting of the Academie diethylstilbestrols Sciences on January 20. 1896. [ hypertext transfer protocol: //www. orcbs. msu. edu/radiation/radhistory/antoinebecquerel. hypertext markup language ] Upon larning that the X raies emerged from the fluorescing glass of the Hittorf tubing. he instantly conjectured that other fluorescing stuffs might besides breathe X raies. He worked for many yearss. proving a figure of phosphorescent and fluorescent substances without success. until he tried a uranium salt. uranyl K sulphate. Sealing a photographic home base in black paper. he sprinkled a bed of the uranium salt onto the paper and put the whole thing in the Sun for several hours.
When he subsequently developed the home base. he saw the silhouette of the phosphorescent substance in black on the negative. He so assumed ( erroneously ) that the sunshine caused the emanation of the penetrating beams ( and that x-rays came automatically from fluorescing substances ) . The following portion of the narrative is celebrated. Becquerel tried reiterating the experiment on February 26 and once more on February 27. nevertheless Paris was cloudy. He put the covered home base. with uranyl K sulphate on top. off in a drawer. Then. on March 1 he went in front and developed the home base. anticipating to see really weak images. Alternatively. the images appeared really intense. Therefore. the uranium salt emitted beams capable of perforating black paper. whether or non it had been antecedently exposed to sunshine.
Becquerel ab initio thought the consequence might hold been a consequence of durable unseeable phosphorescence. but disproved this theory by proving non-phosphorescent U salts and happening they besides produced the silhouettes. At the clip. Becquerel’s find did non look every bit of import as Roentgen’s. ( After all the images were really fuzzed and there was non much U about. in contrast to the relatively high declaration images made with “Roentgen Rays” utilizing a Crooks or Hittorf tube already in the custodies of many. many investigators. ) Becquerel found that the “Becquerel Rays” ionised gases. Thus it was possible to mensurate the activity in a sample merely by mensurating the ionisation that it produced. At the clip this could be done utilizing a rough gold-leaf electroscope.
Becquerel shared the 1903 Nobel Prize in natural philosophies and is known as the inventor of radiation. Becquerel continued to look into the beams emitted by U. However. he restricted himself to uranium since. foremost. it was the stuff he had most experience with and. 2nd. he felt it to be unlikely that another substance would be a more powerful emitter since the beams were foremost discovered from U. Thus it was non Becquerel but the Curies who investigated other elements and. by detecting first Po and so Ra. were able to do really powerful beginnings which helped pave the manner toward a full apprehension of the procedure of radioactive decay.
1897: Clarifying the Nature of Cathode Rays In 1897. the 3rd manager of the esteemed Cavendish Lab at Cambridge University. J. J. Thomson. carried out a figure of experiments with cathode beams. [ See hypertext transfer protocol: //www. orcbs. msu. edu/radiation/radhistory/josephthomson. hypertext markup language for a brief history of J. J. Thompson. and hypertext transfer protocol: //webster. aip. org/history/electron/ for an interesting description of his experiments. ] By virtuousness of the fact that he was able to set up a good vacuity in the cathode tubing. Thomson was able to demo that the cathode beams could be deflected in an electric field. [ He had connected two metal home bases placed inside the tubing to a battery.
He showed that a narrow cathode beam beam. made utilizing a brace of detached slits. created a fluorescent spot on the terminal of the tubing in a different topographic point. depending on whether the battery was connected or not. ] Although it was known that cathode beams could be deflected in a magnetic field. no 1 had yet observed their warp in an electric field. The ground was that J. J. Thomson was able to obtain a better vacuity in his tubing. Unless there is a good vacuity. no electric field can be established. [ A hapless vacuity is a good conductor. ]
Conventional drawing of Thomson’s setup in the 2nd experiment. Rays from the cathode ( C ) pass through a slit in the anode ( A ) and through a slit in a grounded metal stopper ( B ) . An electrical electromotive force is established between aluminium home bases ( D and E ) . and a graduated table pasted on the exterior of the terminal of the tubing measures the warp of the beams.
In 1897 Thomson described his experiments carried out to find the ratio of charge to mass of the atoms doing up the cathode rays. Thomson is credited with the finding that cathode beams ( “electrons” ) are particulates. He besides found that the atoms that constituted the cathode beams were the same no affair what the composing of the cathode or the gas in the tubing. This. and the fact that the negatrons were lighter than H. the lightest known sort of affair. implied that the atom was non indivisible. J. J. Thomson won the Nobel Prize in natural philosophies for showing the particulate nature of the negatron. Interestingly. in 1937. his boy George Thomson won the Nobel Prize in natural philosophies for showing the moving ridge belongingss of the negatron.
1897: The Discoveries of Marie Sklodowska Curie and Pierre Curie In September of 1897. merely after the birth of her first girl. Marie Curie. holding already passed what we would name her doctorial modification test. sought her husband’s advice sing the topic of her Ph. D. thesis. Pierre suggested she look into the new phenomenon discovered by Becquerel. [ hypertext transfer protocol: //www. orcbs. msu. edu/radiation/radhistory/pierremariecurie. hypertext markup language ] She began by reiterating Becquerel’s experiments utilizing better electrometers ( incorporating a piezoelectric vitreous silica – Pierre and his brother Jacques had discussed piezoelectric effect ) . She confirmed that the extent of ionisation ( in air ) created by a uranium sample and therefore the strength of its radiation emanation. was relative to the sum of U in the compound and independent of its chemical province. She so decided to analyze all the elements so known and found that merely Th emitted beams similar to uranium ( a fact discovered earlier by G. C. Schmidt ) . Marie Curie so proposed the word “radioactivity” to depict the phenomenon.
Her following measure was to look into natural ores instead than restrict herself to simple compounds of U and Th. To her surprise. the radiation of some of the ores were three to four times greater than could be accounted for on the footing of merely their U and Th content. Her decision was right. The samples of ore must incorporate something even more radioactive than u or Th. She began her hunt for the new substance which. by a clear experiment. she had determined was some type of dross in the uranium ore. [ That is. when she fabricated the mineral herself out of pure substances. the mineral was no more radioactive than what was expected based on the uranium content. ] To happen the new substance she had to take the natural ore. dissolve it. divide it into its constituents and so mensurate the radiation of each constituent utilizing her electrometer. The undertaking was huge and she recruited aid from her hubby in the procedure of crunching sample after sample of uraninite ore.
They finally concentrated the extremely radioactive portion of the sample in a little residue. They decided they had found a new component since. although their sample was far from pure. it was far more radioactive than either U or Th. They called it Po ( after Poland. Marie’s native state ) . They besides found that the substance disappeared spontaneously cut downing itself to one half in a characteristic clip ( called the half life ) . During their chemical analysis they had found Po in the group of sulfides. indissoluble in acerb solutions. But so they besides found radiation in the Ba group ( Ba. Sr and Ca ) . When they eventually succeeded in dividing the radiation from Ba they found a new substance which they called Ra. Obtaining a 100 kg of residues from the pitchblende mines of Joachimstal. Czechoslovakia ( practically the merely active centre of uranium excavation at the clip ) from which the U had been already removed. Marie and Pierre land it all. by manus. dissolved it in assorted dissolvers. warming and stirring it in a research lab with no fume goons.
After two old ages they had adequate Ra in their sample to observe a alteration in the atomic weight of the substance. [ Barium has an atomic weight of 137 but their samples showed an atomic weight of 174. We now know that pure Ra has an atomic weight of 226. It took Marie 12 more old ages to bring forth a pure sample. ] By 1902 Marie had lost about 20 lbs as a consequence of the heavy labour involved in the extraction of Ra from pitchblende ores. But. she had adequate Ra to enable her to mensurate its atomic weight. She found it to be 225. about the right value. In 1903. the Curies shared the Nobel Prize in Physics with Henri Becquerel. In 1911 Marie Curie received a 2nd Nobel Prize. this clip in chemical science. for her purification of Ra metal. She is the first individual of all time to hold won the award twice.
Pierre died in a passenger car accident in 1906 but Marie lived to the age of 67. She had been badly a long clip and finally died of aplastic anaemia. [ This is a status that can be caused by overexposure to radiation ] If you look at the periodic table you’ll notice that Ra and Ca are both in Group I. They therefore portion similar chemical science. Calcium. as you know. is a bone-seeker excessively. Aplastic anaemia is a disease of the blood caused by faulty map of the blood-forming variety meats ( i. e. the bone marrow ) . Although there is no manner to cognize for certain that Marie Curie died of a radiation-induced aplastic anaemia. it is. of class. rather likely. After her decease. it was found that her research lab notebooks were strongly contaminated. Even her cookery book. at place. were radioactive 50 old ages after her decease.
1899/1900 Alpha. Beta and Gamma
Ernest Rutherford. hypertext transfer protocol: //www. orcbs. msu. edu/radiation/radhistory/ernestrutherford. hypertext markup language. a physicist from New Zealand. was working under J. J. Thompson at the Cavendish Laboratory in 1898-1899. Through a long series of experiments he realized that there were two sorts of radiation emitted from Uranium. He called them alpha and beta. the first two letters in the Grecian alphabet. In a few old ages it was concluded that beta beams were cathode beams. that is. negatrons. The precise nature of alpha atoms remained a enigma although both Rutherford and the Curies suspected they were atoms. atoms electrically charged and projected at high velocity. They besides knew they could be stopped by highly thin shields ( e. g. paper ) and were deflected to merely a little extent in a magnetic field.
In 1900. P. Villard in France had besides found an extra penetrating radiation from Uranium. This radiation was non alpha nor beta. but more penetrating than the beta atoms ; it was given the name gamma. [ It was the effects of gamma radiation that Becquerel had observed when he developed his photographic home bases. The gamma beams are perforating plenty to both do it out of the solid U salts. and through the paper. ] The figure below. taken from the Ph. D. thesis of Marie Curie. shows the behaviour of the ?. ?. and ? beams in a magnetic field. Over the following few old ages many experiments were carried out to find the exact nature and behaviour of these beams.
What is this “radioactivity” ? The first usage of the word “radioactivity” appeared in an 1899 publication by the Curies. But the exact nature of radiation stumped everyone. The emanations did non look to be affected by temperature or province. That is. the perforating Becquerel beams were observed whether the Uranium was in a solid ball or in a het solution. The emanations could alter the colour of glass. they could fire tegument. and they could make heat. Finally it was noted that the emanations were non restricted to Uranium. Radium or Polonium. They were found. to some extent in rain. dirt. and air. To do it more confusing. some elements showed the same rate of emanation ( i. e. “activity” ) while others appeared to diminish harmonizing to a specific half life. [ We now know that all radioactive elements decay with a specific half life.
Those with highly long half-lives merely appeared to be disintegrating at a changeless rate. ] Data to see were supplied by both physicists and chemists. Crookes discovered in 1900 that if Fe hydrated oxide was precipitated in a uranyl salt solution. all the radiation went into the precipitate. and the U remained inactive. However. after a few yearss the precipitate lost its activity. and the U reacquired it. Similar phenomena occurred in other radioactive substances on different clip graduated tables – sometimes hours. sometimes proceedingss.
There were many theories put frontward to explicate the phenomenon of radiation. Becquerel at foremost proposed that radiation was a signifier of delayed phosphorescence. This was proved wrong since some things that did non exhibit phosphorescence were shown to be radioactive. Crookes. the discoverer of the Crookes tubing. idea that energy is extracted from fast traveling air molecules. This was disproved by carry oning experiments in a vacuity. Marie Curie proposed that all infinite is invariably traversed by X raies which are merely absorbed by heavy elements. This theory was tested ( and disproved ) in a mineshaft. Rutherford and Soddy ( a chemist at McGill with Rutherford ) proposed that radiation emanations are the consequence of the self-generated transubstantiation of one component to another.
This theory was right and Rutherford finally won the 1908 Nobel Prize ( in chemical science ) for his presentation of this. However. this theory fundamentally said that the atom is non an indestructible unit. as antecedently believed! The Structure of the Atom It was the find and probe of the phenomenon of radiation that led to our present apprehension of the basic construction of the atom. By 1900 it was known that negative charge is carried by the negatron. It was besides known that the negatron makes up an highly bantam fraction of the mass of the atom. The inquiry was: how is the mass and charge distributed in an atom? J. J. Thompson proposed one theory which is called the “plum pudding model” . He postulated that the bantam negative negatrons are dotted about the really monolithic karyon like plums or raisins in a bar. [ The British plum pudding would be referred to as a bar in North America. ]
