In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles (now called electrons), which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio.^[2] Thomson is also credited with finding the first evidence for isotopes of a stable (non-radioactive) element in 1913, as part of his exploration into the composition of canal rays (positive ions). His experiments to determine the nature of positively charged particles, with Francis William Aston, were the first use of mass spectrometry and led to the development of the mass spectrograph.^[2][3]

Thomson was awarded the 1906 Nobel Prize in Physics for his work on the conduction of electricity in gases.^[4]

Education and personal life

Joseph John Thomson was born on 18 December 1856 in Cheetham Hill, Manchester, Lancashire, England. His mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran an antiquarian bookshop founded by Thomson’s great-grandfather. He had a brother, Frederick Vernon Thomson, who was two years younger than he was.^[5] J. J. Thomson was a reserved yet devout Anglican.^[6][7][8]

His early education was in small private schools where he demonstrated outstanding talent and interest in science. In 1870, he was admitted to Owens College in Manchester (now University of Manchester) at the unusually young age of 14. His parents planned to enroll him as an apprentice engineer to Sharp-Stewart & Co, a locomotive manufacturer, but these plans were cut short when his father died in 1873.^[5]

He moved on to Trinity College, Cambridge, in 1876. In 1880, he obtained his Bachelor of Arts degree in mathematics (Second Wrangler in the Tripos^[9] and 2nd Smith's Prize).^[10] He applied for and became a Fellow of Trinity College in 1881.^[11] Thomson received his Master of Arts degree (with Adams Prize) in 1883.^[10]

Family

In 1890, Thomson married Rose Elisabeth Paget. Beginning in 1882, women could attend demonstrations and lectures at the University of Cambridge. Rose Paget, daughter of Sir George Edward Paget, a physician and then Regius Professor of Physic at Cambridge at the church of St. Mary the Less, was interested in physics. She attended demonstrations and lectures, among them Thomson's. Their relationship developed from there.^[12] They had two children: George Paget Thomson, who was also awarded a Nobel Prize for his work on the wave properties of the electron, and Joan Paget Thomson (later Charnock),^[13] who became an author, writing children's books, non-fiction and biographies.^[14]

Career and researchIn 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles (now called electrons), which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio.^[2] Thomson is also credited with finding the first evidence for isotopes of a stable (non-radioactive) element in 1913, as part of his exploration into the composition of canal rays (positive ions). His experiments to determine the nature of positively charged particles, with Francis William Aston, were the first use of mass spectrometry and led to the development of the mass spectrograph.^[2][3]

Thomson was awarded the 1906 Nobel Prize in Physics for his work on the conduction of electricity in gases.^[4]

Joseph John Thomson was born on 18 December 1856 in Cheetham Hill, Manchester, Lancashire, England. His mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran an antiquarian bookshop founded by Thomson’s great-grandfather. He had a brother, Frederick Vernon Thomson, who was two years younger than he was.^[5] J. J. Thomson was a reserved yet devout Anglican.^[6][7][8]

His early education was in small private schools where he demonstrated outstanding talent and interest in science. In 1870, he was admitted to Owens College in Manchester (now University of Manchester) at the unusually young age of 14. His parents planned to enroll him as an apprentice engineer to Sharp-Stewart & Co, a locomotive manufacturer, but these plans were cut short when his father died in 1873.^[5]

He moved on to Trinity College, Cambridge, in 1876. In 1880, he obtained his Bachelor of Arts degree in mathematics (Second Wrangler in the Tripos^[9] and 2nd Smith's Prize).^[10] He applied for and became a Fellow of Trinity College in 1881.^[11] Thomson received his Master of Arts degree (with Adams Prize) in 1883.^[10]

Family

In 1890, Thomson married Rose Elisabeth Paget. Beginning in 1882, women could attend demonstrations and lectures at the University of Cambridge. Rose Paget, daughter of Sir George Edward Paget, a physician and then Regius Professor of Physic at Cambridge at the church of St. Mary the Less, was interested in physics. She attended demonstrations and lectures, among them Thomson's. Their relationship developed from there.^[12] They had two children: George Paget Thomson, who was also awarded a Nobel Prize for his work on the wave properties of the electron, and Joan Paget Thomson (later Charnock),^[13] who became an author, writing children's books, non-fiction and biographies.^[14]

Career and research<

J. J. Thomson's separation of neon isotopes by their mass was the first example of mass spectrometry, which was subsequently improved and developed into a general method by F. W. Aston and by A. J. Dempster.^[2][3]

Earlier, physicists debated whether cathode rays were immaterial like light ("some process in the aether") or were "in fact wholly material, and ... mark the paths of particles of matter charged with negative electricity", quoting Thomson.^[21] The aetherial hypothesis was vague,^[21] but the particle hypothesis was definite enough for Thomson to test.

Magnetic deflection

Thomson first investigated

Thomson first investigated the magnetic deflection of cathode rays. Cathode rays were produced in the side tube on the left of the apparatus and passed through the anode into the main bell jar, where they were deflected by a magnet. Thomson detected their path by the fluorescence on a squared screen in the jar. He found that whatever the material of the anode and the gas in the jar, the deflection of the rays was the same, suggesting that the rays were of the same form whatever their origin.^[27]

Electrical charge

While supporters of the aetherial theory accepted the possibility that negatively charged particles are produced in Crookes tubes,^{[citation needed]} they believed that they are a mere by-product and that the cathode rays themselves are immaterial.^{[citation needed]} Thomson set out to investigate whether or not he could actually separate the charge from the rays.

Thomson constructed a Crookes tube with an electrometer set to one side, out of the direct path of the cathode rays. Thomson could trace the path of the ray by observing the phosphorescent patch it created where it hit the surface of the tube. Thomson observed that the electrometer registered a charge only when he deflected the cathode ray to it with a magnet. He concluded that the negative charge and the rays were one and the same.^[19]

Electrical deflection

electrometer set to one side, out of the direct path of the cathode rays. Thomson could trace the path of the ray by observing the phosphorescent patch it created where it hit the surface of the tube. Thomson observed that the electrometer registered a charge only when he deflected the cathode ray to it with a magnet. He concluded that the negative charge and the rays were one and the same.[19] In May–June 1897, Thomson investigated whether or not the rays could be deflected by an electric field.[5] Previous experimenters had failed to observe this, but Thomson believed their experiments were flawed because their tubes contained too much gas. Thomson constructed a Crookes tube with a better vacuum. At the start of the tube was the cathode from which the rays projected. The rays were sharpened to a beam by two metal slits – the first of these slits doubled as the anode, the second was connected to the earth. The beam then passed between two parallel aluminium plates, which produced an electric field between them when they were connected to a battery. The end of the tube was a large sphere where the beam would impact on the glass, created a glowing patch. Thomson pasted a scale to the surface of this sphere to measure the deflection of the beam. Any electron beam would collide with some residual gas atoms within the Crookes tube, thereby ionizing them and producing electrons and ions in the tube (space charge); in previous experiments this space charge electrically screened the externally applied electric field. However, in Thomson's Crookes tube the density of residual atoms was so low that the space charge from the electrons and ions was insufficient to electrically screen the externally applied electric field, which permitted Thomson to successfully observe electrical deflection. When the upper plate was connected to the negative pole of the battery and the lower plate to the positive pole, the glowing patch moved downwards, and when the polarity was reversed, the patch moved upwards. Measurement of mass-to-charge ratio In his classic experiment, Thomson measured the mass-to-charge ratio of the cathode rays by measuring how much they were deflected by a magnetic field and comparing this with the electric deflection. He used the same apparatus as in his previous experiment, but placed the discharge tube between the poles of a large electromagnet. He found that the mass-to-charge ratio was over a thousand times lower than that of a hydrogen ion (H+), suggesting either that the particles were very light and/or very highly charged.[21] Significantly, the rays from every cathode yielded the same mass-to-charge ratio. This is in contrast to anode rays (now known to arise from positive ions emitted by the anode), where the mass-to-charge ratio varies from anode-to-anode. Thomson himself remained critical of what his work established, in his Nobel Prize acceptance speech referring to "corpuscles" rather than "electrons". Thomson's calculations can be summarised as follows (in his original notation, using F instead of E for the electric field and H instead of B for the magnetic field): The electric deflection is given by ${\displaystyle \Theta =Fel/mv^{2}}$, where Θ is the angular electric deflection, F is applied electric intensity, e is the charge of the cathode ray particles, l is the length of the electric plates, m is the mass of the cathode ray particles and v is the velocity of the cathode ray particles. The magnetic deflection is given by ${\displaystyle \mathrm{\varphi <!--\; \varphi \; -->}=Hel/mv}$ Thomson constructed a Crookes tube with a better vacuum. At the start of the tube was the cathode from which the rays projected. The rays were sharpened to a beam by two metal slits – the first of these slits doubled as the anode, the second was connected to the earth. The beam then passed between two parallel aluminium plates, which produced an electric field between them when they were connected to a battery. The end of the tube was a large sphere where the beam would impact on the glass, created a glowing patch. Thomson pasted a scale to the surface of this sphere to measure the deflection of the beam. Any electron beam would collide with some residual gas atoms within the Crookes tube, thereby ionizing them and producing electrons and ions in the tube (space charge); in previous experiments this space charge electrically screened the externally applied electric field. However, in Thomson's Crookes tube the density of residual atoms was so low that the space charge from the electrons and ions was insufficient to electrically screen the externally applied electric field, which permitted Thomson to successfully observe electrical deflection. When the upper plate was connected to the negative pole of the battery and the lower plate to the positive pole, the glowing patch moved downwards, and when the polarity was reversed, the patch moved upwards. In his classic experiment, Thomson measured the mass-to-charge ratio of the cathode rays by measuring how much they were deflected by a magnetic field and comparing this with the electric deflection. He used the same apparatus as in his previous experiment, but placed the discharge tube between the poles of a large electromagnet. He found that the mass-to-charge ratio was over a thousand times lower than that of a hydrogen ion (H+), suggesting either that the particles were very light and/or very highly charged.[21] Significantly, the rays from every cathode yielded the same mass-to-charge ratio. This is in contrast to anode rays (now known to arise from positive ions emitted by the anode), where the mass-to-charge ratio varies from anode-to-anode. Thomson himself remained critical of what his work established, in his Nobel Prize acceptance speech referring to "corpuscles" rather than "electrons". Thomson's calculations can be summarised as follows (in his original notation, using F instead of E for the electric field and H instead of B for the magnetic field): The electric deflection is given by ${\displaystyle \mathrm{\Theta <!--\; \Theta \; -->}=Fel/m{v}^2}$ Thomson's calculations can be summarised as follows (in his original notation, using F instead of E for the electric field and H instead of B for the magnetic field): The electric deflection is given by ${\displaystyle \Theta =Fel/mv^{2}}$, where Θ is the angular electric deflection, F is applied electric intensity, e is the charge of the cathode ray particles, l is the length of the electric plates, m is the mass of the cathode ray particles and v is the velocity of the cathode ray particles. The magnetic deflection is given by ${\displaystyle \phi =Hel/mv}$, where φ is the angular magnetic deflection and H is the applied magnetic field intensity. The magnetic field was varied until the magnetic and electric deflections were the same, when ${\displaystyle \Theta =\phi ,Fel/mv^{2}=Hel/mv}$. This can be simplified to give ${\displaystyle m/e=H^{2}l/F\Theta }$. The electric deflection was measured separately to give Θ and H, F and l were known, so m/e could be calculated. As the cathode rays carry a charge of negative electricity, are deflected by an electrostatic force as if they were negatively electrified, and are acted on by a magnetic force in just the way in which this force would act on a negatively electrified body moving along the path of these rays, I can see no escape from the conclusion that they are charges of negative electricity carried by particles of matter. — J. J. Thomson[21] As to the source of these particles, Thomson believed they emerged from the molecules of gas in the vicinity of the cathode. If, in the very intense electric field in the neighbourhood of the cathode, the molecules of the gas are dissociated and are split up, not into the ordinary chemical atoms, but into these primor As to the source of these particles, Thomson believed they emerged from the molecules of gas in the vicinity of the cathode. If, in the very intense electric field in the neighbourhood of the cat If, in the very intense electric field in the neighbourhood of the cathode, the molecules of the gas are dissociated and are split up, not into the ordinary chemical atoms, but into these primordial atoms, which we shall for brevity call corpuscles; and if these corpuscles are charged with electricity and projected from the cathode by the electric field, they would behave exactly like the cathode rays. — J. J. ThomsonThomson imagined the atom as being made up of these corpuscles orbiting in a sea of positive charge; this was his plum pudding model. This model was later proved incorrect when his student Ernest Rutherford showed that the positive charge is concentrated in the nucleus of the atom. Other work In 1991, the thomson (symbol: Th) was proposed as a unit to measure mass-to-charge ratio in mass spectrometry in his honour.[34] J J Thomson Avenue, on the University of Cambridge's West Cambridge site, is named after Thomson.[35] The Thomson Medal Award, sponsored by the Royal Society[1] on 12 June 1884 and served as President of the Royal Society from 1915 to 1920. In November 1927, J. J. Thomson opened the Thomson building, named in his honour, in the Leys School, Cambridge.[33] Posthumous honours In 1991, the thomson (symbol: Th) was proposed as a unit to measure mass-to-charge ratio in < In November 1927, J. J. Thomson opened the Thomson building, named in his honour, in the Leys School, Cambridge.[33] In 1991, the thomson (symbol: Th) was proposed as a unit to measure mass-to-charge ratio in mass spectrometry in his honour.[34] J J Thomson Avenue, on the University of Cambridge's West Cambridge site, is named after Thomson.[35] The J J Thomson Avenue, on the University of Cambridge's West Cambridge site, is named after Thomson.[35] The Thomson Medal Award, sponsored by the International Mass Spectrometry Foundation, is named after Thomson. The Institute of Physics Joseph Thomson Medal and Prize is named after Thomson.