Antiproton
|
Antiproton (p - ) |
|
|---|---|
| classification | |
|
Fermion Hadron Baryon Nucleon |
|
| properties | |
| electric charge | −1 e (−1.602 · 10 −19 C ) |
| Dimensions | 1.672 621 923 69 (51) 10 −27 kg 1836.152 6736 (23) m e |
| Resting energy | 938.272 MeV |
| magnetic moment | −2.792 847 3441 (42) μ N |
| Spin parity | 1/2 - |
| Isospin | 1/2 (z component −1/2) |
| Interactions |
strong weak electromagnetic gravitation |
|
Quark composition |
1 anti-down , 2 anti-up |
The antiproton is the antimatter - particle ( antiparticle ) to the proton . It has the same mass as the proton (mass-proton / mass-antiproton = 1,000,000,000,001 (69)) but has a negative charge.
Antiprotons are part of cosmic rays . They do not occur naturally on earth and can only be produced artificially in particle accelerators ; other antiparticles, namely the anti neutrino and the positron, are also formed in nature during beta decays .
Antiprotons were first artificially generated in 1955 at the Bevatron in the Lawrence Berkeley National Laboratory with a proton beam of 6.3 G eV that hit a copper target . The energy available with this projectile energy in the center of gravity is just enough to generate nucleon pairs (proton and antiproton), so that the antiproton only moves slowly. The magnetic deflection of the particles made it possible to “sort out” the antiprotons. The impulse and velocity analysis in two scintillation counters showed that negatively charged particles with proton mass had arisen; the meson background was suppressed by suitable coincidence circuits . Contrary to expectations, the antiproton does not annihilate with a proton in photons , but several free pions are generated.
In 1959 Emilio Segrè and Owen Chamberlain received the Nobel Prize in Physics “for their discovery of the antiproton”. Clyde E. Wiegand and Thomas Ypsilantis were also involved in the experiment .
For the Study of antiprotons used at CERN of the storage ring Antiproton Decelerator . A facility for antiproton research, called the Facility for Antiproton and Ion Research (FAIR), is under construction at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt .
One application of the antiprotons could be in antiprotonic stereography , which would enable radiation therapy to be carried out much more efficiently. However, generating an antiproton beam is considerably more complex than generating a proton beam. So far (2019) only a few accelerators worldwide are able to do this.
The antiproton forms the core of the simplest anti- atom : anti-hydrogen .
literature
- O. Chamberlain et al .: Observation of Antiprotons . In: Phys. Rev. Band 100 , 1955, pp. 947-950 (English, original publication from 1955).
- O. Chamberlain: Chamberlain Nobel Prize Speech from 1959: The first work on the antiproton . In: Physical sheets . 1961, p. 61 .
Web links
Individual evidence
- ↑ CODATA Recommended Values. National Institute of Standards and Technology, accessed July 8, 2019 . Proton mass in kg . The numbers in brackets denote the uncertainty in the last digits of the value; this uncertainty is given as the estimated standard deviation of the specified numerical value from the actual value.
- ↑ Masaki Hori et al .: Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio . In: Nature . tape 475 , no. 7357 , July 28, 2011, p. 484-488 , doi : 10.1038 / nature10260 .
- ↑ [pdg.lbl.gov/2019/listings/rpp2019-list-p.pdf Particle Data Group 2019]
- ↑ S. Ulmer, C. Smorra, A. Mooser, K. Franke, H. Nagahama, G. Schneider, T. Higuchi, S. Van Gorp, K. Blaum, Y. Matsuda, W. Quint, J. Walz, Y. Yamazaki: High-precision comparison of the antiproton-to-proton charge-to-mass ratio . In: Nature . tape 524 , no. 7564 , August 2015, p. 196–199 , doi : 10.1038 / nature14861 .