[ { "id": "authors:0zdq4-hqq26", "collection": "authors", "collection_id": "0zdq4-hqq26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:ROOpr61b", "type": "article", "title": "Photodissociation of complex nuclei at energies between the mesonic threshold and 1150 Mev", "author": [ { "family_name": "Roos", "given_name": "Charles E.", "clpid": "Roos-C-E" }, { "family_name": "Peterson", "given_name": "Vincent Z.", "clpid": "Peterson-V-Z" } ], "abstract": "The photodisintegration of complex nuclei by gamma rays up to 1150 Mev has been studied by exposing nuclear emulsion to bremsstrahlung from the CalTech electron synchrotron and observing the \"photostars\" produced. Exposures were made at 16 different peak energies between 250 and 1150 Mev. Nearly 10 000 photostars were analyzed for star frequency, prong number, angular distribution, and (at 1143 Mev) the visible energy release per star. The bremsstrahlung yield of multiprong (\u22652 prong) stars increases abruptly as photons capable of producing pions are included. The cross section per photon, derived from the bremsstrahlung yield by the photon difference method, is essentially constant at 250 microbarns/nucleon at all energies above 300 Mev. A model for photostar production is given which involves photopion production followed by absorption or scattering of the pion and recoil nucleon. Experimental free-nucleon photopion cross sections are used, together with the Monte Carlo calculations of Metropolis et al., to determine the probability for star formation. Good agreement with both the shape and magnitude of the excitation curve is obtained if nuclear motion is included. Mean and maximum prong numbers for photostars are the same as for stars produced by pions or protons of equal available energy. The mean-free-paths in nuclear matter of pions and protons are short, so that photostar yields are a measure of the integrated total photomeson cross section. More than 95% of the multiprong stars made by 1-Bev bremsstrahlung are made by photons whose energies exceed the pion production threshold of 150 Mev. Most of the 1-prong events are produced by photons below 150 Mev, and the yield is consistent with giant resonance (\u03b3, p) reactions plus \"pseudodeuteron\" photodisintegration, a process whose cross section rapidly decreases as the photon energy increases. Variation of mean prong number with energy and comparison with nuclear cascade calculations suggests that the excitation of the residual nucleus is nearly constant at 100 Mev over a wide range of incident photon energies. The visible energy release per photostar shows a linear dependence on prong number, and more than half of the photon energy is carried away by neutral particles.", "doi": "10.1103/PhysRev.124.1610", "issn": "0031-899X", "publisher": "Physical Review", "publication": "Physical Review", "publication_date": "1961-12-01", "series_number": "5", "volume": "124", "issue": "5", "pages": "1610-1622" }, { "id": "authors:59tke-bex27", "collection": "authors", "collection_id": "59tke-bex27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MALpr61", "type": "article", "title": "Polarization of the recoil proton from \u03c00 photoproduction in hydrogen", "author": [ { "family_name": "Maloy", "given_name": "J. O.", "clpid": "Maloy-J-O" }, { "family_name": "Salandin", "given_name": "G. A.", "clpid": "Salandin-G-A" }, { "family_name": "Manfredini", "given_name": "A.", "clpid": "Manfredini-A" }, { "family_name": "Peterson", "given_name": "V. Z.", "clpid": "Peterson-V-Z" }, { "family_name": "Friedman", "given_name": "J. I.", "clpid": "Friedman-J-I" }, { "family_name": "Kendall", "given_name": "H.", "clpid": "Kendall-H" } ], "abstract": "The D3/2 nature of the second resonance in neutral single pion photoproduction, \u03b3+p\u2192p+\u03c00, suggested by Peierls, has been confirmed by additional experimental observations of the polarization of the recoil proton over a range of photon energies. The photon energy dependence of the polarization at 90\u00b0 c.m. is in substantial disagreement with alternative models suggested by Stoppini and Pellegrini, and Landovitz and Marshall if the observed angular distributions are also considered. An experimental method using nuclear emulsion as scatterer-detector, in conjunction with a magnetic spectrometer, is shown to have both good energy resolution and reasonable counting rate.", "doi": "10.1103/PhysRev.122.1338", "issn": "0031-899X", "publisher": "Physical Review", "publication": "Physical Review", "publication_date": "1961-05-15", "series_number": "4", "volume": "122", "issue": "4", "pages": "1338-1340" }, { "id": "authors:znmey-3zz79", "collection": "authors", "collection_id": "znmey-3zz79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-101018408", "type": "article", "title": "Photoproduction of Positive Mesons from Hydrogen: Results", "author": [ { "family_name": "Bacher", "given_name": "R. F.", "clpid": "Bacher-R-F" }, { "family_name": "Keck", "given_name": "J. C.", "clpid": "Keck-J-C" }, { "family_name": "Peterson", "given_name": "V. Z.", "clpid": "Peterson-V-Z" }, { "family_name": "Teasdale", "given_name": "J. G.", "clpid": "Teasdale-T-G" }, { "family_name": "Tollestrup", "given_name": "A. V.", "clpid": "Tollestrup-A-V" }, { "family_name": "Walker", "given_name": "R. L.", "clpid": "Walker-R-L" }, { "family_name": "Worlock", "given_name": "R. M.", "clpid": "Worlock-R-M" } ], "abstract": "The center-of-mass differential cross section for photoproduction of positive pions from hydrogen has been measured by the methods described in the two previous abstracts, in the angular range 40\u00b0 to 150\u00b0, for photons from 220 to 475 Mev. (Photon energies refer to the Laboratory System.) Results obtained by the two methods are in essential agreement. At 90\u00b0, d\u03c3/d\u03c9 has a maximum of 2.7 X 10^(-29) cm^2/sterad near 280 Mev and falls by a factor 5 at 450 Mev. The maximum in the excitation curve is even more pronounced at larger angles, but less pronounced at smaller ones. At 40\u00b0 (c.m.) the peak occurs near 350 Mev and at 450 Mev the cross section has decreased only to 0.7 the, peak value. Angular distributions in the center-of-mass system show a marked assymetry about 90\u00b0, which changes character from low energy to high. Below 325 Mev, there ii a backward maximum, whereas above 375 Mev, there is a forward maximum. The total cross section reaches a maximum near 290 Mev and decreases by about a factor 3 at 450 Mev. The results below 300 Mev agree with the data already reported from Berkeley and Cornell.", "issn": "0031-899X", "publisher": "American Physical Society", "publication": "Physical Review", "publication_date": "1953-06-15", "series_number": "4", "volume": "90", "issue": "4", "pages": "1090-1091" }, { "id": "authors:mqdx0-aq320", "collection": "authors", "collection_id": "mqdx0-aq320", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:NEHpr53", "type": "article", "title": "Fluctuations and latitude effect of cosmic rays at high altitudes and latitudes", "author": [ { "family_name": "Neher", "given_name": "H. V.", "clpid": "Neher-H-V" }, { "family_name": "Peterson", "given_name": "V. Z.", "clpid": "Peterson-V-Z" }, { "family_name": "Stern", "given_name": "E. A.", "clpid": "Stern-E-A" } ], "abstract": "Using a newly developed ionization chamber, which transmits its information by radio, simultaneous balloon flights were made from widely separated stations in the summer of 1951. Bismarck, North Dakota (geomagnetic latitude, \u03bbm, 56\u00b0N) was used as a base station. Four flights were made from shipboard going north from Boston and five were made from Thule, Greenland (\u03bbm=88\u00b0N), simultaneous with those at Bismarck. In all, 28 successful flights were made by the two expeditions. In seeking to determine the geomagnetic effects on the low energy primaries, considerable information was gathered on the radiation that fluctuates from day to day. The following are the chief experimental findings together with some of the conclusions that may be drawn.\n\n(1) The fluctuations in the primary radiation at 90 000 feet were as much as 10 percent in a few days. (2) These were simultaneous (except as noted in the text) and very close to the same amount at the two stations. (3) The magnitude of the fluctuations at high altitudes was considerably larger than the geomagnetic effect between Bismarck and Thule. (4) The radiation that fluctuated contained both high (> 15 Bev/c) momentum and low (down to 1.5 Bev/c) momentum particles. (5) There was a good correlation between the fluctuations in the radiation at high altitudes and the fluctuations in the neutron and meson components at ground level. (6) The fact that no particles fluctuated at Thule that did not also fluctuate at Bismarck leads us to conclude that there are few, if any, low energy particles coming in at Thule that are not also present at Bismarck, otherwise they too would be expected to vary. (7) From the manner in which the fluctuating radiation is absorbed in the atmosphere, it is concluded that the fluctuations cannot be due to heavy primaries alone. Rather it appears that the particles that fluctuate are of the same nature as the other incoming particles but have somewhat less energy per particle. (8) Varying magnetic fields of the geomagnetic axially symmetrical type are discarded as being able to produce the kind of fluctuations observed. A more satisfactory mechanism appears to be varying electric fields. (9) There was a negative latitude effect in the total ionization at intermediate altitudes (30 000 to 50 000 feet) at high latitudes. This we attribute to the greater importance of \u03bc-meson decay in the warmer air of the stratosphere which exists at the more northerly latitudes. The temperature coefficient arrived at is -0.19 percent \u00b0C-1. (10) There was a positive latitude effect in the total ionization above 60 000 feet at high latitudes. Evidence is presented to show that this is not likely to be due either to atmospheric effects or to low energy particles admitted by the earth's magnetic field above 66\u00b0N. We attribute this increase to the shadow effect of the earth. (11) The absence of particles with momenta in the range 1.5 to 0.6 Bev/Zc (0.8 to 0.14 Bev for protons), shown by (a) a lack of increase of ionization at very high altitudes between geomagnetic latitudes 58\u00b0 and 66\u00b0N, (b) the absence of an increase of area under the ionization-depth curve at latitudes north of \u03bbm=58\u00b0N, and (c) the absence of any particles that fluctuate at Thule that do not also fluctuate at Bismarck, indicates a cutoff of the primary particles. (12) This cutoff we attribute to a general solar magnetic field. The magnetic moment required is 0.65\u00d710^34 gauss-cm3 corresponding to a field at the solar equator of 19 gauss. (13) Any diurnal effect on cosmic rays due to such a magnetic moment would normally be hidden by the daily fluctuations of the primary particles.", "doi": "10.1103/PhysRev.90.655", "issn": "0031-899X", "publisher": "Physical Review", "publication": "Physical Review", "publication_date": "1953-05-15", "series_number": "4", "volume": "90", "issue": "4", "pages": "655-674" } ]