Lofgren, E J

English

eScholarship - University of California

Lawrence Berkeley National LaboratoryLBL PublicationsTitleMeeting XVI Bevatron Research ConferencePermalinkhttps://escholarship.org/uc/item/6k36t7rcAuthorLofgren, E JPublication Date1954-04-01Copyright InformationThis work is made available under the terms of a Creative Commons Attribution License, available at https://creativecommons.org/licenses/by/4.0/eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaDISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. • P' J./ MEETING XVI BEVATRON RESEARCH CONFERENCE April l.'r, 19 54 4 PM .Auditorium, Bldg. 51 E. J. Lofgren; Bevatron Operation UCRL - 2554 B - 25 The occurence of a fault April 7 caused a short in the stator vlinding of one of the main generators. Repairs will require at least one month and the total time the generator will be down can be determined only after a further inspection of the damage. In a week or tvvo? after a thorough inspection of the genera tor and the igni tron system, Bevatron operation will be continued on one generator. Luis Alvarez~ Devatron Targets Since the targets of use in a Bevatron experiment will depend greatly on the nature of tho experiment and the tecm1iques to be employed the ideas presented here relate primarily to tho area of research which involves the detection with counters of heavy mesons emitted in the backward direction in the laboratory system. These mesons and their decay products have low kinetic energy over the entire range of Bevatron energies above threshold for production. For this reason discrimination by means of momentum resolution collimating slits, ionization density and range will be possible. Thread Targe~ A thread of diameter O.OIH suspended vertically in the beam for about 0.1 second is equivalent to ·about 12 g/cm2 of material because the beam passes through the thread many times with s;.1a1l average energy loss on each traversal. The total average energy loss of about 20 Iilev; spread out ever many revolutions$ is easily me.de up by the (L' acceleration. The follov1ing ar:=;ument indicates that the effect oi multiple coulomb scatterin:~ is not important. The mean square scattering angle of a charged particle passing through matter is proportional to the matter traversed divided by the square of the product of the momentum and the velocity of the particle. 'l'he proposed threac. target has about 103 times as many atoms as the residual gas in the path o£ the be~n. But the factor (p~)2 increases by a factor of about 105 with acceleration from 10 Hev to 6 Bev. Therefore, even for allowance for the reduction in use:ul aperture, the effect of the small target on the beam after acceleration should be no more serious than gas scattering near injection. Ice Cube Target A pure hydrogen "ice cube 11 about 3 ·mm across dropped throu~.;h the beam would have about the same effect as the thread target previously described. It would have the additional advantage of ~roviding a pure target. The solid hydrogen would evaporate quickly and could probably be pumped out without seriously affecting Bevatron operation, although the cube could be removed through a trap door if . necessary. :a: · -~targets described have several obvious advantages for the particular type of experiment considered. 1), The large duty cycle permits higher average counting rates. 2) The small thickness permits low energy particles to escape from the target. • (2~ UCRL - 2554 J) The small source size permits higher momentum resolution of reaction products. Detection efficiencies can be improved by placing counters inside the vacuum chamber, as close as possible to the target. In order to reduce background: the counters could be turned on while the bunched beam is around on the other side of its orbit. The decay of It-mesons coming eventually from the heavy mesons from the target could be detected during this delayed time interval of a small fraction of a micro-second. In order to work in closer to the source of heavy mesons, a large magnet consist-ing of two dipole units located in a straight section could be moved in and out of the beam about once every six seconds in synchronism with the acceleration. To first order, there would be neither deflection nor displacement of the beam passing through the magnet; but a counter and target assembly moving or fixed near the magnet would permit close range observation of reaction products in a variable magnetic field. ---·Beam ) \ -~-~. ~ I / / '-...... / ·------~· ~-------------------This magnet would weigh about 25 tons and would probably be driven externally with simple harmonic motion as it moved in and out on tracks. Burton Moyer; Proposed Experiment-s on 11° Mesons and other Photon Emitting Events The efficient detection of high energy photons, preferably with GOOd energy resolution would be useful for study of the nO meson itself, for the detection of other particles which decay into the no, and for obtaining the energy spectrum of neutral mesons produced in hiGh energy nuclear encounters. In the center of mass system of two interacting nucleons about 2 Bev energy is available for meson produc-tion. The expected pion distribution has an expected maximum at about 0.5 Bev in the center of mass system (or possibly at even· lower energy). The determination of the important features of this distribution requires the detection of photons of energies up to 2 - 3 Bev over ~ angular range of 0 - 900 with respect to the direction. of the accelerated beam. · The large spiral orbit magnet could be used as a pair spectrometer. It has the feature that electrons and positrons; emitted forward from a convertor on the edge of the field, are bent so that they leave the field normally. Variation of energy & ' '. I " (3) UCRL - 2554 resolution around the circumference can be calculated or corrected by varying the geometry of the detectors. A 1.5 Bev electron is deflected 26° in a field of 20 kilogauss, in the 40-inch magnet. Another possible photon detector is a large ceronkov detector made of heavy glass with a high index of refraction. iiith essentially all tho photon energy dissipated in an oloctrori shower in the glass, tho light pulse given out is a good measure of the primary photon energy. 5 t.o 10% energy resolution is not out of the question for the high energy photons with which we arc here concerned. Heavy mesons and hyperons which decay into nO mesons with half lives of the order of lo-9 seconds can be studied with photon detectors. Possible reactions of interest are~ p + N + go + p V0 ----~ n + n° eo -----) no + no v+ ----~ p + no ,., ----~ n.::_ + no + nO A proposed experiment is as follows: Beam Particles from the target decaying to the right of line XY may emit photons which are detected by the counter array in coincidences BCD-A. Pairs are formed in the converter. Anti-coincidence counter A eliminates the effects of charged particles. The converter material is varied to eliminate effects duo to neutrons. ..... I • i ;::-; 5 em : ! . L-i y ' o....=o A Converter :a:xr:zz o:::::::::o B D.----; ~ C 

Meeting XVI Bevatron Research Conference

https://escholarship.org/content/qt6k36t7rc/qt6k36t7rc.pdf?t=sgzvf9

Meeting XVI Bevatron Research Conference

Abstract

Similar works

Full text

Available Versions

eScholarship - University of California