EYAL'C- \TION OF TELEMETRY RECORDS RECEIVED

Transcription

1 j 1 AS -SR-El ?- EYAL'C- \TON OF TELEMETRY RECORDS RECEED FROM EXPLORER \- 1ND POXEER Y THE UNERSTY OF CHCAGO LABORATORES FOR APPLED SCENCES

2 LAS-SR-El85 Otober 196 EALUATON OF TELEMETRY RECORDS RECEED FROM EXPLORER AND PONEER d- National Aeronautis and Spae Administration sp Contrat No. NASw-15) APPLED SCFN- 6 South Drexel Avenue Chiago 7, llinois

3 FOREWORD This is the fourth bi-monthly progress report under National Aero- nautis and Spae Administration Contrat No. NASw- 15, "Evaluation of Telemetry Reords reeived from Explorer and Pioneer, E185, and overs the period 1 July to 1 August 196. LAS Task The following personnel, both from the Laboratories for Applied Sienes and the Enrio Fermi nstitute for ulear Studies, ontributed to this program during the reporting period: J. A. Simpson, Peter Meyer, Marstan Case, C. Y. Fan, and Christine Gloeklery &- lf8.o /'*#. Respetfully submitted, Laboratories for Applied Sienes C. Y. Fan Senior Physiist Approved: * Assoiate Diretor Frank E. Bothwell $- Diretor LAS-SR-E185- iii

4 TABLE OF CONTENTS Page 1. EXPERMENTAL ARRANGEMENT EXPERMENT WTH ENERGY 5 5 KE EXPERMENT WTH ENERGY 5 KE. 5 LAS-SR-E185-

5 LST OF FGURES Figure 1. Projetional iew of Half of Payload Surfae - - Page Counting Rates of Central Counter in Proportional Counter Telesope..... Counting Rates for Payload Bombarded with X-Rays Along Equatorial Region.... Energy Loss of One 1-Mev Eletron vs. l/os , 1 Mev Eletrons along the Equatorial Region Maximum Counting Rates Produed by Eletrons of arious Energies Bombarding along the Equatarial Zone * Counting Rate of Center Counter of Proportional Counter Telesope as Funtion of Eletron Flux Bombarding sotropially over Pa-yload.... io US-SR-El85- vii

6 1. EXPERMENTAL ARRANGEMENT n order to determine the effiieny of the proportional ounter telesope in ounting bremsstrahlung, the bakup payloads of Explorer and Pioneer were taken to High oltage Engineering Corporation on 1 June 196. High oltage Engineering Corporation made two -Mev eletron aelerators available for the experiment in whih the low-energy limit of an external eletron beam was found to be.5 Me, determined by the absorption of the aluminum window ( mg/m ). The beam was well foused at the window so that the x-ray bakground produed at the walls inside of the aelerator was redued to not more than a few perent of the signal produed by the external b eam. The payload, whih is of the shape of an oblate spheroid, with all the sientifi apparatus exept the sintillation ounter of STL distributed on the "equatorial plane, was mounted in suh a way that it ould rotate about the spin axis (the axis perpendiular to the equatorial plane) and about a diameter in the equatorial plane. With a horizontal-beam aelerator, any part of the surfae ould be brought under diret bombardment of eletrons by two rotations. The shaded pathes of Fig. 1 are a projetional view of the portions of half of the payload surfae, seleted for the bombardment of the eletron beam, whih form lattie points at approximately every 5. For eah bom- bardment, the ionization pulse rate of the ion hamber and the ounting rates Figure 1. Projetional iew of Half of Payload Surfae LAS - SR- E

7 of the singles hannel of the proportional ounter telesope, the sintillation ounters, and the GM ounter were then separately monitored for interompari s on. The way in whih the experiment was performed differs in two respets from operation in spae: (1) there were absorption and sattering by air inside of the payload, and () the eletron beam was unidiretional. These are two of the fators whih prevent an aurate omparison of the laboratory experiment with the measurement in spae.. EXPERMENT WTH ENERGY 5 5 KE The shell of Explorer is made of aluminum of 17 mg/m. t is thik enough to stop eletrons of energy < - 5 Kev. The response of a radia- tion detetor to these eletrons inside of the payload is thus totally due to the bremsstrahlung produed in the shell. The ontribution from different parts of the shell for an equal flux of eletrons will be approximately proportional to the inverse square of the distane to the detetor from the irradiated area on the shell. For experimental onveniene, an aluminum absorber in. in diam- eter and. in. thik was plaed in lose ontat with the payload shell and the experiments were performed with the bremsstrahlung thus produed. Figure shows a plot of the ounting rates of the entral ounter in the - proportional ounter telesope per 1 pa eletron beam vs. the inverse squares of the distanes from the absorber to the detetor where the payload positions have been hosen to minimize the absorption in between them. The relation is approximately linear. Figure shows the ounting rates per payload was bombarded with x-rays along the strongly peaked response in the neighborhood pa beam urrent when the equatorial region. The of the proportional ounter tele- sope reflets the absorption by the distributed masses on the equatorial plane. Beause of the omplex onfiguration of the payload, the response of the entral ounter in the ounter telesope to the bombardment over the entire payload by a steady eletron flux of energy E < 5 Kev is done only for the following simplified division of the payload shell: (1) an equatorial zone LA S- SR- E

8 6 ; C U P 5 l C; 5 5 Kev 5 Kev 5 Kev 8 16 G, L. L. E m u m - v, -.. () u nverse Squares of Distanes from Absorber to Detetor, - (m- x L Figure. Counting Rates of Central Counter in Proportional Counter Telesope LA S- SR- E

9 6?, i C U i C " : i C P 5 Kev 5 Kev 5 Kev i i i \ i L d w i. L E m k n,' 9 8, \ h C.d -_ Degrees along the equator of Explorer, Figure. Counting Rates for Payload Bombarded with X-Rays along Equatorial Region LAS-SR-E185-

10 of height 16 m for whih the response urve an be represented by Fig. and,() the remaining portion for whih the response is inversely proportional to the square of the distane to the ounter from an irradiated area on the shell. By using Fig. and Fig., the response an readily be alulated. The result is given in the following table: Table 1 Counting Rate / to-'pa/ m =Energy (Kev) Counting Rate/ io-'pa/ m over the whole payload X io 6 X io 18 X O. EXPERMENTS WTH ENERGY - > 5 KE One of the important differenes between the present experiment and what atually happened in the radiation belts is that in the radiation belts the eletron flux was nearly isotropi while in the present experiment the eletron beam is unidiretional. For eletrons of energy - < 5 Kev this dif- ferene, as we have already seen, is not signifiant. For eletrons of energy > 5 Kev, on the other hand, the response of a detetor to a unidiretional beam will be expeted to be signifiantly different from that to an isotropi flux sine eletrons an then penetrate through the shell of the payload and the energy required for the penetration depends upon the angle between the momentum vetor of the eletrons and the normal to the payload surfae. Figure shows a plot of the energy dissipation in the payload shell by one -Mev eletrons at various angles of bombardment. When 8 > 6O', the eletron will be absorbed in the shell. S an then be shown that for an isotropi flux about 7% of the energy of 1-Mev eletrons is onverted into x-rays in the payload shell while for a vertially inident eletron beam, only 7 of the energy is dissipated. The surfae density of the payload in the equatorial zone (16 m high) is appreiably higher than the other portions sine: (1) only the equatorial zone is lined with honeyomb material 15 mg/m and () there were sien- tifi equipments attahed on many portions of the zone. The average surfae density was approximately mg/ rm. Consequently, the ounts of the LAS-SR-E

11 >. B si m -.5 k k Q, E: W....1 is the angle between the momentum vetor of the eletron and the normal of the payload surfae. 1 i/os e Figure. Energy Loss of One 1-Mev Eletron vs. l/os8 LA S- SR-E

12 proportional ounter produed by the bombardment of eletrons of E > 1 Mev will again be due to bremsstrahlung produed in the payload surfae and thus the angular distribution of the eletrons no longer enters into the piture. - Figure 5 shows the ounting rate/io pa beam urrent produed by i-mev eletrons bombarding along the equatorial zone. dued by 1-Mev eletrons and the peak value produed by 75-Kev eletrons agree quite well with the extrapolation of the straight line determined by the peak values produed by 5, 5, and 5-Kev eletrons respetively, as shown in Fig Mev eletrons reflets the relatively high penetration of the eletrons. The surfae density,-of the rest of the payload was only 17 mg/m, - The peak value pro- The apparent deviation of the peak value produed by and thus the angular distribution of the eletron flux beomes important. How- ever, the ase in whih we are interested is an isotropi distribution and for this distribution with an eletron energy - < 1 Me, more than 77 of the energy is onverted into x-rays in the shell. Furthermore, at least half of the ounts of the proportional ounter are ontributed by eletrons bombarding the equatorial zone of the satellite over the University of Chiago pakage as it is in this zone. Therefore, for the first order approximation, one an as- sume that all the energy of eletrons of energy < i Mev was onverted into x-rays in the payload shell and thus the ounting rate/1-pa/rn over the whole payload an be alulated easily.. Within the experimental auray, it an be expressed in the following equa- tion: when E is in units of Me n =,5X1 E 9 sintillation ounter is plotted as a dotted line. The results are plotted in Fig. 7. For omparison, the same quantity for the STL LAS-SR-E185-7

13 l o 5 C Y e Q & & 1 1 o N 5 M.d U u 1 o Over the pakage lo Degrees Figure 5. 1 Mev Eletrons along the Equatorial Region 8

14 Eletron Energy - Mev. Figure 6. Maximum Counting Rates Produed by Eletrons of arious Energies Bombarding along the Equatorial Zone LAS-SR-E185-9

15 . h X U N E -Y 9 N w m k 7 Ll Q) 7 d r:.d Ll a & lo lo A ED lo ; v N E -5 u, Q, lo f + intillation Counter *.+ (d - d g k a & g C t) m Eletron Energy - Me 1.. Figure 7. Counting Rate of Center Counter of Proportional Counter Telesope as Funtion of Eletron Flux Bombarding sotropially over Payload LAS-SR-E185- io