Operation Tumbler Snapper, Report to the Test Director, Test of Scintillator Optical-Path Technique (Deleted)

Page 2

OPERATION TUMBLER SNAPPER Report to the Test Director Test of Scintillator Optical-Path Technique Naval Research Laboratory This is an extract of WT-567, Operation TUMBLER SNAPPER. Extracted version prepared for DEFENSE NUCLEAR AGENCY

Page 3

Destroy this report when it is no longer needed. Do not return PLEASE NOTIFY THE DEFENSE NUCLEAR AGENCY, ATTN: STTI, WASHINGTON, DC 20305-1000, IF YOUR ADDRESS IS INCORRECT, IF YOU WISH IT DELETED FROM THE DISTRIBUTION LIST,OR IF THE ADDRESSEE IS NO LONGER EMPLOYED BY YOUR ORGANIZATION.

Page 4

REPORT DOCUMENTATION PAGE - OM1) NO. 0704-0188 gap. Dar.: ho 30, 1986 3 DISTRIBUTION i AVAILABILITY OF REPORT Approved for public release; distribution I PERFORMING ORGANIZATION REPORT NUMBER(S) 5. MONITORING ORGANIZATION REPORT NUMBER(S) Defense Atomic Support Agency 7b ADDRESS (City, State, and ZIP Code) k. NAME OF FUNDING t SPONSORING 8b OFFICE SYMEOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER PROGRAM PROJECT TASK ELEMENT NO NO NO I1 TITLE (fnc/udo Secunty Chs/ficatronJ OPERATION TUHBLER SNAPPER, Report to the Test Director,Test of Gcintillator Optical-Path Technique, Extracted Version 13a TYPE OF REPORT 16 SUPPLEMENTARYNOTATlON This report has had sensitive military information removed in order to provide an unclassified version for unlimited distribution. The work was performed by the defense Nuclear Agency in support of the DOD Nuclear Test Personnel Review Program. 17 COSATI CODES 18 SUBJECT TERMS (Conttnue on reverse If necessary and #dent@ by bloc& numberJ FIELD GROUP SUE-GROUP Tumbler Snapper LU 6 Optical Measurements Experiments were conducted to determine the feasibility of a technique employing scintillators 1ear the device in conjunction with remote photosensitive detectors for measurements Of meaction history to be conducted on Mike Shot of Operation Ivy, and to determine the maximum Iamma-ray intensity and total dosage at which scintillators could be employed. The principal objectives of these tests were to: (1) determine the maximum gamma-ray intensity and total iosage at which scintillators could be employed; and (2) determine the feasibility of and lbtain field experience in the employment of a scintillator-remote photosensitive detector technique with the optical-patch problems involved. This included the test of new types of equipment proposed for use on Ivy. All other edmons are obsolete.

Page 6

Classified material has been removed in order to make the information available on an unclassified, open publication basis, to any interested parties. The effort to declassify this report has been accomplished specifically to support the Department of Defense Nuclear Test Personnel Review (NTPR) Program. The objective is to facilitate studies of the low levels of radiation received by some individuals during the atmospheric nuclear test program by making as much information as possible available to all interested parties. The material which has been deleted is either currently classified as Restricted Data or Formerly Restricted Data under the provisions of the Atomic Energy Act of 1954 (as amended), or is National Security Information, or has been determined to be critical military information which could reveal system or equipment vulnerabilities and is, therefore, not appropriate for open The Defense Nuclear Agency (DNA) believes that though all classified material has been deleted, the report accurately portrays the contents of the original. DNA also believes that the deleted material is of little or no significance to studies into the amounts, or types, of radiation received by any individuals during the atmospheric nuclear test program.

Page 7

Report to the Test Director TEST OF SCINTILLATOR OPTICAL-PATH Originally Issued as Report NRL-4158 Naval Research Laboratory

Page 8

Experiments were conducted to determine the feasibility of a technique,employing scintillators near the device in conjunction with remote photosensitive detectors for measurements of reaction history to be conducted on Mike shot of Operation Ivy and to determine the maximum gamma-ray intensity and total dosage at which scintillotors could be employed. Insufficient data were obtained to predict accurately the behavior of scintilIators at high gamma intensities; however, it was unequivocally determined that the technique would not be suitable for Ivy measurement& For the technique to be acceptable a sufficient signal was required from the detectors to cover a wide dynamic range (four orders) of measurements. Since the Teller light wae down in magnitude from the scintillatot light by not more than about two orders, it would have been necessvy to shield the optical path to have sufficient dynamic range. This shielding would have been prohibitively expensive. The signal obtainable at the recording station would have required the use of high-gain photomultipliers and amplifiers throughout the system. In addition, the signal, ,was unpredictable, with unknown spuriour background signals. It was highly improbable that the minimum required data could have been obtained for the Ivy Mike shot.

Page 9

This report contains the scintillator optical-path experiment8 report, in uihich a proposed technique for use on the Mike phase of forthcoming Operation Ivy was tested and found unsatisfactory. These experimenta were performed’during the Tumbler-Snapper series of tests in the spring of 1952 by the Radiation Division of the Naval Research Laboratory (NRL). In addition to the people haying general supervisory responsibilltier, l the following individuala were primarily rerponrible for the accomplishment of these experiments. T. A. Bergstralh Sclntillator test project leader Recording system and scintillator report Strong support was given by other members and groups of NRL and by the Los Alamos Scientific Laboratory group.* The NRL group headed by D. C. Cook, who carried out the Tumbler-Snapper alpha meaaurementa, was especially helpful during these hurried tests. l E. H. Krause and Staff, Ivy Report, Measurement of Reaction History, Vol. I, WT-620,

Page 10

Aims of the Experiment ..... Nature of the Experiment ..... 1.4.1 Gamma intensity and Intensity Relations 1.4.2 Predicted Background and Related Effects 2.1 Description of Experiments .... 2.1.2 Measurement of Gamma Rays as a Function of Time 2.4.4 hdlcators and Associated Equipment . 2.5 Results of the Scintillator Measurements . 3.2 Description of Experiment. .... 3.2.1 Nature of Experiment .... 3.3.2 Detectors and Detector Supplies . .

Page 11

4.3.4 Indicator8 and tirociated Equipment 4.4 Rerulb of the Scintillatot Msaeuremente . Scintillatot - Remote Photoeenaitive Detector Technique 1.2 Nomenclature for Sclntillator Calculatione . . 1.3 Effect of Scintillator Thkknere ..... 1.4 Fluorercence Spectrum of 0.5 Per Cent Terphenyl in Toluene . View of Propagation Path from Tower Plane Tutnine Mirror8 at Tower Base

Page 12

2.12 Front View of Recording Station Electronic Bays 2.13 935 Phototube Spectral Sensitivity ...... 2.14 935 Detector and Laarithmic Attenuator Schematic . . . Sending Mirrors and Tower Baffles ,..... Propagation Path, Baffle 2....... Pit Turning Mirrors ......... Oscfllogram, Channel 4B, Scintillator Monitor Oscillogram, Channel 5, Log-load Gamma Monitor Ml-meter Scintillator and Sending Mirror, Channel 2 . Receivfng Parabolas and Phototube Units .... Side View of Recording Electronic Bays .... 4.12, Oscillogram, Channel 38, 86-meter Sclntillator 4.15 Linearlzed Plot of 163-meter Scintillated, 4.16 Linearized Plot of 86-meter Scintillator,

Page 13

1.1 Charactepdics of Scintfflntor .... 4.3 Results of the Near Sciator - Remote Detector Measurements . .

Page 14

In planning some of the experiments for Mike shat of Operation Ivy, consideration was given to the use of a system with scintillators near the weapon. This system would replace the long runs of transmission lines by utilizing optical-path transmission of the scintillator light to a distant photosensitive detector. If such a system were feasible without extensive opttcal-path shielding, it would provide a simpler and cheaper approach to the problem. The system required that the scintillators be used at gamma-radiation levels about 10’ to lo’ times higher than that at which they had previously been used. There was no method to determine experimentally the characteristics of scintillators under such high radiation levels except by performing tests involving a nuclear weapon. This type of measurement was considered for the Greenhouse tests, but the stringent time requirements prevented it from being attempted. Arrangements were therefore made to perform feasibility tests during the Tumbler-Snapper Operation at Nevada Proving Grounds (NPG) during May 1953. Initial tests were conducted iwhich was detonated on a 300-n tower. It was believed that the results would be sufficient for experimental planning on Operation Ivy; however, the results were inconclusive. Greatly accelerated planning and buildup of experimental parts were then undertaken to perform a modified experiment and still further experiments The results of these tests indicated that the proposed method of measurements would be extremely costly and the results would be dubious. Hence the technique was abandoned ae far a8 the forthcoming Ivy tests were concerned. 1.2 AIMS OF THE EXPERIMENT The pkincipal objectivea of the Snapper-Ivy tests were to: 1. Determine the maximum gamma-ray intensity and total dosage at which scintillators could be employed. 2. Determine the feasibility of and obtain field experience in the employment of a scintillater-remote photosensitive detector technique with the optical-path problems involved. This included the tests of new types of equipment proposed for use on ivy. 1.3 NATURE OF THE EXPERIMENT Organic scintillators had been tested at low radiation levels over a fairly large temperature range.’ These tests indicated that the scintillator would continue to function properly up to a

Page 15

temprature of WC or higher. The measurements were stopped at 8O’c because of difficulties v&h vaporisation cf toluene. As shown in Table 1.1 the number of 2-Mev gammas required to raise the temperature of toluene at the surface 1°C is approximately 1.45 x lO”/cm’. From this value and the expected gamms output of the weapon, a location was chosen for the scintillators where the hesting effect of the radiation was expected to exceed the known safe figure in order to test scintfflator behavior under intensity conditions that would result in a large temperature chsnge. At more distsnt locations and by gsmma shielding, the behavior of the acintillators under conditions of high radiation rates but site temperatures were studied. Table l.l-CCHARACTERISTICS OF SCINTILLATGR Composition: 0.5 per cent by weight of terphenpl in toluene Chemical composition of toluene: C,H, Density of toluene: 0.862 g/ml at 25/4 Boiling point of toluene: 110.8”C Terphenyl emission spectrum: 3300 to 4000 A with pesk at 3450 A (3.6 ev) Fraction of energy loss in scintillator converted to light: 2.4 x 10-** Number of 2-Mev gammss required to raise temperature of toluene 1°C: -1.45 x 10” Fraction of energy Gamma-ray energy Pair pro- given to electron 9 Compton, duction, in Compton process, *This value is in question. It may be as low as 1.4 x lr’. The .first objective was attempted by placing scintillatots at different distances from the bomb and by using gamma-ray attenuators in combination with scintillators, comparing the light output vs time. Differences in the form’of curves lrom any two of the scintillators would indicate that the light output of one of the scintillators was not proportional to the incident gsmma radiation, that the approximate inverse-square relation of the gamma radiations changes with time, or that a time-varying differential optical attenuation was present in the light paths between scintillators and detectors. Except for a position very close to the weapon, it is believed that the inverse-square law can be trusted. By using two scintillators at the same dis-

Page 16

tame from the bomb and a gamma-ray attenuator between the bomb and one of the scintflhtors, the effect of a light-path abeorption can be eliminated. In this case, however, the effect of the lead filter on the gamma spectrum introduces qome uncertainty. For this reaeon the thickness of the attenuator wae limited by the need to ensure that the spectrum effects did nd overshadow any possible saturation effect. In an ideal experiment the optical attenuation in the varfous light’ patha would be measured aa a function of time 80 that information could b obtained on the scintfflator efficiency as a function of the incident gvnma intensity, separated out completely from other effects. On the aemamption that the optical transmission could not be determined, it was believed that the experiment would still answer the second objective of how the new scintfllatordistant detector technique would work. This would improve the experimental design for Ivy ae a result of these Snapper measurements, even if it were not possible to fully distinguish between scintillator failure and attenuation in the optical path. 1.4.1 Gamma Intensity and Intone&y Relations Figure 1.1 shows a predicted curve of the gamma radiation From the gamma intensity bssed on the assumed bomb chuacteristics and the following derived expresaions, the anticipated current expected from a photocell placed at the focus of a collecting mirror can beocalculated. For these calculations the following symbols ue used: I = source strength in gammas per second outside the bomb Fy = gamma transmission of material between the bomb case and scintfflator a0 = fractional solid angle subtended by the phuocathode at the focus of the collectB = joules of terphenyl light emitted in the direction of the detector per 4x steradians per incident gamma T = opticaI tranrmission, including the efficiency of the collecting mirror and 6 and I$ = angles shown in Fig. 1.2 pt = absorption coefficient for gamma rays pa = It times the fraction of gamma-ray energy transferred to Compton electrons or pairs (on the average) P = absorption coefficient for the emitted light 1 = thiclcnees of scintfllator 1.6 x lr*’ = the conversion factor from million electron volts to joules The gammas per second incident on the scintillator are and the current in amperes expected from a photocell placed at the focus of a collecting mirConsidering only the first gamma-ray processes, *OS = A,/4nr& in which AS is the projected area of the scintillator and rs is the distance from source to scintillator.

Page 18

de#hs are shovrnin Fig. 1.3. These VSheS of Bwere Cabhtedfrom Eq. 1.3 us the coI18tmb from Table 1.1 and S88uming thatthe incident gammas and the emergent terphenyl light were directed normallo the surface Of the scintfllator; i.e., 8 = $ = 0. These assumptions were correct for the) t but for the later tests a calculation of B wa,y necessary for eachThe $lUOreSCenCe spectrum Of the terphenyl in toluene scintillator is shown in Fig. 1.4. 1.4.2 Predicted Background and Related Effects (4) Teller L&M The incidence of gamma rays OS the zir lea& to a fluoreecence referred to as “Teller light.” This is caused by simple excitations and decreases as gamma intensity , decresses. Harold S. Stewart, Naval Research Lshoratory (NRL) Optics Division, had verified thst Teller light exists in the air surrounding a nuclesr detonation.* The intensity was not known, but the eKect of the mirror Sydem was to bafflethe optical path and minimize the re@on from which this light could enter the system. the cab walls and structural members of the tcnver, were expected to raiss them to incandescent temperatures. This ls borne out by photographs obined by Edgerton, Germeshausen Q Grier @G&G),’ during Operation Greenhouse, which show thatthe CS~ wslls glow prior to the time they are fractured by the shock wave. Preliminary analysis indicated thst such incandescence would not yield as much light as a scintillator at the same position, provided the scinti&&or efiiciency remained constant. Cab incandescence shatld also occur a little later than the period b’ ai greatest interest. Hence it was believed that this source of background would not prevent the testing of a scintlllator placed a few meters from the bomb. It was also possible to use a filter in …