AE-309 UDC 53S.12S.5.161 539.125.5.523

Measurement of the Decay of Thermal Neutrons in Water Poisoned with the Non-1/v Neutron Absorber Cadmium

L. G. Larsson and E. Möller

AKTIEBOLAGET ATOMENERGI

STOCKHOLM, SWEDEN 1967

AE-309

•MEASUREMENT OF THE DECAY OF THERMAL NEUTRONS IN WATER POISONED WITH THE NON-l/v NEUTRON ABSORBER CADMIUM

L G Larsson ' and E Möller

SUMMARY Measurements have been made of the decay constant of thermal neutrons in water poisoned with the non-1/v absorber cadmium. An experimental method has been used in which proper spatial integration of the neutron flux enables data, representative of the infinite medium to be accumulated without waiting for the establishment of a fundamental mode distribution. The change in effective cross section with concen- daeff tration of the dissolved cadmium, —rr=—. has been determined for in- dN finite medium at 20 C. Two- and three parameter fits of the decay- constant yield -(0. 32 ± 0. 09) • 1 O-1 7 barn cm3 and -(0. 47 ± 0. 1 0) • 1 0"1 7 3 barn cm , respectively. Earlier published measurements have resulted in two to five times larger values, whereas a published calculated value -17 3 for Nelkin's model is - 0. 33 • 10 barn cm .

*) Now at Research Institute of Swedish National Defence.

Printed and distributed in January 1968. LIST OF CONTENTS Page 1 . Introduction 2. Principles of the experiment 3. Results of the measurements 4. Discussion of the results 5. Conclusion Acknowledgements References Table I Table II Figures - 3 -

1 . INTRODUCTION

Various methods may be used for integral studies of thermal neu­ tron scattering in moderators. Well known examples are the measure­ ments of stationary neutron spectra in moderators, pure or poisoned with different absorbers. The pulsed neutron experiment is another example. The decay constant for thermal neutrons in a moderator as­ sembly varies with the absorption and the leakage according to the equa­ tion

X = X + D B2 - CB4 + . . . (1) a o 2 where X is the decay constant for absorption only, B is the geomet- rical buckling of the assembly, D is the diffusion constant and C is the diffusion cooling constant describing the effect of the preferential leak­ age of high energy neutrons from the system. D and C are integral parameters of the scattering law, and the comparison between experi­ mental and calculated values may serve as a check of the validity of the scattering model, on which the calculations are based. The perturbation of a Maxwellian neutron distribution, occurring when an absorber of the non-1/v type is distributed in a moderator is reflected in the decay constant. In the resonance region neutrons are absorbed at a higher rate than in other regions. The result is a smaller value of the effective cross section than calculated by averaging the cross section with a Maxwellian flux. The decay constant for a therma- lized neutron field in an infinite moderator is given by the expression, analogous to (1 )

da rr y X = X + v a ,, . N + v .!:. • N + . . . (2) a o o eff o dN v ' where N is the non-1/v absorber concentration in atoms per cm , v is the most probable velocity of thermal neutrons at a moderator tem­ perature of 20 C, 2200 m/s, CT ,, is the effective cross section of the absorber in a Maxwellian distribution of neutrons, and X is the decay ' o } constant for thermal neutrons in the unpoisoned moderator. This param- doeff eter —-j^j— is, like the diffusion cooling coefficient, related to the rate - 4 -

daeff of energy exchange between the neutrons and the moderator (- v —-rrj— is also called the absorption cooling coefficient). In a pulsed neutron measurement with a moderator assembly of finite size and with non-l/v absorption present the decay constant will be given by combination of all the terms in Eqs. (1) and (2), but now the leakage parameters in Eq. (1 ) are functions of the concentration N and the absorption parameters in Eq. (Z) are functions of the geometri- 2 cal buckling B . Measurements to determine these parameters have been made by Santandrea [l ], Verdaguer [2,3], Meadows and Whalen [4] and Friedman [5, 6]. The values obtained have been given with poor accuracy and of the order of two to five times higher than those given by calculations, based on current models of neutron scattering in water. Calame [7] made an extensive numerical study of the effect and com­ pared his result with experimental results, which led to the conclusion that the experimental results are wrong. Beckurts [8] pointed out that the effect is of principal interest and that efforts ought to be made to resolve the discrepancy. Several factors may contribute to the difficulties in obtaining reliable results in the experiments. It is necessary to wait for a long time after the injection of the fast neutron pulse before the fundamental spatial mode has been established, otherwise Eq. (1) will not be valid. During the waiting time, a great loss of neutrons will occur, resulting in a poor statistical accuracy in the determination of the decay constant. The great number of parameters and specially the intricate coupling between the leakage and the absorption parameters in the combination of Eqs. (1 ) and (2) result in large errors when the parameters are evaluated all at a time from the measurement. Larsson, Möller and Purohit [9] showed how studies of neutron moderation in hydrogeneous media by the time dependent reaction rate method may be performed under conditions which, in the time region from injection to complete thermalization, yield results representative of the case of an infinite medium. This time interval can be expanded to an interval just after the thermalization period, when neutron leakage can still be considered negligible. Using the experimental method pre- _ d-^eff sented in [7 J for the measurement of ,...— , it would be possible to get results which may be analysed on the basis of Eq. (2) only, thus avoiding the above mentioned problems. - 5 -

2. PRINCIPLES OF THE EXPERIMENT The decay of neutrons in a moderator may be followed by the de­ tection and time analysis of gamma radiation from neutron capture in the moderator atoms and in dissolved absorbers. Under certain condi­ tions a gamma detector situated outside a moderator assembly of finite size can be used to record a reaction rate which is representative of the infinite medium. The following requirements should be fulfilled: 1 ) The neutron pulse shall be produced at the center of the moderator vessel and the source shall be isotropic. 2) The energy of the neutrons from the source shall be so low that the number of neutrons reaching the moderator boundary during the slowing down period, is negligible. 3) The sensitivity of the detector shall be such that the same weight is given to all radii in the spatial integration of the gamma radiation from the reaction rate which is performed by the detector. 4) The measure­ ments shall cover only a time period after the neutron pulse injection, during which the leakage is negligible. This means that one should not wait for the establishment of the fundamental mode but perform the decay constant measurement during a short period after the completion of the neutron thermalization. This short period of course, makes the method suitable for measuring decay constants of the order of the in­ verse of the time of measurement. Calculations performed in [9] showed that a detector for gamma radiation placed outside a finite moderator vessel will not immediately satisfy condition 3) above. The efficiency of an available detector could, however, in a chosen geometry be modified by means of a lead collima­ tor to become independent of radius within a few per cent. The suitable conditions were found by trial and error adjustments of the collimator and corresponding measurements of the efficiency for the 2. 6 MeV gam­ ma radiation from a RdTh source, which was rotated on a number of radii. The remaining radial efficiency dependence will in practice be further reduced since the spatial distribution of neutrons will make the contribution to the recorded reaction rate from large radii in the spatial integration relatively small. - 6 -

The method of neutron flux measurement used by Pönitz and Wattecamps [l 0] is based on the same principle with the additional requirement that the leakage can be neglected during the whole life time of the neutrons in the system. In their geometry, which is simi­ lar to ours, the calculated detection efficiency for capture of neutrons in a manganese sulphate bath is constant within 0. 8 per cent in the energy region 1 0 keV - 1 MeV. This is also an indication that decay constant measurements may be performed under infinite medium con­ ditions . The experimental set-up is shown in Fig. 1 . The water container, which is approximately cylindrical with a diameter of 36 cm, height 32 cm and a volume of about 32 liters, is surrounded with a neutron shield of boron loaded plastic. Neutrons are produced at the center, where a pulsed beam of 3 MeV protons hits a thick beryllium target. The choice of this target and accelerator energy results in a very low number of neutrons in the outer region of the assembly, as can be seen in the measurements by Foster [1 1 ] of the spatial distribution of ther- malized neutrons from a 1 MeV neutron source in water. The gamma ray detector is a plastic scintillator with a diameter of 5 cm and a length of 20 cm, connected to a photomultiplier by means of a light pipe. The distance between the moderator and the front surface of the scintillator is 1 1 cm, and the close fitting lead collimator is withdrawn 4 cm to give the desired integrating properties of the detector. The electronics consist of a discriminator and a time-to-pule-height con­ verter as described by Möller and Sjöstrand [l 2], The linearity of the time measuring system was examined by putting a small Co source close to the detector and letting the corresponding pulses stop the time- to-pulse-height converter. The resulting "white" spectrum showed negligible deviation from linearity in channels, in which the decay was analysed. Measurements were performed with pure water, four different cadmium solutions and three different boron solutions. The aim of the boron measurement was to get results for a 1/v absorber which could serve as a test of the accuracy of the experimental method. The solu­ tions were prepared from weighed amounts of the compounds 3CdSOA, - 7 -

8H?0, and H?BO,, respectively and the concentrations were checked by chemical analysis of samples taken immediately after each measure­ ment. The pulse frequency was 1.17 kHz and the time resolution was 0. 64 [xs. In the boron measurements the gamma ray discriminator was set to accept gamma rays with energies higher than 1 MeV, whereas in the cadmium measurements the bias corresponded to 2.2 MeV. In the first case the detected gamma rays originate mainly from neutron capture in hydrogen. The water temperature in the measurements was 20 °C.

3. RESULTS OF THE MEASUREMENTS The results of the measurements with boron and cadmium solu­ tions after dead time and background corrections are shown in Figs. 2 and 3. The curves have been separated by suitable changes of vertical scale factor. The measurement on pure water is also included in Fig. 2. Measurements were also performed under other conditions than those presented in the figures and the table. The maximum neutron energy for 3 MeV protons on beryllium is 1 MeV. A lower accelerating voltage, 2. 6 MeV, did not result in any change in the decay constant, although the spatial distribution will be affected by this change. Meas­ urements with a thick lithium target for the same two proton energies did not show any difference either. An added dummy target tube also resulted in the same decay constants within the experimental error. This insensitivity to changes indicate that the actual deviations from the ideal conditions do not influence the integrating properties of the detec­ tor. Exponential fittings were made by means of the least squares method to the data shown in Figs. 2 and 3, using the channel counts as weights with different starting and stopping points. It was found that the resulting decay constant was quite insensitive to starting points varying between 25 |j,s and 35 |is (except that the ac- curacy will be improved if a larger time period is analysed). This re­ sult is also in agreement with earlier published measurements [7], - 8 -

The dependence of the decay constant on the stopping time, varied from 45 |JLS to 1 00 \is was also examined. For stopping times between 45 |j,s and 65 |j,s the change in the decay constant was within the experi­ mental accuracy. For the time period between 70 |j,s and 100 |is the fitting resulted in a tendency to smaller decay constants than expected, showing the influence of diffusion of neutrons to regions with higher weights in the spatial integration. From the above consideration the starting time for analysing the decay constant was taken to be 30 |i,s and the stopping time 65 (is after the injection. Table I shows the concentrations, experimentally determined decay constants X and a decay constant X, , calculated for an undis- ' exp ' M turbed Maxwellian flux, i.e. X., = X + Nv a ,r. Since boron has an ' Moo eff absorption cross section, following the 1/v law the two decay constants X and X,, should in this case be the same. In the cadmium measure- exp M ments the deviation between X and X... should give the parameter da „ exp M eff dN ' The calculated parameters are based on the following data: For water X = 4780 ± 30 s"1 [15] boron a (v ) = 759 ± 1 barn [13] cL O cadmium a (v ) = 2450 ± 30 barn [13] av o' The effective absorption cross section of cadmium for a Max­ wellian flux is obtained by multiplying the above value for a (v ) by a O the Westcott g-factor, for which a value of 1 . 320 has been used [14] giving a ff = 3240 ± 40. (The uncertainty in the g-factor is assumed to be negligible compared to the uncertainty in o* (v ).) This is also in good agreement with the measurements by Sokolowski et al. [1 8], The decay constants were analysed in two ways. First the ther- malization parameters were obtained by least squares fit to the data shown in Table I. The errors in the parameters were calculated taking the errors in the individual measurements into account. The fitting of the parameters in the second method was done in one fit from the decay curves. Here the decay constant was written as in Eq. (2) and param- dcreff eters X , cr ,., ...— and one amplitude for each decay curve were - 9 -

fitted to the data for cadmium shown in Fig. 3. The same procedure was repeated for the boron data in Fig. 2. The difference between the results from the two ways of analysing the data were insignificant. Table II shows the results from fittings obtained by the first method in one-, two- and three-parameter fits. Although Eq. (2) could repro­ duce the experimental results quite well, an attempt was made to check the possible influence of higher terms by adding a term proportional to 3 N to the decay constant and repeating the fitting procedure. This re­ sulted in enlarged errors in the parameters and the new term was daeff hidden in the uncertaintyy of —-rrr—. dN dcTeff An attempt to fit a term ,. — to the boron measurements did ^ dNT not change a ff and X significantly. Further the uncertainty in the term was about ten times the actual value, but even with error limits in­ cluded, in the decay constant this term was hidden in the uncertainty of cr rf. This shows that from the experiment with boron no systematic error was found.

4. DISCUSSION OF THE RESULTS The measurements with boron as absorber are seen to be in agree­ ment with the calculations although the tendency of the measured decay constant is to lie in the lower part of the expected interval. The decay constants of the weakest cadmium solution, where the deviation of the spectrum from the Maxwellian is so small that its influence on the decay constant is negligible, are also within experimental error in the expected interval. From different independent measurements, however, a tendency was found for the decay constant to be in the upper expected interval. The results for pure water are satisfactory, although the un­ certainty in the decay constants is quite large and it is hard to deter- 'mine some parameters from these measurements alone. As pointed out before, this uncertainty is inherent in the used method; since the period of measurement is limited to 35 |xs it is hard to make accurate meas­ urements of decay constants of order less than •=-=• LIS" « 30000 s" . dae£f 35

The sensitivity of -„— to changes in cr ,f is quite evident. A series of fittings in which X is fixed while a ,, is fixed in a single fit­ ting but varied within the series with limits given by BNL 325 [13] and by Westcott [14], i.e. - 10 -

a = 3240 ± 40 barn eftet

gives the result

da rr i 7 o —Tj|£i- = -(0.32 ±0.09) • 1 0 ' barn cm

dCTe£f A change of 1 % in a „ thus gives a change of 30 % in —-TTJ— . The result when a value of a ,, is also fitted is eff da ,, . _ ^ = - (0.47 ±0.10) • 10" barn cm

i.e. this result is higher than the one obtained above. This is also re­ flected in the relatively high value given to a ,r in this fit, namely

a etttl - 3340 ± 80 barn,

Using the pulsed source method, Meadows and Whalen [14] obtained at 26 °C

o rr = 3394 ± 1 2 barn, eft

a result referred to both by Friedman [6] and Calame [7], Reducing this value to 20 C by using the Westcott g-factors gives

a , = 3348 ± 1 2 barn. ei±c

This is considerably higher than the value referred to above from refs. [13,14 and 1 8 ]. Our result fr om the fit overlaps both values. If all three parameters in Eq. (2) are fitted at the same time, the result is the same as the fit with two parameters, except of course that the uncertainty is larger. The value of the decay constant for pure water is within the expected value as given by Arai and Kiichle [1 5 ], but with quite a large uncertainty (~ 5 %) as was discussed above. A calculation by Calame [7] based on the Nelkin scattering model for water gives

dO* rr -i 7 .3 - ,,T— = - 0. 33 • 10" barn cm . dJN - 11 -

Now for the Nelkin model M2 - the second moment of energy transfer for a Maxwellian distribution - is according to Honeck [16] M~ = 49. 05 barn. According to Gläser and Beckurts [1 7], M~ for the more real­ istic Haywood model is 46. 5 barn. Thus the Haywood model gives a lower value of M and should give an accordingly higher value of 9 da dae££ ^ eff

—-rrrrf—. Starting from the value given by Calame and assuming ,KT— to be inversely proportional to M? this should give -TJ^— =-0.35* 10 barn cm for the Haywood kernel. This calculated result agrees well with what we get assuming a re - 3240 ± 40 barn, giving

da „ 1 , e = - (0. 32 ± 0. 09) ' 10" barn cm dN but not with what we get from the three-parameter analysis

da f, ,7 _ ^ = - (0.47 ±0.10) » 10" barn cm3.

The reason for this difference is difficult to explain. There may be an error in the point for the weakest Cd solution, Cdl, which mostly determines a ff. This point was again checked in the data processing, but no discrepancies were found.

5. CONCLUSION

Our results show that the experimentally found influence on the thermal spectrum of the presence of a non-1 /v absorber is in reason­ able agreement with the predictions from numerical calculations. The earlier published measured values of the coefficient, expressing the change of the effective cross section when the spectrum is distorted, have been too high. It is difficult to attach a value with small error limits to the absorption cooling coefficient from our measurements, and no attempt has been done to increase the accuracy of our experimental data, since our method would not be suitable for precision measure­ ments. - 12 -

ACKNOWLEDGEMENTS We are very grateful to Professor N G Sjöstrand for the interest shown in this study. One of us (L G Larsson) is indebted to AB Atom­ energi for a scholarship during the course of this work. - 13 -

REFERENCES SANTANDREA E, TOSELLI F, and VIANO G, Neutron temperature measurements with pulsed neutron sources. Int. conf. on the peaceful uses of atomic energy, Geneva 1958. Proceedings, Vol. 16, Geneva 1958, p. 265. VERDAGUER F, Enfriamiento de los neutrones por captura y su aplicacion al estudio de su termalizacion en agua ligera. 1963. (J.E.N. 127-DF/l 39.) VERDAGUER F et al., Development of the pulsed neutron source technique at the Junta de Enérgfa Nuclear. Int. conf. on the peaceful uses of atomic energy, Geneva 1964. Proceedings, Vol. 2, New York 1 965, p. 330. MEADOWS J W and WHALEN J F, Thermal neutron absorption cross sections by the pulsed source method. Nucl. Sci. Eng. 9_ (1 961) 132. FRIEDMAN E, A new method for measuring thermalization parameters. Nucl. Sci. Eng. 1_4 (1962) 420. FRIEDMAN E, Studies of neutron thermalization in H^O by the pulsed source and "non ^"absorbers method. Nucl. .Sci. Eng. ]_9 (1964) 203. CALAME G P, Non-1/v thermalization parameters for the Mass-1 and Nelkin scattering kernels. Nucl. Sci. Eng. 20.(1964) 352. BECKURTS K H, A review of pulsed neutron experiments on non-multiplying media. Pulsed Neutron Research, IAEA Symposium, Karlsruhe 1 965. Proceedings, Vol. 1, Vienna 1965, p. 3.

LARSSON L G, MÖLLER E , and PUROHIT S N, Neutron scattering in hydrogenous moderators, studied by the time dependent reaction rate method. 1966. (AE-223.) PÖNITZ W and WAT TEC AMPS E, A grey neutron detector for flux measurements in the intermediate energy range. 1 963. (EANDC-33 "U") p. 102. FOSTER D G Jr. , Age of Na-Be neutrons in water and kerosene. Nucl. Sci. Eng. 8 (i960) 148. - 14 -

MÖLLER E and SJÖSTRAND N G, Measurement of the slowing-down and thermalization time of neutrons in water. Arkiv Fysik 11_ (1 964/65) 501 .

Neutron cross sections. 1964-66. (BNL-325, 2nd ed. , Suppl. No. 2.) WESTCOTT C H, Effective cross section values for well-moderated thermal reactor spectra. 3 corr. ed. I960. (AECL-1 101 .) ARAI E and KttCHLE M, Messung der Diffus ions länge in zeitlich abklingenden Neutronen- feldern. Nukleonik 1_ (1 965) 41 6. HONECK H C, The calculation of the thermal utilization and disadvantage factor in uranium/water lattices. Nucl. Sci. Eng. US (1 964) 49. GLÄSER W and BECKURTS K H, Inelastic Neutron Scattering by some Hydrogenous Moderators. Nucl. Sci. Eng. 2_0 (1964) 236. SOKOLOWSKI E, PEKARE K H, and JONSSON E, Cross section measurements for some elements, suited as thermal spectrum indicators: Cd, Sm, Gd and Lu. Nukleonik 6 (1964) 245. - 15 -

TABLE I Measured and calculated decay constants for the different water solutions

Concentrations Decay constant, s Solute atoms/cm calculated measured xlO-19 l exp

None 4780 ± 40 4780 ± 240 B I 1.069 ±0.005 6570 ± 40 6580 ± 200 B II 11.24 ±0.06 23550 ±110 23270 ± 250 B III 20.48 ±0.10 38980 ± 200 38600 ± 400 Cd I 0.2272 ± 0.0009 6400 ± 45 6520 ± 140 Cd II 2.636 ±0.011 23600 ± 250 23310 ± 150 Cd III 4.849 ±0.019 39400 ± 450 38060 ± 250 Cd IV 5.840 ±0.023 46460 ± 550 43900 ± 270 - 16 -

TABLE II

Values of thermalization parameters, obtained by least squares fit to the decay curves

da ,, eff dN Absorber \ , s a ,,, barn Remark o eff (x 1 0 barn cm )

Cadmium 4740 ± 220 3350 ± 100 0. 50 ± 0.1 3 0) 4780 3343 ± 74 0. 47 ± 0. 10 (2) 4780 3240 0. 32 ± 0.02 (3) 4780 3280 0. 39 ± 0.02 (3) 4780 3200 0. 24 ± 0.02 (3)

Boron 4800 ± 220 749 ± 21 - (4) 4780 750 ± 15 (5) "

da ff \ , a ,, and - „. 0) o eff dN fitted da eff X given the value indicated in the table, a and ..... fitted (2) o ° efrfr dN da eff (3) X and a rr " II II n fitted o eff dN \ and a - fitted (4) o efrjf

(5) X given the value indicated in the table, a ,, fitted, o eff Fig. 1 Experimental setup

Plexiglass tube Be target

Light Lead Plastic •Water pipe shield scintillator

0 10 20 30 i—i—i—i—i i i cm Fig. I Decay curves measured with water and boron solutions

•"'"'"'"' "•'"••'•••-••••-••.•.•,,..•..,. H20 • • ...... "• ^ 2 _ • * '*..•.•••..••'•..• • • .

';r"--^--vy,, BI

10 - • .. •••••-.•.••. •••.••••..• .

• vi ~ 5 _' -. . •. .. c ". *• ra — '•'. * '*". >x **.. """ • l_ .. *"•• - '•• .

JJ " a -.

a 2 ""%.s BI "• .# " U)^ 4-^ • • • 3c • * * • S io • • • •• 05 _ C *. * c _ • *•• o - D 5 - ""•,. • . Bl - ...

• . . [

2 • . . . * ""'. *

0 20 40 60 80 100 t. fjs Fig. 3 Decay curves measured with cadmium solutions

— , .^ /\ • * *

2 -•B • • • » * ••

• « m • '"'••v...... Cdl # * "•• * * • ••• » • . • 10 ^ • **. •• ••• *» ••, - •» • ". "'*•.. • • ••• "" • • ••t ~ 5 - \ " . -. , *•. • • •••... • • * ••• • •• • *,« Cdl '. • •» . '*. "•• *•. • ••* ••• *• ••» •\ «• • ••••• • •• ' * •, c •. O '•. • • •• * * * " 10 • • c • c *•«, o *'•• ''•••• Cd

-v Cd 12 •'.

• » « -. 1 „J 1 » 1 __J 1 ILJ 0 20 40 60 80 t. [JS

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By L. Broman and S. G. Malmskog. 1966. 10 p. Sw. cr. 8:-. 287. Absolute E1, A K = O transition rates in odd-mass Pm and Eu-isotopes. By S. G. Malmskog. 1967. 33 p. Sw. cr. 10:-. 241. Burn-up determination by high resolution gamma spectrometry: spectra from slightly-irradiated uranium and plutonium between 400-830 keV. By 238. Irradiation effects in Fortiweld steel containing different boron isotopes. R. S. Forsyth and N. Ronqvist. 1966. 22 p. Sw. cr. 8:-. By M. Grounes. 1967. 21 p. Sw. cr. 10: -. 1K 289. Measurements of the reactivity properties of the Ågesta nuclear power 242. Half life measurements in Gd. By S. G. Malmskog. 19B6. 10 p. Sw. cr. 8:-. reactor at zero power. By G. Bernander. 1967. 43 p. Sw. cr. 10:—. 243. On shear stress distributions for flow in smooth or partially rough annuli. 290. Determination of mercury in aqueous samples by means of neutron activa­ By B. Kjellström and S. Hedberg. 1966. 66 p. Sw. cr. 8:-. tion analysis with an account of flux disturbances. By D. Brune and K. Jir- low. 1967. 15 p. Sw. cr. 10:-. 244. Physics experiments at the Ågesta power station. By G. Apelqvist, P.-Å. s1 291. Separtaion of Cr by means of the Szilard-Chalmers effect from potassium Bliselius, P. E. Blomberg, E. Jonsson and F. Äkerhielm. 1966. 30 p. Sw. cr. 8:-. chromate irradiated at low temperature. By D. Brune. 1967. 15 p. Sw. cr. 10:-. 245. Intercrystalline stress corrosion cracking of inconel 600 inspection tubes in 292. Total and differential efficiencies for a circular detector viewing a circu­ the Ågesta reactor. By B. Grönwall, L. Ljungberg, W. Hiibner and W. Stuart. 1988. 26 p. Sw. cr. 8:-. lar radiator of finite thickness. By A. Lauber and B. Tollander. 1967. 45 p. Sw. cr. 10:-. 246. Operating experience at the Ågesta nuclear power station. By S. Sand­ 3 293. Absolute M1 and E2 transition probabilities in " U. By S. G. Malmskog and ström. 1966. 113 p. Sw. cr. 8:-. M. Höjeberg. 1967. 37 p. Sw. cr. 10:-. 247. Neutron-activation analysis of biological material with high radiation levels. By K. Samsahl. 1966. 15 p. Sw. cr. 8:-. 234. Cerenkov detectors for fission product monitoring in reactor coolant water. 248. One-group perturbation theory applied to measurements with void. By R. By O. Strindehag. 1967. 56 p. Sw. cr. 10:-. Persson. 1966. 19 p. Sw. cr. 8:-. 295. RPC calculations for K-forbidden transitions in mW. Evidence for large 249. Optimal linear filters. 2. Pulse time measurements in the presence of inertial parameter connected with high-lying rotational bands. By S. G. noise. By K. Nygaard. 1966. 9 p. Sw. cr. 8:-. Malmskog and S. Wahlbom. 1967. 25 p. Sw. cr. 10:-. 250. The interaction between control rods as estimated by second-order one- 296. An investigation of trace elements in marine and lacustrine deposits by group perturbation theory. By R. Persson. 1966. 42 p. Sw. cr. 8:—. means of a neutron activation method. By O. Landström, K. Samsahl and C-G. Wenner. 1967. 40 p. Sw. cr. 10:-. 251. Absolute transition probabilities from the 453.1 keV level in 183W. By S. G. Malmskog. 1966. 12 p. Sw. cr. 8:-. 297. Natural circulation with boiling. By R. P. Mathisen. 1967. 58 p. Sw. cr. 10:-. 252. Nomogram for determining shield thickness for point and line sources of 298. Irradiation effects at 160-240°C in some Swedish pressure vessel steels. gamma rays. By C. Jönemalm and K. Malén. 1966. 33 p. Sw. cr. 8:—. By M. Grounes, H. P. Myers and N-E. Hannerz. 1967. 36 p. Sw. cr. 10:-. 253. Report on the personnel dosimetry at AB Atomenergi during 1965. By K. A. 299. The measurement of epithermal-to-thermal U-238 neutron capture rate (p2B) Edwardsson. 1966. 13 p. Sw. cr. 8:-. in Ågesta power reactor fuel. By G. Bernander. 1967. 42 p. Sw. cr. 10:-. 254. Buckling measurements up to 250°C on lattices of Ågesta clusters and on 300. Levels and transition rates in "'Au. By S. G. Malmskog, A. Bäcklin and B. DiO alone in the pressurized exponential assembly TZ. By R. Persson, Fogelberg. 1967. 48 p. Sw. cr. 10:-. A. J. W. Andersson and C-E. Wikdahl. 1966. 56 p. Sw. cr. 8:-. 301. The present status of the half-life measuring equipment and technique at 255. Decontamination experiments on intact pig skin contaminated with beta- Studsvik. By S. G. Malmskog. 1967. 26 p. Sw. cr. 10:-. gamma-emitting nuclides. By K. A. Edwardsson, S. Hagsgård and Å. Swens- 302. Determination of oxygen in aluminum by means of 14 MeV neutrons with son. 1966. 35 p. Sw. cr. 8:-. an account of flux attenuation in the sample. By D. Brune and K. Jirlow. 256. Perturbation method of analysis applied to substitution measurements of 1967. 16 p. Sw. cr. 10:-. buckling. By R. Persson. 1966. 57 p. Sw. cr. 8:-. 3G3. Neutron elastic scattering cross sections of the elements Ni, Co, and Cu 257. The Dancoff correction in square and hexagonal lattices. By I. Carlvik. 1966 between 1.5 and 8.0 mev. By B. Holmqvist and T. Wiedling. 1967. 17 p. 35 p. Sw. cr. 8:—. Sw. cr. 10:-. 258. Hall effect influence on a highly conducting fluid. By E. A. Witalis. 1966. 304. A study of the energy dependence of the Th232 capture cross section in 13 p. Sw. cr. 8:-. the energy region O.I to 3.4 eV. By G. Lundgren. 1967. 25 p. Sw. cr. 10:-. 259. Analysis of the quasi-elastic scattering of neutrons in hydrogenous liquids. 305. Studies of the reactivity effect of polythene in the fast reactor FRO. By L. By S. N. Purohit. 1966. 26 p. Sw. cr. 8:-. I. Tirén and R. Håkansson. 1967. 25 p. Sw. cr. 10:-. 260. High temperature tensile properties of unirradiated and neutron irradiated 306. Final report on IFA-10, the first Swedish instrumented fuel assembly irra­ 20Cr-35Ni austenitic steel. By R. B. Roy and B. Solly. 1966. 25 p. Sw. diated in HBWR, Norway. By J-Ä. Gyllander. 1967. 35 p. Sw. cr. 10:-. cr. 8:-. 307. Solution of large systems of linear equations with quadratic or non-qua­ 261. On the attenuation of neutrons and photos in a duct filled with a helical dratic matrices and deconvolution of spectra. By K. Nygaard. 1967. 15 p. plug. By E. Aalto and A. Krell. 1966. 24 p. Sw. cr. 8:-. Sw. cr. 10:-. 262. Design and analysis of the power control system of the fast zero energy 308. Irradiation of superheater test fuel elements in the steam loop of the R2 reactor FR-0. By N. J. H. Schuch. 1966. 70 p. Sw. cr. 8:-. reactor. By F. Ravndal. 1967. 94 p. Sw. cr. 10:-. 263. Possible deformed states in '"In and 1"ln. By A. Bäcklin, B. Fogelberg and 309. Measurement of the decay of thermal neutrons in water poisoned with the S. G. Malmskog. 1967. 39 p. Sw. cr. 10:-. non-1/v neutron absorber cadium. By L. G. Larsson and E. Möller. 1967. 264. Decay of the 16.3 min. '"Ta isomer. By M. Höjeberg and S. G. Malmskog. 20 p. Sw. cr. 10:-. 1967. 13 p. Sw. cr. 10:-. 265. Decay properties of '"Nd. By A. Bäcklin and S. G. Malmskog. 1967. 15 p. Sw. cr. 10:-. 266. The half life of the 53 keV level in "'Pt. By S. G. Malmskog. 1967. 10 p. Sw. cr. 10:-. 267. Burn-up determination by high resolution gamma spectrometry: Axial and diametral scanning experiments. By R. S. Forsyth, W. H. Blackladder and N. Ronqvist. 1967. 18 p. Sw. cr. 10:-. Förteckning över publicerade AES-rapporter 268. On the properties of the s,y >- d / transition in '"Au. By A. Bäcklin 2 3 2 1. Analys medelst gamma-spektrometri. Av D. Brune. 1961. 10 s. Kr 6:—. and S. G. Malmskog. 1967. 23 p. Sw. cr. 10:-. 2. Bestrålningsförändringar och neutronatmosfär i reaktortrycktankar — några 269. Experimental equipment for physics studies in the Ågesta reactor. By G. synpunkter. Av M. Grounes. 1962. 33 s. Kr 6:-. Bernander, P. E. Blomberg and P.-O. Dubois. 1967. 35 p. Sw. cr. 10:-. 3. Studium av sträckgränsen i mjukt stål. Av G. Dstberg och R. Attermo 270. An optical model study of neutrons elastically scattered by iron, nickel, 1963. 17 s. Kr 6:-. cobalt, copper, and indium in the energy region 1.5 to 7.0 MeV. By B. 4. Teknisk upphandling inom reaktorområdet. Av Erik Jonson. 1963. 64 s. Holmqvist and T. Wiedling. 1967. 20 p. Sw. cr. 10:-. Kr 8:-. 271. Improvement of reactor fuel element heat transfer by surface roughness. 5. Ågesta Kraftvärmeverk. Sammanställning av tekniska data, beskrivningar By B. Kjellström and A. E. Larsson. 1967. 94 p. Sw. cr. 10:-. m. m. för reaktordelen. Av B. Lilliehöök. 1964. 336 s. Kr 15:-. 272. Burn-up determination by high resolution gamma spectrometry: Fission pro­ 6. Atomdagen 1965. Sammanställning av föredrag och diskussioner. Av S. duct migration studies. By R. S. Forsyth, W. H. Blackadder and N. Ron­ Sandström. 1966. 321 s. Kr 15:-. qvist. 1967. 19 p. Sw. cr. 10:-. 7. Radiumhaltiga byggnadsmaterial ur strålskyddssynpunkt. Av Stig O. W. 273. Monoenergetic critical parameters and decay constants for small spheres Bergström och Thor Wahlberg. 1967. 26 s. Kr 10:-. and thin slabs. By I. Carlvik. 1967. 24 p. Sw. cr. 10:-. Additional copies avaiable at the library of AB Atomenergi, Studsvik, Ny­ 274. Scattering of neutrons by an anharmonic crystal. By T. Högberg, L. Bohlin köping, Sweden. Micronegatives of the reports are obtainable through Film- and I. Ebbsjö. 1967. 38 p. Sw. cr. 10:-. produkter, Gamla landsvägen 4, Ektorp, Sweden.

EOS-tryckerierna, Stockholm 1967