Coppola, M.

Knitter, H.-H.

Archive of European Integration

14C(d,n)15N and 15N(d,n)16O Reactions. EUR 3492.

C(d,n),:>N and lsN<d,n) ,eO $ÌÉÉfcf$ .s¡; fålMiK!* »a»*» i' ' I -tl I M ¡ r ø . i Pilli·! »If ÜB"!1 «i Üi wa&wji »¿.•η «i !S»Î ·»" H**1· ííí !*Μ iii i' - J·' 'i" m iRÆWAin ii i* U H · · ! m LEGAL NOTICE ¡tl' üf »!♦*■· DÍ th« iocument was European Atomic epared Energy under trie sponsorship of the Commission Community ( E U R A T O M ) . m m any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document, or that the use of any information, apparatus, method, or process disclosed in this document may not infringe privately owned Tights; or Assume any liability with respect to the use of, or for damages resulting from the use of any information, apparatus, method or process disclosed in this document. m m w tø' m— m m is report is on sale itm m tfîa W» if.tH!« W, mm PÍ5S5P ! :K; Orø Ui«ï'-rii dresses listed on page 4 . Λ l'ift^»iV at the price of F F 4. FB 4 0 . - D M 3.20 Lit. 500 Fl. W4 » mm hen ordering, please quote the EUR indicated on the cover of each report. tilr.~lJ' | ijay , tLjSííSHWjfiilíwínorí naos ¿*Λ'·<·ΐ* When ordering, please quote the EUR number and the title, which are m* m w m 1 m m m This document was reproduced on the basis of the best Printed by SMEETS Brussels, June 1967 A*« M mmm "ft» ' I available copy. EUR 3492.e EUROPEAN ATOMIC ENERGY COMMUNITY - EURATOM 14C(d,n)15N and 15N(d,n) 1 60 REACTIONS by M. COPPOLA and H.-H. KNITTER 1 9 6 7 Joint Nuclear Research Center Geel Establishment - Belgium Central Bureau for Nuclear Measurements - CBNM SUMMARY 14 15 Angular distributions of neutrons produced in the C id .n ) N and N(d,n) O reactions were measured at incoming deuteron energies of 1.3, 1.8 2.8 MeV and 1.0, 1.8, 3.0 MeV respectively, using a fast neutron time-of-flignt spectrometer. Neutrons leading to the ground 15 16 states and to some of the excited states of N and O were detected showing, in some cases, typical stripping patterns. l4C(d,n)15N and. 15N(d,n)l60 Reactions ( + ) 1· Introduction The possible use of the 14C(d,n)l5N and 15N(d,n)160 reactions as neutron sources for future work was studied in the present experiment. A "good" neutron source should fulfill several re­quirements. First it should "be easy to "be made and easy to he handled. Second, it should be monocromatic. Third, it should yield a large amount of neutrons over a relative broad range of energies. Typical neutron sources, like the Τίρ,η^Ηβ (Q =-0.764 MeV), the D(d,n)3He (Q =+3.268 MeV) and the T(d,n)4He (Q =+17.588 MeV) reactions meet all these requirements and are widely used in neutron experiments. In the case of the present study, the more advanced technology makes now easily available highly enriched C and Ν targets which are also easy to be handled because they are solid. In the second place, the C(d,n) PN reaction has a Q-value of +7.987 MeV and the 15N(d,n)1oO reaction a Q-value of+9.886 MeV. 15 Furthermore the Ν nucleus has the first excited level at 5.28 MeV and the 160 the first excited level at 6.04 MeV. This brings that the ground state neutrons are produced in an energy region well suited to fill the gap between the D(d,n) and the T(d,n) neutron sources and that these ground state neutrons are well separated from the ones leading to excited states. Concerning the intensities of the neutron groups cor­responding to the ground states, one finds that for both reac­tions the cross sections are relatively small and remain so over a wide range of deuteron energies (1, 2, 3). In the case of the C(d,n) reaction, the excitation curve at 0° for the ground state neutrons stays between 3.5 and 10 mb/sr about from 1.31 to 3.08 MeV deuteron energy, while for the N(d,n) reaction it stays between 0 and 6 mb/sr from 0.5 to 5.3 MeV deuteron energy. For comparison purpose one can look at the available results (4) of the D(d,n)^He reaction for production of neutrons with energies higher than about 8 MeV. Here the zero degree excitation curve is monotonically in­creasing and goes roughly from 70 mb/sr at 5 MeV to 95 mb/sr at 9 MeV deuteron energy. With a deuteron target, then the neutron production at 0° is more than an order of magnitude Manuscript received on February 27, 196? 2. larger than with 4C and ^N targets in the above neutron energy range, but unfortunately the deuteron energies re­quired cannot be usually reached with a single stage Van de Graaff accelerator and not at all with the 3 MeV machine of CBNM. In sum it turns out that the C and 5N targets are to be considered a useful tool for investigating neutron in­teraction processes at neutron energies larger than 8 MeV, when discrimination between the ground state group and the other neutron groups can be obtained. Of course, for inten­sity reasons, the use of relative thick targets has to be envisaged. The usefulness of these neutron producing targets is demon­strated by H.Liskien and A.Paulsen (5) who have recently measured in this laboratory the cross sections of the Ni(n,p) Co and ^Cu(n,a) Co reactions, using activation techniques, at neutron energies between 8.46 and 11.48 MeV. Experimental Equipment and Procedure The measurements were made at the 3 MeV pulsed Van de Graaff accelerator of CBNM, using fast neutron time-of-flight tech­niques. A pulsed deuteron beam with 1 nsec burst width and 1 MHz repetition rate was focussed on enriched targets of C and N respectively. For the C(d,n) -'N experiment, the graphite target, mounted on an aluminium backing, was 2.03 ρ ΛΑ mg/cm thick and contained 97% C. For the measurements of the neutron angular distributions of the reaction N(d,n) 0 a target was used which consisted of a 1.75 mg/cm thick Si,N. layer mounted on a copper backing. The nitrogen of this chemi-.15 cal compound was 95% N. The neutron time-of-flight detector was inserted in a shielding which also collimated the neutrons produced in the target. The shielding, including the detector, could be rotated in the horizontal plane around the beam spot on the target. The detector and the associated electronics was already described in detail (6). The target-to-detector dis­tance was 227 cm for the measurements performed in the angle range between 0° and 137°. For geometry limitations the dis­tance had to be decreased to 148.5 cm when measurements were made between 137° and 148°. 3. As a neutron monitor a second time-of-flight detector system in connection with a single channel analyzer and a preset sca­ler was used. This time-of-flight monitoring system allows to select certain events coming from the target against most of the machine background, which is not negligible if deuterone are accelerated. In order to get from the experimental time spectra the final neutron angular distributions it was necessary to introduce a correction for the relative detector efficiency. Up to a neutron energy of 2.03 MeV the relative detector efficiency was obtained "by comparing the measured yield of neutrons scat­tered from the hydrogen nuclei of a polyethylene sample, at several angles between 20° and 67.5°, with the known η-p dif­ferential scattering cross section (7). The primary neutrons were produced by the T(p,n)-*He reaction at E = 3.1 MeV. These data on hydrogen were corrected for the attenuation of the out­going scattered neutrons (8). As a scatterer a hollow polyethy­lene cylinder, 1.00 cm outside diameter, 0.60 cm inside dia­meter and 4.00 cm height, was used. The weight was 1.840 g and the hydrogen content (14.31 + 0.06)%. In the energy range be­tween 1.84 MeV and 6.27 MeV the relative efficiency was ob­tained by measuring directly the neutron yield of the D(d,n)^He reaction at several angles between 0° and 145° and comparing this result with the known differential cross section of this reaction (4). Angular distributions were measured at E, = 2.0 MeV and 3.0 MeV. In the same way the relative detector effi­ciency was determined in the energy range between 12.76 MeV and 16.75 MeV, using the T(d,n)4Re reaction. The differential cross section needed for comparison was taken from ref. (4). The composed efficiency curve is shown in fig. 1. Results l4C(d,n)15N reaction Fig. 2 shows a typical time-of-flight spectrum at a deuteron energy of 1.35 MeV and an angle of 137° in the laboratory system, 4. Here one can recognize the peak η γ due to gamma-rays from the target and several other peaks due to neutron groups leading to different levels in the ^T nucleus: η to the ground state, n l 2 to the 5.28 and 5.31 MeV levels which are not resolved, n, to the 6.33 MeV level, n^6 to the 7.16, 7.31 and 7.57 MeV le­vels which are also not resolved in the present experiment. In the time spectrum.it is also recognized a small peak, deno-27 minated n41, which is presumly due to neutrons from the Al (d,n) Si reaction in the thick aluminium backing of the tar­get. A test made with the aluminium backing alone, shows that these neutrons give rise to a smeared spectrum which is more pronounced in the region of the n.. peak. From the shape of such a diffused distribution of neutron pulses the right cor­rection to the η -neutrons was always applied» while for the other neutron groups the relative small contribution from the reactions in the backing material was always neglected and on­ly time uncorrelated background was subtracted. From the resolved peaks in the time spectrum at 1.35 MeV, the angular distributions of the η , nl2, n,, η.,-g neutrons groups were derived. As mentioned, a constant background was estima­ted from the count rate in the region between the gamma and the η peaks, and was subtracted from the angular distribu­tion points. The same applies to the measurements at E,=2.00 MeV where angular distributions of the η , n l 2, n,, and η.,-g neutron groups were measured, while at E,=2.80 MeV only the η -angular distribution was obtained, because of insufficient time resolution. The results are presented in figs. 3, 4 and 5. 3N(d,n) 0 reaction Fig . 6 shows a typ ica l t ime-of - f l igh t spectrum taken a t a deuteron energy of 1.00 MeV and ^HQ-U = 60°. As in the case of the previous reac t ion , severa l peaks are here resolved too . Using the same notat ion as before we see the peak η γ due to gamma rays , η due to the ground s t a t e neutrons 1 fi of 0, n 1 2 to the 6.06 and 6.14 MeV l e v e l s , n , . to the 5. 6.92 and 7.12 MeV levels, n^ to the level at 8.88 MeV and nCr, to the 9.58 and 9.84 MeV levels. The prominent peak °' 14 12 n N C at low energy is due to N and C content in the target material. A contribution to the low energy tail of pQ pQ the n,- peak comes from the Si(d,n) ^ P ground state neutrons, because of the chemical composition Si,N. of the target. Such an effect becomes evident at higher energies, but at 1.00 MeV, it is still small and was not subtracted from the n,- results. Backing material effects are in this case negligible because of the high Coulomb barrier of the copper material used as a target backing. The time uncorre-lated background was always subtracted using the above described procedure. Because of the resolution limitations only at E, = 1.00 MeV angular distributions of the n , n12, n^. and n,. were eva-luated, while at E, = 1.80 and E, = 3.0 MeV the n angular distributions alone were extracted. The results are presented in figs. 7, 8 and 9. Discussion 1A 1R A. C(d,n) N reaction The excitation curves of the ground state neutrons at diffe-rent angles show a resonance-like structure, although the peaks are not very prominent. Comparison of the data of Ren Chiba (1) and W.L.Imhof (2) indicates that for deuteron ener-gies smaller than 1 MeV the excitation falls to zero, while for somewhat higher energies, at least three resonances or re-sonance-groups are present at 1.3, 2.0 and 2.8 MeV respective-ly. Ren Chiba gives also an attempt of unfolding the excita-tion curves by postulating a certain number, seven, of reso-nances between 1.0 and 3.3 MeV deuteron energies. The presence of such a resonance structure suggests that the 4C(d,n) ''N reaction must proceed, at least partially, through compound, nucleus formation. The attempt of explaining the asymmetric shape of some an-gular distributions only as a result of interference between 6. netøitouring resonances may be considered too, but it is un-likely that such an effect can justify the strong asymmetries observed in some cases of the present experiment. In other hand strong asymmetric angular distributions may be explained assuming the (d,n) reaction proceeding through a direct process, like deuteron or heavy ion stripping. In this situation we can say that in the energy region of the present experiment both compound nucleus formation and direct interaction processes are present and contribute to the neutron yield. Since the relative importance of these two modes of interacting is not known it appears surely difficult to fit reasonably the experimental data with a simple and consistent theory. Such an effort would be, moreover, outside the goal of the present paper. Ed = 1.35 MeV The only distribution which shows clearly a deuteron strip-ping pattern is the one corresponding to the doublet at 5.28 and 5.31 MeV. The direct reaction proceeds with an angular momentum transfer of 1 = 0. Evidence for heavy particle stripping may be found, instead, in the case of the ground state neutrons where the angular distribution is strongly backward peaked. Ed = 2.0 MeV The results at this energy confirm the previous considera-tions and assignments. Moreover, in the case of the neutrons to the 6.33 MeV level the compound neutron contribution ap-pears to be predominant. Ed = 2.8 MeV Here the absence of a well defined pattern does not allow to make any definite statement about the reaction mechanism. 7. Β. 1^N(d.n)160 reaction The same general remarks apply here as in the case of the l4C(d,n)l5N reaction. J.L.Weil and K.W.Jones calculated dif­ferential cross sections for the ground state neutron group from 1.148 to 5.026 MeV deuteron energies, using the exchange stripping theory of Owen and Madansky (9). As they point out the large variability left to the parameters introduced in the formalism is only justified on a phenomenological base. With this in mind, one can say that their fits with the ex­perimental results are rather good but at the lower energies, which are the ones of the present experiment, where the exci­tation curve at zero degree shows that the resonance structure is more pronounced. Ed = 1.0 MeV Anything about evidence of direct interactions can hardly be said at this energy. It seems, instead, that in all the distributions the compound nucleus interaction mechanism is the very predominant one. Ed = 1.8 MeV Here the reaction to the ground state seems to proceed through deuteron stripping with 1 = 0 . Ed = 3.0 MeV At this larger energy the possibility of interpreting the reaction to the ground state mainly in terms of exchange stripping theory show« to be adequate and the present expe­rimental results are in reasonable agreement with the cal­culations of Weil and Jones. As pointed out, this agreement is consistent with the fact that at this energy the deuteron 15 energy is larger than the Coulombbarrier of the Ν nucleus. Indeed, in this conditions, the probability of absorption of both deuteron nucléons by the yN nucleus followed by direct emission of a neutron is increased. 8. The a u t h o r s g r a t e f u l l y acknowledge the coope ra t i on given by Messrs . A. Crametz, R. Duchez and J . Leonard dur ing the exper iment . References 1) Ren Chiba, Phys.Rev. J23 (1961) 1316 2) W.L.Imhof e t a l . , Nuol .Phys . 49_ (1963) 503 3) J .L.Wei l and K.W.Jones, Phys.Rev. _Π2 (1958) 1975 4) N.Jaremie and J .D.Seagrave , LA-2014 (1956) 5) A.Paulsen and H.Lisk ien , p r i v a t e communication 6) M.Coppola and H . -H .Kn i t t e r , EUR.2798.e (1966) 7) J.L.Gammel i n Fast Neutron Physics p a r t I I J .Wiley e Sons, New York and London (1963) 8) L.Cranberg and J . S . L e v i n , LA-2177 (1959) 9) G.E.Owen and L.Madansky, Phys.Rev. 105 (1957) 1766 12 I 1 4 . J _ 2 . ; _ 4 6 β 10 Fig.1 Detector efficiency curve. 12 14 16 ï o . < * H! ¡2 o 24000 20000 16000 12000 8000 4000 n¡2 En= 1.35 MeV *Lab.= 137° 10 CHANNEL NUMBER. _L -L 50 100 150 200 250 Fig.2 '*C(d.ny5N reaction. Typical t ime-of-f light spectrum. 22 20 1.8 1.6 1.4 1 *> i.éC 1.0 0.8 0.6 ΩΔ 02 22 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 02 i dQ diï' ι da dn uC(d.n)15N UC (d,n) 15N1 Φ 1AC(d.n)ì5NÌ2 —H 1 ' KC(d.n)15N¿fí θ 20 40 6Ö 60 /ΟΟ /2Ö 74Ö 760 20 40 60 δΟ 100 120 140 160 Fig. 3 Neutron angular distributions in the CM-system. Deuteron laboratory energy 1.35 MeV ,4C(d.n) 'V* uC(d.n) %*56 θ 20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160 Fig.4 Neutron angular distributions in the CM-system. Deuteron laboratory energy 2.00 MeV. 22 2.0 1.8 1.6 1.4 1.2 1.0' 08 0.6 OA 02 ¡ dö*** t \ 4 14C(d,n)15N $ 20 AO 60 80 100 120 140 160 15 Fig.5 Angular distribution in the CM-system for the N ground state neutrons. Deuteron laboratory energy 2.Ò0 MeV. 5000 -! 4000 μ? ft 3000 ß 2000 7000 η Εη= WO MeV *. -60° 44 t J1» CHANNEL NUMBER 50 100 150 200 250 300 350 IS 16 Fig.6 N(dtn) 0 reaction. Typical time-of-flight spectrum. 22 20 1.8 1.6 1 ¿ 1.2 10 ι ΩΑ 0.6 0.4 02 22 20 ΙΑ 1.6 1.4 12 m 1.0 OB 0.6 0.4 02 - w ñ W d ?/η·ι dii" ' dÕ(*' Oi d_ ?(Cf) dii ^ \ K ^ s. N-15N(d.n)160 15N(d.n)160*¿ H^  ¥^ j r** Ò Λ' n 1 , 1 ƒ r |^ K 1+ Π H-U | Γ +-H '5N(d.n)wOmu ι te 1 ι ι l> Λ r 15N(d.n)160*s g I t+ ^ \r » 20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160 Fig. 7 Neutron angular distributions in the CM-system. Deuteron laboratory energy 1.00 MeV. 22 2.0 1.8 16 U 12 1.0' 0.β 0.6 0.4 0.2 ι \ > > & < * '5N(d.n),s0 'S , > 20 40 60 80 100 120 140 160 Fig β Angular distribution in the CM-system for the 0 ground state neutrons. Deuteron laboratory energy IdOMeV. 22 2.0 1.8 1.6 1.4 12 1.0 i 0.8 0.6 0.4 0.2 ♦ da « ctø' ' 42(0') dö ~ 15N(dtn)i60 θ "** 20 40 60 80 100 120 140J6 160 Fig.9 Angular distribution in the CM-system for the 0 ground state neutrons. Deuteron laboratory energy 300MeV. 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14C(d,n)15N and 15N(d,n)16O Reactions. EUR 3492.

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