Excitation functions for the (d, p) reactions on 96Ru, 102Ru and 104Ru

Nuclear Physics A129 (1969) 165 -171; (~) North-Holland Publishin# Co., Amsterdam N o t to be reproduced by photoprint ot microfilm without written permission from the publisher

EXCITATION FUNCTIONS FOR THE (d, p) REACTIONS ON 96Ru, I°2Ru AND t°4Ru A. MITO, K. K O M U R A , T. MITSU(/ASHIRA ~' and K. OTOZAI

Faculty of Science, Osaka Unirersity, Toyonaka, Osaka, Japan Received 13 January 1969 A b s t r a c t : Excitation functions for (d, p) reactions on O6Ru, l°2Ru and l°4Ru were measured with

the activation method up to 14.0 MeV deuteron energy. The results were explained with the modified Peaslee theory by using different values of the absorption parameter p. It was found on the doubly even target nuclei that the values of f, for (d, p) reactions became large as their isotopic numbers N-Z increase. E

NUCLEAR REACTIONS 96Ru(d, p), ~°2Ru(d, p), l°4Ru(d, p), E <=-"14.0 MeV; measured o(E). Natural target.

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I. Introduction Previously, Otozai et al. 1,2) measured excitation functions for the deuteron-induced reactions (d, p), (d, n), (d, 2n) and others on 142Ce, 7°Ge, 96Zr and 13°Te, and reproduced the results with the theory based on the semiclassical model. Only the experimental data for 7°Ge required quite different values of the parameters from those common for the other three target nuclei. The excitation functions for 7°Ge were reproduced by the calculation with the smaller values of the absorption parameter p and the proton-sticking probability ~p. The nucleus 7°Ge has the following two characteristic features compared with the other three nuclei: (i) Its atomic number is the smallest, and (ii) only it is located at the neutron-deficient side with respect to the fl-stability line. Present work was undertaken to investigate which feature contributes to the small p-value for 70Ge" For this purpose, the (d, p) reaction was chosen because of the following two reasons based on previous studies 1,2): (i) The agreement between the experimental and calculated excitation functions is very good for the (d, p) reactions. (ii) In the region of atomic number Z ~ 30, the (d, p) reaction is contributed predominantly by a neutron-stripping process. Therefore, the calculated cross section of the (d, p) reaction is affected mainly by the values of p, the nuclear radius parameter ro and the neutron-sticking probability ¢,, and is scarcely influenced by the values of ~p and the parameters concerned with the evaporation processes which follow the stripping t Present address: The Research Institute for Iron, Steel and Other Metals, Tohoku UniversitY, Sendai, Japan. 165

166

^. MITOet al.

process. Therefore, if reasonable values are adopted for r o and ~n, the calculated cross section of the (d, p) reaction is exclusively affected by the value of p. The ruthenium isotopes were chosen as the target nuclei because: (i) The atomic number of ruthenium is high enough to satisfy the condition Z >~ 30 mentioned above and is larger than that of zirconium which has the common values of parameters. (ii) Ruthenium has stable isotopes which produce radiochemically measurable products of (d, p) reactions, and which are located in both neutron-rich and neutrondeficient sides of the//-stability line, i.e. neutron numbers differ greatly from each other. Thus in this work the excitation functions for the reactions 96Ru(d, p)gVRu, t°2Ru(d, p)l°aRu and l°4Ru(d, p)l°SRu were measured radiochemically, and the p-values obtained from them were compared in order to see if the p-value correlates with the neutron number of the target nucleus. From this result, we tried to ascertain which feature of 7°Ge mentioned above affects its small p-value.

2. Experimental procedure

About 3 m g . cm -2 of metallic ruthenium of natural isotopic abundance was electrodeposited onto l0 pm copper foils from a 2N H2SO4 solution of RuNOCI3, which was synthesized from JIS guaranteed RuCI 3 • H 2 0 and N2 04 gas. The target foils were stacked with aluminium foils for energy degradation. The stacked targets were irradiated for 20 min by the 0.5 #A deflected deuteron beam from the cyclotron at Osaka University (Ed = 12. I and 11.2 MeV) and Kyoto University (E d = 14.6 MeV). The energy and its spread were determined by the aluminium-range method. The spread of energy was about 0.1 MeV. Irradiated targets were chemically treated as fast as possible in order to depress the effect of the decay 5) of 97Rh (32 min) into 97Ru. The copper backing of each target was removed with hot aqua regia. The remained metallic ruthenium was dissolved in a strong oxidizing reagent of hot 6N NaOH containing a sufficient amount of C12 coloured in golden yellow. The extent of C12 gas blown into the solution was carefully controlled by the colour of the solution and by the ruthenium dissolving test, since an excess of CI 2 causes a large decrease in the dissolving rate and a great loss of ruthenium. The NaOH solution containing ruthenium was converted into the dilute H2SO4 solution to form RuO4, which is extractable in CCI 4. The separation of ruthenium from rhodium was carried out by extracting RuO,~ with CCI,, from the H2SO4 solution under the existence of each carrier. The separation between ruthenium and rhodium was required three times (i) the first-step isolation of ruthenium from the rhodium and technetium produced by the side reactions in the irradiated target, (ii) the isolation of l°SRh (35.88 h) grown from l°SRu (4.43 h) in the ruthenium fraction two days after the first-step separation and (iii) the isolation of 97Ru (2.88 d) grown from 97Rh (32 min) in the rhodium fraction one day after the first-step separation.

au(d, p) REAOrloIqs

167

The third-step isolation was needed to estimate the effect o f 97Rh decayed into 97Ru" When it was necessary to stand the ruthenium and the rhodium fractions for a long period, the fraction solutions were covered with water and CCI 4, respectively, and kept cool on ice lest ruthenium vaporize as RuO4. The yield o f the extraction o f ruthenium was about 95 ~ . The extraction was always repeated three times to collect ruthenium quantitatively. The decontamination factor of rhodium was more than 102 at a single separation. F r o m the l°SRh fraction, rhodium sulphide was precipitated and deposited on a defined area for a ~°SRh counting source. From the ruthenium fraction o f CCI~ which is free from 105 Rh, ruthenium was backextracted into 2N N H 4 O H , precipitated as a sulphide and used as the source for 97Ru and l°3Ru. It was ascertained that the losses o f ruthenium and rhodium were negligible in each step. The activities o f each counting sGurce were measured with the methods summarized in table 1 using a 7.6 cm × 7.6 cm N a I ( T I ) scintillation crystal and a 200-channel pulse-height analyser. TABLE 1 Outline of radioactivity measurements Reaction

~Ru(d, p)97Ru ~°ZRu(d, p)t°aRu l°4Ru(d, p)l°~Ru

a) Ref. e).

Half-life of product

2.88 d *) 39.5 d ~) 4.43 h c)

h) Ref. 7),

Radiation measured

Determination of counting efficiency

Decay scheme ref.

0.216 MeV 7-ray of °TRu

defined solid angle method

et al. 9)

0.498 MeV 7-ray of ~°aRu

compared with ZZNa standard

et al. 1o)

0.306, 0.319 MeV 7-ray of l°SRh (35.88 h) c)

defined solid angle method

Cretzu Mukerji Pierson 11)

e) Ref. 8).

3. Experimental results Cross sections obtained for the 96Ru(d,p)97Ru, l ° 2 R u ( d , p ) t ° 3 R u and l°4Ru(d, p ) l ° S R u reactions are shown in table 2. The data are also plotted in fig. 1 in the form of excitation functions. Errors shown in the table and the figure are the standard deviations of the experiments repeated three times. It is seen in the figure that the excitation curves for the three reactions converge in the low-energy region. It is also seen that as the neutron numbers o f the target nuclei decrease, the cross sections become large at the high-energy region, and the positions o f the m a x i m u m cross sections shift gently to the higher-energy side.

168

A. MITO et al. TABLE 2

Measured cross sections of Ru(d, p) reactions in mb

~

Target ucleus

~Ru

~OZRu

~O*Ru

190±40 220 230±30 280 280 240 220 190 120 20

140±30 140 150 210 220 180 140 140 120 30

(MeV) . . . . 14.0 12.7

230~60 290 320~20 360 350 330 240 190 110 20

11.7

9.8 8.7 8.0 7.1 6.5 5.9 4.4 10 3

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96 Ru(d,p)97Ru 102Ru(d,p)tO3Ru 104Ru(d.p)105Ru

O & {:]

0.8 1.6 2.2

.... ....

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Fig. 1. Excitation functions of 96Ru(d, p)97Ru, ~°2Ru(d, p ) l ° 3 R u and t°*Ru(d, p)t°SRu reactions.

4. Discussion

E x p e r i m e n t a l excitation functions were a n a l y s e d by the m e t h o d o f O t o z a i et al. 1). This is a modification o f Peaslee's t h e o r y 3) by i n t r o d u c i n g the a b s o r p t i o n p a r a m eter p. In the m e t h o d o f Otozai et al., the cross section o f the (d, p ) reaction is expressed by the e q u a t i o n a(d, p ) = a ( d , P).-.~,,ip + a ( d , P)~b~,

R,;((|, p) REACTIONS

169

where a(d, P).-.,.,ip and a(d, P)=b, are the contributions to or(d, p) from the neutron stripping and from the proton evaporation after the entire absorption of deuteron, respectively. According to the results in the previous calculation t.2), the former contribution is exceedingly predominant in the region of Z ~ 30, and it is expressed by the equation

rplq~c(rp)J2F[2~(rp-R)]fdro,

a(d, P)n-strip = 2.18 •~ 2a(R + p)

where ~ is a constant on a deuteron itself 3), ~. the neutron-sticking probability, the radius of target nucleus R = ro A ¢, r o the distance from a proton in a deuteron to the centre of target nucleus, 9c the wave function of a deuteron in the Coulomb field of (a)

103

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15

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r

r i

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5

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15

Fig. 2. T h e effects o f the parameters in the modified Peasleo theory on the excitation function o f the t°2Ru(d, p)X°aRu reaction. T h e effect o f (a) ~ea, (b) r 0 and (c) p.

A. M1TO et al.

170

the target nucleus, F(x) a combination of the exponential and the cosine integrals s) and f the "reduction factor", which means the probability of capturing the negativeenergy neutron in the neutron-stripping process. The absorption parameter p corresponds to such a critical distance that a deuteron is absorbed entirely when one nucleon attaches to the nuclear surface and another nucleon exists within the distance R + p from the centre of the nucleus. If the same values of ~n, ro and p were taken for 96Ru, I ° 2 R u and l°4Ru, their calculated excitation functions are nearly equal, though their mass numbers and the neutron binding energies are different. In I ° 2 R u for instance, the independent influences of en, r o and p on the excitation function are shown in fig. 2. As seen, only the depression of the p-value enlarges the cross sections except in the low-energy region and shifts the peaks of the excitation functions to the higher-energy side. The excitation curves in fig. 2(c) are similar to the one in fig. I. It was tried to explain the experimental results by using different p-values, with constant values of r o and ~,. The values 1.6 fm for r o and 1.0 for ~. were used as in the case 1) of 142Ce. The values of Peaslee 3) were used for the parameters on the deuteron itself. The final calculated results are shown by the curves in fig. I. It is seen that the calculated excitation functions reproduce the experimental ones quite well. TABLE 3

Values of the parameter p Target nucleus

96RH ~°2Ru l°4Ru 142Ce V°Ge 96Zr l nOTe 94Zr

Z

N

N-Z

p(fm)

44 44 44 58 32 40 52 40

52 58 60 84 38 56 78 54

8 14 16 26 6 16 26 14

0.8 1.6 2.2 2.2 0.5 2.2 2.2 1.6

Ref. present work 1) 2) 2) 2) 4)

The p-values obtained are summarized in table 3. The p-values for ruthenium isotopes become larger as their neutron numbers decrease. The p-values which were obtained in the previous experiments 1.1) are also shown in table 3 with the value obtained by analysing the excitation function for the 94Zr(d, p)95Zr reaction measured by Bock "~). It should be noted here that all of these nuclei have even Z and even N, and that the common values of 1.6 fm and 1.0 are used for the parameters r o and ~,, respectively. It was found empirically that the p-values given in table 3 are univocally correlated with the isotopic numbers N - Z of the target nuclei as shown in fig. 3, where # increases monotonously with isotopic number up to N - Z = 16, and in the region N - Z > 16, it becomes 2.2 fm, which corresponds to the average separation between nucleons in a deuteron.

Ru(d, p) REACTIONS

171

In the previous experiments for V°Ge, the correlation shown in fig. 3 suggests that both the effect of the small atomic n u m b e r a n d o f the n e u t r o n deficiency makes the isotopic n u m b e r small and hence required the small value o f p .

~°~Rulid / 96Zr

2.0

C~- . . . . 13°Te ~2Ce

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Fig. 3. Correlation between p-value and isotopic number. The authors are indebted to Drs. Y. U e m u r a a n d T. Nishi for their help in the operation of the cyclotron a n d in the measurements of the beam energy a n d to Dr. M. K o y a m a for suggestions on the chemistry of technetium.

References 1) K. Otozai, S. Kume, M. Koyama, T. Mitsuji, T. Nishi and I. Fujiwara, Nucl. Phys. 81 (1966) 322 2) K. Otozai, S. Kume, H. Okamura, A. Mito, T. Nishi and I. Fujiwara, Nucl. Phys. A107 (1968) 427 3) D. C. Peaslee, Phys. Rev. 74 (1948) 1001 4) R. Bock, Z. Phys. 169 0961) 546 5) B. Basu and A. P. Patro, Nucl. Phys. 32 (1962) 347 6) S. Katcoff, Phys. Rev. 111 (1958) 575 7) K. F. Flynn, L. E. Glendenin and E. P. Steinberg, Nucl. Sci. Eng. 22 0965) 416 8) H. W. Brandholst, Jr. and J. W. Cobble, Phys. Rev. 125 (1962) 1323 9) T. von Cretzu, K. Hohmuth, G. Winter and J. Schintlmeister, Ann. d¢r Phys. 17 (1966) 1 10) A. Mukerji, D. N. McNelis and J. W. Kane, Jr., Nucl. Phys. 67 (1965) 466 ll) W. R. Pierson, Phys. Rev. 140 0965) 1516