A study of the B10(d, p)B11 reaction

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Noilh-Holland Publisking Co ., A mSfej, , : Utn . Ni_icleay Physics 38 (1962) 114-12(1 ; (g) jj j ) jij er without written permission from the r_ Not to be reproduced by photoprint or microfilm

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S. HINDS AND R. MIDDLETON Atomic Weapons Research Establishment, Aldermaston,

erkshire

Received 26 May 1962 Abstract : Angular distributions of th-_ proton groups fmin the B 10(d, p)BI" reaction leading to the ground .and first eleven excited states of B 11 have been measured using a multi-channel magnetic spectrograph with an angular range of 5' to 175'. The incident deuteron energy was 1 .10 Me`'. The more intense distributions have been fitted with Butler plane wave stripping curves which enabled some 1-value assignments to be made and some absolute reduced widths to be extracted. The 1-values are in agreement with previous assignments except for the 8.923 MeV state. The transition to this state had previously been assigned as I == 0 and I = 2 by Bilaniuk :and tinsel whereas the present result strongly suggests I = 1 . in agreement with other 1°(d, p)B" ~,.nd Bt.- 9 (lei, p)B 11 measurements. troduc

The angular distributions of the protons t7rom the B"(d, p)B" reaction have bcen eV (see Nzenbergmeasured previously at incident deuteron energies up to 15 Selove and Lauritsen ')) . These experiments included most of the states of B" up to about 9 eV excitation but usually inadequate energy resolution preverted .1, detailed study of all the energy levels . The state at 8 .923 eV is of particular interest since there is disagreement as to its parity. Bilaniuk and tinsel 2) observed an unusual distribution for the proton oupfrom, the B"(d, p) reaction leading to this state which they fitted with a coinTnKon of I = 0 and I = 2 stripping curves, althouggh the group was obscrv4:d to he a single group. This even parity assignment disagrees with the negative. parity one of Hfinds and Middleto n 3) from the Be"(He 3 , 1p)B" double stripping reaction and also with that of Pollen and. Whitehead') from a recent study of the B , 0(d, P) reac!.ion at an incident energy of 3 .5 MeV. In the present rove -,tigation absolute differential cross-sections have been measured, at an incident deuteron energy of 10.10 Me, of the proton groups from the "(.d, p) 11 reaction leading to the ground and first eleven excited states of B" . These were measured over an angular range of 5' to 175' using a multi-channel magnetic spectrograph . 2 . Experimental Proc A beam of 10.10 MeV deuterons from the Aldermaston tandem electrostatic + gee -1-1 was of BL I. These were Use L bombard thin self supportie targets prepared by evaporating separated isotope B' o on to a lass slide ßh2d stripping Off the resulting layer, which was then transferred to a target frame . 114

THE

10(d . P)

8:

REACTION

he reacti ro ducts were analysed in the multi-channel magn-etic spectrograph which has tready been described (Middletoil and Hinds ')). Two exposures were niade of 3 pC each, .ising targets of different thicknesses . The areal density of the thicker tar, et was detemined by weiglAng to be 63 jig/CM2, with an estimated arror of ± 30 %. esults obtained using this target were used to normalise those fr the thinner tar et from which angular distributions of the more intense proton grou were obtained . 3. RauIts A typical proton, spectrum obtained with the thicker target and at an a gle of observation of 421' is shown in fig. 1 . The field strength was 10 806 G. Similar sDectra were simultaneously recorded at 23 other angles, ranging from 5' to 1753 . PROTON ENERGY MaV '5 "

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1 . A typical proton spectrurn .

roues arising from tht- B"(d, p) B" reactions are labelled numerically in the figure, the ground state group labelled zero. These groups were identified by their characteristic rate of change of energy with angle of observation . Two strong groups were observed from the 016 (d, p)017 reaction leading to the ground and Est excited states of i', and arose from oxygen impurity in the target. These groups are labelled by the symbol for the residual nucleus with a subscript indicating the excited state . Weaker groups due to C" and B" target impurities are similarly la

S . 14INDS ANO R . MIDDLETON

corresponding to the ground and firat angular distributions of the groups were obtained mearly from the eleven excited states of B" are shown in fig. 2 . These been determined to an accuracy thicker B10 target, and absolute cross-sections have to MP 0.r.P , th ,- 'r- a Wand of ± 30 %. The exposure, wim ine ininnici Lair,L vvrAo -_ to the states at 6 .753, 8 .923, angle distributions of the intense groups corresponding for all other groups at angles less 9.189 and 9.278 MeV. By scanning both exposures . than 60', a normalisation factor was obtained for the two exposures The stronger groups have been fitted with Butler stripping clirves calculated using the method of Macfarlane and French ') . It was found that the best is (shown by the full lines) to the ground and 6.753 MeV states were or-stained using a radius of interaction of 5 .0 fm, but all other states were best fitted using a radius of 4.3 fm, which is the Gamow radius, 1 .7+1 .22 Ai frn. The proton groups leading to the 2 .144, 6.805 and 7.989 MeV excited states are very weak and do not show any stripping Their intensity is probably all due to the fog anon and decay of the compound nucleus . The 5437 and 8.567 MeV level distributions have been tentatively fitted with I = I and I = 2 curves respectively, wing the Garrow radius of 4.3 Q. Since these distributions are weak it is not possible to make definite /-value assignments, but the assignment of I = I to the 5.073 MeV state is probably correct since the spin and parity of this state are known 7) to be 2-1- - . Stripping curves having /-values of I and 2 are plotted on the distribution for the 7 .299 MeV state. Neither curve is a good fitbut if the transition to this state does proceed weakly by stripping, then I = 2 is the most probable assignment. The I-value assignments are surnmarised in table 1, together with the maxiniura a . solute differential cross-sections for each group. In the fourth column the radii of interaction ro used to obtain the best fit in each case are shown, and the nexi column gives the corresponding values of the absolute reduced widths ~ailti lied by (2J+ 1) . The column J" gives the most probable spins and parities which were 2 used to obtain the absolute reduced widths, 0, n shown in the next column . These 02, may be compared with P shown in the ninth column, which are the abso!ute reduced widths for the mirror nucleus states measured from the W O (He 3 , d)C" reaction Ithough these valves o f 02P depend on the factor A occurring in the expression for he

the (He 3 , d) cross-section (see Macfarlane and Ftench ')) the overall agreement is reasonable . In column (a) of the table are the relative reduced widths measured in the present 2) investigation, m Nch may 4 compared Nvourably with those of Bitemu k and HenSC1 which were measured at an incident deuteron energy of 7 .78 e

ssi The present I-value assignments are tinsel ') consistent with those of ila.niuk ate except for the 8 .923 Me V state . These authors interpreted their angular distribution

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S. MNTDS AND R. MIDDLETON

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p) of 0124, 0128 and 0.030 respectively . Similarly the 9.189 and 9 .278 D&V of 02 (2s) of 0 .030 and 0.029 respectively . These are the states yield absolute values 0 02 o f BI I so that it is not possible to compue them for rst absolute measurements 0 ith other values . Nevertheless they are in agreement with the general trend of 02(l p) nad 02s) ®( when plotted as a function of nucleon binding energy 6) sinize for 0 1 1 values of about 0.037 and 0.027 respectively would be expected . 0(

lien for his encouragement and interest in this work e are grateful to e would like to thank r. H. Marchant and the tandem accelerator operating staff for their assistance with the exposures, Mr. A . H . F . Muggleton for preparing the targets and Mrs . G. Burgess for assistance with the data analysis. eferences I ) F. Nzenberg-Selove and T. Lauritsen, Nuclear Physics 11 (1959) 1 2) A Alaniuk and A C Hensel, Phys. Rev . 120 (1960) 211 31 S . Hinds and R. Middleton, Proc. Phys. Soc, 75 (1960) 754; 75 (1959) 196 4) . A Hen and X & Whitehead, Proc. Int. Conf. on Nuclear Structure (Univ. of Toronto Press, Toronto, 1960) p. 40 5) iddleton and S. Hinds, Nuclear Physics, 34 (1962) 4 6) M . H. Macfarlane and J. B. French, Rev. Mod . Phys. 32 (1960) 567 7) P. F. Donovan, A T Kane, R. E. Pix1ey and H. Wilkinson . Phys. Rev . 123 (1961) 589 8) I A Ferguson, H. E. Gove, J. A. Kuehneq A. E. Litherlaric'.1 E. Almqvist and D. A . B ro r.`cy, Phys. Rev . Letters 1 (1958) 414 S. Hinds and R. Middleton, Proc. Phys. Soc. 78 (11961) 81 . Wilkinson, Phys. Rev. 105 (1957) 666 . T. S . Evans and A. P. French ; Phys . Rev . 109 (1958) 1272; J. C. Hensel and W. C. Parkinson, Phys. Rev . 110 (1958) 128 72) A E . Bowc-ock, Phys. Rev. 112 (1958) 923 ; . Zeidman and J. M . Fowler, Phys. Rev . 112 (1958) 20 - Kurath, Phys. Rev . 1 0, (1956) 216

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