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Excitation functions of proton induced nuclear reactions on highly enriched 78Kr: Relevance to the production of 75Br and 77Br at a small cyclotron
A/.$. Radial. Isor. Vol. 44, No. 8, pp. 1105-l Printed in Great Britain. All rights reserved
I I I,
1993 Copyright
0969-8043/93 $6.00 + 0.00 6 1993 Pergamon Press Ltd
Excitation Functions of Proton Induced Nuclear Reactions on Highly Enriched 78Kr: Relevance to the Pro&&ion of 75Br and 77Br at a Small Cyclotron F. TARKANYI’,‘, ‘Institut
Z. KOVACS’,*
and S. M. QAIM’*
fiir Nuklearchemie, Forschungszentrum Jillich GmbH, 5170 Jfilich, Germany and *Institute Nuclear Research, Hungarian Academy of Sciences, 4001 Debrecen, Hungary
of
(Received 4 January 1993) Excitation functions were measured for ‘sKr(p,pn)“Kr, ‘sKr(p,x)“Br and 7*Kr(p,a)75Br reactions from threshold to 20 MeV by the activation technique using 99.4% enriched 78Kr as target gas. There is a strong discrepancy between our data and the literature values for the 78Kr(p,pn)77Kr and 78Kr(p,a)‘5Br reactions. Differential and integral yields of 77Kr, “Br and 7SBr were calculated from our excitation functions. The calculated integral yields of 75Br and “Br are approximately in agreement with the low-current irradiation experimental yield data reported in the literature. The thick target yields of both 75Br and “Br at a small and 70 PCi (2.6 MBq)/pAh, respectively] and cyclotron (E, zz 17 MeV) are small [1.9 mCi (70 MBq)/pAh due to the very high cost of the target gas, the two production processes are uneconomical. At a medium-sized cyclotron with Er, 3 25 MeV, however, the “Br yield would be appreciably higher and the process could be very suitable for production of “Br.
Introduction Several radioisotopes of bromine have found applications in labelling biomolecules [cf Stijcklin (1977, 1986); Maziere and Loc’h (1986)]. Of particular interest are the neutron deficient bromine isotopes “Br (t,,r = 1.6 h) and “Br (tljz = 57 h). The former is a positron emitter and has found use in positron emission tomography (PET) and the latter is more suitable for longer lasting studies with y-cameras having a high-energy collimator. Detailed reviews of the production methods [cf Qaim and Stocklin (1983); Qaim (1986)] suggest that both “Br and “Br can be produced in sufficient quantities only if a medium-sized cyclotron or a high-energy accelerator is available. The most suitable methods for the production of “Br are the 75As(3He,3n)75Br [cf Blessing et al. (1982)] and 76Se(p,2n)75Br [cf Paans et al. (1980); Kovacs et al. (1985)] reactions. For “Br production, on the other hand, the “As(a,2n)“Br [cfBlessing et al. (1982); and references cited therein] and ““‘Mo(p,spall)“Br [cf Grant et a/.(1981)] processes are most suitable. In an attempt to produce “Br at a small cyclotron Friedman et al. (1982) measured the 75Br-yield in the 7*Kr(p,a)75Br reaction at 15 MeV using 20% enriched gas as target material. Later De Jesus and Friedman
(1988) determined the 75Br-yield in the ‘*Kr(d,na)“Br process for deuteron energies from 10 to 21.5 MeV. Recently Helus et al. (1989, 1991) and Helus and Zeisler (1992) also measured the 75Br yield. The cross section data for the 78Kr(p,~)7SBr process deduced by the two groups from their respective measured yields are scanty and appeared to us to be in error. As regards “Br production, Helus et al. (1989, 1991) and Helus and Zeisler (1992) investigated the ‘sKr(p,x)“Br process and reported some yield data. Here again the deduced cross section values are scanty and apparently incorrect. We performed detailed excitation function measurements on reactions relevant to the production of both “Br and “Br in the interactions of protons with highly enriched “Kr.
Experimental Excitation functions were measured on 99.4% enriched “Kr (Isotec, U.S.A.) by the activation technique using gas cells as irradiation samples. The techniques used were essentially the same as described in several earlier publications [cf Backhausen et al. (1981); Tarkanyi et al. (1988a,b, 1991a, 1992); Kovacs et al. (1991)]. Irradiations
*Author for correspondence.
Stainless steel gas cells (2 cm dia, 2.5 cm length Al windows were vol. = 8mL) having 50-100pm 1105
1106
F.
TARKANYI et al.
filled with the enriched gas at pressures of 0.27-0.64 bar. Either a single cell or several cells stacked together were irradiated at a time, depending on the reaction product to be studied. The irradiation time varied between 6 and 60min. All the irradiations were carried out at the variable energy Jiilich Compact Cyclotron (CV 28) at beam currents of 200-500 nA. Following primary incident proton energies were used: 20.4, 18.7 and 14.8 MeV. Other energies were obtained using Cu and Al degrader foils. The beam current was measured via a Faraday cup and by means of monitor reactions induced in Cu foils placed in front and at the back of each irradiated cell. A collimated beam (4 = 0.5 cm) was used. Chemical
separation
In general the produced activities were measured without a chemical separation. In a few cases, however, the bromine isotopes were separated chemically and counted to check the reliability of the nondestructive radioactive assay. After cryogenic removal of the irradiated krypton, the cell was rinsed with a solution containing 20mg each of KBr and KBrO, . An activity balance of the gas cell in the gas recovery and rinsing process was done. There was no loss of bromine activity during the gas recovery and >98% bromine activity was obtained in the solution. The solution was then heated to 90°C. Bromine was precipitated as AgBr and the activity of the solution measured before and after the precipitation. Almost no activity was left in the solution, indicating that the radiobromine occurred mostly as bromide. The overall separation yield of radiobromine was found to be 90 + 4%. Measurement
of radioactivit)
The activity of the gas cells, monitor foils and the precipitated samples was measured via standard high resolution y-ray spectroscopy. The samples were measured at a large source-detector distance to ensure good counting geometry and to avoid pile-up and coincidence losses. The decay data used for activity determinations are given in Table 1 (Browne and Firestone, 1986; Farhan et al., 1989).
Table I. Radiation
characteristics
Beam
Half-life
Check
“Kr
1.24h
“Br
57.0 h
P + (0.7) EC (99.3)
1.62 h
p + (75.5) EC (24.5)
on the purity
of enriched
gas
The enriched gas was used repeatedly in irradiations. An occasional check on its quality was therefore necessary. This was done as follows. Natural krypton was mixed with different amounts of air and its pressure at liq. N, temperature was compared with the pressure of the used enriched krypton gas under similar conditions (same temperature and volume). They were found to be identical when pure natural krypton was used. The components of air which condensed at liq. N, temperature (Xe, Kr, Ar) were searched for via analysis of some activation products; practically no activity was found. These tests showed that in the repeated filling and recovery process a small amount of the enriched gas was lost, its chemical composition, however, did not change significantly. Calculation
of cross sections
and their errors
Cross sections were determined using the activation formula. The errors of the cross sections were estimated by combining the individual errors in quadrature: beam current lo%, number of target atoms 5%, detector efficiency 5%, decay data 3%, chemical separation 5%, peak area analysis l-2% (in a few cases around the threshold 2 10%). The main errors in the energy scale were estimated on the basis of monitor reactions; they originated from the non-perpendicular position of cell windows to the beam direction, from the density reduction along the beam line, as well as from the beam broadening.
of the radionuclides reactions
Mode of decay W)
monitoring
The beam currents, the primary beam energies as well as the degraded energies along the stack were determined via Cu monitor reactions (Colle et al., 1974; Griitter, 1982; Kopecky, 1985; Tarkanyi et al., 1991b; Pie1 et al., 1992) and by range-energy calculations (Williamson et al., 1966; Andersen and Ziegler, 1977). The beam current measured directly in the Faraday cup and that obtained via the monitor reactions agreed within 10%.
y-ray Nuclide
current
studied and Q-values
of the contributing
energies in
keV (% abundance) 129.8 146.4 276.2 312.1 239.0 281.6 297.3 520.6 578.9 286.6 377.4 427.9 952.3
(80.0) (36.8) (2.88) (3.68) (23.9) (2.38) (4.30) (23.1) (3.06) (92.1) (4.1) 14.51 il.7k)
Contributing reaction
Q-value (MeV)
“Kr(p,pn)
~ 12.0
“Kr+“Br ‘*K~(P,~P)
- 12.0 -8.2
“Kr(p,m)
-0.1
Proton Table
2. Cross sections for the formation proton induced reactions
induced
reactions
of “Kr, “Br and “Br in on ‘*Kr
Cross section (mb) Energy WV) 10.82 & 0.28 11.72 +_0.25 12.17 + 0.21 12.19 + 0.37 12.28 + 0.40 13.38 i_ 0.18 13.73 * 0.31 14.13 if: 0.32 14.16+0.15 14.74 * 0.30 14.95 + 0.26 15.17+0.25 15.67 i_ 0.23 15.73 + 0.25 15.74 + 0.26 15.90 i: 0.25 16.17+0.32 16.35 + 0.20 16.45 +_0.22 16.51 + 0.20 16.68 + 0.22 17.02 +0.18 17.03 * 0.30 17.10 + 0.30 17.15 + 0.19 17.19 * 0.20 17.56+ 0.18 17.66 & 0.27 17.67+0.15 17.77 kO.15 17.82 + 0.16 17.97 + 0.25 18.19~0.15 18.30 k 0.25 18.41 i 0.22 IS.81 +0.15 18.93 k 0.22 19.53 * 0.20 19.62 f 0.20
“Kr(p,pn)“Kr
‘*Kr(p,x)“Br
+ f + f f +
0.8 0.6 0.6 3.0 I.5 2.5
5.8 7.0 29.6 16.7
k + f f
3.3 7.0 9.5 5.4 5.4 10.6 9.9 14.4 17.5 10.0 14.3 15.4 19.0 15.8 15.8 27.9 17.0 20.9 22.8 19.9 17.6 23.4 27.4 18.9 25.9 28.2 19.2 28.1 23.5 19.7 27.6 18.5 29.5 30.0 21.2 18.9 25.8 24.4 20.2
0.8 0.9 4.1 2.1
60.8 + 7.7 63.1 _+ 8.0 54.2 +_ 6.9 65.9 f 8.3
61.4 + 8.4 57.2 +_1.2 69.8 f 8.8
67.1 + 8.6
III f 138 f 130* 112*
15 I8 I7 15
I38 k I8 179k23 160 + 21 155+_20 I81 + 23 192 f 24 240 + 31 242 k 31 214 + 27 241 + 31 293 k 37 343 + 44 292 f 37
I I4 f 16 l24+ I6 109 f 14 153f20 184 f 24 154*21 I38 F 18 175+23 234 f 30 228 f 29
274 + 35 293 f 37
f 0.4 + 0.9 * 1.2 f 0.7 f 0.8 f 1.4 f I .3 * 1.9 + 2.3 * I.4 * 2.0 * 2.0 + 2.5 f 2.0 f 2.0 f 3.6 * 2.2 _+2.7 +_2.9 + 2.5 f 2.3 k 3.1 f 3.5 k 2.4 + 3.3 f 5.0 f 2.6 f 3.6 + 2.9 +_2.5 k 3.5 + 2.4 f 3.8 f 4.3 f 2.8 + 2.4 f 3.3 f 3. I f 2.6
Measurements on natural krypton In a separate series of irradiations the “Br yield was determined using krypton gas of natural isotopic composition. The gas cells were filled up to 3 bars and irradiations done at the Jiilich Isochronous Cyclotron (JULIC) for 2 h with protons of primary energies of
0 -.“““““““‘~“““”
12
enriched
78Kr
1107
38 and 30 MeV at beam currents of 200 nA. Radiobromine was separated as described above and the activity measured via y-ray spectroscopy.
‘*Kr(p,a)“Br
0.10+0.06
I .2 3.6 4.5 23.4 II.5 18.7
on highly
IL Proton
Excitation
Functions
The nuclear reactions studied and their Q-values are given in Table 1. The measured cross section data are given in Table 2 and the excitation functions are shown in Figs 1-3. The solid curves were obtained by fitting the data with polynomials. 77Kr(p,pn) 77Kr-+ 77Brprocess The interactions of protons with the 99.4% enriched “Kr used in this work would lead to the radioisotope “Br via the following three routes: (a) ‘*Kr(p,2n)“Rb
2
“Kr z
“Br l.Zh
(b) “Kr(p,pn)“Kr
5
“Br
(c) “Kr(p,2p)“Br. The Q-value of the 78Kr(p,2n)77Rb reaction is - 18.1 MeV; the reaction threshold would therefore lie at ~20 MeV. In our studies up to 20 MeV we specifically searched for this reaction product but did not detect it. The emphasis was therefore on the study of routes (b) and (c). The excitation function of the “Kr(p,pn)“Kr process is shown in Fig. 1. The threshold lies at around 14 MeV. Beyond 16 MeV the cross section increases rapidly and reaches a value of about 300mb at 20 MeV. The cumulative production cross sections for “Br were measured after complete decay of “Kr and the excitation function based on both radiochemical and nondestructive measurements is given in Fig. 2. The excitation function for the ‘“Kr(p,x)“Br reaction reported in this work has been measured for the first time. The identical values of cross sections in Figs 1
16 energy
18 (MeV)
Fig. I. Excitation function of ‘*Kr(p,pn)“Kr nuclear process.
20
F.
1108
T.~RKANYI et al.
ii
E 300 1 “Kr(p,x)“Br
s z
1 /-
u
16
18 Proton
energy
20
(MeV)
for the formation of “Br in proton induced reactions on “Kr. Measurement of radioactivity was done after complete decay of “Kr to “Br.
Fig. 2. Excitation
function
results of Helus et al. (1991) shows large discrepancies Our cross section values are a factor of 4 lower than their data. From a consideration of the cross section systematics and magnitudes of various competing reactions in this mass and energy region, it is inferred that the (p,pn) reaction cannot have a cross section of 1400 mb, as reported by Helus et al. (1991) (see below for further discussion).
and 2 lead to the conclusion that “Br is produced almost exclusively via the decay of “Kr. The contribution of the “Kr(p,2p)“Br reaction, if any, is thus small (< 15%) and within the error limits of the measured “Kr(p,pn)“Kr and 78Kr(p,x)77Br excitation functions. It should be mentioned that our enriched target gas contained 0.6% “Kr, hence the “Kr(p,Cc)“Br direct production channel would also be involved in the production of “Br. However, taking into account the small percentage of “Kr and the expected low cross section of the ‘OKr(p,Cc)“Br reaction, the contribution from this process was estimated to be ~0.2%. A similar consideration in the case of natural Kr (with ‘*Kr and “Kr abundances of 0.35% and 2.25%, respectively) led to an exact description of the measured “Br yield in irradiation of natural Kr with proton energies up to 20 MeV (at higher energies other processes also contribute). A comparison of our excitation function for the ‘*Kr(p,pn)“Kr process with the recently published
78Kr(p,x)7sBr
reaction
The excitation function of the 78Kr(p,cz)75Br reaction is given in Fig. 3. The data show some fluctuations, presumably due to large errors. The excitation function exhibits a maximum around 18 MeV and the cross section amounts to about 25 mb. This value is also lower by a factor of 4 than that reported recently by Helus et al. (1991) for the same reaction. The preliminary cross section values of Friedman ef al. (1982) are even 6 times higher than our data. We believe that our data are more accurate (see below for further discussion).
LO c”“““l”“““““““““““““”
z
E 30 1
5 .-
3
7*Kr(p,a)75B-
z
-
*
,&:_I
s 20: E
*
2 0
*
::-.:___
1
10
* *
0 10
*
**
*
1
If
1
12
1L Proton
Fig. 3. Excitation
function
16 energy
of 78Kr(p,a)75Br
18 (MeVI nuclear
reaction.
20
Proton induced reactions on highly enriched ‘*Kr
78Kr(p,a)75Br I
/ 10
/
, /’ / /
1109
./j
/ 14
12
16
18
20
Proton energy (MeV) Fig. 4. Integral thick target yields of “Kr and ‘sBr at saturation (calculated from the excitation functions given in Figs 1 and 3) as a function of proton energy on ‘*Kr.
Calculated Thin and Thick Target Yields for the Formation of “Kr, “Br and 75Br From our measured excitation functions of ‘*Kr(p,x)“Br and ‘*Kr(p,a)“Br pro“Kr(p,pn)“Kr, cesses (solid curves in Figs l-3) both thin and thick
target yields were calculated as described in several earlier publications. The thick target integral yields of “Kr and 75Br are given in Fig. 4 and that of “Br in Fig. 5. In view of the short half-lives of “Kr and “Br we present saturation yield values at EOB for the two isotopes. In the case of “Br, however, yield values for 1 h irradiation are given. The yields refer to the complete decay of “Kr to “Br but have been extrapolated to EOB. Our calculated yield curves show that the saturation target yield of 75Br amounts to 2.5 mCi (92.5 MBq)/pA with 15 MeV protons and 10 mCi (370 MBq)/pA with 19.5 MeV protons. These values
are comparable to the experimentally obtained yields of Friedman et al. (1982) in low current irradiations (~2 mCi/pA at 15 MeV), and of Helus et al. (1989, 1992) in low to medium current irradiations (X 1.5 mCi/pAh, corresponding to 3.5 mCi/pA at saturation at 20 MeV). For comparison of our “Br yields only the data of Helus et al. (1989) are available. They report a value of x 100 pCi/pAh for high intensity irradiations with 20 MeV protons. Our calculated thick target yield for the same energy range is 600 PCi (22.2 MBq)/pAh. Critical Evaluation
of the Published Data
From the foregoing discussion it is concluded that the thick target yields calculated from our measured excitation functions are approximately in agreement with the experimental yields reported by Friedman et al. (1982) and Helus et al. (1989), Helus and Zeisler
lo3 m 2 a I
a 0 I
-
“Kr(p,x)“Br
16
18 Proton energy (MeV)
20
Fig. 5. Integral thick target yield of “Br calculated from the excitation function given in Fig. 2 (assuming an irradiation time of 1 h) as a function of proton energy on 78Kr (for other details cf text).
F. T~KANYI et al.
1110
(1992). The cross sections deduced by Friedman et al. (1982) and Hems et al. (1991) from their respective yield data are exceptionally high and presumably contain large calculational errors. As a check of our presumption, we also calculated thick target yields using the excitation functions presented by the two groups. The results were prohibitively high and inconsistent with the experimental data for both “Br and “Br. We therefore conclude that the cross section data given in the two earlier reports (Friedman et al., 1982; Hems et al., 1991) are incorrect.
Possibility
of Production of “Br and “Br using Highly Enriched ‘*Kr
Our excitation function measurements and the yields calculated therefrom, as well as the earlier experimental yields show that proton irradiation of highly enriched ‘*Kr could be applied for production purposes on a limited scale. The theoretically expected thick target yield of 75Br via the 78Kr(p,a)75Br reaction at 17 MeV amounts to 1.9 mCi (70 MBq)/ PAh, without any 76Br or “Br impurity. An irradiation at 30pA could in principle lead to about 57 mCi (2.1 GBq)“Br. In practice, however, the high current irradiation yield would be appreciably lower. It is therefore expected that in a production run the batch yield of 75Br would be limited to about 25 mCi (925 MBq). This value is considerably lower than those obtained via the 75As(3He,3n)75Br 76Se(p,2n)75Br processes, where > 150 mCi and (5.55 GBq) amounts are routinely produced. The amount of 25 mCi (925 MBq) may be sufficient for a few simple applications but is not enough for large scale labelling of biomolecules for PET applications. The theoretically expected thick target yield of “Br via the 78Kr(p,pn)77Kr+ “Br reaction at 17 MeV is 70 PCi (2.6 MBq)/pAh. Production of “Br at a small cyclotron using the present process is thus not suitable. The method could be used in the energy range of 19.5-+16.5 MeV where the calculated yield amounts to 0.54 mCi (20 MBq)/pAh. An irradiation at 20pA should in principle lead to 10 mCi (370 MBq)/h”Br. The concomitantly formed 75Br as impurity would not be a problem due to its short half-life. The yield of “Br via this process at Er z 20 MeV is comparable to that via the 75As(a 2n)“Br reaction at 26 MeV. If higher energy protons would be available (e.g. 25 MeV), the yield of “Br would be considerably higher. The proton interaction of highly enriched 78Kr at a medium sized cyclotron is thus more valuable for the production of however, as “Br than 75Br. At a small cyclotron, discussed above. due to the high cost of the enriched target gas, the production of both 75Br and “Br is very uneconomical. Acknowledgements-We
active support
thank Professor G. Stiicklin for his of this field of study. This work was carried
out in the frame of a German-Hungarian bilateral agreement (Project No. 13/X 237.1) and we are grateful to the Ministry of Research and Technology (Bonn) and the Government Office for Technical Development (Budapest) for support, Acknowledgement is made to the crew of the compact cyclotron CV 28 at Julich for irradiations. We also wish to thank T. Molnar for his assistance.
References Andersen powers
H. H. and Ziegler J. F. (1977) Hydrogen stopping and ranges in all elements. The Stopping and Ranges of Ions in Mailer, Vol. 3 (Ziegler J. F., ed.). Pergamon Press, New York. Backhausen H.. Stocklin G. and Weinreich R. (1981) Formation of ‘“F via its ‘“Ne precursor: excitation functions of the reactions ‘“Ne(d.x)18Ne and ‘“Ne(‘He,an)‘*Ne. Radiochim.
Acta 29, 1.
Blessing G.. Weinreich R.. Qaim S. M. and Stocklin G. (1982) Production of 75Br and “Br via the 75As(‘He.3n)75Br and isAs(c(,2n)77Br reactions using Cu,As--alloy as ‘high current target material. Inf. J. Appl. Radial. Isof. 33, 339.
Browne C. and Firestone R. B. (I 986) Table qf Radioacrice I::otopes (Shirley V. S, ed.). Wiley, New York. CollP R., Kishore R. and Cumming J. B. (1974) Excitation functions for (pn) reactions up to 25 MeV on “Cu. “‘Cu and ““Ag. I’hys. Rec. C9, 1819. De Jesus 0. T. and Friedman A. M. (1988) Production of 75Br via the 7”Kr(d,na)75Br reaction. Appl. Radial. Isol. 39. 709.
Farhan A. R., Shaheen Rab and Singh B. (1989) Nuclear data sheets for A = 77. Nucl. Data Sheers 57, 220. Friedman A. M., De Jesus 0. T.. Harper P. and Armstrong C. (1982) Preparation of “Br by the 78Kr(p,r)75Br reaction. J. Label. Corn& Radiopharm. 19, 1427. Grant P. M., Whippld R. E., Barnes J. W., Bentley G. E., Wanek P. M. and O’Brien Jr H. A. (I 98 I ) The production . and recovery of “Br at Los Alamos for nuclear medicine studies. J. Inorg. Nucl. Chem. 43, 2211. Critter A. (1982) Excitation functions for radioactive isotopes produced by bombardment of Cu and Al in energy range of 16 to 70 MeV. Nucl. Phys. A383, 98. Helus F. and Zeisler S. (1992) On the production of bromine-75 and bromine-77 from enriched krypton. In Proceedings_ of’the 4/h International Workshop on Targeti-) ” and Target Chemistry, PSI Villigen. Switzerland. Septem-
ber 1991 (Weinreich R., ed.), PSI, p. 164. Helus F., Zeisler S., Gasper H., McQuarrie S. and MaierBorst W. (1989) A feasibility study of “Br and 77Br production from enriched krypton. J. Radioanal. Nucl. Chml.
Lrtr.
136, 95.
Helus F.. Zeisler St., Gschwandtner G.. Marx H. and Maier-Borst W. (1991) Production of 75Br and “Br from enriched krypton: excitation functions. J. Radioanal. Nucl.
Chem
Lerl.
153, 41.
Kopecky P. (1985) Proton beam monitoring via the Cu(p,x)‘“Co, “‘Cu(p.2n)h’Zn and 6iCu(p,n)“5Zn reactions in Conner. In!. J. Apal. Radiat. Isor. 36, 657. Kovacs’Z.. Blessing G.: Qaim S. M. and Stocklin G. (1985) Production of ‘5Br via the “Se(p,2n)“Br reaction at a compact cyclotron. Inr. .I. Appl. Radiar. Isor. 36, 635. Kovacs Z.. Tarkanvi F.. Oaim S. M. and Stocklm G. (1991) Excitation functl’ons for the formation of some radioisotopes of rubidium in proton induced nuclear reactions on ““‘Kr, ‘?Kr and “Kr with special reference to the production of 8’Rb(X’mKr) generator radionuchde. Appl. Radial. Isot. 42. 329.
Maziere B. and Loc’h C. (1986) Radropharmaceuticals labelled with bromine isotopes. Appl. Radiat. Iror. 37,703. Paans A. M. J.. Welleweerd J., Vaalburg W., Reiffers S. and Woldrine M. G. (1980) Excitation functions for the
Proton
induced
reactions
production of 75Br: a potential nuclide for the labelhng of radiopharmaceuticals. Int. J. Appl. Radiat. Isot. 31, 261. Pie1 H., Qaim S. M. and Stiicklin G. (1992) Excitation functions of (p,xn)-reactions on nP’Ni and highly enriched 62Ni: possibility of production of medically important radioisotope %u at a small cyclotron. Radiochim. Acta 57, 1. Qaim S. M. (1986) Recent developments in the production of ‘sF, 75,76.77Brand 12’I. Appl. Radial. Isot. 37, 803. Qaim S. M. and Stocklin G. (1983) Production of some medically important short-lived neutron-deficient radioisotopes of halogens. Radiochim. Acta 34, 25. Int. Stocklin G (1977)-“Br and ‘23I radiopharmaceuticals. J. Aool. Radiat. Isot. 28. 131. Stockh‘n G. (1986) Molecules labelled with positron emitting halogens. Nucl. Med. Biol. 13, 109. Tbrkanyi F., Qaim S. M. and Stiicklin G. (1988a) Excitation functions of ‘He- and u-particle induced nuclear reactions on natural krypton: production of “Sr at a compact cyclotron. Appl. Radiat. Isot. 39, 135.
on highly
enriched
‘*Kr
1111
Tarklnyi F., Qaim S. M. and Stocklin G. (1988b) Excitation functions of 3He-particle induced nuclear reactions on enriched *2Kr and 83Kr. Radiochim. Acta 43, 185. Tarkanyi F., Qaim S. M., Stiicklin G., Sajjad M., Iambrecht R. M. and Schweickert H. (1991a) Excitation functions of @,2n) and (p,pn) reactions and differential induced nuclear and integral yields of ‘23I in proton reactions on highly enriched “‘Xe. Appl. Radiat. Isot. 42, 221. Tdrklnyi F., Szelecstnyi F. and Takacs S. (1991 b) Determination of effective bombarding energies in the measurement of excitation functions via stacked foil technique. Acta Radiolog. Suppl., 376, 72. Tarkanvi F., KovLcs Z., Qaim S. M. and Stiicklin G. (1992) Production of )sK via-the 38Ar@,n)-process at a‘smah cyclotron. Appl. Radiat. Isot. 43, 503. Williamson C. F., Boujot J. P. and Picard J. (1966) Tables of range and stopping power of chemical elements for charged particles of energy 0.05 to 500 MeV. Report CEA-R-3042, Saclay, France.
I I I,
1993 Copyright
0969-8043/93 $6.00 + 0.00 6 1993 Pergamon Press Ltd
Excitation Functions of Proton Induced Nuclear Reactions on Highly Enriched 78Kr: Relevance to the Pro&&ion of 75Br and 77Br at a Small Cyclotron F. TARKANYI’,‘, ‘Institut
Z. KOVACS’,*
and S. M. QAIM’*
fiir Nuklearchemie, Forschungszentrum Jillich GmbH, 5170 Jfilich, Germany and *Institute Nuclear Research, Hungarian Academy of Sciences, 4001 Debrecen, Hungary
of
(Received 4 January 1993) Excitation functions were measured for ‘sKr(p,pn)“Kr, ‘sKr(p,x)“Br and 7*Kr(p,a)75Br reactions from threshold to 20 MeV by the activation technique using 99.4% enriched 78Kr as target gas. There is a strong discrepancy between our data and the literature values for the 78Kr(p,pn)77Kr and 78Kr(p,a)‘5Br reactions. Differential and integral yields of 77Kr, “Br and 7SBr were calculated from our excitation functions. The calculated integral yields of 75Br and “Br are approximately in agreement with the low-current irradiation experimental yield data reported in the literature. The thick target yields of both 75Br and “Br at a small and 70 PCi (2.6 MBq)/pAh, respectively] and cyclotron (E, zz 17 MeV) are small [1.9 mCi (70 MBq)/pAh due to the very high cost of the target gas, the two production processes are uneconomical. At a medium-sized cyclotron with Er, 3 25 MeV, however, the “Br yield would be appreciably higher and the process could be very suitable for production of “Br.
Introduction Several radioisotopes of bromine have found applications in labelling biomolecules [cf Stijcklin (1977, 1986); Maziere and Loc’h (1986)]. Of particular interest are the neutron deficient bromine isotopes “Br (t,,r = 1.6 h) and “Br (tljz = 57 h). The former is a positron emitter and has found use in positron emission tomography (PET) and the latter is more suitable for longer lasting studies with y-cameras having a high-energy collimator. Detailed reviews of the production methods [cf Qaim and Stocklin (1983); Qaim (1986)] suggest that both “Br and “Br can be produced in sufficient quantities only if a medium-sized cyclotron or a high-energy accelerator is available. The most suitable methods for the production of “Br are the 75As(3He,3n)75Br [cf Blessing et al. (1982)] and 76Se(p,2n)75Br [cf Paans et al. (1980); Kovacs et al. (1985)] reactions. For “Br production, on the other hand, the “As(a,2n)“Br [cfBlessing et al. (1982); and references cited therein] and ““‘Mo(p,spall)“Br [cf Grant et a/.(1981)] processes are most suitable. In an attempt to produce “Br at a small cyclotron Friedman et al. (1982) measured the 75Br-yield in the 7*Kr(p,a)75Br reaction at 15 MeV using 20% enriched gas as target material. Later De Jesus and Friedman
(1988) determined the 75Br-yield in the ‘*Kr(d,na)“Br process for deuteron energies from 10 to 21.5 MeV. Recently Helus et al. (1989, 1991) and Helus and Zeisler (1992) also measured the 75Br yield. The cross section data for the 78Kr(p,~)7SBr process deduced by the two groups from their respective measured yields are scanty and appeared to us to be in error. As regards “Br production, Helus et al. (1989, 1991) and Helus and Zeisler (1992) investigated the ‘sKr(p,x)“Br process and reported some yield data. Here again the deduced cross section values are scanty and apparently incorrect. We performed detailed excitation function measurements on reactions relevant to the production of both “Br and “Br in the interactions of protons with highly enriched “Kr.
Experimental Excitation functions were measured on 99.4% enriched “Kr (Isotec, U.S.A.) by the activation technique using gas cells as irradiation samples. The techniques used were essentially the same as described in several earlier publications [cf Backhausen et al. (1981); Tarkanyi et al. (1988a,b, 1991a, 1992); Kovacs et al. (1991)]. Irradiations
*Author for correspondence.
Stainless steel gas cells (2 cm dia, 2.5 cm length Al windows were vol. = 8mL) having 50-100pm 1105
1106
F.
TARKANYI et al.
filled with the enriched gas at pressures of 0.27-0.64 bar. Either a single cell or several cells stacked together were irradiated at a time, depending on the reaction product to be studied. The irradiation time varied between 6 and 60min. All the irradiations were carried out at the variable energy Jiilich Compact Cyclotron (CV 28) at beam currents of 200-500 nA. Following primary incident proton energies were used: 20.4, 18.7 and 14.8 MeV. Other energies were obtained using Cu and Al degrader foils. The beam current was measured via a Faraday cup and by means of monitor reactions induced in Cu foils placed in front and at the back of each irradiated cell. A collimated beam (4 = 0.5 cm) was used. Chemical
separation
In general the produced activities were measured without a chemical separation. In a few cases, however, the bromine isotopes were separated chemically and counted to check the reliability of the nondestructive radioactive assay. After cryogenic removal of the irradiated krypton, the cell was rinsed with a solution containing 20mg each of KBr and KBrO, . An activity balance of the gas cell in the gas recovery and rinsing process was done. There was no loss of bromine activity during the gas recovery and >98% bromine activity was obtained in the solution. The solution was then heated to 90°C. Bromine was precipitated as AgBr and the activity of the solution measured before and after the precipitation. Almost no activity was left in the solution, indicating that the radiobromine occurred mostly as bromide. The overall separation yield of radiobromine was found to be 90 + 4%. Measurement
of radioactivit)
The activity of the gas cells, monitor foils and the precipitated samples was measured via standard high resolution y-ray spectroscopy. The samples were measured at a large source-detector distance to ensure good counting geometry and to avoid pile-up and coincidence losses. The decay data used for activity determinations are given in Table 1 (Browne and Firestone, 1986; Farhan et al., 1989).
Table I. Radiation
characteristics
Beam
Half-life
Check
“Kr
1.24h
“Br
57.0 h
P + (0.7) EC (99.3)
1.62 h
p + (75.5) EC (24.5)
on the purity
of enriched
gas
The enriched gas was used repeatedly in irradiations. An occasional check on its quality was therefore necessary. This was done as follows. Natural krypton was mixed with different amounts of air and its pressure at liq. N, temperature was compared with the pressure of the used enriched krypton gas under similar conditions (same temperature and volume). They were found to be identical when pure natural krypton was used. The components of air which condensed at liq. N, temperature (Xe, Kr, Ar) were searched for via analysis of some activation products; practically no activity was found. These tests showed that in the repeated filling and recovery process a small amount of the enriched gas was lost, its chemical composition, however, did not change significantly. Calculation
of cross sections
and their errors
Cross sections were determined using the activation formula. The errors of the cross sections were estimated by combining the individual errors in quadrature: beam current lo%, number of target atoms 5%, detector efficiency 5%, decay data 3%, chemical separation 5%, peak area analysis l-2% (in a few cases around the threshold 2 10%). The main errors in the energy scale were estimated on the basis of monitor reactions; they originated from the non-perpendicular position of cell windows to the beam direction, from the density reduction along the beam line, as well as from the beam broadening.
of the radionuclides reactions
Mode of decay W)
monitoring
The beam currents, the primary beam energies as well as the degraded energies along the stack were determined via Cu monitor reactions (Colle et al., 1974; Griitter, 1982; Kopecky, 1985; Tarkanyi et al., 1991b; Pie1 et al., 1992) and by range-energy calculations (Williamson et al., 1966; Andersen and Ziegler, 1977). The beam current measured directly in the Faraday cup and that obtained via the monitor reactions agreed within 10%.
y-ray Nuclide
current
studied and Q-values
of the contributing
energies in
keV (% abundance) 129.8 146.4 276.2 312.1 239.0 281.6 297.3 520.6 578.9 286.6 377.4 427.9 952.3
(80.0) (36.8) (2.88) (3.68) (23.9) (2.38) (4.30) (23.1) (3.06) (92.1) (4.1) 14.51 il.7k)
Contributing reaction
Q-value (MeV)
“Kr(p,pn)
~ 12.0
“Kr+“Br ‘*K~(P,~P)
- 12.0 -8.2
“Kr(p,m)
-0.1
Proton Table
2. Cross sections for the formation proton induced reactions
induced
reactions
of “Kr, “Br and “Br in on ‘*Kr
Cross section (mb) Energy WV) 10.82 & 0.28 11.72 +_0.25 12.17 + 0.21 12.19 + 0.37 12.28 + 0.40 13.38 i_ 0.18 13.73 * 0.31 14.13 if: 0.32 14.16+0.15 14.74 * 0.30 14.95 + 0.26 15.17+0.25 15.67 i_ 0.23 15.73 + 0.25 15.74 + 0.26 15.90 i: 0.25 16.17+0.32 16.35 + 0.20 16.45 +_0.22 16.51 + 0.20 16.68 + 0.22 17.02 +0.18 17.03 * 0.30 17.10 + 0.30 17.15 + 0.19 17.19 * 0.20 17.56+ 0.18 17.66 & 0.27 17.67+0.15 17.77 kO.15 17.82 + 0.16 17.97 + 0.25 18.19~0.15 18.30 k 0.25 18.41 i 0.22 IS.81 +0.15 18.93 k 0.22 19.53 * 0.20 19.62 f 0.20
“Kr(p,pn)“Kr
‘*Kr(p,x)“Br
+ f + f f +
0.8 0.6 0.6 3.0 I.5 2.5
5.8 7.0 29.6 16.7
k + f f
3.3 7.0 9.5 5.4 5.4 10.6 9.9 14.4 17.5 10.0 14.3 15.4 19.0 15.8 15.8 27.9 17.0 20.9 22.8 19.9 17.6 23.4 27.4 18.9 25.9 28.2 19.2 28.1 23.5 19.7 27.6 18.5 29.5 30.0 21.2 18.9 25.8 24.4 20.2
0.8 0.9 4.1 2.1
60.8 + 7.7 63.1 _+ 8.0 54.2 +_ 6.9 65.9 f 8.3
61.4 + 8.4 57.2 +_1.2 69.8 f 8.8
67.1 + 8.6
III f 138 f 130* 112*
15 I8 I7 15
I38 k I8 179k23 160 + 21 155+_20 I81 + 23 192 f 24 240 + 31 242 k 31 214 + 27 241 + 31 293 k 37 343 + 44 292 f 37
I I4 f 16 l24+ I6 109 f 14 153f20 184 f 24 154*21 I38 F 18 175+23 234 f 30 228 f 29
274 + 35 293 f 37
f 0.4 + 0.9 * 1.2 f 0.7 f 0.8 f 1.4 f I .3 * 1.9 + 2.3 * I.4 * 2.0 * 2.0 + 2.5 f 2.0 f 2.0 f 3.6 * 2.2 _+2.7 +_2.9 + 2.5 f 2.3 k 3.1 f 3.5 k 2.4 + 3.3 f 5.0 f 2.6 f 3.6 + 2.9 +_2.5 k 3.5 + 2.4 f 3.8 f 4.3 f 2.8 + 2.4 f 3.3 f 3. I f 2.6
Measurements on natural krypton In a separate series of irradiations the “Br yield was determined using krypton gas of natural isotopic composition. The gas cells were filled up to 3 bars and irradiations done at the Jiilich Isochronous Cyclotron (JULIC) for 2 h with protons of primary energies of
0 -.“““““““‘~“““”
12
enriched
78Kr
1107
38 and 30 MeV at beam currents of 200 nA. Radiobromine was separated as described above and the activity measured via y-ray spectroscopy.
‘*Kr(p,a)“Br
0.10+0.06
I .2 3.6 4.5 23.4 II.5 18.7
on highly
IL Proton
Excitation
Functions
The nuclear reactions studied and their Q-values are given in Table 1. The measured cross section data are given in Table 2 and the excitation functions are shown in Figs 1-3. The solid curves were obtained by fitting the data with polynomials. 77Kr(p,pn) 77Kr-+ 77Brprocess The interactions of protons with the 99.4% enriched “Kr used in this work would lead to the radioisotope “Br via the following three routes: (a) ‘*Kr(p,2n)“Rb
2
“Kr z
“Br l.Zh
(b) “Kr(p,pn)“Kr
5
“Br
(c) “Kr(p,2p)“Br. The Q-value of the 78Kr(p,2n)77Rb reaction is - 18.1 MeV; the reaction threshold would therefore lie at ~20 MeV. In our studies up to 20 MeV we specifically searched for this reaction product but did not detect it. The emphasis was therefore on the study of routes (b) and (c). The excitation function of the “Kr(p,pn)“Kr process is shown in Fig. 1. The threshold lies at around 14 MeV. Beyond 16 MeV the cross section increases rapidly and reaches a value of about 300mb at 20 MeV. The cumulative production cross sections for “Br were measured after complete decay of “Kr and the excitation function based on both radiochemical and nondestructive measurements is given in Fig. 2. The excitation function for the ‘“Kr(p,x)“Br reaction reported in this work has been measured for the first time. The identical values of cross sections in Figs 1
16 energy
18 (MeV)
Fig. I. Excitation function of ‘*Kr(p,pn)“Kr nuclear process.
20
F.
1108
T.~RKANYI et al.
ii
E 300 1 “Kr(p,x)“Br
s z
1 /-
u
16
18 Proton
energy
20
(MeV)
for the formation of “Br in proton induced reactions on “Kr. Measurement of radioactivity was done after complete decay of “Kr to “Br.
Fig. 2. Excitation
function
results of Helus et al. (1991) shows large discrepancies Our cross section values are a factor of 4 lower than their data. From a consideration of the cross section systematics and magnitudes of various competing reactions in this mass and energy region, it is inferred that the (p,pn) reaction cannot have a cross section of 1400 mb, as reported by Helus et al. (1991) (see below for further discussion).
and 2 lead to the conclusion that “Br is produced almost exclusively via the decay of “Kr. The contribution of the “Kr(p,2p)“Br reaction, if any, is thus small (< 15%) and within the error limits of the measured “Kr(p,pn)“Kr and 78Kr(p,x)77Br excitation functions. It should be mentioned that our enriched target gas contained 0.6% “Kr, hence the “Kr(p,Cc)“Br direct production channel would also be involved in the production of “Br. However, taking into account the small percentage of “Kr and the expected low cross section of the ‘OKr(p,Cc)“Br reaction, the contribution from this process was estimated to be ~0.2%. A similar consideration in the case of natural Kr (with ‘*Kr and “Kr abundances of 0.35% and 2.25%, respectively) led to an exact description of the measured “Br yield in irradiation of natural Kr with proton energies up to 20 MeV (at higher energies other processes also contribute). A comparison of our excitation function for the ‘*Kr(p,pn)“Kr process with the recently published
78Kr(p,x)7sBr
reaction
The excitation function of the 78Kr(p,cz)75Br reaction is given in Fig. 3. The data show some fluctuations, presumably due to large errors. The excitation function exhibits a maximum around 18 MeV and the cross section amounts to about 25 mb. This value is also lower by a factor of 4 than that reported recently by Helus et al. (1991) for the same reaction. The preliminary cross section values of Friedman ef al. (1982) are even 6 times higher than our data. We believe that our data are more accurate (see below for further discussion).
LO c”“““l”“““““““““““““”
z
E 30 1
5 .-
3
7*Kr(p,a)75B-
z
-
*
,&:_I
s 20: E
*
2 0
*
::-.:___
1
10
* *
0 10
*
**
*
1
If
1
12
1L Proton
Fig. 3. Excitation
function
16 energy
of 78Kr(p,a)75Br
18 (MeVI nuclear
reaction.
20
Proton induced reactions on highly enriched ‘*Kr
78Kr(p,a)75Br I
/ 10
/
, /’ / /
1109
./j
/ 14
12
16
18
20
Proton energy (MeV) Fig. 4. Integral thick target yields of “Kr and ‘sBr at saturation (calculated from the excitation functions given in Figs 1 and 3) as a function of proton energy on ‘*Kr.
Calculated Thin and Thick Target Yields for the Formation of “Kr, “Br and 75Br From our measured excitation functions of ‘*Kr(p,x)“Br and ‘*Kr(p,a)“Br pro“Kr(p,pn)“Kr, cesses (solid curves in Figs l-3) both thin and thick
target yields were calculated as described in several earlier publications. The thick target integral yields of “Kr and 75Br are given in Fig. 4 and that of “Br in Fig. 5. In view of the short half-lives of “Kr and “Br we present saturation yield values at EOB for the two isotopes. In the case of “Br, however, yield values for 1 h irradiation are given. The yields refer to the complete decay of “Kr to “Br but have been extrapolated to EOB. Our calculated yield curves show that the saturation target yield of 75Br amounts to 2.5 mCi (92.5 MBq)/pA with 15 MeV protons and 10 mCi (370 MBq)/pA with 19.5 MeV protons. These values
are comparable to the experimentally obtained yields of Friedman et al. (1982) in low current irradiations (~2 mCi/pA at 15 MeV), and of Helus et al. (1989, 1992) in low to medium current irradiations (X 1.5 mCi/pAh, corresponding to 3.5 mCi/pA at saturation at 20 MeV). For comparison of our “Br yields only the data of Helus et al. (1989) are available. They report a value of x 100 pCi/pAh for high intensity irradiations with 20 MeV protons. Our calculated thick target yield for the same energy range is 600 PCi (22.2 MBq)/pAh. Critical Evaluation
of the Published Data
From the foregoing discussion it is concluded that the thick target yields calculated from our measured excitation functions are approximately in agreement with the experimental yields reported by Friedman et al. (1982) and Helus et al. (1989), Helus and Zeisler
lo3 m 2 a I
a 0 I
-
“Kr(p,x)“Br
16
18 Proton energy (MeV)
20
Fig. 5. Integral thick target yield of “Br calculated from the excitation function given in Fig. 2 (assuming an irradiation time of 1 h) as a function of proton energy on 78Kr (for other details cf text).
F. T~KANYI et al.
1110
(1992). The cross sections deduced by Friedman et al. (1982) and Hems et al. (1991) from their respective yield data are exceptionally high and presumably contain large calculational errors. As a check of our presumption, we also calculated thick target yields using the excitation functions presented by the two groups. The results were prohibitively high and inconsistent with the experimental data for both “Br and “Br. We therefore conclude that the cross section data given in the two earlier reports (Friedman et al., 1982; Hems et al., 1991) are incorrect.
Possibility
of Production of “Br and “Br using Highly Enriched ‘*Kr
Our excitation function measurements and the yields calculated therefrom, as well as the earlier experimental yields show that proton irradiation of highly enriched ‘*Kr could be applied for production purposes on a limited scale. The theoretically expected thick target yield of 75Br via the 78Kr(p,a)75Br reaction at 17 MeV amounts to 1.9 mCi (70 MBq)/ PAh, without any 76Br or “Br impurity. An irradiation at 30pA could in principle lead to about 57 mCi (2.1 GBq)“Br. In practice, however, the high current irradiation yield would be appreciably lower. It is therefore expected that in a production run the batch yield of 75Br would be limited to about 25 mCi (925 MBq). This value is considerably lower than those obtained via the 75As(3He,3n)75Br 76Se(p,2n)75Br processes, where > 150 mCi and (5.55 GBq) amounts are routinely produced. The amount of 25 mCi (925 MBq) may be sufficient for a few simple applications but is not enough for large scale labelling of biomolecules for PET applications. The theoretically expected thick target yield of “Br via the 78Kr(p,pn)77Kr+ “Br reaction at 17 MeV is 70 PCi (2.6 MBq)/pAh. Production of “Br at a small cyclotron using the present process is thus not suitable. The method could be used in the energy range of 19.5-+16.5 MeV where the calculated yield amounts to 0.54 mCi (20 MBq)/pAh. An irradiation at 20pA should in principle lead to 10 mCi (370 MBq)/h”Br. The concomitantly formed 75Br as impurity would not be a problem due to its short half-life. The yield of “Br via this process at Er z 20 MeV is comparable to that via the 75As(a 2n)“Br reaction at 26 MeV. If higher energy protons would be available (e.g. 25 MeV), the yield of “Br would be considerably higher. The proton interaction of highly enriched 78Kr at a medium sized cyclotron is thus more valuable for the production of however, as “Br than 75Br. At a small cyclotron, discussed above. due to the high cost of the enriched target gas, the production of both 75Br and “Br is very uneconomical. Acknowledgements-We
active support
thank Professor G. Stiicklin for his of this field of study. This work was carried
out in the frame of a German-Hungarian bilateral agreement (Project No. 13/X 237.1) and we are grateful to the Ministry of Research and Technology (Bonn) and the Government Office for Technical Development (Budapest) for support, Acknowledgement is made to the crew of the compact cyclotron CV 28 at Julich for irradiations. We also wish to thank T. Molnar for his assistance.
References Andersen powers
H. H. and Ziegler J. F. (1977) Hydrogen stopping and ranges in all elements. The Stopping and Ranges of Ions in Mailer, Vol. 3 (Ziegler J. F., ed.). Pergamon Press, New York. Backhausen H.. Stocklin G. and Weinreich R. (1981) Formation of ‘“F via its ‘“Ne precursor: excitation functions of the reactions ‘“Ne(d.x)18Ne and ‘“Ne(‘He,an)‘*Ne. Radiochim.
Acta 29, 1.
Blessing G.. Weinreich R.. Qaim S. M. and Stocklin G. (1982) Production of 75Br and “Br via the 75As(‘He.3n)75Br and isAs(c(,2n)77Br reactions using Cu,As--alloy as ‘high current target material. Inf. J. Appl. Radial. Isof. 33, 339.
Browne C. and Firestone R. B. (I 986) Table qf Radioacrice I::otopes (Shirley V. S, ed.). Wiley, New York. CollP R., Kishore R. and Cumming J. B. (1974) Excitation functions for (pn) reactions up to 25 MeV on “Cu. “‘Cu and ““Ag. I’hys. Rec. C9, 1819. De Jesus 0. T. and Friedman A. M. (1988) Production of 75Br via the 7”Kr(d,na)75Br reaction. Appl. Radial. Isol. 39. 709.
Farhan A. R., Shaheen Rab and Singh B. (1989) Nuclear data sheets for A = 77. Nucl. Data Sheers 57, 220. Friedman A. M., De Jesus 0. T.. Harper P. and Armstrong C. (1982) Preparation of “Br by the 78Kr(p,r)75Br reaction. J. Label. Corn& Radiopharm. 19, 1427. Grant P. M., Whippld R. E., Barnes J. W., Bentley G. E., Wanek P. M. and O’Brien Jr H. A. (I 98 I ) The production . and recovery of “Br at Los Alamos for nuclear medicine studies. J. Inorg. Nucl. Chem. 43, 2211. Critter A. (1982) Excitation functions for radioactive isotopes produced by bombardment of Cu and Al in energy range of 16 to 70 MeV. Nucl. Phys. A383, 98. Helus F. and Zeisler S. (1992) On the production of bromine-75 and bromine-77 from enriched krypton. In Proceedings_ of’the 4/h International Workshop on Targeti-) ” and Target Chemistry, PSI Villigen. Switzerland. Septem-
ber 1991 (Weinreich R., ed.), PSI, p. 164. Helus F., Zeisler S., Gasper H., McQuarrie S. and MaierBorst W. (1989) A feasibility study of “Br and 77Br production from enriched krypton. J. Radioanal. Nucl. Chml.
Lrtr.
136, 95.
Helus F.. Zeisler St., Gschwandtner G.. Marx H. and Maier-Borst W. (1991) Production of 75Br and “Br from enriched krypton: excitation functions. J. Radioanal. Nucl.
Chem
Lerl.
153, 41.
Kopecky P. (1985) Proton beam monitoring via the Cu(p,x)‘“Co, “‘Cu(p.2n)h’Zn and 6iCu(p,n)“5Zn reactions in Conner. In!. J. Apal. Radiat. Isor. 36, 657. Kovacs’Z.. Blessing G.: Qaim S. M. and Stocklin G. (1985) Production of ‘5Br via the “Se(p,2n)“Br reaction at a compact cyclotron. Inr. .I. Appl. Radiar. Isor. 36, 635. Kovacs Z.. Tarkanvi F.. Oaim S. M. and Stocklm G. (1991) Excitation functl’ons for the formation of some radioisotopes of rubidium in proton induced nuclear reactions on ““‘Kr, ‘?Kr and “Kr with special reference to the production of 8’Rb(X’mKr) generator radionuchde. Appl. Radial. Isot. 42. 329.
Maziere B. and Loc’h C. (1986) Radropharmaceuticals labelled with bromine isotopes. Appl. Radiat. Iror. 37,703. Paans A. M. J.. Welleweerd J., Vaalburg W., Reiffers S. and Woldrine M. G. (1980) Excitation functions for the
Proton
induced
reactions
production of 75Br: a potential nuclide for the labelhng of radiopharmaceuticals. Int. J. Appl. Radiat. Isot. 31, 261. Pie1 H., Qaim S. M. and Stiicklin G. (1992) Excitation functions of (p,xn)-reactions on nP’Ni and highly enriched 62Ni: possibility of production of medically important radioisotope %u at a small cyclotron. Radiochim. Acta 57, 1. Qaim S. M. (1986) Recent developments in the production of ‘sF, 75,76.77Brand 12’I. Appl. Radial. Isot. 37, 803. Qaim S. M. and Stocklin G. (1983) Production of some medically important short-lived neutron-deficient radioisotopes of halogens. Radiochim. Acta 34, 25. Int. Stocklin G (1977)-“Br and ‘23I radiopharmaceuticals. J. Aool. Radiat. Isot. 28. 131. Stockh‘n G. (1986) Molecules labelled with positron emitting halogens. Nucl. Med. Biol. 13, 109. Tbrkanyi F., Qaim S. M. and Stiicklin G. (1988a) Excitation functions of ‘He- and u-particle induced nuclear reactions on natural krypton: production of “Sr at a compact cyclotron. Appl. Radiat. Isot. 39, 135.
on highly
enriched
‘*Kr
1111
Tarklnyi F., Qaim S. M. and Stocklin G. (1988b) Excitation functions of 3He-particle induced nuclear reactions on enriched *2Kr and 83Kr. Radiochim. Acta 43, 185. Tarkanyi F., Qaim S. M., Stiicklin G., Sajjad M., Iambrecht R. M. and Schweickert H. (1991a) Excitation functions of @,2n) and (p,pn) reactions and differential induced nuclear and integral yields of ‘23I in proton reactions on highly enriched “‘Xe. Appl. Radiat. Isot. 42, 221. Tdrklnyi F., Szelecstnyi F. and Takacs S. (1991 b) Determination of effective bombarding energies in the measurement of excitation functions via stacked foil technique. Acta Radiolog. Suppl., 376, 72. Tarkanvi F., KovLcs Z., Qaim S. M. and Stiicklin G. (1992) Production of )sK via-the 38Ar@,n)-process at a‘smah cyclotron. Appl. Radiat. Isot. 43, 503. Williamson C. F., Boujot J. P. and Picard J. (1966) Tables of range and stopping power of chemical elements for charged particles of energy 0.05 to 500 MeV. Report CEA-R-3042, Saclay, France.