Introduction The internal pressure experienced by a gas tar-get during irradiation is dependent on the beam energy deposited in the target, the beam cur-rent, and the thermal behaviour of the target. [1] The maximum beam energy deposited is a function of the cyclotron capabilities and the gas inventory within the target. The maximum beam current is limited by the pressure produced in the target and the ability of the target assembly to remain intact. This is also a function of the thermal behaviour of the target, which is difficult to predict a priori since it is dependent on such things as convection currents that occur during irradiation. We conducted bench tests with model gas targets with and without forced convection currents to observe the effect on thermal behaviour. Based on those results we constructed a prototype gas target, suitable for irradiation, with an internal fan assembly that is rotated via external magnets. Material and Methods Bench tests were conducted with cylindrical and conical target bodies of aluminum. A nickel-chromium heater wire was inserted into the gas volume through the normal beam entrance port (FIGURE 1) to heat the gas while water cooling was applied to the target body. The voltage and current of the heater coil was monitored along with the pressure inside the target and the water inlet and outlet temperature. In the case of tests with a driven fan blade either the voltage applied to the electric motor was monitored or the fan speed itself was recorded. By assuming the ideal gas law, the pressure gives the average bulk temperature and a global heat transfer coefficient can be calculated between the target gas and the cooling water. [2] A cylindrical target body was constructed that incorporated a fan blade driven by an external motor. This assembly used a simple o-ring seal on the rotating shaft. This seal was not robust enough for any tests under beam conditions. A prototype design suitable for in-beam operation employs a propeller mounted on a rotating disc housing two samarium cobalt magnets and spinning on two micro-bearings which are constructed to operate in high temperature environments. The micro-bearings are mounted on a pin projecting from a plate welded to the back of the gas target to allow assembly of the fan mechanism prior to attachment to the body (FIGURE 2).

Introduction Short-lived isomer 83mKr (T½ = 1.83 h) is an ideal calibration source in several low-energy experiments like or KATRIN (determining the neutrino rest mass, monitoring high voltage stability and investigation of the main spectrometer properties) or XENON (detection of the dark matter). The isomer 83mKr is formed by decay of 83Rb (T½ = 86.2 d) that can be produced predominantly via the reaction 84Kr(p,2n)83Rb by irradiation of natKr (57 % abundance of 84Kr). The design and construction of the new gas target for effective production of radionuclide 83Rb as well as target processing will be shortly described. Material and Methods For the target design, we selected the following criteria: minimizing activation of target components; efficient cooling system allowing higher beam currents; easy handling; high life-time of the target chamber (low impact of the irradiation and radionuclide separation process on the target chamber surface and 83Rb recovery). The target consists of three parts: 1. Water cooled aluminium (alloy EN 6082) mechanical interface for easy connection of the target to the beam line. It also serves as a beam collimator (diameter 9 mm). 2. Holder of He-cooled foils (vacuum separation foil – Havar 0.025 mm, target body window – Ti 0.1 mm). 3. Aluminium (alloy EN 6082) water cooled target body with 150mm long cone-shaped target chamber of the volume 27.1 ml. Internal surface of the chamber is nickel-coated. The target filled with natural Kr of purity 0.9999 and absolute pressure 13 bar was irradiated on the external beam of the isochronous cyclotron U-120M of the NPI AS CR. The proton beam energy was set so that it is decreased after deg-radation in the separation foils to 25.6 MeV. Beam energy loss in the natural Kr gas filling is 9.6 MeV. The target was tested up to 25 µA beam current. After irradiation, the target is left for a week to let the short-lived activation products to decay. Then, 83Rb is washed out from the target walls by two portions of freshly prepared de-ionized water, target is rinsed by high-purity ethanol and dried. The two portions of 83Rb aqueous solution are then connected and activity and radionuclidic purity of the product is determined via γ-spectrometry (HPGe detector). Large-distance sample-detector measurements of the target prior and after the separation are used in order to determine recovery of 83Rb. Results and Conclusion The new gas target for routine production of 83Rb was successfully designed, tested and im-plemented for regular 83Rb production. Six-hour irradiation with 15 µA proton beam resulted repeatedly in ca 300 MBq of 83Rb (EOB). Besides 83Rb, we identified in the separated product also 84Rb (T½ = 32.82 d) at levels ca 31 % of the 83Rb activity (EOB) and 86Rb (T½ = 18.631 d) at levels ca 8 % of the 83Rb activity (EOB). Both radionuclidic impurities do not disturb the use of 83Rb, since none of them emanates any radioactive krypton isotope. Moreover, their relative content decreases in time. Rubidium isotopes are recovered from the target almost quantitatively (98–99 %).

Introduction The internal pressure experienced by a gas tar-get during irradiation is dependent on the beam energy deposited in the target, the beam cur-rent, and the thermal behaviour of the target. [1] The maximum beam energy deposited is a function of the cyclotron capabilities and the gas inventory within the target. The maximum beam current is limited by the pressure produced in the target and the ability of the target assembly to remain intact. This is also a function of the thermal behaviour of the target, which is difficult to predict a priori since it is dependent on such things as convection currents that occur during irradiation. We conducted bench tests with model gas targets with and without forced convection currents to observe the effect on thermal behaviour. Based on those results we constructed a prototype gas target, suitable for irradiation, with an internal fan assembly that is rotated via external magnets. Material and Methods Bench tests were conducted with cylindrical and conical target bodies of aluminum. A nickel-chromium heater wire was inserted into the gas volume through the normal beam entrance port (FIGURE 1) to heat the gas while water cooling was applied to the target body. The voltage and current of the heater coil was monitored along with the pressure inside the target and the water inlet and outlet temperature. In the case of tests with a driven fan blade either the voltage applied to the electric motor was monitored or the fan speed itself was recorded. By assuming the ideal gas law, the pressure gives the average bulk temperature and a global heat transfer coefficient can be calculated between the target gas and the cooling water. [2] A cylindrical target body was constructed that incorporated a fan blade driven by an external motor. This assembly used a simple o-ring seal on the rotating shaft. This seal was not robust enough for any tests under beam conditions. A prototype design suitable for in-beam operation employs a propeller mounted on a rotating disc housing two samarium cobalt magnets and spinning on two micro-bearings which are constructed to operate in high temperature environments. The micro-bearings are mounted on a pin projecting from a plate welded to the back of the gas target to allow assembly of the fan mechanism prior to attachment to the body (FIGURE 2).

Introduction Short-lived isomer 83mKr (T½ = 1.83 h) is an ideal calibration source in several low-energy experiments like or KATRIN (determining the neutrino rest mass, monitoring high voltage stability and investigation of the main spectrometer properties) or XENON (detection of the dark matter). The isomer 83mKr is formed by decay of 83Rb (T½ = 86.2 d) that can be produced predominantly via the reaction 84Kr(p,2n)83Rb by irradiation of natKr (57 % abundance of 84Kr). The design and construction of the new gas target for effective production of radionuclide 83Rb as well as target processing will be shortly described. Material and Methods For the target design, we selected the following criteria: minimizing activation of target components; efficient cooling system allowing higher beam currents; easy handling; high life-time of the target chamber (low impact of the irradiation and radionuclide separation process on the target chamber surface and 83Rb recovery). The target consists of three parts: 1. Water cooled aluminium (alloy EN 6082) mechanical interface for easy connection of the target to the beam line. It also serves as a beam collimator (diameter 9 mm). 2. Holder of He-cooled foils (vacuum separation foil – Havar 0.025 mm, target body window – Ti 0.1 mm). 3. Aluminium (alloy EN 6082) water cooled target body with 150mm long cone-shaped target chamber of the volume 27.1 ml. Internal surface of the chamber is nickel-coated. The target filled with natural Kr of purity 0.9999 and absolute pressure 13 bar was irradiated on the external beam of the isochronous cyclotron U-120M of the NPI AS CR. The proton beam energy was set so that it is decreased after deg-radation in the separation foils to 25.6 MeV. Beam energy loss in the natural Kr gas filling is 9.6 MeV. The target was tested up to 25 µA beam current. After irradiation, the target is left for a week to let the short-lived activation products to decay. Then, 83Rb is washed out from the target walls by two portions of freshly prepared de-ionized water, target is rinsed by high-purity ethanol and dried. The two portions of 83Rb aqueous solution are then connected and activity and radionuclidic purity of the product is determined via γ-spectrometry (HPGe detector). Large-distance sample-detector measurements of the target prior and after the separation are used in order to determine recovery of 83Rb. Results and Conclusion The new gas target for routine production of 83Rb was successfully designed, tested and im-plemented for regular 83Rb production. Six-hour irradiation with 15 µA proton beam resulted repeatedly in ca 300 MBq of 83Rb (EOB). Besides 83Rb, we identified in the separated product also 84Rb (T½ = 32.82 d) at levels ca 31 % of the 83Rb activity (EOB) and 86Rb (T½ = 18.631 d) at levels ca 8 % of the 83Rb activity (EOB). Both radionuclidic impurities do not disturb the use of 83Rb, since none of them emanates any radioactive krypton isotope. Moreover, their relative content decreases in time. Rubidium isotopes are recovered from the target almost quantitatively (98–99 %).

The nuclear structme of 17Ne and 13O has been studied by the 20Ne(3He,6He)17Ne and 16O(3He,6He)13O reactions at 70 MeV and 80 MeV, respectively. Fifteen levels were identified, and angular distributions have been measured for nine of these levels in 17Ne, while for 13O eighteen levels were identified, but angular distributions were obtained for only ten levels. The observed transferred angular momentum dependence of these angular distributions allowed spin-parity assignments. The T= 3/2 quartet analog states in mass A=17 have been completed for six levels. The results of the isobaric multiplet mass equation analysis show a slight linear dependence of the b and c coefficients on the excitation energy. It was found that the coefficients for the positive parity states do not follow the systematics of the negative parity states. The absolute values of the b and c coefficients are larger for the positive parity states. An analysis in terms of Coulomb energy displacement indicates a possible configuration mixing or core polarization effect in these states. The d coefficient also has a large deviation from zero, only for the positive parity states indicating a possible expansion of the radial wavefunction or some isospin symmetry breaking effects. Further detailed theoretical interpretation of these effects may bring valuable information about the configuration and structure of these states. The leveis in 13O were measured with good energy resolution, and thus, it was possible to identify the first excited state unambiguously. However, if one identifies this state as the analog of the known first excited state in the mirror nucleus 13B, this leads to one of the largest level shifts known in literature. / The nuclear structme of 17Ne and 13O has been studied by the 20Ne(3He,6He)17Ne and 16O(3He,6He)13O reactions at 70 MeV and 80 MeV, respectively. Fifteen levels were identified, and angular distributions have been measured for nine of these levels in 17Ne, while for 13O eighteen levels were identified, but angular distributions were obtained for only ten levels. The observed transferred angular momentum dependence of these angular distributions allowed spin-parity assignments. The T= 3/2 quartet analog states in mass A=17 have been completed for six levels. The results of the isobaric multiplet mass equation analysis show a slight linear dependence of the b and c coefficients on the excitation energy. It was found that the coefficients for the positive parity states do not follow the systematics of the negative parity states. The absolute values of the b and c coefficients are larger for the positive parity states. An analysis in terms of Coulomb energy displacement indicates a possible configuration mixing or core polarization effect in these states. The d coefficient also has a large deviation from zero, only for the positive parity states indicating a possible expansion of the radial wavefunction or some isospin symmetry breaking effects. Further detailed theoretical interpretation of these effects may bring valuable information about the configuration and structure of these states. The leveis in 13O were measured with good energy resolution, and thus, it was possible to identify the first excited state unambiguously. However, if one identifies this state as the analog of the known first excited state in the mirror nucleus 13B, this leads to one of the largest level shifts known in literature.

The nuclear structme of 17Ne and 13O has been studied by the 20Ne(3He,6He)17Ne and 16O(3He,6He)13O reactions at 70 MeV and 80 MeV, respectively. Fifteen levels were identified, and angular distributions have been measured for nine of these levels in 17Ne, while for 13O eighteen levels were identified, but angular distributions were obtained for only ten levels. The observed transferred angular momentum dependence of these angular distributions allowed spin-parity assignments. The T= 3/2 quartet analog states in mass A=17 have been completed for six levels. The results of the isobaric multiplet mass equation analysis show a slight linear dependence of the b and c coefficients on the excitation energy. It was found that the coefficients for the positive parity states do not follow the systematics of the negative parity states. The absolute values of the b and c coefficients are larger for the positive parity states. An analysis in terms of Coulomb energy displacement indicates a possible configuration mixing or core polarization effect in these states. The d coefficient also has a large deviation from zero, only for the positive parity states indicating a possible expansion of the radial wavefunction or some isospin symmetry breaking effects. Further detailed theoretical interpretation of these effects may bring valuable information about the configuration and structure of these states. The leveis in 13O were measured with good energy resolution, and thus, it was possible to identify the first excited state unambiguously. However, if one identifies this state as the analog of the known first excited state in the mirror nucleus 13B, this leads to one of the largest level shifts known in literature. / The nuclear structme of 17Ne and 13O has been studied by the 20Ne(3He,6He)17Ne and 16O(3He,6He)13O reactions at 70 MeV and 80 MeV, respectively. Fifteen levels were identified, and angular distributions have been measured for nine of these levels in 17Ne, while for 13O eighteen levels were identified, but angular distributions were obtained for only ten levels. The observed transferred angular momentum dependence of these angular distributions allowed spin-parity assignments. The T= 3/2 quartet analog states in mass A=17 have been completed for six levels. The results of the isobaric multiplet mass equation analysis show a slight linear dependence of the b and c coefficients on the excitation energy. It was found that the coefficients for the positive parity states do not follow the systematics of the negative parity states. The absolute values of the b and c coefficients are larger for the positive parity states. An analysis in terms of Coulomb energy displacement indicates a possible configuration mixing or core polarization effect in these states. The d coefficient also has a large deviation from zero, only for the positive parity states indicating a possible expansion of the radial wavefunction or some isospin symmetry breaking effects. Further detailed theoretical interpretation of these effects may bring valuable information about the configuration and structure of these states. The leveis in 13O were measured with good energy resolution, and thus, it was possible to identify the first excited state unambiguously. However, if one identifies this state as the analog of the known first excited state in the mirror nucleus 13B, this leads to one of the largest level shifts known in literature.