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A windowless gas target for secondary beam production
Nuclear Instruments and Methods in Physics Research A 438 (1999) 70}72
A windowless gas target for secondary beam production T. Kishida!, Y. Gono",*, M. Shibata", H. Watanabe", T. Tsutsumi", S. Motomura", E. Ideguchi!, X.H. Zhou!, T. Morikawa", T. Kubo!, M. Ishihara!,# !RIKEN, Wako, Saitama 351-0106, Japan "Department of Physics, Kyushu University, Fukuoka, Hiashi-ku 812-8581, Japan #Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
Abstract A windowless gas target was developed for the production of secondary high-spin isomer beams (HSIB). An 16O target in the compound form of CO gas was used to produce a 145.Sm beam by using an 16O(136Xe, 7n)145.Sm reaction. The 2 target gas pressure was kept constant at 50 Torr. A target thickness of about 1 mg/cm2 was achieved with a 10 cm target length. Gas was recirculated and the consumption was very little. ( 1999 Elsevier Science B.V. All rights reserved. Keywords: Gas targets; Nitrogen } N; Oxygen } O; Xenon } Xe
1. Introduction High-spin isomers were sought by using heavyion beams provided by the RIKEN Ring Cyclotron. A recoil-catcher technique was adopted. The reaction in inverse kinematics, 24Mg(136Xe, 8n) 152Dy, was used to minimize the #ight time and to maximize the spatial acceptance of the recoil nuclei. A gas-"lled recoil separator system was applied. Gases used to equilibrate charge states of a primary beam as well as recoiling reaction products were He, N , O , and Ne. In the case of N gas, c-rays of 2 2 2 144Pm were observed after a 200 ns #ight time. An isomer of 144Pm turned out to be produced by the reaction of 14N(136Xe, 6n)144.Pm [1]. A high-spin isomer was also found in 145Sm produced from the reaction 16O(136Xe, 7n)145Sm [2,3]. * Corresponding author. Fax: #81-92642-2553. E-mail address: [email protected] (Y. Gono)
Since these reactions were inverse kinematic reactions, the recoil energy of the reaction products was high enough to induce secondary reactions. Therefore, the aim of these experiments was shifted to developing high-spin isomer beams [4].
2. A blow-in type windowless gas target While the development was going on, the primary beam intensity was up-graded by more than an order of magnitude, i.e. from &10 pnA to &200 pnA. Since no thin metal foil could withstand this beam intensity, it was necessary to introduce a windowless gas target. Its thickness should be about 1 mg/cm2. We adopted a blow-in windowless gas target which was developed by Sagara et al. [5]. To realize our purpose, the gas target developed by them, was enlarged to a length of 10 cm. With a constant pressure (50 Torr) of the
0168-9002/99/$ - see front matter ( 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 9 ) 0 0 9 4 2 - 0
T. Kishida et al. / Nuclear Instruments and Methods in Physics Research A 438 (1999) 70}72
71
Fig. 2. Schematic diagram of the gas target with its di!erential pumping system. Pumps are adjoined to their vacuum chambers and the pumping speeds are indicated.
Fig. 1. Schematic cross-sectional view of the windowless blow-in gas target with the equipment for di!erential pumping. MBP stands for mechanical booster pump, TMP for turbomolecular pump, all these pumps are backed with oil rotary pumps (RP).
target gas, a target thickness of about 1 mg/cm2 could be adjusted. The conceptual drawing of the set-up for the new gas target is shown in Fig. 1. The target gas is injected into the gas target volume through narrow conical gaps from both the downstream and the upstream sides. All four of the apertures before the beam entrance into the target volume were 6 mm in diameter to ensure that they are not touched by the incoming ion beam. The exit of the target volume and the exit of the "rst di!erential pumping volume had 6 mm diameter apertures, too. The apertures of the following di!erential pumping volumes at the beam exit had 8 and 10 mm diameter apertures, respectively, taking into account a high emittance of the forward-peaked reaction products. Pumping speeds of the vacuum pumps used for di!erential pumping are indicated in Fig. 2. A vane-type low-vacuum pump (MBP1) with
Fig. 3. Pressure of each chamber with the notation de"ned in Fig. 2.
a pumping speed of 1020 m3/h is attached to the vacuum chamber P2. It takes most of the target gas leaking out of the 6 mm diameter apertures of the target cell. The next surrounding vacuum chamber P3 is equipped with a pumping speed of 600 m3/h (MBP2). Both pumps are backed with oil rotary pumps with the exhaust connected to a recirculation line. The last two outward vacuum chambers, P4 and P5, are equipped with turbomolecular pumps at pumping speeds of 1450 l/s (TMP1) and 550 l/s (TMP2), respectively. With this set-up, a pressure
II. STABLE TARGETS
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T. Kishida et al. / Nuclear Instruments and Methods in Physics Research A 438 (1999) 70}72
of 6]10~6 Torr could be maintained in the outermost vacuum chamber at a constant target gas pressure of 50 Torr. The pressure drops from the gas target to the following surrounding chambers for di!erential pumping are shown in Fig. 3. The target thickness was determined by the amount of reaction products using the measured beam intensity and the calculated reaction cross section. The target gas was recirculated to prevent contamination of the environment by reaction product activities. This resulted in a very small amount of gas consumption, i.e. less than 1 m3 (standard pressure) for two days beam time.
Acknowledgements We would like to thank Prof. K. Sagara for his kind cooperation in constructing the gas target of his design.
References [1] [2] [3] [4] [5]
T. Muraklami et al., Z. Phys. A 345 (1993) 123. A. Ferragut et al., J. Phys. Soc. Jpn 62 (1993) 3343. A. Odahara et al., Nucl. Phys. A 620 (1997) 363. Y. Gono et al., Nucl. Phys. A 588 (1995) 241c. K. Sagara, A. Motoshima, T. Fujita, H. Akiyoshi, N. Nishimori, Nucl. Instr. and Meth. A 378 (1996) 392.
A windowless gas target for secondary beam production T. Kishida!, Y. Gono",*, M. Shibata", H. Watanabe", T. Tsutsumi", S. Motomura", E. Ideguchi!, X.H. Zhou!, T. Morikawa", T. Kubo!, M. Ishihara!,# !RIKEN, Wako, Saitama 351-0106, Japan "Department of Physics, Kyushu University, Fukuoka, Hiashi-ku 812-8581, Japan #Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
Abstract A windowless gas target was developed for the production of secondary high-spin isomer beams (HSIB). An 16O target in the compound form of CO gas was used to produce a 145.Sm beam by using an 16O(136Xe, 7n)145.Sm reaction. The 2 target gas pressure was kept constant at 50 Torr. A target thickness of about 1 mg/cm2 was achieved with a 10 cm target length. Gas was recirculated and the consumption was very little. ( 1999 Elsevier Science B.V. All rights reserved. Keywords: Gas targets; Nitrogen } N; Oxygen } O; Xenon } Xe
1. Introduction High-spin isomers were sought by using heavyion beams provided by the RIKEN Ring Cyclotron. A recoil-catcher technique was adopted. The reaction in inverse kinematics, 24Mg(136Xe, 8n) 152Dy, was used to minimize the #ight time and to maximize the spatial acceptance of the recoil nuclei. A gas-"lled recoil separator system was applied. Gases used to equilibrate charge states of a primary beam as well as recoiling reaction products were He, N , O , and Ne. In the case of N gas, c-rays of 2 2 2 144Pm were observed after a 200 ns #ight time. An isomer of 144Pm turned out to be produced by the reaction of 14N(136Xe, 6n)144.Pm [1]. A high-spin isomer was also found in 145Sm produced from the reaction 16O(136Xe, 7n)145Sm [2,3]. * Corresponding author. Fax: #81-92642-2553. E-mail address: [email protected] (Y. Gono)
Since these reactions were inverse kinematic reactions, the recoil energy of the reaction products was high enough to induce secondary reactions. Therefore, the aim of these experiments was shifted to developing high-spin isomer beams [4].
2. A blow-in type windowless gas target While the development was going on, the primary beam intensity was up-graded by more than an order of magnitude, i.e. from &10 pnA to &200 pnA. Since no thin metal foil could withstand this beam intensity, it was necessary to introduce a windowless gas target. Its thickness should be about 1 mg/cm2. We adopted a blow-in windowless gas target which was developed by Sagara et al. [5]. To realize our purpose, the gas target developed by them, was enlarged to a length of 10 cm. With a constant pressure (50 Torr) of the
0168-9002/99/$ - see front matter ( 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 9 ) 0 0 9 4 2 - 0
T. Kishida et al. / Nuclear Instruments and Methods in Physics Research A 438 (1999) 70}72
71
Fig. 2. Schematic diagram of the gas target with its di!erential pumping system. Pumps are adjoined to their vacuum chambers and the pumping speeds are indicated.
Fig. 1. Schematic cross-sectional view of the windowless blow-in gas target with the equipment for di!erential pumping. MBP stands for mechanical booster pump, TMP for turbomolecular pump, all these pumps are backed with oil rotary pumps (RP).
target gas, a target thickness of about 1 mg/cm2 could be adjusted. The conceptual drawing of the set-up for the new gas target is shown in Fig. 1. The target gas is injected into the gas target volume through narrow conical gaps from both the downstream and the upstream sides. All four of the apertures before the beam entrance into the target volume were 6 mm in diameter to ensure that they are not touched by the incoming ion beam. The exit of the target volume and the exit of the "rst di!erential pumping volume had 6 mm diameter apertures, too. The apertures of the following di!erential pumping volumes at the beam exit had 8 and 10 mm diameter apertures, respectively, taking into account a high emittance of the forward-peaked reaction products. Pumping speeds of the vacuum pumps used for di!erential pumping are indicated in Fig. 2. A vane-type low-vacuum pump (MBP1) with
Fig. 3. Pressure of each chamber with the notation de"ned in Fig. 2.
a pumping speed of 1020 m3/h is attached to the vacuum chamber P2. It takes most of the target gas leaking out of the 6 mm diameter apertures of the target cell. The next surrounding vacuum chamber P3 is equipped with a pumping speed of 600 m3/h (MBP2). Both pumps are backed with oil rotary pumps with the exhaust connected to a recirculation line. The last two outward vacuum chambers, P4 and P5, are equipped with turbomolecular pumps at pumping speeds of 1450 l/s (TMP1) and 550 l/s (TMP2), respectively. With this set-up, a pressure
II. STABLE TARGETS
72
T. Kishida et al. / Nuclear Instruments and Methods in Physics Research A 438 (1999) 70}72
of 6]10~6 Torr could be maintained in the outermost vacuum chamber at a constant target gas pressure of 50 Torr. The pressure drops from the gas target to the following surrounding chambers for di!erential pumping are shown in Fig. 3. The target thickness was determined by the amount of reaction products using the measured beam intensity and the calculated reaction cross section. The target gas was recirculated to prevent contamination of the environment by reaction product activities. This resulted in a very small amount of gas consumption, i.e. less than 1 m3 (standard pressure) for two days beam time.
Acknowledgements We would like to thank Prof. K. Sagara for his kind cooperation in constructing the gas target of his design.
References [1] [2] [3] [4] [5]
T. Muraklami et al., Z. Phys. A 345 (1993) 123. A. Ferragut et al., J. Phys. Soc. Jpn 62 (1993) 3343. A. Odahara et al., Nucl. Phys. A 620 (1997) 363. Y. Gono et al., Nucl. Phys. A 588 (1995) 241c. K. Sagara, A. Motoshima, T. Fujita, H. Akiyoshi, N. Nishimori, Nucl. Instr. and Meth. A 378 (1996) 392.