- Email: [email protected]
Phase I of the PIAFE project
__ _l!B
cQ23
Nuclear Instruments
and Methods in Physics Research
B 126 (1997) 22-24 LMMI
B
Beamlnteractiono with Materials 8 Atoms
ELSEVIER
Phase I of the PIAF’E project J.A. Pinston
*
Institut de.7 Sciences Nucliaires fIN2P3. UJF), 53 uvrnue des Murtyrs, F-38026 Grenoble Cedex, Frunce
Abstract In the PIAFE project it is foreseen to combine the ILL high flux reactor and an accelerator to produce RNBs of fission products. Phase I of the project concerns the ILL part of the facility, where 30 keV beams will be used for ISOL type experiments. A description of the facility and the expected beam intensities are given. 29.25.Rm Keywords: RNB facility;
PACS:
Fission product beams
1. Introduction The aim of the PIAFE (Production, Ionisation, AccClCration de Faisceaux Exotiques) project is to produce radioactive beams of neutron-rich nuclei in the mass region 75
2. The PIAFE I facility A schematic view of the ILL part of the project is shown in Fig. 1. A source of the same type as the one used at the OSIRIS facility in Studsvik [l] will be placed in a beam tube of the ILL reactor, in a neutron flux of 3 X 10’” n cmm2 s- ‘. It consists of a porous graphite cylinder of
* For the PIAFE collaboration. 0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SO168-583X(97)01014-2
about 60 mm length in which 4 g of 235U are dispersed. The expected fission rate is about lOI fissions/s and the power released by the slowing down of the fission products (IT) of about 3 kW, will keep the temperature of the graphite at 2400°C. The graphite is enclosed in a Re container at a temperature of 2000°C. This envelope prevents the diffusion of the FP outside the graphite and protects it from accidental air or water entrances. A hole in the Re, of 2 mm diameter, allows the effusion of the FP outside the target chamber. The ion source can be used both in surface and plasma ionization mode. The plasma ionization makes use of an intense electron beam, emitted by a W ring placed in front of the effusion hole. Elements Rb, Sr, Cs, Ba, Sm and In will be produced by thermoionization on the Re ionizer at rates ranging between 30 and 2%. The other elements, except refractory elements not released from the graphite, will be produced by the same source running in plasma mode with an almost constant efficiency of 0.2%. The 1 + ions extracted from the source will be accelerated by an electrical potential of 30 kV. A more complete description of the source and the results the first tests are given in [2]. At the entry of the beame line, in the reactor hall, the beam is filtered through a pre-separator made of two dipole magnets, Dl and D2, and the Fl slit in between. Only ions, in a preselected mass window A A/A = + 5%, can go through the diaphragm Fl and reach the mass separator SIR. The system becomes achromatic via the
JA. Pinsron/Nucl.
Insrr. und Meth. in Phys. Res. B 126 (1997) 22-24
second magnet D2. This concept of pre-separator was developed to implant a very large fraction of the unwanted activity on a fixed point of the beam line, the slit Fl which is easy to shield efficiently. Afterwards, the beam is mass-analysed in a standard mass separator (SFR) with a resolution, A/AA = 1000. Four beams are available simultaneously at the exit of the SFR. They will be connected with two major facilities: ( I) MISTRAL [3], a RF mass spectrometer with a mass resolution A/A A > 50000,especially designed for direct mass measurements, located in the reator hall; (2) a spectrometer with a high resolution A/A A 10000 and a high transmission, located in an experimental area outside the reactor hall. The beams at its exit will be used for nuclear and laser spectroscopy measurements.
3. The pumping ment of gases
23
rotary pumps. The radioactive gases cannot be directly released in the atmosphere, but are sent to balloons, where they can decay. After one reactor cycle of irradiation, about 4.5 d. the cold plate of the cryo-pump is warmed up to room temperature. The daughters of the rare gases will stay in the pump as well as a large part of the halogens absorbed in the char coal. Only rare gases with long half-lives will be released by the pump and stocked in the balloons. The oil of the rotary pumps will contain mainly the decay products of these rare gases. Calculations have shown that after 3 reator cycles of irradiation, about 130 d, the dose rate in the oil and in the first section of the beam line will be - 100 and IO mR/h respectively at I m, after one month of cooling time, which is acceptable. In conclusion, the definition of Phase I of the PIAFE project is in a stage where the realisation is easy to start.
system and the radioactivity-manage-
PIAFE will produce a very large amount of non-ionized rare gases and volatile species, like halogenes; it is thus important to fix a major part of this radioactivity in the beam tube or its close vicinity. For this purpose it is foreseen to install a cryo-pump inside the beam tube. The fraction of gases not trapped by the pump and then entering the beam tube are expected to be less than 0.1%. In order to decrease rapidly the progression of the remaining gases in the beam line, it is proposed to divide it into different sections, separated by diaphragms, so that the major fraction of the gases enter in the pumps. The pumping system is made of turbo-pumps associated with
Ri
LINES FOR EXTERNAL
4. PIAFE
I production
rates
The expected intensities immediately after the PIAFE mass separator are shown in Fig. 2. For the calculation a rate of IO” fissions/s was assumed. The overall efficiencies and delays of the different species are assumed to be those determined at OSIRIS by Rustdam et al. [4]. Halflives are taken into account in the calculation. The particles intensities expected from PIAFE will be several orders of magnitude higher than those which are available to date from the other facilities for the n-rich region with 75
BEAM
Fig. I. Overview of Phase I in the ILL experimental reactor hall SECTION II. ONE-LINE MASS SEPARATION
JA. Pinston / Nucl. Insrr. und Merh. in Phys. Res. B 126
24
I1997)
22-24
Beam Intensities at PIAFE Mass Separator lO’O-10’2
lo*-lo’o 106-l@ lo’-106 lo?-1cr’ 1.100
65
75
40
Fig. 2. Estimation
45 of PIAFE
$01
N---W
I production. The zigzag trail corresponds lo an estimaltion of the neutron r -process
to determine the gross properties (masses, lifetimes, moments and spectroscopic properties) of many new nuclei. All this information will be extremely useful in the context of astrophysics, since many of the nuclei expected to be produced at PIAFE lie on or in the immediate vicinity of the r-process path (see Fig. 2).
References (I] 1. Jacobsson et al., Nucl. Instr. and Meth. B 26 (1987) 223. [2] M. Fnmeau, these Proceedings (EMIS-13). Nucl. Ins&. and Meth. B 126 (1997) 55. [3] M.D. Lunney et al., Pro. ENAM’ p. 829. 141 G. Rustdam et al., Radiochem. Acta 49 (1990) 155.
cQ23
Nuclear Instruments
and Methods in Physics Research
B 126 (1997) 22-24 LMMI
B
Beamlnteractiono with Materials 8 Atoms
ELSEVIER
Phase I of the PIAF’E project J.A. Pinston
*
Institut de.7 Sciences Nucliaires fIN2P3. UJF), 53 uvrnue des Murtyrs, F-38026 Grenoble Cedex, Frunce
Abstract In the PIAFE project it is foreseen to combine the ILL high flux reactor and an accelerator to produce RNBs of fission products. Phase I of the project concerns the ILL part of the facility, where 30 keV beams will be used for ISOL type experiments. A description of the facility and the expected beam intensities are given. 29.25.Rm Keywords: RNB facility;
PACS:
Fission product beams
1. Introduction The aim of the PIAFE (Production, Ionisation, AccClCration de Faisceaux Exotiques) project is to produce radioactive beams of neutron-rich nuclei in the mass region 75
2. The PIAFE I facility A schematic view of the ILL part of the project is shown in Fig. 1. A source of the same type as the one used at the OSIRIS facility in Studsvik [l] will be placed in a beam tube of the ILL reactor, in a neutron flux of 3 X 10’” n cmm2 s- ‘. It consists of a porous graphite cylinder of
* For the PIAFE collaboration. 0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SO168-583X(97)01014-2
about 60 mm length in which 4 g of 235U are dispersed. The expected fission rate is about lOI fissions/s and the power released by the slowing down of the fission products (IT) of about 3 kW, will keep the temperature of the graphite at 2400°C. The graphite is enclosed in a Re container at a temperature of 2000°C. This envelope prevents the diffusion of the FP outside the graphite and protects it from accidental air or water entrances. A hole in the Re, of 2 mm diameter, allows the effusion of the FP outside the target chamber. The ion source can be used both in surface and plasma ionization mode. The plasma ionization makes use of an intense electron beam, emitted by a W ring placed in front of the effusion hole. Elements Rb, Sr, Cs, Ba, Sm and In will be produced by thermoionization on the Re ionizer at rates ranging between 30 and 2%. The other elements, except refractory elements not released from the graphite, will be produced by the same source running in plasma mode with an almost constant efficiency of 0.2%. The 1 + ions extracted from the source will be accelerated by an electrical potential of 30 kV. A more complete description of the source and the results the first tests are given in [2]. At the entry of the beame line, in the reactor hall, the beam is filtered through a pre-separator made of two dipole magnets, Dl and D2, and the Fl slit in between. Only ions, in a preselected mass window A A/A = + 5%, can go through the diaphragm Fl and reach the mass separator SIR. The system becomes achromatic via the
JA. Pinsron/Nucl.
Insrr. und Meth. in Phys. Res. B 126 (1997) 22-24
second magnet D2. This concept of pre-separator was developed to implant a very large fraction of the unwanted activity on a fixed point of the beam line, the slit Fl which is easy to shield efficiently. Afterwards, the beam is mass-analysed in a standard mass separator (SFR) with a resolution, A/AA = 1000. Four beams are available simultaneously at the exit of the SFR. They will be connected with two major facilities: ( I) MISTRAL [3], a RF mass spectrometer with a mass resolution A/A A > 50000,especially designed for direct mass measurements, located in the reator hall; (2) a spectrometer with a high resolution A/A A 10000 and a high transmission, located in an experimental area outside the reactor hall. The beams at its exit will be used for nuclear and laser spectroscopy measurements.
3. The pumping ment of gases
23
rotary pumps. The radioactive gases cannot be directly released in the atmosphere, but are sent to balloons, where they can decay. After one reactor cycle of irradiation, about 4.5 d. the cold plate of the cryo-pump is warmed up to room temperature. The daughters of the rare gases will stay in the pump as well as a large part of the halogens absorbed in the char coal. Only rare gases with long half-lives will be released by the pump and stocked in the balloons. The oil of the rotary pumps will contain mainly the decay products of these rare gases. Calculations have shown that after 3 reator cycles of irradiation, about 130 d, the dose rate in the oil and in the first section of the beam line will be - 100 and IO mR/h respectively at I m, after one month of cooling time, which is acceptable. In conclusion, the definition of Phase I of the PIAFE project is in a stage where the realisation is easy to start.
system and the radioactivity-manage-
PIAFE will produce a very large amount of non-ionized rare gases and volatile species, like halogenes; it is thus important to fix a major part of this radioactivity in the beam tube or its close vicinity. For this purpose it is foreseen to install a cryo-pump inside the beam tube. The fraction of gases not trapped by the pump and then entering the beam tube are expected to be less than 0.1%. In order to decrease rapidly the progression of the remaining gases in the beam line, it is proposed to divide it into different sections, separated by diaphragms, so that the major fraction of the gases enter in the pumps. The pumping system is made of turbo-pumps associated with
Ri
LINES FOR EXTERNAL
4. PIAFE
I production
rates
The expected intensities immediately after the PIAFE mass separator are shown in Fig. 2. For the calculation a rate of IO” fissions/s was assumed. The overall efficiencies and delays of the different species are assumed to be those determined at OSIRIS by Rustdam et al. [4]. Halflives are taken into account in the calculation. The particles intensities expected from PIAFE will be several orders of magnitude higher than those which are available to date from the other facilities for the n-rich region with 75
BEAM
Fig. I. Overview of Phase I in the ILL experimental reactor hall SECTION II. ONE-LINE MASS SEPARATION
JA. Pinston / Nucl. Insrr. und Merh. in Phys. Res. B 126
24
I1997)
22-24
Beam Intensities at PIAFE Mass Separator lO’O-10’2
lo*-lo’o 106-l@ lo’-106 lo?-1cr’ 1.100
65
75
40
Fig. 2. Estimation
45 of PIAFE
$01
N---W
I production. The zigzag trail corresponds lo an estimaltion of the neutron r -process
to determine the gross properties (masses, lifetimes, moments and spectroscopic properties) of many new nuclei. All this information will be extremely useful in the context of astrophysics, since many of the nuclei expected to be produced at PIAFE lie on or in the immediate vicinity of the r-process path (see Fig. 2).
References (I] 1. Jacobsson et al., Nucl. Instr. and Meth. B 26 (1987) 223. [2] M. Fnmeau, these Proceedings (EMIS-13). Nucl. Ins&. and Meth. B 126 (1997) 55. [3] M.D. Lunney et al., Pro. ENAM’ p. 829. 141 G. Rustdam et al., Radiochem. Acta 49 (1990) 155.