This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Foster, C.

Murray, K.

Rinckel, T.

English

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I 
EXPERIMENTAL FACILITIES DEVELOPMENT 
RADIATION-EFFECTS RESEARCH FACILITIES 
C. Foster and T. Rinckel 
Indiana Universi ty  Cyclotron Facility, Bloomington,  Indiana 47408 
K. Murray 
KM Sciences, Beech Grove, Indiana 46107  
There are a variety of electronc devices and radiation detectors that are flown in the 
harsh radiation environment of space. High energy protons which penetrate spacecraft 
shielding are the major cause of single event and other radiation effects in microelectronic 
devices and a major component of signals in detectors. Accelerator-based irradiations 
of electronic components and detector studies are used to provide information essential 
to understanding the performance of these devices in the space radiation environment. 
Facilities and software needed to support radiation-effects studies, detector calibrations 
and detector background measurements have been developed and used at IUCF. This 
report describes the facilities and beams available, outlines the radiation-effects research 
program (which encourages use of the facilities by the radiation-effects research community 
and participation in appropriate improvement of the facilities) and lists recent users of the 
facilities. 
Figure 1 shows the radiation-effects research station (RERS) which is used in beam 
line 4 when sharing beam with users of the K600 spectrometer, the beam swingerlneutron 
time-of-flight facility, the polarized-neutron facility or the beam line 5 general purpose 
station, or in the beam line 5 general purpose station when sharing beam with users of 
the Cooler. The research station is used in beam line 4 if not using beam shared with 
another user. The RERS uses a carbon target (not shown) to spread the beam by multiple 
scattering. The target thickness is chosen so that about 60% of the beam passes through a 
6-cm-diameter by 5-cm-thick copper collimator (shown) located about 2.5 m downstream 
of the target. This results in a circular beam intensity profile which falls off by about 30% 
from the center to the edge. The beam profile is determined by exposure of GafChromic 
film, which is read by a photometer. 
Immediately downstream of the collimator is located a secondary-electron monitor 
(SEM) followed by a removable copper block, with magnetic electron-emission suppression, 
which is used as a Faraday stop to measure the beam current through the SEM. Calibration 
of the SEM is accomplished by measuring the ratio of the Faraday stop current to the SEM 
current. This ratio is then used in dosimetry calculations. About 10 cm downstream of the 
Faraday stop is a 5-mil thick Kapton window 9 cm in diameter, through which the beam 
passes into an air gap of 50 cm before passing through a similar Kapton window into an 
evacuated beam-dump Faraday Cup. The device under test (DUT) is placed in the air gap 
EXIT 
WINDOW 
\ SEM \ 
k ~ ~ ~ { ~ S y  FARADAY STOP 
1 INSERTED POSITION 
Figure 1. Schematic drawing of the downstream end of the radiation-effects research 
station. 
just behind the upstream Kapton window. It is mounted on a device that allows vertical, 
horizontal and rotary positioning of the DUT. There is a remotely-operable beam stop 
located well upstream of the carbon scatterer that is used to control the time of device 
exposure. 
The upstream stop and the Faraday stop are controlled by a personal computer, which 
also records the measured currents from the SEM and Faraday stop, computes the SEM 
calibration and monitors the dose that is corrected for the actual measured beam profile. 
User-friendly software provided by Ken Murray of KM Sciences allows exposure of the 
DUT for a preset dose. Data from each exposure are stored on disk and a printed run log 
is maintained as well. 
A protype SEM has been developed and tested that has a Faraday-stop-current-to- 
SEM-current ratio of 2.0 at 200 MeV, leakage currents less than 0.5 PA, and noise less 
than f 0.02 PA. This would allow measurements with fluxes of 200-MeV protons as low 
as 1 x lo6 protons/s/cm2 with a 10% uncertainty in dose. Scaling this SEM to one 
with 80 foils is possible in the available space. This would allow measurements in the 
lo4 protons/s/cm2 range with somewhat increased uncertainty in the dose. Such low fluxes 
are necessary for exposures of certain radiation-sensitive devices. Usual exposures require 
fluxes in the lo6 to lo9 protons/s/cm2 range. Proton fluxes as high as 10" protons/s/cm2 
are available. 
The energy of the protons incident on a DUT is controlled either by changing the 
energy of the beam through retuning the cyclotron and beam lines at the cost of several 
hours, or by degrading the beam energy by placing copper degrader plates in air just in 
front of the DUT at a cost of increased beam energy spread. The latter technique is usually 
acceptable and has been used to degrade the beam energy from from 200 to 30 MeV. See 
Table 1 for a summary of the proton capabilities of the RERS. 
Table 1. Proton Capabilities of RERS 
Energy Range: 30 to 200 MeV 
Flux: lo4 to > 10" protons/s/cm2 
Area: Less than 2 cm to '7 cm diameter 
Uniformity: < 30% variation over area 
Absolute dosimetry: Better than 10% routinely 
Exposure durations: A few seconds upward routinely 
This radiation-effects research station is fully operational and has been used by groups 
from the Johns Hopkins Applied Physics Laboratory, Sandia National Laboratories, the 
Naval Research Laboratory, the Crane Naval Surface Warfare Center, Clemson University, 
and NASA. 
In order to provide funds for automation and other improvements of the research 
station, the Indiana Radiation Effects Research Alliance has been created. Users are given 
the opportunity to join the Alliance by making an "up front" investment of a minimum 
of $20,000. This provides them access to beam at IUCF for two years at a much reduced 
cost, participation in planning improvements to the research station, priority consideration 
during beam scheduling, dosimetry and technical consultation. A group from NASA has 
joined the Alliance and several other groups are considering doing so. 
When fluxes less than lo5 protons/s/cm2 are required for detector studies or device 
tests, it is difficult to use the RERS described above because the SEM and Faraday stop 
currents become comparable to leakage currents and rapidly changing noise currents cre- 
ate significant uncertainties. The "tagged proton" technique described below has been 
effectively used for such purposes. 
As shown schematically in Figure 2, protons scattered from protons in a polyethylene 
(CH2) target (about 1 mg/cm2 thick), pass through a 5-mil-thick Kapton foil and 10 cm of 
air into a collimated AE - E telescope, which is used to identify them as protons. Recoiling 
protons, which scatter at an angle of about 90" from the telescope, are tagged by the 
protons detected in the telescope. This flux of tagged recoil protons, which passes through 
a 5-mil Kapton window and are incident on the DUT located 90" from the telescope, is 
determined by the collimator aperture, the target thickness, the beam intensity, reaction 
kinematics, and the proton-proton elasctic-scattering cross section. Kinematics of the 
scattering determines energies of the recoiling protons from knowledge of the energy of 
the beam protons and the scattering angles. Correction can be made for the small loss of 
energy in the exit window and air. Therefore, events occurring in the DUT in coincidence 
with the tagging protons are the result of a known flux of protons of known energies. Other 
particles produced as reaction products in the carbon target, window and air, which may 
cause events in the DUT, will not satisfy the coincidence requirements. Fluxes in the range 
from 1 to lo4 protons/s/cm2 are readily obtained with this technique. 
The energies of the tagged protons may be readily varied in the range from about 25 to 
about 180 MeV by varying the angles of the telescope and the DUT while maintaining the 
90" angle between them. This technique has been used to measure detection efficiencies of 
scintillator, wire chamber, phoswich and other detectors. The hardware for this technique 
TAGGER 
TAGGER 
5 MIL KAPTON 
TEST DETECTOR 
MOVABLE \ 
ARM 
Figure 2. Schematic plan-view drawing of the tagged-proton facility. 
can be set up at the same time as the RERS and in the same beam line to allow rapid 
change between use of the two techniques. 
IUCF has implemented two techniques, direct exposure to the beam and exposure to 
a tagged proton beam, for the study of radiation effects in electronic devices and detectors. 
These techniques have been used several times and have served several user groups. They 
are user friendly and cover a wide range of energies and fluxes with accurate dosimetry. 
A program to encourage commercial and other users to to use and help improve these 
facilities is being offered to and is being accepted by the radiation effects community. 
STATUS OF TWO SUPERCONDUCTING SOLENOIDS 
Kevin Komisarcik 
Indiana University Cyclotron Facility, Bloomington, Indiana 474 08 
The new spin-precession solenoid manufactured by Cryomagnetics, Inc. arrived in 
December, 1994. Its purpose is to replace the magnet in beam line 3 which developed a 
large leak in its helium cryostat. The new magnet has an integrated field of 2 Tom at 90 A, 
slightly larger than the BL3 solenoid (1.6 Tom). The helium boiloff rate is approximately 
1.1 l/hr, similar to the boiloff rate of the BL3 solenoid. This translates into a 20 hr refill 
period for both beamline magnets. The new magnet has a 10 cm diameter bore. This will 
allow it to be used not only in the high energy beamlines but also the Cooler if necessary. 
So far, the new magnet has been used successfully by E368, E378 and in several INPOL 
runs. 


Radiation-effects Research Facilities

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Radiation-effects Research Facilities

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