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CONF-6050306-54
LEGAL NOTICES
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RESIDUAL RADIATION STUDIES
w my we want t mod directed in the report
..Mihr www Com... wewe mwe.
We captur
i n, o completo ed antractor, the entend thes
C. B. Fulmer and K. S. Toth
la byw trwater e tootme, e t mod controler preparat,
Commen, we provide the s torm
wo employment or contrast Oak Ridge Natior al Laboratory
will be cond
u plement content."
Oak Ridge, Tennessee
and
M. Barbier
CERN, European Organization for Nuclear Research
Geneva, Switzerland
MASTER
Summary
Studies of residual radiation levels to be
encountered in high beam intensity accelerators
are reported. Calculated residual radiation
decay curves are compared with experimental
data. Previously reported work with 600-MeV
protons is extended to a wider range of bombard-
ment times. The experimental and calculated
decay curves for C, Al, Fe, and Cu are com-
pared by normalizing the intensities of the 32 Na
activity in the aluminum. The experimental and
calculated decay curves agree within a factor of
2 or 3 over a range of cooling times for boinbard-
ment times that range from 3 hrs to 2 years.
Data obtained from one group of samples exposed
to 19 - 26 GeV protons for 5 months are also
compared with the calculated decay curves,
The method of calculation takes into
account each of the spallation products (those
with half lives less than 10-min are neglected)
and sums the contributions to obtain the gross
residual radiation level as a function of bombard.
ment time and cooling time. Both gamma flux
and radiation dose rate were calculated. If
cross section data were available for all spalla-
tion products formed by the interaction of high
energy particles with the structural materials
in an accelerator installation the residual
radiation levels could be computed for any
assumed bombardınent. Since such data are
not available for all materials, we have made
calculations for a few materials which are
extensively used in accelerator construction,
and for which spallation cross section data37
are available over the range of 0.5 - 1 GeV.
Introduction
The experimental data were obtained from
samples of materials exposed to either the
direct or the scattered beam of 600-MeV protons
in the CERN Synchrocyclotron. The residual
radiation measurements were made by counting
the emitted gammas with a 3 x 3 in. Nal(TI)
scintillation counter. Integral counting rates
were measured as a function of cooling time.
Accelerator technology is sufficiently
developed that serious consideration is being
given to construction of machines capable of
producing 0.5 to 1 GeV proton beams with inten-
sities ranging from hundreds of micro-amperes
to tens of milliamperes. An essential part of
the planning of an accelerator of such high inten-
sity is a quantative estimate of the residual
radiation levels that will result from operation
of the machine, Adequate shielding and remote
handling facilities must be provided for safe
operation and maintenance of the accelerator and
associated experimental facilities,
.
Exact agreement between calculated and
experimental results is not expected. The
total detection efficiency of NaI(TI) crystals
varies with gamma energy; it decreases by a
factor of ~ 2 between 0, 1 and 2 MeV. Gamma
dose rates are approximately linearly dependent
(in the calculations a linear dependence was
assumed) over the range of gamma energies
involved. For the calculations of gamma flux
there is no energy dependence.
Calculations and Data at 600 MeV.
Estimates of residual radiation levels for
a particular accelerator will be based on detailed
calculations for that installation. The work
reported in this paper is an attempt to determine
the reliability of such calculations. Our
approach to the problem is to compare calcu...
lated decay curves with experimental data for a
wide range of bombardment time. The calcu.
lations were done at ORNL and the experimental
data were obtained at CERN. In an earlier
report" calculated decay curves were compared
with experimental data obtained from 3-hr and
3-mo bombardments. In the work reported
here the calculations are compared with data
obtained over a wider range of bombardment
time.
Experimental and calculated residual
radiation decay curves for a 3-hr bombardment
with 600-MeV protons can be compared in
Figure 1. The experimental data were obtained
from thin samples exposed to a proton flux of
~ 109 p/cms-sec, An averaged counting
efficiency, based on previous measurements,
was used to convert the experimental counting
rates to dose rates. Good agreement is
obtained for C and Al. For Fe and Cu the
general shapes of the calculated and experi.
mental decay curves agree and the magnitudes
agree within a factor of two or three. The
**Research sponsored in part by the U. S. Atomnic.
Energy Commission under contract with the
Union Carbide Corporation,
L
MANCE OBTAINED: NETEKO TO
OUD IS APPROVED. PROOFMURES
ARE ON FILE IN THE
LLLL
1144
1 al 1
P
.
A
discrepancies are not surprising when the experi-
mental errors in a boinbardment of short duration
by a beam of low intensity are considered.
The calculated dose rate and the experi.
mental counting rates obtained for a 3-mo
exposure to scattered 600-MeV protons can be
compared in Fig. 2. The two sets of curves are
normalized at the flat part of the Al decay curve
where 32 Na (T1a = 2.58 y) is the dominant
activity. The calculated and experimental decay
curves agree within a factor of ~ 2 throughout the
range of the data. Figures 1 and 2 were pre-
sented in an earlier report but are included here
for comparison with data from a larger range of
exposures.
The experimental gross activity decay
curves for several samples that were bombarded
for 96 hrs with a 600-MOV proton beam are :
shown in Fig. 5. The ordinate scales were
determined from calculations for Al; the scale
is the dose rate at 1 meter for a collimated
beam of 1 HA. It is also the dose rate outside
a large slab uniformly irradiated with a fl* of
106 particles/ cm - 800. The calculation is for
a collimated beam. The conversion of the
results of the calculation for distributed fluxes
is discussed in Ref. l.
The experimental gross activity decay
curves obtaired for the 2-yr borribardment are
shown in Fig. 6. The ordinate acale was
determined by the calculation for Al. We
believe that these curves are reliable to within
a factor of ~3, which is probably as accurate
as the intensities of bombarding particles can
be predicted.
The calculated and experimental decay
curves for a 96-hr 600-MeV proton bombardment
are shown in Fig. 3. Again, the curves are
normalized for the aa Na activity in Al. The
ordinate scale is in gamma flux for the calculated
curves and in counting rate of the detector for
the experimental curves. Except for the portions
of the curves for Cu for cooling time < 100 hrs
the experimental and calculated curves agree
within a factor of 2 througho: 6 the range of
cooling time.
The ordinate scales in Fig. 5 and 6 are
for targets of specific thickne88e8, as indicated.
Residual radiation levels are obviously dependent
on target thickness. In Fig. 7 calculated
residual radiation decay curves are shown for
Al samples of various thicknesses for bombard.
ment times of 96 hrs and of 2 years. These
curves can be used with those in Fig. 5 and 6
to extrapolate residual radiation dose rates for
targets of specific thicknesses.
Also, thin samples were exposed inside
the CERN Synchrocyclotron for a period of two
years and the gross activity decay curves
measured. The measurements cover the range
of cooling time from 660 to 7600 hours. The
experimental and calculated decay curves are
shown in Fig. 4. The ordinate scales are the
same as in Fig. 3 and the sew of curves are
normalized on the same basis. The experi.
mental and calculated decay curves agree within
a factor of <2 throughout the range of the experi-
mental data.
Accelerator designers and operators are
interested not only in the decay of residual
radiation but also the radiation level at some
specific time after machine shutdown In Fig. 8
are shown calculated residual radiation dose
rates as functions of bombardment time. The..
curves shown are for 20 cm thick samples
bombarded with 600-Mey protons. There are
two curves for each sample. The upper one is
for 1 day of cooling time and the lower is for
1 month.
Residual Radiation Dose Rates
Figures 1 to 4 permit comparison of
experimental and calculated gross activity decay
High Energy Data and Calculations ...,
curves for a wide range of bombardment times.
Although the beam intensity for the experimental
While most of our experimental data were
data was not measured, except for the low
obtained with 600-MeV protona, one group of
intensity 3-hr bombardment (Fig. 1), the agree thin samples was exposed at the CERN Proton
ment obtained for the .96-hr, 3-mo, and 2-yr
Synchrotron.. They were placed 3.5 meters
irradiations demonstrates that the spallation
cross section data used in the calculation are
direction. The samples were exposed to
reasonably accurate and complete, and that
19-26 GeV protons and fast neutrons. After
calculations can be used with confidence to
5 months they were removed and the residual
predict residual radiation levels in accelerator radiation decay curves were measured.
installations.
Spallation cross section data for 28-GeV
The experimental data obtained at the CERN protons on C, Al, and Cu were tabulated from .
Synchrocyclotron include a number of samples published measurements, and used to calculate
that are not shown in Fig. 1-4. For most of residual radiation decay curves for a 5-mo
these the available spallation cross section data exposure. The calculated and experimental
are not as complete as for C, Ali, Fe, and Cu. decay curves are shown in Fig. 9. The
The agreement between calculated and experi. ordinates for the experimental curves are
mental results in the above figures suggests that: counting rates and for the calculated curves
calculated dose rate curves for Al might be used . they are gamma flux. The curves were
to determine dose rate scales for the larger num. ,, normalized for the 88 Na activity in Al. Except
ber of curves included in the experimental data... for the short-life activity in Al the agreement
.
Fig. 4-Calculated and experimental residual
radiation decay curves for samples
irradiated with 600-MeV protons for 2
years. (Details as per Fig. 3.)
is reasonably good. The data suggest that the
Na cr088 section for 19-26 GeV protons on
Al is somewhat larger than the value used in
the calculations. The agreement obtained
between the calculated and experimental decay
curves is encouraging but additional work is
needed before conclusions about residual radia-
tion calculations for this high energy region will
be as valid as fos: the 600-MeV energy.
Fig. 5-Residual radiation levels for l-cm thick
samples irradiated for 96 hours with
600-MeV protons. The ordinate scale
is also applicable for dose rates outside
large I-cm thick slabs irradiated with a
uniform flux of 108 protons/cms-sec for
96 hours.
References
1.
C. B. Fulmer, K. $. Toth, and M. Barbier,
Nucl. Instr. and Meth, (in press).
J. B. Ball and C. B Falmer, Report
ORNL-3554 (1964).
Fig. 6-Residual radiation levels for 20-cm thick
samples irradiated for 2 years with
603-MeV protons. The ordinate scale
is also applicable for dose rates outside
large 20-cm thick slabs irradiated with a
uniform flux of 108 protons/cmsec for
2 years.
3.
M Honda and D. Lal, Phys. Rev. 118,
1618 (1960).
P. Benioff, Phys. Rev. 119, 316 (1960).
Fig. 7-Dose rate vs cooling time for aluminum
4.
with 600-MeV protons for periods of 96
hours and 2 years.
5.
G. Rudstam, E. Bruninx, and A. C. Pappas,
Phys. Rev. 126, 1852 (1962).
J. Hudis, et al., Phys. Rev. 129, 434
(1963).
Fig. 8-Residual radiation levels for 20-cm thick
targets irradiated with 1-4A beams of
600-MeV proton. Phong thurve for
cachmenplanatdayooking and
the lowes auronofogmonth.
E. Bruninx, Reports CERN-61-1 (1961)
and CERN-62-9 (1962).
E. A. Wolicki, R. Jastrow, and F. Brooks,
Report NFL-833.(1956).
J. B. Cumming, et al. , Phys. Rev. 127,
950 (1962).
Fig. 9-Calculated and experimental residual
radiation decay curves for samples
exposed in the CERN proton Synchrotron
for 5 inonths. (Details as per Fig. 3
and 4.)
9.
Figure Captions
Fig. 1-Calculated and experimental residual
radiation decay curves for thin samples
irradiated for 3 hrs with 600-MeV protone
Fig. 2. Calculated and experimental residual
radiation decay curves for samples
irradiated with 600-MeV protons for 3
months. The calculated curves are dose
rates and the experimental curves are
counting rates of the detector per gram of
sample material. The experimental and
flat part of the Al curve.
g. 3. Calculated and experimental residual
radiation decay curves for samples
irradiated with 600-MeV protons for 96
hours. The calculated curves are gamma
fluxes i meter from the sample and the
experimental curves are counting rates of
the detector per gram of sample material.
The experimental and calculated curves
::..are normalized for the flat part of the Al
curve,
:

.
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.
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.
ORAL -DWG 63-2859
AFEETAHEAEFFD
| CURVES REPRESENT CALCULATED RESULTS
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EXPERIMENTAL
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DOSE RATE (r/hr)
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5
5
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2
5
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TIME (hr)
Fig. 1. Calculated and experimental residual radiation decay curves for thi:
Hamples irradiated for 3 hrs with 600 MeV protons.
ORNL-LR-OWG 79523R
1000

CUAL
# 3-month PROTON EXPOSURE
CU
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INTENSITY
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RA
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10
100
COOLING TIME (days)
Fix. d. Calculated and exporiniental roaldual radiation decay curves for samploi
irradialed with 600-MeV protuns (or 3 months. The calculatod curvus
are doso ratus and ihe oxperimental curves are counting rate of the
dutccior pur yram of sample material. The oxperimental and culculatad
curves aro normalized for the flat part o tho al curve.
----
top
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ORNL-DWG 65-1721

--- -
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96-hr PROTON EXPOSURE
CALCULATEDt
----EXPERIMENTAL
--
-
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-
1
INTENSITY
.
.
.
.
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10 20 50 100 200 500 1000 2000 5000 10,000
COOLING TIME (hr)
Fig. 3. Calculated and experiinontal residual radiation ducay curves for samples
irradiated with 600-MeV protons (or y hours. 'The calculated curvos
arc gamma fluxos 1 meter from the sample and the experimuntal curves
arc counting rates of the detector pur gram of samplo material. The
experimental and calculated curves are normalized for the fal part of the
Al curve.
ORNL-OWG 65-1722
1000

2-year PROTON EXPOSURE
CALCULATED
----- EXPERIMENTAL
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INTENSITY
100
10,000..40,000
1000
COOLING TIME (hr)
Fig. 4. Calculated and experimental rusidual radiation decay curvou for samples
Irradiated with 600-MeV proton. for 2 yoars. (Detalls as por Fig. 3.).

ORNL-OWO 65-1723
BaSOAS
Alit
DOSE RATE AT ONE METER (MR/hr-HA OF INCIDENT BEAM)
11
T
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(BARITETA
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Alcat
to
20
50
100
200 500 1000 2000
COOLING TIME (hr)
3000 10,000
Fig. 5. Kusidual radiation levels lur 1-сin thick samples irradiatod for 96 hours
with 600-MeV protons. The ordinatu scale is also applicable for dose
ralus outside large l-cm thick wlaluirradiated with a unui o flux of 10
prolonr/cmºsoc lor 96 hours.
ORNL-DWG 65-1725

NII
MO
DOSE RATE AT ONE METER (MR/hr-HA OF INCIDENT BEAM)
EXPERIMENTAL
EXTRAPOLATED
100
10,000
COOLING TIME (hr)
Fig. 6. Residual rudlauon lovolo for 20.cm thick sample. Irradluted for 2 yuar,
with 600.MaV protons. The ordinata scato so also applicable for dono
ratas outaido large 20-cm thick slabs Irradiated with a unltorm. nux of
100 protons/cmtec for 2 yuar..
ORNL-DWG 65- 1726

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1
DOSE RATE AT ONE METER (mR/hr-HA OF INCIDENT BEAM)
2-yr EXPOSURE; THICKNESS (cm)
H
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96-hr EXPOSURE; THICKNESS (cm)
| 0.5
U
0.3
50.2
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10
10,000
ICO
1000
COOLING TIME (hr)
Fig. 7. Dose rate ve cooling time (or aluminuni suniples of various thicknesses
irradiated with 600-MUV protons for periods of 96 houry ind 2 years,
ORNL-DWG 65-1864

Fe
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41
DOSE RATE AT 10 cm (R/hr)
1
.
--- 1 day COOLING
mo COOLING
100 :! 1000
10,000
EXPOSURE TIME (hr)
Fig. 8. Residual radiation lovel. for 20-cm thick targets irradiated with
1 - A beams of 600 MeV protons.
ORNL-OWG 65-1724

5-month EXPOSURE
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---- EXPERIMENTAL
INTENSITY
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5
10
: 1000
100
COOLING TIME (hr)
Fig. 9. Calculated and experimental residual radiation decay curves for samples
exposed in the CERN proton Synchrotron for 5 months. (Details as per
Fig. 3 and 4.)
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This report was prepared as an account of Government sponsored work. Neither th:9 United
Statec, nor the Commission, nos any person acting on behalf of the Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or usefulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disclosed in this report may not infringe
privately owned rights; or
B. Assumes any liabilities with respect to the use of, or for damages resulting from the
use of any information, apparatus, method, or process disclosed in this report.
As used in the above, "person acting on behalf of the Commission" includes any em-
ployee or contractor of the Commission, or employee of such contractor, to the extent tat
such employee or contractor of the Commission, or employee of such contractor prepares,
disseminates, or provides access to, any information pursuant to his employment or contract
with the Commission, or his employment with such contractor.
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