Shielding Estimates for the AM. Advanced Photon Source

1.0 Introduction

LS-90 t a ) H. J. Moe V. R. Veluri April 1987

Shielding estimates for the Advanced Photon Source ( A P S ) have been

computed utilizing presently available design parameters. Calculations of the

resulting radiation fields have been made for several considerations involving

normal beam loss, as well as for certain postulated accidental beam losses.

Whenever available, experimental data from existing accelerators and light

sources have been used in lieu of theoretical estimates.

2.0 Shielding Design Objective

The Department of Energy's (DOE) basic occupational exposure limit

is 5 rem per year (DOE 81). However, in applying the ALARA ("as low as

reasonably achievable") philosophy, one must strive to maintain exposures

below this limit. In particular, the DOE guidance in the same document states

that the ALARA design objective for new facilities is t o limit exposures to

one-fifth of 5 rem per year (-0.5 mrem/h for a 40-h work week). An additional

ALARA guideline proposed in 1984 (DOE 8 4 ) is that predicted exposures to individual members of the public should not exceed 25 mrem per year. These

dose limiting objectives have been used as the basis for the shielding design

estimates for the normal operations of the facility.

3.0 Types of Radiation Considered

Depending upon the positron energy and beam characteristics, a

number of radiation products need to be considered. High-energy positrons or

electrons produce electron-photon cascades or showers when deliberately or

accidentally stopped in materials. These electromagnetic showers give rise to

a spectrum of bremsstrahlung photons with energies ranging up to the incident

particle energy, in addition to releasing more electrons and positrons. This

component of the radiation field is referred t o as bremsstrahlung (BREM)

DISCLAIMER

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.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, process, or service by trade name, trademark, manufac- turer, or otherwise docs not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect thosc of the United States Government or any agency thereof.

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r a d i a t i o n and can l ead t o photon r a d i a t i o n f i e l d s ou t s ide of t h e sh i e ld . The

r a d i a t i o n o r i g i n a t i n g i n t h e shower i s h ighly peaked i n t h e forward d i r e c t i o n

of the p o s i t r o n beam. However, t h e t r ansve r se component is s t i l l s i g n i f i c a n t

and cannot be neglected. A s t h e energy of t h e p o s i t r o n beam i n c r e a s e s , t h r e e

o t h e r component r a d i a t i o n s need t o be considered. The f i r s t of t hese

components i s the Giant Resonance Neutrons (GRN) produced by photonuclear

i n t e r a c t i o n s ( th re sho ld energy -7-20 MeV). This component has an average

e f f e c t i v e energy of about 2 MeV and i s emi t ted almost i s o t r o p i c a l l y . As t h e

pos i t ron energy moves above several hundred MeV, high-energy neutrons

(>lo0 M e V ) and muons are a l s o produced.

7.7 GeV, and an upper l i m i t of 0.3A f o r t h e c u r r e n t , t h e muons are of minimal

importance, s i n c e t h e i r product ion rate is s t i l l small and they are h igh ly

peaked i n t h e forward d i r e c t i o n (FAS 84) . The high energy neut ron component

(HEN) i s not i s o t r o p i c , but i n many s h i e l d i n g s i t u a t i o n s , on ly t h e neut ron

r a d i a t i o n f i e l d i n t h e t r a n s v e r s e d i r e c t i o n is important . A l l t he se

r a d i a t i o n s have been considered under appropr i a t e cond i t ions t o estimate t h e

s h i e l d i n g requirements

Considering a maximum energy of

I n a d d i t i o n t o t h e above r a d i a t i o n s which arise when p o s i t r o n s

i n t e r a c t wi th matter, o t h e r photon r a d i a t i o n , r e f e r r e d t o as synchrotron

r a d i a t i o n , is produced when p o s i t r o n s are bent i n magnetic f i e l d s . This

r a d i a t i o n is gene ra l ly i n t h e keV reg ion f o r t h e APS and i s g r e a t l y a t t enua ted

by the vacuum chamber i t s e l f . The presence of s h i e l d i n g f o r t h e above-

mentioned r a d i a t i o n components a s s u r e s t h a t synchrotron r a d i a t i o n which

escapes t h e vacuum chamber w i l l a l s o be adequately sh i e lded by t h e tunnel .

4.0 Badia t ion At tenuat ion Parameters

Information on t h e a t t e n u a t i o n of bremsstrahlung, g i a n t resonance

neutrons, and the high-energy component by va r ious s h i e l d i n g materials w a s

ob ta ined from t h e l i t e r a t u r e . For a given material, one d i scove r s a spread

i n t h e quoted va lues for t h e a t t e n u a t i o n l eng ths f o r a given type of

r a d i a t i o n . A v a r i e t y of r e fe rences which d i s c u s s these a t t e n u a t i o n lengths

have been reviewed, such as ALS 73, BAT 67, BAT 70, D I N 77, FAS 8 4 , NEL 68, SWA 79, SWA 85, TES 79 and o thers .

3

I n a l l cases, w e have at tempted t o use conserva t ive va lues f o r t h e

a t t e n u a t i o n l e n g t h s i n order t o provide a margin of s a f e t y .

t a b l e l ists t h e a t t e n u a t i o n l eng ths f o r var ious p o t e n t i a l s h i e l d i n g materials examined i n t h i s study.

The fo l lowing

At tenuat ion 2 Radiat ion Component Shie ld ing Material Length (g/cm )

Bremsstrahlung Lead

Concrete

Heavy Concrete

I ron

Sand ( e a r t h )

Giant Resonance Neutrons Concrete

Heavy Concrete

Dense Polyethylene

Sand ( e a r t h )

I r o n (backed by H)

Lead (backed by H)

High Energy Neutrons Concrete 100 MeV)

115 (E 3 100 M e V )

Dense Polyethylene * 6 2 (E> 100 MeV)

* Scaled from GRN d a t a

25

49 50

37

70

40

45

6 .3 33 100

161

65 (E

4

4.1 Radiation Dose Equivalent Factors

"he unshielded radiation-dose equivalent factors used in the

shielding computations have been adapted from Fasso, et al. (FAS 8 4 ) , with

their suggested modifications. These factors are:

Radiation Dose Equivalent 2

1 mrem m J Factor, FH.(

Radiation Component

Bremsstrahlung

Giant Resonance Neutrons

High Energy Neutrons

2.8*

0.63

0.075

2 * mrem m Use 28 for the completely unshielded bremsstrahlung component.

These factors refer to unshielded dose rates at 1 m in the

transverse direction to the positron beam. As noted, in the absence of any

shielding, the bremsstrahlung component will include a soft radiation

component (e- and e+), which is generally neglected since the above factors

assume that sufficient shielding is present to assure attenuation of the

particle component, 25 cm of concrete (DIN 7 7 ) .

In the forward direction with respect to the positron beam

(0 degrees), the value of FH for bremsstrahlung is given by

2

(FAS 8 4 , SWA 79), mrem m J 8.3 Eo

in which Eo is the initial positron energy in MeV. In general, the same

values given in the table above are used for the GRN and HEN components in the

forward direction.

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4.2 Bulk Shie ld ing Ca lcu la t ions

The fo l lowing express ion was used t o compute the bulk s h i e l d i n g

requirements f o r po in t l o s s e s i n t h e var ious components of t h e APS system.

The t o t a l dose equiva len t rate H is given by -

0

. FH -d/Xi l e

r

H = C- ¶

1 2

0

i n which H has u n i t s of m r e m / s o r mrem/h, FH i s t h e appropr i a t e f a c t o r from 1

t h t h e t a b l e above, f o r t h e 1 r a d i a t i o n component, r i s t h e source t o dose

po in t d i s t ance i n m, d i s t h e s h i e l d th ickness i n g/cm , A I i s t h e a t t e n u a t i o n

length f o r t h e lth r a d i a t i o n component, i n g/cm , and W i s the energy l o s s

rate i n J/s o r J /h .

2

2

The sh ie ld ing s t r a t e g y employed w a s t o use s u f f i c i e n t concre te as a

bulk s h i e l d t o provide reasonable g l o b a l sh i e ld ing of t h e va r ious a c c e l e r a t o r

components f o r t h e d i s t r i b u t e d l o s s e s i n the system. The s h i e l d i n g was the,n

supplemented by l o c a l i z e d s h i e l d i n g employing l ead and/or dense polyethylene

t o reduce t h e r a d i a t i o n f i e l d from high l o s s po in t s i n order t o meet t h e

guide l ines .

5.0 Shielding for Linacs and P o s i t r o n Converter

5.1 Linac Parameters

The phys ica l parameters used f o r t h e e l e c t r o n l i n a c , t h e pos i t ron

conver te r , and t h e p o s i t r o n l i n a c are as fol lows: 4- E = 200 MeV f o r e- f o r pos i t ron conversion, 450 MeV f o r e

I = 3A a t 16.5-11s pu l se width, 8 Hz f o r e-, 10 mA f o r e+

Conversion e f f i c i e n c y i n tungsten - 300 t o 1 Linac tunne l - 9 ' by 9 ' B e a m he ight - 5 ' above f l o o r l e v e l

Distance t o dose po in t - 4 m

I

’ * 6

5.2 E s t i n r a t e d B e a m Losses i n Linac System

For t h e components of t h e Linac system, t h e sh i e ld ing computations

were p r imar i ly based upon po in t l o s s e s in t h e var ious s e c t i o n s of t h e

system. S ince t h e beam c h a r a c t e r i s t i c s of t h e ANL system are somewhat similar

t o the CERN-LEP l i n a c system, estimates of f r a c t i o n a l beam l o s s e s i n t h e

var ious components of t h e system were taken from Fasso, e t a l . (FAS 8 4 ) .

These are:

Estimated Linac System Losses

Average E Average Power (Watts) Component (W Loss ( X ) (MeV) e+ e-

Gun Output 1 .o 55 5 2.75

Buncher Output 0.45

10 100 4.5

F i r s t Linac output ’ 0.405

100 200 81

Second Linac output 1.35 x 10-3

40 22 5 0.12

Resolved Output 8.1 x

5.3 Shie ld ing Es t ima tes

5.3.1 E l e c t r o n Linac

The s h i e l d i n g f o r t h e E lec t ron Linac w a s based upon the est imated

The r equ i r ed s h i e l d i n g i n any s e c t i o n w a s For t h e E lec t ron Li%ac, t he

power l o s s e s i n t h e above t ab le .

determined by t h e h ighes t va lue of power l o s t .

l a r g e s t power l o s s is 4.5 W.

of 2 m and a t o t a l d i s t a n c e of 4 m are:

The computed dose rates for a concre te sh i e ld ing

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3 200 (2.35) L 49 = 0.19 mrem/h

2.8 (4.5) 3.6 x 10 e - - %REM -

- 200 (2.35) . L 40

- 0.63 (4.5) 3.6 x 10 e H~~~ - = 0.05 mrem/h

The total dose rate is 0.25 mrem/h, which is within the design guidelines.

5.3.2 Positron Converter

The power loss in the positron converter is significantly higher

(81W) than that in the first linac (4.5W). Referring to the results for the

first linac, the dominant radiation component penetrating the shield is the

bremsstrahlung. With 0.3 m of steel (iron), followed by 1.7 m of concrete,

the computed dose rates at 4 m are:

. 3 30 (7.8) 170 (2.35)

'GRN - e- 100 e 40 = 0.051 mrem/h 0.63 (81) 3.6 X 10 - (412

3 200 (2.35) L 65 = 0.99 mrem/h

0.075 (81) 3.6 x 10 e - (4)

%EN =

In the expression for the HEN component, the results of Alsmiller and Barish

(ALS 73) were used. They indicate that the attenuation of the high-energy

component by a thickness of iron, followed by a certain thickness of

hydrogenous media, is approximately equal to the attenuation afforded by a

total thickness of hydrogenous material equal to the thickness of the iron

plus the hydrogenous medium. In this case, the total dose rate, 1.07 mrem/h,

exceeds the design goal. However, since the operational time for injection

will be less than 20% of the total operation time, the average dose rate will

be < 0.21 mrem/h. With the addition of localized shielding, dense

polyethylene and/or lead, around the converter target, the total dose rate

outside of the Linac tunnel can be reduced to within the guideline

(< 0.5 mrem/h).

8

Y

5.3.3 P o s i t r o n UMC

In t h e pos i t ron Linac, t he power l o s s e s are down s i g n i f i c a n t l y due

t o the reduced p o s i t r o n c u r r e n t and t h e suggested 2 m of conc re t e s h i e l d i n g i s adequate.

d i r e c t i o n which r e s u l t s from e l e c t r o n s and photons produced by i n t e r a c t i o n s i n

t h e tungsten conver te r t a r g e t .

Th i s s h i e l d i n g a l s o s t o p s the s c a t t e r e d r a d i a t i o n in t h e forward

6.0 Shie ld ing for t h e Booster Synchrotron

6.1 Shie ld ing f o r I n j e c t i o n f r o m L ~ M C to Synchrotron

For t h e boos te r synchrotron, we assume a p o s i t r o n energy of 450 MeV, 9

with a l o s s rate of 50% a t t h e i n j e c t i o n poin t . For i n j e c t i o n of 5 x 10

e /s, t h e l o s s rate i s +

9 13 3 5 X 10 ( . 5 ) ( 4 5 0 ) (1.6 x 10- ) (3 .6 X 10 ) = 648 J /h .

For an 0.8 m conc re t e s h i e l d and a d i s t a n c e of c l o s e s t approach of 3 m, t h e

es t imated dose rates are:

: 4.35 mrem/h

: 0.41 mrem/h

kN : 0.30 mrem/h HGRN

The t o t a l dose rate of 5.06 mrem/h is above t h e gu ide l ines . With t h e a d d i t i o n

of 10 c m of l e a d s h i e l d i n g a t high l o s s po in t s , t h e bremsstrahlung dose ra te w i l l be reduced t o 0.04 mrem/h.

r e s u l t s i n a remaining average dose rate of about 0.15 mrem/h.

a l t e r n a t i v e , €or t h e a d d i t i o n of 10 cm of dense polyethylene, i n a d d i t i o n t o

t h e l ead , a t h igh l o s s po in t s , t h e t o t a l dose rate w i l l be reduced t o about

0.3 mrem/h

Assuming a 20% o p e r a t i o n a l t i m e f o r i n j e c t i o n

As a n

Except f o r t h e i n j e c t i o n and e x t r a c t i o n areas, t h e s h i e l d i n g f o r t h e

synchrotron c o n s i s t s of 0.3 m of concre te on t h e s i d e s and roof of t h e tunnel ,

supplemented by e a r t h berms t o achieve an equiva len t s h i e l d of 0.8 m concrete .

9

6.2 Accidental Loss of Beam in Booster 9

For this case, consider a point loss of the positron beam (5 x 10

e+ at 7 GeV) along the circumference of the synchrotron ring (367 m). Assuming the distance of closest approach is 3.5-m and 0.8-m concrete-

equivalent shielding, the dose per occurrence would be:

-2 : 2.8 x 10 mrem

: 2.6 x 10 mrem H~~~ - 3

HGRN -2 ’

%EN : 6.7 x lo-’ mrem

For 1000 fills of the storage ring per year, considering one occurrence for

each 500 pulses in the synchrotron during filling, the number of occurrences

per year would be about

- 6.62 x lo1* e+/fill 1000 fills

5 x 10’ e+/pulse (0.5) 500 occ. 5300 ( pulses 1 -

This would result in a total dose of about 200 mrem from all occurrences, and

this dose would be expected to be somewhat distributed around the synchrotron

ring.

6.3 Shielding for Extraction from Synchrotron to Storage Ring

For the extraction of the beam from the synchrotron into the storage 9

ring, a point loss of 50% was assumed.

the loss rate is 1.008 X 10 J/h. The computed dose rates at a distance of

4 m with 0.8 m of concrete shielding are:

For a beam of 5 x 10 e+/s at 7 GeV, 4

: 38 mrem/h

: 3.6 mrem/h

: 9.2 mrem/h HGRN

%EN

The total dose rate is 50.8 mrem/h. Addition of 20 cm of lead at high-loss

points would reduce the bremsstrahlung dose rate to 0.38 mrem/h.

of dense polyethylene at these same high l o s s points would reduce the GRN and HEN dose rates to 6.5 X 10” and 2.28 mrem/h, respectively.

Adding 25 cm

For an assumed

I - - l o

extraction time of about 20% operational time, the average total dose rate will be reduced to the design goal.

polyethylene will be required only at the high-loss points of the extraction

system, such as at septum, bump, or other bending and focusing magnets.

The additional lead and dense

7.0 Storage Ring Shielding

7.1 Parameters

Shielding calculations for the storage ring were based upon the

assumption that a maximum beam of 6.62 x 10

Minimum tunnel dimensions of 9' by 9' were used, and a concrete thickness of

0.8 m on both sides and 1 m on the top of the tunnel were assumed. The

circumference of the positron orbit was taken as 1060 m. The distance of

closest approach was taken as 2 m. The shielding on the inside of the tunnel

consists of a circular annulus (0.8 m concrete), concentric with the orbit.

The shielding on the outside of the tunnel (experimental area side) is in the

form of a ratchet wheel, or saw-tooth, pattern in order to increase the space

available f o r photon beam line equipment.

e+ at 7 GeV must be shielded.

7.2 Continuous Loss Durina Beam Decav

As the positron beam moves around the storage ring, there will be a continuous loss of positrons from the beam due to several different factors.

Collisions of positrons with gas molecules, interactions among beam particles,

and orbital excursions, all lead to positrons being lost from the beam and

striking the vacuum chamber. The following empirical formula, adapted from

Swanson, et al. (SWA 85), can be used to estimate the bremsstrahlung dose at

1 m due to a positron interaction:

- es / i io - 2 -( eB/ e 1/ 2) - = 1.67 x 10 W Eo 2 + (0.833) 10- eB'21+ (0.025) 10 s

where H is in rems, W is in joules, Eois the positron energy in MeV, % is the bremsstrahlung angle in degrees and 01,2 Eo = 100 MeV deg.

the right side of the expression accounts for the highly peaked forward

component of the bremsstrahlung. Figure 1 illustrates the geometry for the

The first term on

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continuous-loss case assuming uniform interactions around the ring. For a

positron striking the vacuum chamber at point Q, the bremsstrahlung dose

(rem/J) at P will be expressed by

in which H/W is evaluated for the relevant angle os, which is the angle between the forward direction of the positron beam at Q and the line segment

QP. The contributions from each point, due to uniform interactions around the

orbit circumference, were calculated for both the unshielded case and for

0.8 of concrete shielding. This is shown in Fig. 2. Assuming isotropic

emission for both the GRN and HEN components, the contributions (mrem/J) to

the point P will be given by

'%EN" -

0.075 e I ' IGRN~

and 0.63 e

(?PI2 (QN2 .

These contributions are shown in Figs. 3 and 4 , for both the unshielded and 0.8-m concrete shielding cases. When the distributions are integrated over

all angles, the result is the cumulative contribution at the point P due to a

uniform loss around the ring. The integrated contributions for the 0.8-

concrete shielding case are

-2 = 2.03 x 10 mrem*deg/J

mrem*deg/J -3

mrem*deg/J

'BREM -3 HGRN = 1.96 X 10

%EN = 7.92 x 10

Assuming 6.62 x 10 l2 e+ at 7 GeV gives a total stored energy of 7414.4 J.

a uniform l o s s rate around the ring and a beam mean lifetime of 10 h, the

energy l o s s rate is 1 . 3 J/h deg and the resultant dose rates are

For

- 2 : 2.64 x 10 mrem/h

: 2.55 x 10 mrem/h

kN : 1.03 x 10 mrem/h

:BREM -3

EZGRN -2

The total dose rate is 3.93 x lo-* mrem/h, which is within the guideline. According to Swanson (SWA 85), the results are good to within about a factor

12

of 3.

e n t i r e circumference of t h e r i n g gene ra l ly does not prove out .

Aladdin and NSLS (SWA 85, BNL 51584) i n d i c a t e s increased r a d i a t i o n l e v e l s i n

t h e v i c i n i t y of open ends of bending magnets, around t h e s t r a i g h t s e c t i o n s , a t

maximum d i s p e r s i o n po in t s i n quadrupole magnets, and bremsstrahlung jets a t

t h e ends of s t r a i g h t s ec t ions .

bremsstrahlung and dense polyethylene f o r t he high-energy neutron component

may have t o be provided a t high-loss po in t s i n t h e system.

However, t h e s impl i fy ing assumption of uniform beau l o s s a long t h e

Experience a t

Addit ional l o c a l i z e d l e a d s h i e l d i n g f o r

7.3 Loss of T o t a l Beam at a S ing le Po in t

For t h e case of a t o t a l beam l o s s a t a s i n g l e po in t , both the

t r ansve r se and r a d i a l components need t o be evaluated. For t h e t r a n s v e r s e

component, we assume a d i s t a n c e of c l o s e s t approach of 3 m and 0.8 m of

concre te s h i e l d i n g i n place. For a po in t l o s s of 7414.4 J, t h e est imated

doses are

sREM : 50 m r e m : 4.7 m r e m

: 1 2 m r e m H~~~

%EN

For t h e r a d i a l dose component, t h e c l o s e s t d i s t ance is about 25.3 m,

of which 6 m would be concre te due t o t h e s l a n t p e n e t r a t i o n through t h e

s h i e l d i n g w a l l . The increased d i s t a n c e t o t h e dose po in t , as w e l l as the

increased s h i e l d i n g th ickness , would o f f s e t t h e increased bremsstrahlung i n

t h e forward d i r e c t i o n and r e s u l t i n n e g l i g i b l e doses.

7.4 Bremsstrahlung into a Photon Beam Line

It is necessary t o guard aga ins t an a c c i d e n t a l p o s i t r o n beam l o s s

dur ing i n j e c t i o n , which could r e s u l t i n high energy bremsstrahlung r a d i a t i o n

being d i r e c t e d down a photon beam l i n e . This could r e s u l t i n very high

r a d i a t i o n levels i n t h e experimental area. To prevent t h i s , a l e a d s h u t t e r i s

i n s e r t e d i n t o the photon beam l i n e before i n j e c t i o n begins. A l l beam l i n e s

r e q u i r e l e a d s h u t t e r s , 25-cm t h i c k i n t h e beam d i r e c t i o n and 10 c m t r ansve r se

t o t h e beam d i r e c t i o n . The s h u t t e r s should be loca ted wi th in t h e s h i e l d

13

tunnel t o adequate ly s h i e l d t h e neutrons produced by the e lec t romagnet ic

shower i n t h e l e a d .

On t h e assumption t h a t 10% of the pos i t ron beam is l o s t , a r e s u l t a n t unshielded bremsstrahlung dose of 4 .3 X 10 4 rem a t 1 m, due t o s topping t h e

pos i t ron beam, would be produced i n the forward d i r e c t i o n . I f t h i s were t o

occur j u s t i n s i d e of t h e s h i e l d w a l l , t h e t o t a l dose a t 1 m from t h e o u t s i d e

of t h e s h i e l d would be 5 m r e m due t o t h e 25 c m l e a d s h u t t e r and 80 c m of

concre te , and a n assumed d i s t a n c e of 2.1 m.

7.5 Forward Bremsstrahlung Beam into Ratchet W a l l

S ince a po r t ion of t h e s h i e l d i s i n the form of a r a t c h e t wheel, one

must guard aga ins t forward bremsstrahlung s t r i k i n g the s h i e l d head on. The

sh ie ld ing des ign f o r t hese s e c t i o n s f e a t u r e s an 0.8-m concre te w a l l except f o r

a 2' X 2 ' s l o t through t h e w a l l , centered around the a x i s of t h e photon beam

l i n e . The s h i e l d i n g i n t h i s s l o t c o n s i s t s of 25-cm of lead followed by 55 c m

of concrete . Assuming 10% of the pos i t ron beam i s l o s t and t h e r e s u l t i n g

bremsstralung beam s t r i k e s t h i s s h i e l d head on, and t h e d i s t a n c e of c l o s e s t

approach i s 1.8 m, t he r e s u l t a n t t o t a l dose per occurrence would be about

18 mrem.

7.5 Sca t t e red Brenss t rah lung into a Beam Line

I n a d d i t i o n t o t h e l e a d s h u t t e r s i n t h e photon beam l i n e s , l e a d

c o l l a r s which surround t h e photon beam tube w i l l need t o be i n s t a l l e d t o

i n s u r e t h a t any s c a t t e r e d bremsstrahlung r a d i a t i o n i s i n t e r c e p t e d by 10 c m of

l e a d sh ie ld ing . These l ead c o l l a r s must be s t r a t e g i c a l l y placed around t h e

beam pipe and be of s u f f i c i e n t l eng th t o block a l l o p t i c a l pa ths except t h a t

between the p o s i t r o n o r b i t and t h e beam tube aper ture .

7.7 Dose Rates i n Module ExDerimental Areas

The dose ra te i n t h e module experimental areas w a s computed with t h e

a i d of Fig. 5 which shows t h e va r ious dose con t r ibu te s o u t s i d e t h e r i n g a t

d i f f e r e n t d i s t a n c e s , assuming uniform beam l o s s around the circumference. For

t h e module areas, a nominal d i s t a n c e of 22.8 m w a s used f o r t h e d i s t a n c e of

c l o s e s t approach and a beam mean l i f e t i m e of 10 h w a s assumed. The energy

14

loss rate for these conditions is 1.3 J/h*deg.

Fig. 5, the dose rates become

Using the dose components from

$REM : 2.1 premlh

: 0.21 prem/h

: 0.77 prem/h H~~~

%EN

The total dose rate of 3.1 prem/h is well within the guideline.

7.8 Direct Radiation Dose Rate

The direct radiation dose rate versus distance from the positron

orbit is shown in Fig. 6 for the assumption of a 0.3A positron beam of 7 GeV

and 0.8 m of concrete shielding. The circumference of the orbit is 1060 m and

a 10 h mean lifetime for the beam was assumed.

8.0 Dose to the Publ ic

Assuming a minimum distance of 220 m to the nearest site boundary,

and a total operation tine of 8000 h per year, the site boundary annual dose

is found with the use of Fig. 6 to be 1.2 mrem due to direct radiation.

The skyshine contribution due to the high energy component was

computed using the expression for a well-shielded accelerator (RIN 75):

r x - -

@ (r) -- 48 r

in which a and A are constants, @(r) is the fluence rate (n/crn2 s), Q is the source strength in n/s, and r is the distance to the dose point, in cm.

Values of a and A quoted for DESY measurements by Rindi and Thomas (RIN 75)

were used. These values (a = 7, d = 3.3 x 10 cm) give the largest fluence

rate values for the DESY measurements. No other electron accelerator data was

cited by Rindi and Thomas, but values of X given for proton machines varied from about 3-8.5 x 10 cm.

Values of the source strength Q were computed based upon the yield

(0.12 n/e) given by Bathow, et al. (BAT 67) for 6.3 GeV e- :

15

6 12 + -2 Q = e12 (T) = 1.88 10 n/s *63 (6*62 lo e e

e 3.6 x lo4 f o r a n assumed 10 h mean l i f e t i m e .

increased by a f a c t o r of 3 s i n c e the equat ion f o r t h e f luence rate i s bel ieved

t o be good t o a f a c t o r of 3. Using t h e f a c t o r

The source s t r e n g t h Q w a s conse rva t ive ly

3*2 n/cm2 s mrem/h

t o convert t o dose equ iva len t rate, fi:

5 3.3 l o 4 9.82 x 10 e H - -7

rL

m r e m ( T I

For r = 220 m = 2.2 x l o4 c m , t h e above g ives a dose rate of 1.04 prem/h.

Assuming 8000 h opera t ion , g ives a n annual dose of about 8.3 mrem. The t o t a l

p ro jec ted annual dose a t 220 m from t h e p o s i t r o n o r b i t (at t h e n e a r e s t s i t e

boundary) i s on t h e o rde r of 10 mrem/y, which i s a l s o wi th in t h e guide l ines .

Computations have a l s o been made f o r t h e d i r e c t and skyshine

c o n t r i b u t i o n s out t o 5 lcm. These r e s u l t s can be found i n LS-84 (MOE 87) .

16

REFERENCES

DOE 81

DOE 84

FAS 84

BAT 67

ALS 73

TES 79

DIN 77

NEL 68

BAT 70

RIN 75

SWA 79

U.S. Department of Energy requirements for radiation protection,

DOE order 5480.1 Chg. 6 , Chap. XI-3 (1981) .

U.S. Department of Energy, Proposed Revision of DOE Order 5480.18,

"Radiation Standards for Protection of Public," memorandum dated

Sept. 1 7 , 1984. REF. P.E.-243 (1984) .

A. Fasso, K. Goebel, M. Hoefert, G. Rau, H. Schonbacher, G. R.

Stevenson, A. H. Sullivan, W. P. Swanson, and J.W.N. Tuyn,

"Radiation Problems in the Design of the Large Electron-Positron

Collider (LEP)," CERN 84-02, (5 March 1984) .

G. Bathow, E. Freytag, and K. Tesch, "Measurements on 6.3 GeV

Electromagnetic Cascades and Cascade Produced Neutrons," - NUC.

PHYS., B2 (1967) , 669-689.

R.G. Alsmiller, Jr. and J. Barish, "Shielding Against the

Neutrons Produced when 400-MeV Electrons are Incident on a Thick

Copper Target,*' Particle Accelerators, - 5, (1973) , 155-159.

K. Tesch, "Data for Simple Estimates of Shielding Against Neutrons

at Electron Accelerators," Particle Accelerators, - 9 , (1979) , 201-

206.

H. Dinter and K. Tesch, Dose and Shielding Parameters of Electron-

Photon Stray Radiation from a High Energy Electron Beam," - NUC.

Inst. Meth., 143, (1977) , 349-355.

W. R. Nelson, "The Shielding of Muons Around High Energy Electron

Accelerators:

- Theory and Measurement," NUC. Inst. Meth., 66,

(1968) , 293-3030

G. Bathow, E. Freytag, M. Kobbeling, K. Tesch, and R. Kajikawa,

"Measurement of Longitudinal and Lateral Development of Electromagnetic Cascades in Lead, Copper, and Aluminum at 6.0

GeV," Nuc. Phys., - B20, (1970) , 592-602.

A. Rindi and R. H. Thomas, "Skyshine - A Paper Tiger?," Particle Accelerators, Vol. 7 (1975) , 23-39.

W. P. Swanson, Radiological Safety Aspects of the Operation of

Electron Linear Accelerators," Technical Report Series No. 188,

IAEA, Vienna, (1979) , and references therein. -

17

SWA 85 W. P. Swanson, P. M. DeLuca, R. A. O t t e , and S. W. Schilthelm,

"Aladdin Upgrade Design Study:

Wisconsin, 1985.

Shie ld ing ," Univers i ty of

BNL 51584 K. Batchelor , Ed i to r , Nat ional Synchrotron Light Source Sa fe ty

MOE 87

Analysis Report , Brookhavaen Nat ional Laboratory, J u l y 1982.

H. J. Moe, "Radiological Impacts from Operation of Argonne

Synchrotron X-ray Source," ANL Report , L ight Source Note LS-84

(March 1987).

FigL Geometry for Component Doses due to Continuous Loss around the Storage Ring

f '

eo0 240 280 320

BREMSSTRAHLUNG DOSE. UNIFORM LOSS AROUND STORAGE RING. E-7.0 GeV

l t I

4 I

I I

40 80 120 160

e ANGLE AROUND RING (DEGREES)

F i g y e 2, Bremsstrahlung Dose - Unffonn toss Around Storage Ring

-1 10

l0-I.

lo-*.

UNSHIELDED -

SHIELDED , 0.8M CONCREll?

I I

t I

I I

260 265 310 335

GIANT RESONANCE NEUTRON DOSE. UNJFORM LOSS AROUNO STORAGE RING. E-7.0 GeV

- 2s 50 7 5 100

8 ANGLE AROUND RING (DEGREES)

Figure 3. Giant Resonance Neutron Dose-. Unf form Loss Around Storage Ring

3

-1 10

ONSHIELDED -

SHIELDED

0.8M CONCRFTE I

.-8J ~

10

HIGH ENERGY NEUTRON DOSE. UNtFORM LdSS-AROUND STORAGE RIEJQ. E-7.0 GieV

25 50 7 5 100 280 285 910 33 5 0

8 ANGLE AROUND RING (DEGREES)

Figure +. High Energy Neutron Dose - Uniform Loss Around Storage Ring

. * .

3

! 2

2

. . . . . . . . . , . . . .--__

. . . . , . .

. . . . . . .

* > - .

Y

2

-6

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .- _- - - . . . . . . . .- . ._ . . . . . . . . . . . . . . . - ... . . _- ----

~ . .- - - -- . . . . . . . . . . . . . . . . . . . . .- -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- . . .

. . . . , . . . I I ' 1 I I 1 ! , . , . . 1