Ground Water, Air-Borne and Soil Activation from the Operation of the MI-40 Beam Absorber During the FMI Era

C.M. Bhat

(December 1, 1997)

MI Note 0219

Beam absorber built near the MI-40 straight section [1,2] will be used during the Fermilab Main Injector commissioning and operation. This will also be used during the Recycler Ring commissioning and its study using proton beam. A proton beam of engery from 8 GeV to 150 GeV will be aborted towards the absorber and stopped in it. The interaction of these particles (and secondaries) with the absorber and its surrounding soil induces radioactivity in them which will be of concern for operation of the Main Injector.

In this report we address the ground water, air-borne and soil radioactivations arising from the use of the absorber. The total beam transported and aborted from the Recycler Ring towards the MI40 beam absorber is expected to be only a fraction of a precent of that from the Main Injector. The precautionary steps established for the Main Injector operation to protect personnel from radiation should provide enough coverage both for the MI and Recycler Ring. Hence, in the rest of the report we concentrate only on the Main Injector operating conditions.

1. Ground Water Activation :

The ground water issue related to the MI40 beam absorber is explained in detail in ref.[2]. Here we summarize the final result of our analysis. The ground water activation arising from the MI40 beam absorber is estimated by using concentration model [3,4]

The following quantities are used in our calculations:

Using Eq. 3 of reference 3, we get the initial concentration

Ci ( 3H ) = 9.0 x 10-19 pCi/ml-year/150GeV proton

Ci ( 22Na ) = 2.0 x 10-20 pCi/ml-year/150GeV proton

Assuming instantaneous mixing of the produced radioactive nuclei in the ground water, we obtain the final concentration as

Cf ( 3H ) = 1.69 x 10-18 pCi/ml-year/150GeV proton

Cf ( 22Na ) = 5.8 x 10-21 pCi/ml-year/150GeV proton

The EPA and DOE, however, allow 20 pCi/ml-year from 3H nuclei and 0.4 pCi/ml-year

from 22Na nuclei in ground water. Thus we find that the upper limit on the total 150 beam stopped in the absorber without contaminating the ground water above the EPA allowed limites is 1.0x1019 protons / year. A preliminary safety analysis of the MI , however, suggest that allowed yearly beam aborted to be 3.52 x 1018 protons at 150 GeV [2,5], which is about 2.8 times smaller than the beam intensity limit suggested by the concentration model.

2. Air-borne Radioactivity :

In the past, the air-borne radioactivity have been measured at various loacations around Fermilab accelerators [6 and Appendix-A]. The location include many beam extraction regions and AP0 prevault. Necessary precautions were taken if the air-borne activity is larger than the allowed limits. In the case of newly built Main Injector enclosure, one encounters many locations of concern. The present study focuses on two regions: a) MI tunnel in the vicinity of MI40 beam extraction region and b) inside the MI40 beam absorber enclosure. Below, we investigate them separately.

a) MI enclosure

During the beam extraction towards the MI40 beam absorber we expect beam losses at the extraction region. The beam loss would give rise to radioactivity of the air in the MI enclosure. We use the results of the measurements carried out in the Tevatron 800 GeV proton beam extraction region at PSEPs [Appendix-A] and scale it to estimate the air-borne radioactivity level in the MI enclosure.

During the Tevatron fixed target experiments Derived Air Concentration (DAC)

Ratio sum around the Tevatron EXTRACTION PSEPS (SWYD PSEP) is 0.445 [Appendix-A]2 immediately after the beam delivery is stopped. Hourly extracted beam was 2.4 x 1015 p at 800 GeV. In the case of MI40 extraction region the "Fermilab Main Injector Preliminary Safety Analysis Report" [5] allows an average of total beam aborted on the MI40 absorber as 5.9E14 p /hour @ 150 GeV during the commissioning period and regular operation (allowed beam aborted on the beam absorber is 3.53E18/year; 1 year = 6000 hr). To estimate the air-borne activity around the MI40 beam extraction region we make following assumptions :

  1. the air-borne activity measured at SWYD PSEP location can be scaled down to the operating condition at MI40 beam extraction region.

  2. the average amount of beam extracted via the SWYD PSEP location is 2.4E15p@800GeV /hr and at MI40 extraction region is 5.9E14p @150 GeV/hr

  3. the beam losses around both locations are essentially the same.

  4. the air-borne activity scales as E0.75.

Then the expected DAC at the MI40 beam extraction point is

DAC = 0.445 x (5.9E14/ 2.4E15) x (150/800)**0.75

= 0.031

which is smaller than the DOE allowed limit of 0.1. The DAC value scales 1 linearly

with the beam loss at the extraction point.

Estimated air-borne activity for other five regions of interests in the Main Injector tunnel is listed in Table I. The estimation to all regions were done relative to the values evaluated at MI40 beam extraction region. The columns 4 and 5 indicate expected beam losses at these locations. However, these losses are not used in the estimation.

Table I : Estimated air-borne activity near six injection and extraction regions of MI.
Location of the Extraction region Method of Beam Transport Beam Extracted /hr Expected Hourly Beam loss Estimated Beam loss/hr Estimated

Air Borne Activity


MI10 8 GeV Injection 5.7E16 <1% 5.7E13 0.32
MI30 120 GeV Resonant Extraction 3.9E16 ~2% 7.8E14 2.0
MI40 8- 150 GeV Single Turn 5.9E14@ <1% 5.9E12 .03
MI52 120 GeV Single Turn for pbar production


150 GeV to Tevatron Single Turn


150 GeV to Tevatron Single Turn


120 GeV Resonant Extraction


8 GeV beam for tuneup,

Single Turn





1.8E15/Tevatron store#



























1.8E13 per Tevatron Store






















MI609 120 GeV Resonant Extraction 5.8E16 ~2% 1.16E15 2.9
MI62 150 GeV Single Turn 2.52E12/Tevatron store# <1% 2.52E9 per Tevatron Store <0.01

@ Beam loss only during Commissioning or study

# Only during collider operation. Beam is extracted approximately once for every 20hr.

b) MI40 beam absorber enclosure

The MI40 beam absorber is installed in a separate enclosure in the vicinity of the MI40 straight section. The entry to this enclosure is near location MI-409 and the entry way (which is under the MI tunnel enclosure) is provided with locked gate (not air tight).The beam absorber enclosure has an exhaust (normall off), can be activated prior to the entry to the dump enclosure.

The extracted beam towards the absorber is transported through a vacum pipe for about 100 ft and about 10 ft of air before it is stopped in the MI40 absorber. To estimate the air-borne activity we take the measured air-borne radioactivity in the AP0-vault area [6] and scale it to the MI40 beam absorber operating scenarios.

During the pbar production a 120 GeV proton beam traverses about 10 ft of air prior to its interaction with the pbar target in the AP0-vault. The primaries and secondaries further interact with many beam line elements in air before they are stopped in the AP0 beam absorber. The approximate total distance traversed by the particles is about 25 ft. Average hourly beam stopped in the absorber is about 4.1 x 1015 p @ 120 GeV one expecteds the resulting DAC ratio as 2.19 [6].

To estimate the air-borne activity in the MI40 beam absorber enclosure we make following assumptions:

  1. the air-borne activity measured at AP0 vault area may be scaled3 down to the operating conditions of the MI40 beam absorber.

  2. the average amount of beam stopped in AP0 beam absorber is 5.4 x 1015 p@120 GeV/hr and that in the MI40 beam absorber is 5.9E14p @ 150 GeV/hr.

  3. the air-borne activity scales as E0.75.

Then, the expected average DAC Ratio at the MI40 beam absorber :

DAC = 2.19 X (5.9E14 / 5.4E15) x (150/120)**0.75 = 0.28

This value is greater than the allowed limit of 0.1. We estimate that the air-borne activity will be reduced to about 20% of its original value in 40 min. However, we recommend monitoring of the air-borne activity at the exhaust before the air in the enclosure is let to atmosphere. During commissioning of the MI40 beam absorber, the air activation will be monitored and appropriate signs should be posted in accordance with FRCM. Also, the Beam Division procedure [8] should be followed for entry into the absorber enclosure.

3. Soil Activation :

The radioactivity induced in the soil forming the bulk shielding around an accelerator enclosure is of special interest from the point of view of groung water contamination which is explained in section 1. However, a number of other long lived radioactive elements can be seen in the soil samples from the area around the beam absorber sheilding. Some of these radioactive elements have life times comparable to the 3H and 22Na isotopes. The maximum star density in the soil adjacent to the beam stop enclosure is estimated to be 5x10-10 stars/cc @ 150 GeV. This corresponds to a residual activity D of

D (max) = (5E-10 / 1E-10) x (3.52E18 / 2.93E19) x 2.0E-4 rad at contact4

= 0.13 mRad

However, if this area of any section of the beam line tunnel is to be decommissioned or remodeled in future, the soil will be tested and necessary precautions will be taken in accordance with FRCM [7].

Author would like to thank A. Leveling for providing the measurement data ao air-borne activity at different locations in the accelerator complex.


[1] "A Design Study of MI40 Beam-Abort Dump" C.m. Bhat, MI Note 86, 1993.

[2] Ground-water Activation from the upcoming operation of MI40 Beam Absorber, C.M. Bhat and L. Read, Fermilab TM-1985 (1996).

[3] "Use of a Concentration-based Model for Calculating the Radio activation of Soil and Ground water at Fermilab", J.D. Cossairt, Environmental   Protection Note 8 (1994)

[4] "Ground water Migration of Radionucleides at Fermilab", A. J. Malensek et al., FERMILAB TM 1851, (1993). Private communication with A. J.   Malensek and Kamran Vaziri (January 30, 1997)

[5] "Fermilab Main Injector Preliminary Saftey Analysis Report" , by S.D. Holmes et al , May 1992.

[6] "Airborne Radioactivity in Accelerator Divivion", G. Lautenschlager and A.F. Leveling, Radiation Physics Note 128 (1996).

[7] Fermilab Radiological Control Manual.

[8] Beams Division procedure to enter the MI40 beam Absober Enclosure (under preperation)

[9] A design study of the MI40 beam -abort dunp, C.M. Bhat MI-86 (1993)