PRIMEX Targets

Objective:

To obtain the “effective” number of 12C atoms/cm2 for the Primakoff analysis

See Primex Note 28, “Analysis of Primex Targets”, Philippe Martel and Rory Miskimen, for experimental details.

Carbon target:

• Pyrolytic graphite, 9mm thick (5% RL)

• Low porosity compared to graphite (1% versus 10%)

• Doesn’t fragment, easier to machine than graphite

• Natural isotopic abundance, 98.89%

• Elemental analysis:

Proton induced x-ray emission (72 elements) and Combustion (CHNO)

Carbon 99.63% Aluminum .006%

Hydrogen <.10% Silicon .006%

Nitrogen <.05% Chlorine .003%

Oxygen 0.19% Calcium .003%

• Measuring T for the carbon target:

measured using water displacement technique.

Thickness measurements using a ±.05 mil accuracy micrometer.

Average the first 5 measurements, and use the error from the 3rd measurement:

= 2.1979 ± .0006 g/cm3

Block II:

380.40

380.50

380.55

380.50

380.50

380.40

380.35

(mils)

Target thickness (mil) = 380.4 ± 0.1

Target impurities

Define an effective carbon areal density

)q(F6

)q(F)Z(NZ

)6Z(N 2imPr

26z

21Z

2imPr

2Z

2

eff

Neff(Z=6) = 1.06585 x 1023 atoms/cm2

This is about 0.1% higher than what you obtain by assuming everything in the target is carbon.

Beam absorption in the target

Include this effect in the “effective” target thickness

Te1

T

)T( Teff

The NIST XCOM data base gives =56.5 g/cm2 at 5.2 GeV. The estimated error in is ±1.5%.

Neff(Z=6) = 1.04606 x 1023 atoms/cm2

Do we need to worry about magnetic scattering from 13C in the target?

7

2

22

22

2E

2M22

2

103eargCh

Magnetic

ZcM4

Q

G

GcM4

Q

eargChMagnetic

Conclusion: for our purposes 13C is equivalent to 12C

Neff(Z=6) = 1.0461 x 1023 atoms/cm2 ± 0.05%

The errors in each experimental parameter were propagated to find the total error in Neff.