Radiation Materials for Hall-A Polarized $^3$He Target

Xiaochao Zheng, xiaochao@jlab.org

December 7, 2001

http://hallaweb.jlab.org/physics/experiments/he3/A1n/ana/radlen.ps

This document summarizes thickness and radiation length for materials crossed by incident and scattered electrons for Hall-A Polarized $^3$He experiments. Information listed here can be used for radiation effect caused by internal and external bremsstrahlung, and energy losses due to ionization for incident and scattered particles.

Figure 1: Radiation materials for hall A polarized $^3$He target

1. exit window of beam pipe, 16 mils $^a$ Be;
2. 5cm air;
3. entrance window of scattering chamber, 15 mils Al;
4. target cell window, $\sim$ 130 $\mathrm{\mu}$m $^b$ glass;
5. $\sim$ 10 atm $^3$He, 1/2 of target cell length $^c$;
6. $\sim$ 10 atm $^3$He, $(r-x_{tg})/sin\theta$, where r$\sim$1cm is target cell radius, $x_{tg}$ is x position of scattering point in hall coordinates, $\theta$ is scattering angle;
7. target cell wall, $\sim$ 1.3mm glass $^d$;
8. $^4$He inside target enclosure, 45.7 cm;
9. target enclosure exit window, 16 mil Al $^e$;
10. air gap between target enclosure and HRS, 65.1 cm for left arm and 64.2 cm for right arm;
11. spectrometer entrance window, 14 mils Kapton;
12. spectrometer exit window, 4 mils Ti.

material	$X_0$ (g/cm$^2$)	(cm)	density
air	36.66	30420	1.205 g/l  $^f$
$^4$He	94.32	755164	0.1249 g/l
$^3$He	67.42	-
Be	65.19	35.28	1.848 g/cm$^3$
Al	24.01	8.9	2.70 g/cm$^3$
Kapton	40.56	28.6	1.42 g/cm$^3$
Ti	16.17	3.56	4.54 g/cm$^3$
glass	19.5	7.04	use GE180, 2.77 g/cm$^3$

a. 1 mil=2.54 $\times 10^{-3}$cm
b. depends on cell geometry
c. depends on target chamber density in beam, 1 amg=1.25 $\times 10^{-4}$g/cm$^3$
d. depends on cell geometry
e. for E94010 it was 10 mil
f. density for gases are evaluated at 20$^\circ$ C, 1 atm